Miscellaneous

Question 1

What Are the Important Physiologic Changes Associated with Pregnancy?

Answer 1

○ Pregnancy is characterized by an increase in alveolar ventilation, chronic respiratory alkalosis, and decreased functional residual capacity (FRC).
○ The reduced FRC means that pregnant patients desaturate quickly and have less tolerance for apnea or positioning such as lithotomy or Trendelenburg before the onset of hypoxemia.
○ Capillary engorgement caused by circulating progesterone may result
in airway edema and difficulty with mask ventilation and endotracheal intubation.
○ There is a decrease in systemic
vascular resistance but a concomitant increase in heart rate
and stroke volume that results in a large overall increase in cardiac output (50% at term).
○ Aortocaval compression from the gravid uterus can lead to maternal hypotension, decreased uteroplacental perfusion, and increased risk of deep vein thrombosis in the supine position after 20 weeks of gestation; for this reason, patients in the second half of pregnancy should always be positioned tilted to the left or with the uterus displaced laterally.
○ A disproportionate rise in plasma volume relative to red cell mass results in the “physiologic anemia of pregnancy,” which is most pronounced in the second trimester.

Question 2

How Should We Assess the Airway of a Pregnant Patient Prior to Non-obstetric Surgery?

Answer 2

○ The airway can be challenging in pregnant patients because of capillary engorgement, tissue friability, and edema.
○ Elements of a standard airway examination are useful in pregnant patients; a combination of thyromental distance and upper lip bite test has recently been shown to be highly specific and sensitive for difficult intubation.
○ The Obstetric Anaesthetists’ Association and the Difficult Airway Society in the UK have published a set of guidelines for the management of difficult and failed intubations in obstetrics.
○ They emphasize the role of preoperative planning and communication, team decision-making, and the complexities of dealing with difficult airway scenarios when two patients (mother and fetus) need to be considered.

Question 3

Why Are Pregnant Patients Considered at Risk of Aspiration Under Anesthesia?

Answer 3

Increased progesterone leads to decreased lower esophageal
sphincter tone. Additionally, increased intraabdominal pres-
sure from the gravid uterus predisposes pregnant patients to
reflux of gastric contents and may lead to aspiration under
general anesthesia. Gastric emptying, however, is not delayed
in pregnant patients until they are in labor [3]. Rapid sequence
induction of anesthesia should be performed whenever general
anesthesia is employed in a pregnant patient. The combination
of nonparticulate antacids and H2-blockers may be somewhat
useful to mitigate risk by reducing intragastric pH [4]

Question 4

Are Fasting Guidelines Different
in the Pregnant Patient?

Answer 4

Despite the potential for increased aspiration risk after
20 weeks’ gestation, no difference in fasting guidelines exists
for pregnant undergoing non-obstetric surgery. Adherence
to the recommendations of national societies such as those
of the American Society of Anesthesiologists and Canadian
Anesthesiologists’ Society that clear fluids are permitted up
to 2 hours prior to elective surgery, and that a light meal or a
heavier meal be restricted to 6 and 8 hours prior to surgery,
respectively, is prudent [5, 6]. Current guidelines further sug-
gest that solid foods not be permitted for pregnant patients
once active labor is established, and that individual institu-
tions develop protocols with respect to clear fluid intake dur-
ing labor [5].

Question 5

What Are the Fetal Risks Associated with Non-obstetric Surgery During Pregnancy?

Answer 5

There are three major categories of risk to the unborn fetus, which can vary depending on when, during pregnancy, surgery and anesthesia are undertaken, namely, preterm labor, teratogenicity, and intrauterine asphyxia.

Question 6

Can the Risk of Preterm Labor Be Mitigated?

Answer 6

Preterm labor is a theoretical risk with any procedure; it is possible that either direct mechanical irritation or inflammation caused by abdominopelvic procedures may increase this risk compared to procedures performed in other areas of the body. Unfortunately, there has been no proven benefit demonstrated with the use of tocolytic drugs (e.g., magnesium sulfate and terbutaline) to try and prevent preterm labor in a pregnant patient underdoing non-obstetric surgery [7].

Question 7

What Role Do Glucocorticoids Play in Procedures Undertaken During Pregnancy?

Answer 7

Antenatal administration of glucocorticoids (e.g., dexamethasone or betamethasone) in select patients has been shown to improve neonatal morbidity and mortality related to preterm complications, e.g., respiratory distress syndrome, intracranial hemorrhage, and necrotizing enterocolitis.
○ The American College of Obstetricians and Gynecologists (ACOG) recommends a single course of corticosteroids for patients at risk of preterm delivery within 7 days who are between 24 0/7 and 33 6/7 weeks gestation and that it may be considered in late preterm patients (i.e., between 34 0/7 and 36 6/7 weeks).
○ Suggested treatment consists of either two 12-mg doses of betamethasone given intramuscularly 24 hours apart or four 6-mg doses of dexamethasone administered intramuscularly every 12 hours

Question 8

Are Any Drugs Used in the Conduct of General Anesthesia Teratogenic?

Answer 8

○ Teratogenicity is most likely to occur in the first trimester, and the former US Food and Drug Administration (FDA) category “X” drugs are those that must absolutely be avoided during pregnancy.
○ This classification, in use since 1979, was replaced in 2015 with a new, narrative system.
○ Importantly, no drugs used as part of anesthetic practice, including nitrous oxide (N2O), neuromuscular blocking agents, volatile anesthetics, induction drugs, or opioid analgesics, have been shown to be teratogenic in clinically relevant concentrations in humans.
○ Nitrous oxide can affect DNA synthesis and has been shown to be teratogenic in animals after long exposures in high concentrations.
○ Research in human subjects has been limited to case-control studies with many confounders, and the ACOG does not recommend avoidance of specific anesthetic drugs in pregnant patients if they are indicated

Question 9

Are Non-steroidal Anti-Inflammatory Drugs (NSAIDs) Safe During Pregnancy?

Answer 9

○ NSAIDs may be prescribed by a physician for tocolysis in preterm labor or for prevention of vascular complications from disorders such as pre-eclampsia.
○ Alternatively, they may be self-administered by pregnant patients for common ailments such as joint pain or fevers and malaise.
○ Fetal complications of maternal NSAID use may include premature
closure of the ductus arteriosus, leading to persistent pulmonary hypertension of the newborn, necrotizing enterocolitis, and oligohydramnios.
○ For these reasons, NSAIDs are best avoided after 30 weeks’ gestation and used in the lowest doses for the shortest duration possible if maternal benefit outweighs fetal risk.

Question 10

What Are the Risk Factors for Intrauterine Asphyxia?

Answer 10

○ The age-old directive to “avoid hypoxia and hypotension” is especially important when considering the pregnant patient undergoing non-obstetric surgery, as perfusion to the fetus through the placenta is highly dependent on these (and other factors).
○ There is no autoregulation in the uteroplacental circulation, unlike in the brain. Blood flow is directly related to mean uterine perfusion pressure (and therefore maternal mean arterial pressure) and inversely related to the vascular resistance of uterine vessels.
○ Support of maternal blood pressure with fluid administration or vasopressors is important to prevent uteroplacental insufficiency during the perioperative period.
○ Direct acting α-agonists such as phenylephrine are safe and cause less neonatal acidosis than ephedrine; both are likely safe, however, during non-obstetric surgery during pregnancy.
○ Finally, maternal hypoxemia leads to fetal hypoxemia and uterine vasoconstriction, which, if prolonged, can lead to irreversible brain damage or intrauterine death.
○ Similarly, maternal hypercarbia can cause uterine vasoconstriction as well as fetal acidosis.

Question 11

What Is a Biophysical Profile (BPP) and What Is the Significance of a BPP of 6/8?

Answer 11

○ A BPP is an antenatal test meant to evaluate fetal well-being.
- Fetal heart rate (FHR) monitoring (the nonstress test or NST) is combined with four unique ultrasound measurements (breathing, movement, muscle tone, and amniotic fluid level) to give a snapshot of fetal health.
- Each of the resulting five elements is given a score of 0 or 2.
○ BPP scores of 8 or 10 are considered reassuring.
○ Depending on many factors, including individual clinical circumstances and gestational age, scores of 6 or below may simply require repeat testing either the same or the next day, or in some cases a plan for delivery is required

Question 12

How Should We Assess Fetal Well-Being During Surgery?

Answer 12

○ The timing of the proposed procedure, access to the maternal abdomen, and the availability of personnel equipped to respond to an ominous fetal heart rate tracing should it occur.
○ Decreased fetal heart rate variability may not always represent fetal distress, however, and can be seen with the administration of general anesthesia, maternal hypothermia, or drugs that affect the maternal cardiovascular system.
○ The optimal choice of fetal monitoring is therefore a complex decision-making process.
○ According to ACOG “Because of the difficulty of conducting large-scale randomized clinical trials in this population, there are no data to allow for specific recommendations.
- It is important for a physician to obtain an obstetric consultation before performing non-obstetric surgery and some invasive procedures (e.g., cardiac catheterization or colonoscopy) because obstetricians are uniquely qualified to discuss aspects of maternal physiology and anatomy that may affect intraoperative maternal–fetal well-being”

Question 13

For Which Non-obstetric Surgical Cases Should Fetal Monitoring Be Utilized?

Answer 13

○ The decision to use fetal monitoring should be individualized, and each case warrants a team approach for optimal safety of both mother and baby.
○ Generally speaking, Doppler assessment of the FHR before and after the procedure is sufficient for previable fetuses.
○ For fetuses that have passed the age of viability, FHR assessment and contraction monitoring (tocodynamometry) can be performed before and after the procedure to ensure fetal well-being and rule out preterm labor.
○ Intraoperative monitoring is useful only if there is a possibility of intervention (i.e., emergency caesarean delivery) should fetal distress be encountered.
- This necessitates having access to the maternal abdomen, as well as the immediate availability of a physician capable of performing an emergency delivery.

Question 14

How Are Fetal Heart Rate Tracings Categorized?

Answer 14

○ A three-tier classification scheme for FHR tracings was adopted in 2008, in which Category 1 tracings are those with no ominous features and are considered normal, Category 3 are fetal heart rate tracings thought to represent significant fetal compromise and are abnormal, and Category 2 being those that fall into neither of the other two categories and
are therefore indeterminate [13].
○ A detailed review of FHR tracings is beyond the scope of this chapter, and the reader is encouraged to refer to numerous existing publications on this subject.

Question 15

Is There Any Evidence That Obstetric or Neonatal Outcomes Are Worse When Non-obstetric Surgery Has Been Performed During Pregnancy?

Answer 15

○ Isolating the effects of anesthesia from the surgical procedure and the underlying surgical condition is difficult if not impossible.
○ It has been estimated that 1–2% of pregnant patients will undergo procedures unrelated to pregnancy, and quantifying the risks associated with these procedures has proved elusive.
○ Analysis of administrative data suggests that the risk of complications for both mother and fetus/newborn is low when surgery is performed during pregnancy and that it is relatively safe, especially with modern anesthetic and surgical techniques [14].

Question 16

When Should Surgery Be Undertaken? Pregnancy

Answer 16

○ Traditional dogma, including the most recent Committee Opinion by ACOG [9], suggests that surgery be carried out in the second trimester if possible, as the risk of teratogenicity and miscarriage may be higher in the first trimester of pregnancy and risk of preterm labor highest closer to term.
○ There has recently been a reappraisal of this time-honored teaching given the fact that maternal-fetal care, surgical technique, and diagnostic testing have all advanced since the initial studies examining this topic were performed [15].
○ Withholding surgery when indicated because a patient is pregnant may actually confer more risk to the patient due to the severity of the underlying surgical disease and is therefore unwarranted.
○ This is important, as the overwhelming majority of procedures undertaken during pregnancy are not elective, and therefore being able to time them to coincide with the second trimester is often neither practical nor possible.

Question 17

True/False Questions
1. Which factors are involved in the decision about whether or not to perform continuous intraoperative fetal monitoring during non-obstetric surgery during pregnancy?
(a) Duration of procedure
(b) Access to maternal abdomen
(c) Immediate availability of physician capable of performing emergency delivery
(d) Anesthetic technique (e.g., neuraxial vs. general)
(e) Gestational age of fetus

Answer 17

1a. F
1b. T
1c. T
1d. F
1e. T

Question 18

T/F
Which anesthetic medication is absolutely contraindi-
cated during pregnancy?
(a) Nitrous oxideb
(b) Ketamine
(c) Neostigmine
(d) Fentanyl
(e) None of the above

Answer 18

2a. F
2b. F
2c. F
2d. F
2e. T

Question 19

A Suggested Approach to the Patient with a Pre-existing Psychiatric Diagnosis

Answer 19

1. Perform a brief mental status examination.
2. Determine if the patient is stable or in need of referral for further psychiatric management prior to surgery.
3. Review current medications and assess for potential side effects, drug interactions, and consequences of withdrawal or interruption of these medications perioperatively.

Question 20

What Are the Components of a Mental Status
Examination (MSE)?

Answer 20

A Appearance and behavior
S Speech and motor activity
E Emotion (mood and affect)
P Perception
T Thought content and process
I Insight and judgment
C Cognition
Appropriate questions to ask any patient with a psychiatric history include the following:
• How is your mood?
• Have you felt sad/down recently?
• Have you felt in control lately?
While many components of the MSE are elicited through observation during a routine history and physical examination, assessing some aspects, including thoughts, perceptions, attitude, and insight, requires directed interrogation.
○ Assessing cognition can be challenging.
- The Mini-Cog is a screening tool that is accessible in the public domain (https://mini-cog.com), simple to administer, and helpful in determining many aspects of cognition: attention, language, memory, orientation, and visuospatial proficiency.
- It is very sensitive, in the absence of other acute mental health issues, in determining the presence of dementia

Question 21

What Is the Prevalence of Mental Illness
in the Population?

Answer 21

The National Institute of Mental Health estimates that nearly
one in five adults in the United States live with a mental ill-
ness, with 4.5% of the population suffering serious mental
illness. The latter is defined as “a mental, behavioral, or emo-
tional disorder resulting in serious functional impairment,
which substantially interferes with or limits one or more
major life activities” [2]. Up to 25% of those with serious
mental illness remain untreated

Question 22

Is It Important to Identify Those with Decompensating Mental Illness Prior to Elective Surgery?

Answer 22

○ In general, many patients with serious mental illness have social and occupational challenges and engage in behavioral choices that contribute to poor physical health.
○ These factors include inadequate diet, tobacco use, excess alcohol, and
illicit drug intake.
○ In consequence, the baseline risk for this patient group is elevated.
○ However, it is clear that if patients with serious mental health issues require an intervention to manage their psychiatric illness during admission following elective surgery, their morbidity and mortality far exceed that
of the general population.
○ These data underscore the need to identify, assess, and treat decompensated mental illness prior to an elective surgical procedure in a similar fashion as is routine for occult coronary and respiratory illness.

Question 23

What Are the Potential Consent Issues in Patients with Decompensating Mental Illness Prior to Elective Surgery?

Answer 23

○ Individuals with an inadequately managed serious mental disorder may not have the capacity to legally provide informed consent to elective surgery.
○ Consent requires that one both understands the information that is relevant to deciding and has the capacity to make such a decision.
- The decision to agree to a surgical procedure does not necessarily extend to consent to undergo an anesthetic.
- Indeed, in elective surgery, the evolving and fluctuating nature of mental status in patients with unstable comorbidities may require reassessment of a previously obtained consent.
○ Cognitive rather than psychotic or mood disorders are more likely to impair appropriate decision-making capacity.
○ It was clear in this case that the patient understood the risk and benefits of treatment, appreciated her clinical situation, was independently able to arrive at a reasonable decision, and communicate that decision. The latter are the four essential components of the decision-making capacity.

Question 24

What Are the Classes of Drugs Currently Used to Manage Psychiatric Disorders and What Are the Issues to Be Aware of When Evaluating Patients Using These Medications?
1. Ssri

Answer 24

1. Selective serotonin reuptake inhibitors [SSRIs] (citalopram; fluoxetine and others).
   Issues:
   (a) Fluoxetine inhibits the cytochrome P450—dose adjustment may be required of drugs metabolized by P450 system.
   (b) Serotonin syndrome can occur and presents with symptoms and signs including agitation, confusion, tachycardia, hypertension, dilated pupils, and muscle rigidity.
   (c) SSRIs decrease platelet serotonin content and are associated with an increased GI bleeding especially is co-prescribed with NSAIDs

Question 25

Tricyclic antidepressants

Answer 25

2. Tricyclic antidepressants (amitriptyline, imipramine, and
   others).
   Issues:
   (a) QRS, PR, and QTc prolongation due to the depletion of cardiac noradrenergic catecholamines.
   (b) There is an increased propensity to develop malignant dysrhythmias.
   (c) Exaggerated response to ephedrine due to increased postsynaptic norepinephrine content. The use of a direct-acting vasopressor drug, such as phenylephrine, is advisable.
   (d) Serotonin syndrome may occur

Question 26

MAOI

Answer 26

3. Monoamine oxidase inhibitors (phenelzine, moclobemide,
   and others).
   Issues:
   (a) Exaggerated response to ephedrine. Use direct-acting
   vasopressor drugs (phenylephrine).

Question 27

Mood stabilizers

Answer 27

4. Mood stabilizers.
   Issues:
   (a) Lithium is approved for the treatment of manic episodes and for maintenance and as a relapse preventative strategy in bipolar disorder. Lithium has anti-suicidal and neuroprotective properties. The use of lithium has decreased somewhat in recent years due to concerns about its toxicity (vide infra) [8].
   Blood level monitoring is recommended in view of its narrow therapeutic range (0.8–1.2 mmol/l measured 12 hours after last dose)
   Issues:
   (i) Side effects that can occur within the therapeutic range include hypothyroidism and diabetes insipidus.
   (ii) Toxicity can be caused by excessive intake or decreased excretion of lithium is seen when levels of the drug exceed the therapeutic range.
   Symptoms of toxicity include tremor, lethargy, low muscle tone, restlessness, ataxia, and eventually coma.
   (iii) Lithium is not metabolized but almost entirely excreted by the kidney. Renal impairment is a contraindication to the use of lithium.
   Dehydration increased plasma lithium levels.
   (iv) Cardiac effects include reversible T wave changes and increase risk of Brugada syndrome in susceptible individuals.
   (v) Increased sensitivity to anesthetic agents—decreases neurotransmitter release in the central and peripheral nervous systems.
   (vi) NSAIDs may decrease excretion of lithium.
   (vii) Nephrotoxic.
5. 20% will suffer a decline in renal function.
6. 20% will develop diabetes insipidus.
   (viii)Consensus recommendation is not to discontinue preoperatively.

Question 28

Carbamezapine

Answer 28

(b) Carbamazepine is an anticonvulsant used in the management of bipolar disorder, trigeminal neuralgia, and epilepsy.
Issues:
(i) Toxic epidermal necrolysis and Stevens-Johnson syndrome have been reported espe-cially in individuals from Asia or of Asian ancestry.
(ii) Aplastic anemia and agranulocytosis have been reported.
(iii) Induces the P450 enzyme system and chronic treatment will enhance metabolism of benzodiazepines, opioids, and most volatile anesthetics.
(iv) Inappropriate antidiuretic hormone (ADH) syndrome can occur as carbamazepine stimulates the release of vasopressin. Hyponatremia
should be investigated by assessing the serum and urine osmolality. Serum osmolality <280 mOsm/kg and a high urine osmolality >100 mOsm/kg is diagnostic of inappropriate ADH syndrome

Question 29

Valproate

Answer 29

(c) Valproate is used to treat bipolar disorder, anxiety, epilepsy, and to prevent migraine.
Issues:
(i) Hepatoxicity especially in children under 2 years of age, usually occurs within the first 6 months of treatment.
(ii) Teratogenicity such as neural tube defects, careful consideration is required when used in female migraine patients.
(iii) Pancreatitis that can occur at any time during treatment (even years after commencement)

Question 30

Antipsychotics

Answer 30

5. Antipsychotics.
   (a) Typical (prochlorperazine, chlorpromazine, and others): act by blocking dopamine, histamine, and α1 adrenergic and cholinergic receptors.
   Issues:
   (i) Extra-pyramidal syndromes can occur.
   (ii) Seizures (especially chlorpromazine).
   (iii) Postural hypotension is not uncommon.
   (iv) Neuroleptic malignant syndrome may occur; this is manifest by hyperthermia, rigidity, and autonomic dysfunction.

Question 31

Atypical antipsychotics

Answer 31

(b) Atypical (quetiapine, risperidone, and others): these block receptor subtypes of dopamine and less likely to have extra-pyramidal syndromes.
Issues:
(v) Seizures (especially quetiapine).
(vi) Neuroleptic malignant syndrome.
(vii) Postural hypotension.

Question 32

Clonazapam

Answer 32

(c) Patients being treated with clozapine for the management of treatment-resistant schizophrenia deserve special surveillance perioperatively. Although especially effective in managing this condition and reducing suicide rates, it is associated with the development of myocarditis and cardiomyopathy, usually within the first month of treatment [9]. Additionally, there is a risk of agranulocytosis after initiation of therapy.

Question 33

How Should Psychiatric Patients Be Managed
Preoperatively?

Answer 33

○ Patients should be maintained on their psychotropic medications perioperatively, mindful of drug side effects and interactions. The consequences of abrupt withdrawal of therapy can be very distressing for the patient and significantly exacerbate the underlying psychiatric state. In a brittle patient who is undergoing a procedure with an anticipated inhospital admission of longer than 24 hours, requesting a psychiatric consultation during the hospital stay is appropriate and worthy of consideration.
○ The patient was restarted on lithium and quetiapine with rapid resolution of her hypomania. Surgery was rescheduled within 1 month of re-initiation of therapy and proceeded without inciden

Question 34

True/False Questions
1. Mental illness is
(a) Not common in the surgical population
(b) Untreated in a significant minority of patients
(c) Difficult to assess in the clinic
(d) A consideration in the consent process
(e) Not a factor in postoperative morbidity

Answer 34

1a.F
1b.T
1c.F
1d.T
1e.F

Question 35

T/F
2. In the psychiatric patient being assessed for surgery the following are appropriate:
(a) A mood assessment by the patient and the physician
(b) An inquiry regarding sadness/being down
(c) Assessment of renal function in the patient on lithium
(d) Assessing the ECG for QTc prolongation in a patient on tricyclic antidepressants
(e) Discontinuing psychotropic medications preoperatively to avoid side effects

Answer 35

2a.T
2b.T
2c.T
2d.T
2e.F

Question 36

What Is Super Morbid Obesity? How Is Obesity Defined and Classified?

Answer 36

○ Obesity is defined and classified according to body mass index (BMI), which is weight in kilograms divided by the height in meters squared (kg/m2). ○ The World Health Organization (WHO) and National Institutes of Health (NIH) have classified obesity according to BMI (Table 45.1) [1].
○ The terms “severe obesity” (BMI 35–39.9), “morbid obesity” (BMI 40–49.9), and “super morbid obesity” (BMI ≥ 50) are also in occasional use [2]

Question 37

What Medical Comorbidities Can Be Seen in Patients with a High BMI?

Answer 37

• Cardiovascular disease
– Hypertension, coronary artery disease, heart failure, hyperlipidemia, cerebrovascular disease, thromboembolic disease
• Respiratory
– Obstructive sleep apnea, obesity hypoventilation syndrome, pulmonary hypertension
• Endocrine
– Diabetes mellitus, hypothyroidism, metabolic syndrome
• Gastrointestinal
– Hiatus hernia, GERD, non-alcoholic fatty liver disease

Question 38

What Complications Is the Obese Patient
Subject to in the Perioperative Period?

Answer 38

• Venous thromboembolism—obesity is an independent risk factor.
- Mechanical compression devices, early ambulation, andthromboprophylaxis with low molecular weight or unfractionated heparin are recommended by the American Society for Bariatric and Metabolic Surgery.
• Rhabdomyolysis.
• Wound infection—strong evidence exists for surgical site infection in obese patients undergoing a variety of orthopedic and non-orthopedic surgeries.
• Pulmonary aspiration secondary to GERD and/or the presence of a gastric band.
• Atelectasis and pneumonia—found to be the two leading pulmonary complications following bariatric surgery in study of over 158,000 patients.
• Failed intubation.
• Postoperative cognitive decline.

Question 39

What Physiological Changes Can Be Seen in the Respiratory System of the Obese Patient?

Answer 39

○ Respiratory mechanics are significantly altered in obesity.
○ Reduction in chest wall compliance (secondary to increased chest wall mass) and lung compliance (secondary to the effects of increased intraabdominal pressure on the diaphragm) produces a restrictive pattern of lung impairment.
○ Lung volumes are reduced, especially functional residual capacity (FRC), leading to de facto right-to-left shunting in dependent regions with ensuing rapid desaturation during apnea [12].
○ The increased resting metabolic rate of obesity leads to increased work of breathing and increased oxygen demands, resulting in rapid, shallow breathing

Question 40

What Is the Incidence of OSA in Obese Patients?

Answer 40

○ Severe OSA has been diagnosed in 10–20% patients with BMI > 35, and it may be undiagnosed in at least a further 10–20% [13]. Indeed, in a study of 1042 volunteers who underwent polysomnography, the incidence of moderate to severe OSA [apnea hypopnea index ≥15) was 11% in normal
weight males, 21% in overweight males, and 63% in obese males [14]

Question 41

How Is OSA Screened for in the Anesthesia
Pre-admission Clinic?

Answer 41

○ The STOP-Bang screening questionnaire has been validated in several studies of surgical patients.
○ If positive, formal testing with overnight oximetry or polysomnography is appropriate in elective surgery when time permits.
- Polysomnography results will give an indication of severity of OSA.
○ Risk of morbidity and mortality increases with increasing severity of OSA. ○ CPAP is the usual mode of treatment for OSA.
○ OSA patients who use CPAP should be questioned with regard to compliance with the device as well as device settings. It is normally set between 5 and 20 cm H2O.
○ A more comprehensive overview of OSA can be found in Chap. 13.

Question 42

What Is Obesity Hypoventilation Syndrome (OHS)?

Answer 42

○ OHS is a combination of daytime/awake hypoventilation and obesity which results in hypoxemia and hypercapnia.
○ It is a diagnosis of exclusion made after other conditions known to be associated with hypoventilation have been ruled out.
○ Patients with OHS have a significantly higher BMI compared to obese patients without hypercapnia.
○ In obese patients with OSA, the prevalence of OHS is estimated at
9–20%

Question 43

Why Do Obese Patients Get Pulmonary Hypertension?

Answer 43

○ This may be a consequence of untreated OSA, OHS, obesity-related heart failure, or chronic thromboembolic disease.
○ OSA and OHS are independent risk factors for the development of pulmonary hypertension.
○ Up to 20% of patients with OSA and as many as 50% of patients with OHS develop pulmonary hypertension.

Question 44

Right Ventricular Systolic Pressure (RVSP) and Pulmonary Artery Systolic Pressure (PASP) Were Reported Together for our Patient. Is RVSP the Same as PASP?

Answer 44

○ RVSP is equal to PASP in the absence of right ventricular outflow tract obstruction [20].
○ Pulmonary hypertension and its diagnosis are explored in more detail in Chap. 8.
○ Bearing in mind the limitations of echocardiography when compared with
right heart catheterization for diagnosis of pulmonary hyperten-sion, an echocardiography-derived PASP <40 mmHg is reassuring for ruling out the presence of pulmonary hypertension in the absence of other clinical or echocardiographic findings.

Question 45

How Should Respiratory Function Be Assessed Preoperatively in the Obese Patient?

Answer 45

• If OSA is undiagnosed, use a validated screening tool, e.g., STOP-Bang score, and proceed to polysomnography or overnight oximetry if indicated.
• If OSA is diagnosed, assess compliance with CPAP treatment.
• Arterial blood gas (ABG) is useful for establishing baseline levels of hypoxemia and hypercapnia, if present.
- Moreover, a diagnosis of OHS is made using ABG on room air during wakefulness. PaO2 < 70 mmHg and, PaCO2 ≥ 45 mmHg indicate OHS [21]. - Finally, serum HCO3 ≥ 28 mmol/L in the presence of a STOP-Bangscore ≥ 3 increases the specificity of this screening tool to 85% for diagnosis of OSA.
• Chest radiograph may be useful if heart failure or risk factors are present.
• Spirometry and body plethysmography.
• Echocardiogram +/− right heart catheterization to assess for presence and severity of pulmonary hypertension.

Question 46

What Perioperative Complications Is the Patient with OSA Subject To?

Answer 46

○ Several studies demonstrate a higher perioperative complication rate in the presence of OSA.
○ Indeed, untreated OSA can almost double (44% vs. 28%) the risk of postoperative cardiac and respiratory complications [26].
○ Complications reported across multiple studies include respiratory failure, opioid-exacerbated respiratory depression, aspiration pneumonia, emergency postoperative re-intubation, arrhythmia, myocardial infarction, confusion and delirium, unanticipated ICU admission, and prolonged duration of stay.

Question 47

How Can the Obese Patient with OSA Be Optimized Preoperatively?

Answer 47

○ Compliance with CPAP use should be assessed.
- In a study of CPAP adherence of newly diagnosed OSA patients prior to
elective surgery, only 25% were using their CPAP devices for ≥4.5 hours per night [27], the typical minimal number of hours of use thought to be of benefit.
- The systemic benefits of CPAP are well documented; when used as prescribed it has been shown to reduce postoperative blood pressure,
cardiovascular complications , and length of stay.
- Clinical improvement becomes significant after 3 months of CPAP therapy, and a shorter period may be beneficial.

Question 48

Are Obese Patients More Difficult to Intubate? Are Any Airway Evaluation
Techniques of Specific Value in This Patient Population

Answer 48

○ This is controversial, and the evidence is not overwhelming for or against. ○ The Fourth National Audit Project (NAP4) found airway problems to occur twice as commonly in obese and four times as commonly in morbidly obese patients compared with patients with BMI ≤ 30 [32].
- However, “airway problems” do not equate to difficult intubation.
- Airway problems also included supraglottic airway-related problems, failed face mask ventilation, and extubation-related problems.
- The proportion of primary airway problems related to intubation was similar in obese and non-obese patients in this large audit.
- The primary airway problems which did occur more frequently in obese patients were related to supraglottic device placement and failed mask ventilation.
- Further evidence can be found in a retrospective study of almost 500,000 patients in four tertiary care centers which found that BMI ≥ 30 was an independent risk factor for difficult mask ventilation combined with difficult direct laryn-goscopy, i.e., simultaneous occurrence [33].
- Short neck, higher neck circumference, Mallampati score III or IV, and mandibular protrusion have been associated with difficult mask ventilation in obese patients [34].
○ Mallampati score III or IV, OSA, reduced cervical spine mobility, thyromental distance, and neck circumference have been identified as risk factors for difficult intubation in obese patients [35, 36]. A finding of note in all of these studies is that predictors of difficult intubation in obese patients are no different than those in non-obese patients.

Question 49

What Physiological Changes Can Be Seen in the Cardiovascular System in the Presence of Obesity?

Answer 49

• Left ventricular failure: Increased total body weight promotes a larger circulating blood volume and cardiac output. This increase in cardiac output is generated by an elevation in stroke volume. The increased systolic work-
load leads to left ventricular (LV) hypertrophy, which progresses over time to LV dilatation and LV failure. LV diastolic dysfunction also develops, resulting in incomplete left atrial (LA) emptying, LA dilatation, and atrial fibrillation [37]. LVF in the presence of sleep apnea/obesity hyperventilation-induced pulmonary hypertension may be accompanied by right ventricular failure (RVF).
• Hypertension: The increased prevalence of primary hypertension in obesity is multifactorial in pathogenesis.
- Endothelial dysfunction and atherosclerosis in combination with pathological activation of the renin-angiotensin-aldosterone system and altered sodium metabolism have all been implicated.
• Coronary artery disease: Diabetes, dyslipidemia, hypertension, and a chronic inflammatory and prothrombotic state are risk factors for myocardial infarction in obesity.

Question 50

What ECG Abnormalities Are Associated with Obesity?

Answer 50

○ Most ECG changes seen in obese patients result from altered cardiac morphology, although fatty infiltration of the conduction system can cause arrhythmias [37].
○ More commonly seen alterations include leftward shift of the P, QRS, and T wave axes (reversible with significant weight loss), alterations in P wave morphology, changes associated with left ventricular hypertrophy, low QRS voltage, T wave flattening in the inferolateral leads, and QT interval prolongation.
○ There have been several case reports of sudden death in obese individuals usually involving co-existent LVH and/or congestive cardiac failure.

Question 51

How Is the Obese Patient Assessed Preoperatively from a Cardiac Perspective?

Answer 51

• A focused history should assess for the presence of hypertension, hyperlipidemia, diabetes, symptoms of coronary artery disease, cardiac failure, and peripheral vascular disease, e.g., transient ischemic attacks (TIAs) or intermittent claudication.
• The Revised Cardiac Risk Index (RCRI) and the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) risk model calculator can be useful in determining which patients require further
investigation [41, 42].
• Typical symptomatology of coronary artery disease may not be available as a result of the patient’s physical inactivity or immobility. If functional assessment, e.g., meta-bolic equivalent (MET) or Duke Activity Status Index
(DASI) score [43], is not helpful or indicates poor functional capacity, a dobutamine stress echocardiogram or myocardial perfusion scan proceeding to angiography as appropriate should be performed where clinical suspicion
is strong.
• The decision to proceed to angiography after abnormal pharmacological stress testing depends on the patient’s willingness to undergo a revascularization procedure (angiography and stenting or coronary artery bypass grafting), and the urgency of the elective surgery under consideration. ○ The American College of Cardiology/American Heart Association Guideline on Perioperative Cardiovascular Evaluation and Management of Patients Undergoing Noncardiac Surgery can be a useful guide in this regard [46].
• For patients with heart failure who are clinically stable, resting preoperative echocardiography is not routinely recommended for cardiac risk estimation unless there is evidence of an undiagnosed severe obstructive abnormality, e.g., aortic stenosis, mitral stenosis, or severe pulmonary hypertension. If echocardiography is indicated, a transthoracic approach may not provide adequate views.

Question 52

Is the Management of Hypertension Any Different in Obese Versus Non-obese Patients?

Answer 52

○ In obese patients, ACE inhibitors and angiotensin II receptor blockers (ARBs) are the first line of treatment.
- This is based on the role of the renin-angiotensin-aldosterone system in the pathogenesis of hypertension in obesity.
- Moreover, ACE inhibitors and ARBs may be beneficial as a result of their ability to increase insulin sensitivity [48].
○ A thiazide or loop diuretic can be used as a second-line agent or in combination with an ACE inhibitor.
- Care must be taken with thiazides, as they may exacerbate insulin resistance and dyslipidemia.
○ Beta blockers, particularly of the non-vasodilating variety, e.g., metoprolol and atenolol, unless specifically indicated for treatment of atrial fibrillation, should be avoided due to their association with insulin resistance.

Question 53

What Is Metabolic Syndrome?

Answer 53

○ In simple terms, it is the co-existence of multiple risk factors for type 2 diabetes and cardiovascular disease.
○ At various times, it has also been called insulin resistance syndrome,
syndrome X, and obesity dyslipidemia syndrome.
○ Several definitions exist, the most common being that of the National Cholesterol Education Program, which says that metabolic syndrome requires three or more of the following criteria:
(a) Abdominal obesity (waist circumference >102 cm in males and >88 cm in females)
(b) Glucose intolerance (fasting glucose ≥110 mg/dL)
(c) Hypertension (≥130 mmHg systolic and / or ≥85 mmHg diastolic)
(d) Hypertriglyceridemia ≥150 mg/dL
(e) HDL cholesterol <40 mg/dL in males and <50 mg/dL in females
○ The incidence of metabolic syndrome in the Bariatric Outcomes Longitudinal Database investigation of more than 158,000 bariatric surgery patients was 12.7%.
- It was an independent significant risk factor for postoperative pulmonary complications.

Question 54

Is Awareness More Common in Obese Patients?

Answer 54

○ The Fifth National Audit (NAP5) into awareness under anesthesia found that obesity is associated with a higher risk of accidental awareness [51].
○ Several reasons were postulated, including inadequate drug dosing secondary to the altered pharmacokinetics seen in obesity, i.e., increased body fat content, blood volume, and cardiac output in combination
with alterations in plasma protein binding.
○ The association between obesity and difficult airway was also implicated,
though evidence is lacking.
○ The possibility of performing this surgery under a regional anesthesia technique was proposed by the patient’s surgical team.
- A paravertebral or epidural block would be required to provide surgical anesthesia for this patient. High thoracic neuraxial and paravertebral techniques require an advanced skill set even in non-obese individuals. The higher risk of failure was deemed not acceptable in this instance, and the
option was not explored further. The need for urgent airway intervention after failed regional anesthesia is a concept also explored in NAP4 [32]. Awake fiberoptic intubation in controlled circumstances was opted for and successfully executed. Regional anesthesia may have been an option as part
of a multimodal analgesia approach with the aim of reducing opioid use and associated postoperative complications. The patient was admitted for overnight monitoring. Regarding suitability for ambulatory surgery, this decision must be made on a per case basis, taking into account comorbidities, severity of OSA, surgical risk, type of anesthesia delivered,
and home support. Currently, there is insufficient evidence available to create guidelines for obese patients undergoing ambulatory surgery, a fact acknowledged by the Society for Ambulatory Anesthesia on Clinical Practice Guidelines [52].

Question 55

True/False Questions
1. (a) A patient classified as having super morbid obesity could also be said to have class II obesity.
(b) There is strong evidence that obesity is an independent risk factor for the development of postoperative wound infection.
(c) Pneumothorax resulting from positive pressure ventilation is a common perioperative complication.
(d) Increased neck circumference has been identified as a predictor of difficult intubation in obese patients.
(e) ACE inhibitors are contraindicated for the management of hypertension in obesity.

Answer 55

1a.F
1b.T
1c.F
1d.T
1e.F

Question 56

True/False
2. (a) The STOP-Bang questionnaire is not validated for use in obese patients.
(b) Obesity hypoventilation syndrome by definition occurs in awake patients.
(c) CPAP for OSA is not effective when used for less than 6.5 hours per night.
(d) Untreated OSA has been shown to almost double the risk of postoperative pulmonary and cardiac complications.
(e) Measurement of serum HCO3 ≥ 28 mmol/L in the presence of a STOP-Bang score ≥ 3 increases the specificity of this screening tool.

Answer 56

2a.F
2b.T
2c.F
2d.T
2e.T

Question 57

What Are the Physiological Changes Associated with Advanced Age?

Answer 57

○ This subject has recently been comprehensively reviewed by
Young and Maguire [1].
○ With aging, cognitive function is decreased, independent of dementia, due to neuronal loss, reduced neuronal growth and synaptic dysfunction.
- These changes make the older patient more vulnerable to delirium.
- The impairment of sensory functions, especially vision and auditory capabilities, can present practical and cognitive challenges.
○ Pulmonary function begins an inexorable decline in most individuals after the mid-30s.
- Structural reductions in elastic recoil, increased chest wall rigidity, and decreased respiratory muscle effort reduce effective lung volumes, and
closing capacity reaches supine functional residual capacity by the mid-40s.
- Ventilation-perfusion mismatch is increased with age as the changes redistribute ventilation towards the less perfused apices of the lungs.
- Diffusion capacity also diminishes with age.
○ The cardiovascular system undergoes a plethora of changes with aging.
- One of the most consequential is the loss of elastin in the media of the vascular tree and its replacement by collagen and Ca++.
- These alterations increase pulse wave velocity and augment systolic blood pressure, which in turn evokes compensatory changes in myocyte physiology, function, and structure, enhancing vulnerability to cardiac ischemia, infarction, and failure.
- Baroreceptor and β-receptor function deteriorate impairing blood pressure stability, particularly under anesthesia or preload-reduced conditions.
○ Temperature regulation is less effective, and basal metabolic rate is reduced with aging underscoring the need for assessment of nutritional status during preoperative assessment.

Question 58

How Does Aging Influence Medication Kinetics?

Answer 58

○ Body water content and muscle mass decrease up to 30% with age and fat content may increase by 30%, leading to altered volumes of drug distribution, in addition, glomerular filtration rate and liver blood flow decrease, as does enzymatic function, prolonging drug elimination half-lives [3].
○ Drug dynamics are also influenced by age-related decreases in receptor density, function, and signaling. In the case of anesthetic drugs, titration and reduction in the administered dose by up to 50% may be warranted.
○ It is now well established that older patients can be subject to underuse of appropriate drugs, overuse of inappropriate drugs, failure to recognize adverse drug events, polypharmacy (> five drugs/day), and failure to adjust drug dosing in the face of reduced renal function/lean body mass.
○ In the perioperative setting, renal function should be assessed as many drugs indicated in the management of age-related conditions are subject to renal elimination.
- These include sotalol, olmesartan, metformin, most antibiotics, lithium, rivaroxaban, and apixaban.
- All nonessential medications and supplements should be discontinued

Question 59

What Is Frailty?

Answer 59

• It can be described as a a multidimentional syndrome of decresed physiological reserveand deminished response to stress, this includes physical status, mental health and cognition.
• Frailty indices relate deficit accumulation such as inability to perform routine physical tasks, recent weight loss, perceived mental status, co-existing disease, and impaired physical fitness to a vulnerability state
  that portends an adverse outcome in the face of even relatively
  minor stresses.
• Frailty has also been described phenotypically where the presence of specific physical attributes such as self-reported exhaustion, unintentional weight loss, poor grip strength, and slowness on walking define, depending on how many are present, the degree of frailty.
• Both these approaches have limitations, not the least being the role of
  weighting of individual deficits or physical attributes to risk outcome.
• Nevertheless, these measures of frailty offer a general framework for identifying a cohort who are greater risk from an otherwise relatively minor trespass.

Question 60

How Can Frailty Be Identified in the Preoperative Clinic?

Answer 60

○ There are multiple scales available to assess aged individuals with the goal of identifying the frail subgroup.
○ When studied in the surgical setting, most, if not all, appear to identify those patients most at risk for death.
○ In an elegant review of this topic, McIsaac et al [8]. concluded that the Clinical Frailty Scale (CFS) is an instrument that seems reasonable to use in the busy preoperative setting.
- The CFS (Fig. 46.1) scores subjects from 1 (Very fit) to 9 (Terminally ill) with those scoring 5 (Mildly frail – needs help in high-order inde-pendent activities of daily living such as shopping, walking outside alone, meal preparation, and housework), or above, being described as being in varying degrees of frailty.
- The CFS score can be rapidly obtained and does not require any special training or equipment to administer.

Question 61

Is Frailty Associated with Adverse Outcome Following Surgery?

Answer 61

○ There is a clear relationship between frailty and surgical morbidity and mortality.
○ There is emerging data that subjecting frail or very frail patients to low stress (e.g., inguinal hernia repair) or moderate stress procedures (e.g.,,cholecystectomy) may result in 90-day mortality rates approaching 10% and 30%, respectively.

Question 62

Can One Predict Which Individual Patient Is Most Likely to Die Using a Frailty Scale?

Answer 62

○ This is not a question that can be answered using frailty scales .
○ What is clear is that, even for those of identical chronological age, being frail as distinct from not frail carries with it a significant burden of morbidity and mortality after both elective and emergency surgery.
○ Awareness and identification of frailty allows patients consider risk appropriately and can facilitate directed interventions to possibly improve outcome.
○ For those undergoing surgical procedures who already have limited life expectancy, risk of death may not be as important as an improvement in the quality of remaining life promised by the surgical intervention.
- Here too, identification of frailty, provides context and facilitates choice.

Question 63

Are There Interventions That Can Ameliorate Adverse Outcomes of Surgery in the Elderly?

Answer 63

• Encouragingly, there is emerging evidence that adapting proven models of geriatric care in medical patients to the surgical setting can result in a decrease in major complications and death even in emergency surgery.
• This approach is built on the concept that patient co-location, interdisciplinary team care, mindfulness of geriatric physiology pharmacodynamics, and focused rehabilitation can positively influence outcome.
• In addition, in the elective surgical population targeted interventions to improve physical performance, nutrition, and manage mental issues prior to surgery may offer promise in reducing morbidity and mortality in older patients.

Question 64

What Are the Specific Issues That Should Be Addressed in the Preoperative Assessment of the Frail Patient?

Answer 64

Best practice recommendations regarding the perioperative care of the geriatric patient have been published by the American College of Surgeons and the American Geriatrics Society. The following issues should be addressed during the preoperative visit:
(a) The treatment preferences of the patient and documentation of advanced directives
(b) Documentation of the proxy or surrogate decision maker
(c) Comprehensive discussion of risks and what responses are acceptable in the face of life-threatening problems
(d) Consider shortened clear fluid fasting (allow up to 2 hours preoperatively)
(e) Follow medication recommendations as discussed above
(f) Offer regional anesthesia techniques if feasible
(g) Develop a postoperative pain management plan using an opioid-sparing technique

Question 65

True/False Questions
1. The following are normal features of aging:
(a) A decrease in cognitive function
(b) Redistribution of ventilation to the base of the lungs
(c) A decrease in pulse wave velocity due to replacement of elastin by collagen
(d) Body water content decreases of up to 30%
(e) An increase in β-receptor density

Answer 65

1a.T
1b.F ;
1c.F
1d.T
1e.F

Question 66

True/False
2. In patients older than 65 years of age
(a) inability to perform routine physical tasks is a marker of frailty
(b) a frailty assessment may be helpful in determining risk
(c) if frailty is diagnosed then a CT should be performed to our rule a cerebral lesion
(d) polypharmacy is not uncommon
(e) renal function should be assessed before major surgery

Answer 66

2a.T
2b.T
2c.F
2d.T
2e.T

Question 67

What Is Opioid Tolerance?

Answer 67

• Tolerance to any drug is a decrease in pharmacological effect occurring after repeated administration.
• It may be a consequence of receptor desensitization, downregulation, or internalization.
• Tachyphylaxis can be thought of as the development of tolerance in a shorter time frame, possibly within hours, when patients are exposed to a
  high initial dose or repeated small doses .
• The dose-response curve is shifted to the right, i.e., decreased potency can be overcome by increasing the dose of the drug (Fig. 47.1).

Question 68

What Is the Difference Between Opioid Tolerance and Opioid-Induced Hyperalgesia (OIH)?

Answer 68

• OIH is a process that has been shown to occur where the administration of opioids can activate pronociceptive mechanisms in the central nervous system, resulting in a paradoxical increase in pain sensitivity with continued opioid administration (Fig. 47.2).
• Formerly thought to take months to develop (e.g., methadone maintenance patients), it is now known to occur over a matter of hours in certain situations, e.g., high-dose intraoperative remifentanil administration [4].
• Remifentanil has been particularly implicated, but it is possible that OIH occurs with acute or chronic exposure, high or low doses, of any opioid or route of administration.
• Nociceptive sensitization is likely caused by neuroplastic changes in the central and peripheral nervous systems caused by opioid exposure, leading to paradoxical worsening of pain with increasing opioid doses.
• Both opioid tolerance and OIH require an increased dose to achieve an increase in effect
• The difference is that in the long term, OIH is made worse by increasing opioid administration

Question 69

What Is the Significance of the Similarities Between Opioid Tolerance and OIH? Can a Definitive Diagnosis Be Made During Preoperative Evaluation?

Answer 69

• The significance lies in how each condition is treated.
• Determining whether a patient is opioid tolerant or has OIH cannot be achieved with complete confidence, i.e., there are no definitive diagnostic criteria. However, increasing the dose of opioid is a simple measure that may be informative—the tolerant patient improves, while the OIH patient
  does not improve or worsens.
• Presence of allodynia and hyperalgesia, particularly widespread hyperalgesia, makes a diagnosis of OIH more likely
• Quantitative sensory testing (a variety of tests can be used to test the response to light touch, vibration, pressure, and temperature) may be helpful.
• If the clinical picture clearly points towards opioid tolerance, the patient should be advised to continue taking their normal daily opioid dose up to and throughout the perioperative period. Conversely, a trial of opioid dose reduction could be utilized in the patient with clear diagnostic indicators of
  OIH.

Question 70

How Are the Terms Addiction and Physical Dependence Defined?

Answer 70

• Addiction is a chronic, relapsing neurobiological disease with genetic, psychosocial, and environmental factors influencing its development.
• It is characterized by compulsive drug seeking and use, impaired control over use, and continued use despite harm.
• Physical dependence is a state of neuro-adaptation to a specific opioid characterized by a withdrawal syndrome produced by abrupt cessation, rapid dose reduction, decreasing plasma drug level, or administration of an antagonist.

Question 71

How Should the Opioid-Tolerant Patient Be Evaluated Preoperatively?

Answer 71

• An important component of the preoperative visit is to identify patients with opioid tolerance to facilitate establishing a comprehensive perioperative analgesia plan.
• A thorough history of opioid use is required, including specific agents, dose, frequency, and duration.
• The patient presented above was noted to require controlled release hydromorphone 15 mg twice daily and immediate release hydromorphone 2–4 mg as required every 4 hours for breakthrough pain. On further questioning, it emerged that he used 2 mg four times per day on average to control breakthrough pain. This amounts to hydromorphone 38 mg daily on average, his baseline daily requirement.
• Clinical indicators of OIH may warrant further investigation at this juncture.
• At the very least, an enquiry should be made into the outcome of any recent increase in opioid dose.
• The acute perioperative pain service should be consulted or at least made aware of the patient.
• Patient education and reassurance with the aim of alleviating perioperative anxiety are likely as important as any other step at the preoperative phase.
• An analgesia treatment plan can be discussed with the patient and documented
• This can include a written opioid agreement. It is helpful for both physician and patient to have a discussion regarding pain management expectations.
• Clinical indicators of addiction should be sought, e.g., out-of-control opioid use, pain treatment plans unavailable, unclear reason for opioid use, illicit opioid use, impaired quality of life, or lack of concern regarding harmful effects of opioid use.
• Preoperative opioid misuse has been associated with increased morbidity and mortality after elective orthopedic surgery. Menendez et al.
  demonstrated a combined adverse risk incidence of 13% in postoperative patients with opioid-use disorder [7].
• Pneumonia, respiratory failure, myocardial infarction, and renal failure were some of the complications seen. Therefore, referral to addiction services for evaluation and treatment may improve postoperative outcomes

Question 72

How Should the Patient Taking Oral Opioids Be Managed Preoperatively?

Answer 72

• This patient population is at high risk for severe postoperative pain and is likely to benefit from advance analgesia planning.
• The patient should be advised to take their usual baseline opioid dose on the day of surgery. If oral administration is not possible, the oral opioid dose can be converted to a corresponding intravenous dose of the same agent
  (Table 47.1).

Question 73

How Should the Patient Taking Transdermal Opioids Be Managed Preoperatively?

Answer 73

• The most common transdermal preparations are fentanyl and buprenorphine.
• Regardless of the specific agent, there is a risk of decreased absorption in complex surgeries involving large fluid shifts or skin temperature fluctuation, e.g., hypo-thermia and rewarming affects the kinetics of transdermal
  fentanyl. If this is expected, the fentanyl patch can be removed at induction.
• An equianalgesic dose of intravenous morphine or hydromorphone can then be used intraoperatively and for the first 24–48 postoperative hours via patient-controlled analgesia (PCA) such that the daily opioid requirements are met.
• If the surgery is of a less complex nature, the fentanyl patch can be maintained throughout the perioperative period.

Question 74

Describe an Approach to Preoperative Evaluation and Management of the Patient Taking Buprenorphine

Answer 74

• Buprenorphine is a partial mu opioid receptor agonist that has kappa antagonist properties.
• It is used for a variety of indications, including treatment of opioid addiction and acute and chronic pain.
• Perioperative management of patients taking buprenorphine is based on expert opinion and is largely inconsistent.
• It has previously been thought that adequate perioperative analgesia cannot be achieved in the patient taking buprenorphine long term due to its opioid antagonist properties.
• This reasoning may not be entirely accurate. A recent systematic review of 18 studies (mostly comprised of case reports and series but with one controlled and four observational studies) concluded that there was no evidence against continuing buprenorphine use perioperatively, particularly when the dose ≤16 mg sublingually [10].
• When the indication for buprenorphine use is addiction with a significant risk of relapse, a strong rationale for perioperative discontinuation should be present, supported by both the patient and the surgical team.
• Our practice is to continue buprenorphine perioperatively as a matter of routine.

Question 75

How Should the Patient Taking Intrathecal Opioids Be Managed Preoperatively?

Answer 75

• Intrathecal drug delivery systems for patients with malignant and chronic non-malignant pain or spasticity can be maintained during surgery for baseline opioid requirements.
• The intrathecal opioid dose should be recorded at the preoperative visit.
• The dose cannot be adjusted to treat acute postoperative pain, and supplemental multimodal analgesia should be used for this purpose.
• The intraoperative anesthetist and surgeon should be informed of the presence of an intrathecal drug delivery system, as it may interfere with the surgical field, or associated implanted electrodes may be subject to
  heating with the use of cautery.
• Lumbar epidural anesthesia is not contraindicated but should be attempted with image guidance to avoid implanted components .
• The perioperative analgesia plan should include non-opioid multimodal
  adjuncts, e.g., nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, ketamine, regional anesthesia techniques, and/or lidocaine infusion.
• Long-acting opioids should be avoided postoperatively. This includes PCA with a continuous basal rate, though PCA is not contraindicated.
• Continuous pulse oximetry should be utilized postoperatively.
• Communication with the chronic pain physician who attends to the patient is necessary both pre- and post-operatively.

Question 76

How Should the Patient on Maintenance Methadone Be Managed Preoperatively?

Answer 76

• Methadone is a synthetic opioid agonist used both for analgesia and withdrawal management in opioid-dependent patients.
• With an elimination half-life significantly longer than other opioids (8–59 hours; average 23 hours), it is administered once daily for opioid agonist therapy.
• Despite the fact that its effect on opioid withdrawal can last up to 48 hours, its analgesic effect is much shorter at approximately 6 hours [12].
• Subsequently, the authors prefer to continue baseline methadone throughout the perioperative period, if possible, while using shorter acting opioids, e.g., morphine or hydromorphone as part of a comprehensive multimodal analgesia technique with an emphasis on the non-opioid component.
• Several factors can complicate perioperative analgesic management in the patient using methadone maintenance therapy. These patients are likely to have elements of both tolerance and OIH.
• They also develop cross-tolerance entailing higher and more frequent doses of other opioid analgesics [13, 14].
• Finally, patients employing methadone for opioid agonist therapy are occasionally concerned about the risk of addiction relapse perioperatively
  when supplementary opioids are used to treat surgical pain.
• The evidence is sparse, but two small studies did not find evidence of relapse in patients on methadone maintenance therapy treated with additional opioids for surgery [15] and cancer-related pain.

Question 77

What Opioid-Sparing Multimodal Analgesia Techniques Should Be Discussed with This Patient?

Answer 77

• Single shot or continuous neuraxial and peripheral nerve blockade
• Acetaminophen
• NSAIDs
• Ketamine
• Intravenous lidocaine
• Gabapentinoids
• Dexmedetomidine
• Psychosocial, e.g., relaxation, education, behavioral instruction
• Physiotherapy/exercise

Question 78

What Is the Evidence in Favor of Opioid Rotation?

Answer 78

• Opioid rotation (switching from one opioid to an equianalgesic dose of another) is commonly used in palliative care to improve analgesia and reduce the side effects related to one opioid.
• Most evidence for efficacy comes from expert opinion and case series [17], and there is very limited substantiation in the acute pain setting.
• Possible mechanisms include incomplete cross-tolerance and differing receptor activity.
• Rotation is performed by converting to an equivalent dose of a different opioid, using equivalency tables (see Table 47.1) and initially reducing
  the calculated dose by 30–50% to account for incomplete cross-tolerance.

Question 79

Is There Any Evidence That Regional Anesthesia Techniques Are less Effective in Opioid-Tolerant Patients?

Answer 79

• Practitioners of regional anesthesia are familiar with the concept of apparent decreased efficacy of neuraxial and peripheral nerve blockade among opioid-tolerant patients.
• The biopsychosocial model of pain is commonly held accountable, but there is emerging evidence that opioid-tolerant patients may also be less amenable to the effects of regional nerve blockade. Liu et al. demonstrated loss of lidocaine potency in the rat sciatic nerve in vitro after seven daily morphine injections.
• Although analgesic efficacy to morphine recovered completely within days, the loss of lidocaine potency remained 35 days after the last morphine injection.
• Similarly, Vosoughian and colleagues describe shorter duration of spinal anesthesia in opium users (60 +/− 7 minutes vs. 83 +/− 10 minutes p <0.0001).

Question 80

What Modifiable Preoperative Risk Factors Contribute to the Development of Chronic Postsurgical Pain?

Answer 80

• Chronic postsurgical pain (CPSP) occurs in approximately 10% of patients who have surgery [20].
• Several preoperative patient-specific risk factors are known to predispose towards the development of CPSP.
• Preoperative chronic pain and opioid use are notable red flags. These patients can be targeted for preoperative tapering of opioids if OIH is a significant contributory factor.
• Other modifiable risk factors include fear, obesity, preoperative use of benzodiazepines and antidepressants, smoking, alcohol, and illicit drug use.
• Education, psychological counseling, modification of addiction behavior, and weight loss programs may be initiated as part of an integrated multidisciplinary approach to prevention of CPSP.
• Even in the absence of modifiable risk factors, identification of patients who may benefit from perioperative monitoring, opioid restrictive strategies, and postoperative follow-up by a transitional pain service may prove beneficial.

Question 81

True/False Questions
1. (a) Pharmacological tolerance results in a rightward shift of the drug dose-effect curve.
(b) Opioid-induced hyperalgesia results in a leftward shift of the drug dose-effect curve.
(c) Opioid- induced hyperalgesia is usually treated by increasing the opioid dose.
(d) Allodynia is a common sign in the opioid-tolerant patient.
(e) Preoperative opioid misuse is associated with increased postoperative morbidity and mortality.

Answer 81

1a.T
1b.F
1c.F
1d.F
1e.T

Question 82

T/F
2. (a) Buprenorphine should never be continued throughout the perioperative period when the indication for use is opioid addiction.
(b) Patients with intrathecal opioid delivery systems usually have the intrathecal opioid dose increased preoperatively to aid in the treatment of postoperative surgical pain.
(c) Methadone is not an ideal opioid for management of postsurgical pain.
(d) Transdermal preparations of fentanyl may be subject to altered absorption during complex surgeries involving large fluid shifts.
(e) Lidocaine may have reduced potency for nerve blockade in opioid-tolerant patients.

Answer 82

2a.F
2b.F
2c.T
2d.T
2e.T

Question 83

What Is Splenosis?

Answer 83

• Heterotopic transplantation of viable splenic tissue is termed “splenosis.”
• This may occur particularly after traumatic splenic rupture but can also arise following elective splenic surgery.
• The soft tissue nodules are usually located in the abdomen and pelvis but can on occasion be found elsewhere and be mistaken for cancerous lesions

Question 84

What Is Eltrombopag?

Answer 84

Eltrombopag is an oral agonist of the c-mpl receptor, the physiological target of thrombopoietin, and has been approved for the treatment of chronic ITP and aplastic anemia.

Question 85

What Is the Prevalence of Drug Use in the Adolescent/Adult Population?

Answer 85

• The Monitoring the Future study performed annually since 1975 by the University of Michigan’s Institute for Social Research provides a contemporary snapshot of drug use among adolescents in the United States. - The sample size in 2017 was 43,700 students across the nation. Annual prevalence of any cannabis use was 10%, 26%, and 37% in grades 8, 10, and 12, respectively. Daily use was 1%, 3%, and 6%, respectively. Annual prevalence of use across all grades of amphetamine/stimulants ~7%; inhalants (glue, nail polish, solvents etc.) ~ 4%; LSD, cocaine, and 3,4-Methylenedioxy methamphetamine (MDMA) ~ 3%; narcotics other than
  heroin ~2%; methamphetamine ~1%; and heroin ~0.5%.
• In contrast, binge drinking (5+ drinks in a row at least once in the last 2 weeks) across all grades was reported by ~16% of adolescents surveyed.
• The 2017 U.S. National Survey on Drug Use and Health prepared by the Substance Abuse and Mental Health Services Administration provides an insight into adult substance use and abuse in the United States [5].
• Focusing on substance use/misuse in those aged 26 or older reveals the following estimates:
  Past month cannabis use 7.9%; past month misuse of psychotherapeutic drugs (defined as use in a way not directed by a doctor, use without a prescription, and use in supra-therapeutic amounts of tranquilizers, stimulants, and sedatives) ≤ 0.5%; and past month use of cocaine, inhalants,
  heroin, and methamphetamine ≤0.5%. Opioid misuse was more prevalent (3.8%); the most common opioids misused were hydrocodone and oxycodone. Binge drinking was reported by 25% of participants.

Question 86

What Are the Key Issues to Address in the Preoperative Evaluation of a Substance-Using Patient?

Answer 86

• Adolescent and adult patients should be questioned regarding drug and alcohol intake.
• If a positive history is obtained, the nature, dose, frequency, method of administration, and time of last use should be elicited.
• Polysubstance use is very common, and the patient should be prompted to reveal all substances used within the last 3–6 months.
• Recent data suggest that methamphetamine use is increasing. It is being used as an opioid substitute, to manage the side effects of concurrent opioid use, and in some cases to provide a synergistic high.
• Obtaining even a very remote history of illicit drug use (years ago) can be helpful, as it can prompt one to advise the patient to be screened for occult hepatitis/HIV.
• Substance use is a marker for mental health issues. The appearance, behavior, speech, motor activity, mood, and cognitive status may provide clues to an uncontrolled psychiatric state and/or current intoxication or withdrawal.
• If the patient is acutely intoxicated, a safety evaluation should be performed and further assessment postponed until the patient is in a sensate state. This decision should be communicated respectfully to the patient and, if feasible, an offer made to assist in referral to an appropriate addiction service.
• Currently addicted users may not follow instructions and frequently put themselves at risk through inappropriate behavior. Admission the day prior to an elective procedure -should be considered.
• Acute/chronic excessive substance use has consequences for the entire organism.
• The cardiovascular (cardiomyopathy, endocarditis, and heart failure); pulmonary (COPD, fibrosis, pneumonia, pneumonitis, and edema); renal (impairment and failure) gastrointestinal (pancreatitis, hepatitis, and
  cirrhosis), and central nervous system (dementia, ischemic/hemorrhagic strokes, and traumatic brain injury) are all susceptible.
• Symptoms suggestive of decompensation should prompt a thorough assessment to see if improvement is possible prior to surgery.
• Acute/chronic viral or bacterial infections are commonplace as in our patient

Question 87

What Is Heroin?

Answer 87

• Heroin is a semi-synthetic opioid (diacetylmorphine).
• Morphine is extracted from opium and through a complex chemical process (involving the use of acetic anhydride, chloroform, sodium carbonate, ether, and HCL) refined to heroin.
• Heroin is hydrolyzed to 6-monoacetylmorphine (6-MAM) in the body, and in turn is metabolized to morphine.
• 6-MAM is more lipid soluble than morphine and thus has a more rapid onset of cerebral effect

Question 88

What Is the Potency of Heroin Relative to Morphine, and What Are the Signs and Issues of Concern with Recent Use?

Answer 88

• Heroin is approximately twice as potent as morphine.
• The initial response to heroin exposure is a sense euphoria followed rapidly by sedation and tranquility.
• Physical signs of recent use include decreased respiratory rate, bradycardia, miosis, pruritus, and perspiration.
• Daily heroin users will experience symptoms of withdrawal if they abstain from use for more than 6–12 hours.
• Consultation with an addiction specialist to develop a plan to avoid withdrawal postoperatively is prudent.
• Oral methadone or buprenorphine has been used successfully in this situation.
• Chronic users will be tolerant to opioids, and adjustment of intraoperative and postoperative doses is appropriate

Question 89

What Is Cocaine and What Are the Signs and Issues of Concern with Recent Use?

Answer 89

• Cocaine is extracted from the leaves of the coca plant.
• Among multiple effects, cocaine inhibits the reuptake of serotonin, epinephrine, norepinephrine, and dopamine peripherally and centrally. It is a potent Na+ channel blocker.
• Cocaine exposure initially elicits an intense feeling of happiness or may provoke agitation and loss of contact with reality
• Physical signs of recent use include pyrexia, hypertension, tachycardia, dysrhythmias, myocardial ischemia, mydriasis, perspiration, seizures, and psychosis.
• Cocaine exerts its effects usually within 10 minutes of use, and effects last from 15 to 90 minutes.
• ECG findings of acute intoxication include Na+ channel blockade-induced widening of the QRS complex (treated with sodium bicarbonate) and QTc prolongation associated with blockade of the K+ rectifier channels.
• There are many more recreational cocaine users than chronic users (> 4 times/month).
• It is imperative that all users are advised to desist from cocaine use in the immediate preoperative period, given the potentially catastrophic cardiovascular consequences of blocking neurotransmitter
  re-uptake and voltage-gated Na+ channels during and immediately after surgery

Question 90

What Is Methamphetamine (“Ecstasy/Meth/Chalk/Ice/Glass”) and What Are the Signs of Recent Use?

Answer 90

• Methamphetamine is a synthetic stimulant that is an indirect agonist at dopamine, noradrenaline, and serotonin receptors .
• Methamphetamine is smoked, sniffed, injected, and taken orally.
• The responses to low-/moderate-dose ingestion include arousal, euphoria, disinhibition, and positive mood.
• Physiologically dose-dependent hypertension, tachycardia, and pupillary dilatation are elicited by methamphetamine use. Violent, abusive, and incoherent behavior may occur.
• In overdose situations, hyperpyrexia, cardiac and renal failure, coma, and seizures have been observed.
• Chronic use of methamphetamine can result in the development of early
  onset coronary artery disease and/or cardiomyopathy.
• If the patient complains of chronic fatigue and/or dyspnea, obtaining an echocardiogram prior to surgery would be prudent.

Question 91

Causes and management of acute chest pain in acute cocain use?

Answer 91

• Beta-blockers are relatively contraindicated in the face of acute cocaine-induced coronary vasoconstriction due to concerns about the consequences of unopposed alpha-adrenergic stimulation.
• Chest pain in the scenario described could also be a manifestation of acute aortic dissection.
• This is best ruled out by echocardiographic assessment.

Question 92

True/False Questions
1. In adults in North America
(a) alcohol is the most common substance abused
(b) cannabis use is infrequent
(c) methamphetamine use is increasing
(d) methamphetamine is commonly used with opioids
(e) heroin use is uncommon

Answer 92

1a.T
1b.F
1c.T
1d.T
1e.T

Question 93

2. Cocaine
   (a) is a potent Na + channel blocker
   (b) inhibits reuptake of serotonin and dopamine
   (c) causes miosis of the pupil
   (d) is associated with Wellens syndrome
   (e) QTc shorting is an ECG sign of recent cocaine use

Answer 93

2a.T
2b.T
2c.F
2d.T
2e.F

Question 94

What Is Amyloidosis?

Answer 94

• Amyloidosis is the extracellular deposition of insoluble fibrils that from circulating low molecular weight subunits of soluble precursor proteins.
• Fibrillogenesis is initiated by multiple processes, including heritable mutations and inflammatory, malignant, and chronic disease states.
• Deposition of amyloid protein leads to tissue destruction and organ dysfunction.
• There are multiple subtypes of amyloidosis, depending on the precursor protein predominantly involved in fibril formation.
• Amyloidosis is rare but the following are some recognized entities:
  1. Amyloid light chain (AL) and, less commonly, immunoglobulin heavy chain (AH) amyloidosis arising from deposition of fibrils derived from immunoglobulin light and heavy chain fragments, respectively. AL is the most commonly occurring form of amyloidosis. AL and AH are associated with clonal plasma cell dyscrasias, especially monoclonal gammopathy of undetermined significance (MUGUS) and multiple myeloma. Amyloid AL
  cardiomyopathy can progress rapidly after the onset of symptoms and carries a poor prognosis.
  2. Amyloid A (AA) or acquired amyloid, arising from deposition of fibrils derived from serum amyloid A proteins, associated with chronic inflammatory disease states including rheumatoid arthritis and juvenile inflammatory arthritis, and intravenous drug abuse.
  3. Amyloid transthyretin (ATTR), which is inherited due to mutations in the gene encoding transthyretin (a protein that transports thyroxine and retinol, previously called pre-albumin).
• This protein is produced by the liver, so liver transplantation may be recommended as therapy depending on the status of the patient.
  4. Amyloid transthyretin wild type (ATTRwt), previously called senile amyloidosis, where non-mutated (normal) transthyretin forms fibrils that seem to be preferentially deposited in the heart. ATTRwt is responsible for transthyretin amyloid cardiomyopathy, an increasingly recognized entity in patients diagnosed with diastolic heart failure.
  5. Dialysis-related or Aβ2M amyloidosis, where deposition of fibrils formed from β2 microglobulin (not filtered by the dialysis process), occurs primarily in synovium, joints and bone, causing severe arthralgia in patients undergo-
  ing dialysis. The symptoms are resolved with renal transplantation.

Question 95

What Are the Common Manifestations of Amyloidosis?

Answer 95

• Amyloid deposits can affect any organ system; in consequence, the presenting clinical features are variable and frequently nonspecific.
• Neuropathy is a frequent occurrence.
• Renal and hepatic dysfunction are common and early features of AA and AL, but organ dysfunction related to plasma cell dyscrasias can occur in the absence of amyloid disease.
• In AL, most patients have renal dysfunction with nephrotic-range proteinuria (spot urine showing a protein to creatinine ratio of >3–3.5 mg protein/mg creatinine (300–350 mg/mmol).
• Liver involvement is suggested by elevated alkaline phosphatase levels [2].
• Cardiac amyloidosis is frequently observed in AL and ATTR/ATTRwt. In the latter, misfolded ATTR monomers aggregate to form amyloid fibrils that are found in the interstitial space of the myocardium, causing increased wall thickness and evoking conduction disorders and diastolic
  dysfunction.
• It has been estimated that ATTRwt is an etiological factor in up to 10% of older patients’ heart failure. Given the emerging treatment options for ATTR-related cardiomyopathy, screening for ATTR/ATTRwt has been proposed in populations deemed at risk of the condition. Suggested red
  flag signs/symptoms of possible early stage ATTR/ATTRwt disease include a discrepancy between left ventricle thickness on echocardiography and QRS findings on ECG.
• A history of the combination of bilateral carpel tunnel syndrome, polyneuropathy, and atrioventricular block should prompt screening for ATTR/ATTRwt [3].
• Echocardiography and 99mTc-labelled bisphosphonate scintigraphy (as used in bone scans) are both very helpful in screening and diagnosis
  of ATTR/ATTRwt cardiac amyloidosis.
• Specificity of scintigraphy in the diagnosis of ATTR cardiomyopathy approaches 100% in the absence of detectable monoclonal proteins or an
  abnormal serum free light chain ratio.

Question 96

What Are the Treatment Options for Amyloid
Disease?

Answer 96

The cornerstone of management is to reduce the production
of precursor proteins.
1. Supportive therapy, and in the case of cardiomyopathy,
salt restriction, diuretics, and pacemaker/ICD insertion to
manage rhythm and conduction disorders.
2. In AL, therapy is guided by risk assessment and may involve
chemotherapy/immunomodulation (cyclophosphamide, tha-
lidomide, dexamethasone, and proteasome inhibitors,
among other agents) to reduce or eliminate light chain pre-
cursors, stem cell transplant, and/or organ transplant [4].
3. In AA, tumor necrosis factor (TNF) inhibitors and inter-
leukin-1 blockers have shown effectiveness in ameliorat-
ing progression of the disease.
4. In ATTR, multiple drugs are under investigation that suppress
or stabilize transthyretin and appear to reduce mortality and
hospitalization rates [5]. These include the recently approved
tafamidis, which binds to transthyretin and prevents its disas-
sociation into monomers. Although effective in reducing the
rate of hospitalization in patients with cardiomyopathy, its
cost-effectiveness has been called into question [6].

Question 97

What Are the Key Issues to Identify During
the Preoperative Evaluation?

Answer 97

This has been concisely and comprehensively reviewed by
Fleming et al. [7]
1. A high index of suspicion for the presence of the disease
in patients who are at risk and may present with symp-
toms suggestive of organ failure, particularly cardiac
decompensation.
2. In patients with an established diagnosis of amyloidosis
assess:
(a) Airway—macroglossia is common (20% of patients
with AL); voice alteration, stridor, and odynophagia
are suggestive of laryngeal involvement.
(b) Cardiovascular system—conduction disorders,
orthostatic hypotension, and diastolic heart failure
may be present. Concerning features of impending
severe decompensation include poor exercise per-
formance, NYHA functional class ≥3, systolic
BP < 100 mmHg, and elevated BNP and troponin
levels.
(c) Neurological system—neuropathy is common and
should be documented especially prior to regional
techniques.
(d) Coagulation abnormalities including acquired factor
X deficiency have been reported.
3. A clear disposition plan following surgery is indicated
with a low threshold for admission to a monitored envi-
ronment following surgical procedures, particularly in
patients with poor functional status.

Question 98

True/False Questions
1. Amyloidosis is a disease that
(a) Is caused by the intracellular deposition of insoluble fibrils
(b) Is frequently associated with renal impairment
(c) Can occur as a consequence of renal dialysis
(d) Can manifest as a neuropathy
(e) Has no known effective treatment

Answer 98

1a.F
1b.T
1c.T
1d.T
1e.F

Question 99

2. In the preoperative assessment of a patient with amyloidosis
   (a) A history of carpel tunnel syndrome may be a feature
   (b) Airway issues may be noted due to macroglossia
   (c) Heart failure may be present
   (d) A bone scan should be performed
   (e) Coagulation abnormalities may be observed

Answer 99

2a.T
2b.T
2c.T
2d.F
2e.T