The Postanesthesia Care Unit

Question 1

In a prospective study of more than 18,000 consecutive admissions to the postanesthesia care unit (PACU), the complication rate was found to be as high as …%.

The most common problems were …

Answer 1

24

Nausea and vomiting (9.8%), the need for upper airway support (6.8%), and hypotension (2.7%)

Question 2

Pharyngeal function is not normalized until an adductor pollicis train-of-four (TOF) ratio is greater than …

Answer 2

0.90

Question 3

The most frequent cause of airway obstruction in the immediate postoperative period is …

Answer 3

the loss of pharyngeal muscle tone in a sedated or obtunded patient

Question 4

Drugs that contribute to prolonged nondepolarizing neuromuscular
blockade

Answer 4

• Inhaled anesthetic drugs
• Local anesthetics (lidocaine)
• Cardiac antiarrhythmics (procainamide)
• Antibiotics (polymyxins, aminoglycosides, lincosamines [clindamycin], metronidazole [Flagyl], tetracyclines)
• Corticosteroid agents
• Calcium channel blockers
• Dantrolene

Question 5

Metabolic and Physiologic States that contribute to prolonged nondepolarizing neuromuscular blockade

Answer 5

• Hypermagnesemia
• Hypocalcemia
• Hypothermia
• Respiratory acidosis
• Hepatic or renal failure
• Myasthenia syndromes
• Excessive dose of succinylcholine
• Reduced plasma cholinesterase activity
  Decreased levels
  □ Extremes of age (newborn, old age)
  □ Disease states (hepatic disease, uremia, malnutrition, plasmapheresis)
  □ Hormonal changes
  □ Pregnancy
  □ Contraceptives
  □ Glucocorticoids
  Inhibited activity
  □ Irreversible (echothiophate)
  □ Reversible (edrophonium, neostigmine, pyridostigmine)
  Genetic variant (atypical plasma cholinesterase)

Question 6

Postoperative residual neuromuscular blockade is unfortunately very common. The literature reports incidences between …% and a recent study even found that …% of patients had residual neuromuscular blockade upon arrival in the PACU

Answer 6

20% and 40

56

Question 7

How to evaluate the air way patency in a patiente thai is at risk of air way edema?

Answer 7

The patient’s ability to breathe around the endotracheal tube can be evaluated by suctioning the oral pharynx and deflating the endotracheal tube cuff. With occlusion of the proximal end of the endotracheal tube, the patient is then asked to breathe around the tube. Good air movement suggests that the patient’s airway will remain patent after tracheal extubation.

An alternative method involves measuring the intrathoracic pressure required to produce a leak around the endotracheal tube with the cuff deflated This method was originally used to evaluate pediatric patients with croup before extubation. When used in patients with general oropharyngeal edema, the safe pressure threshold can be difficult to identify.

Lastly, when ventilating patients in the volume control mode, one can measure the exhaled tidal volume before and after cuff deflation. Patients who require reintubation generally have a smaller leak (i.e., less percentage difference between
exhaled volume before and after cuff deflation) than those who do not. A difference greater than 15.5% is the advocated cutoff value for extubation of the trachea.

*** The presence of a cuff leak demonstrates the likelihood of successful extubation, not a guarantee, just as a failed cuff leak doesnot rule out a successful extubation. The cuff leak test does not and should never take the place of sound clinical judgment, as it is neither sensitive nor specific; it may be used as an adjunct to aid in providing another layer of guidance

Question 8

In order to facilitate the reduction of airway edema, one may …, and consider administering …

Answer 8

sit the patient upright to ensure adequate venous drainage

a diuretic and intravenous dexamethasone (4-8 mg every 6 hours for 24 hours), which
may help decrease airway swelling.

Question 9

What are the most common causes of transient postoperative arterial hypoxemia in the immediate postoperative period?

Answer 9

Atelectasis and alveolar hypoventilation

Question 10

Factors Associated with Postoperative Arterial Hypoxemia

Answer 10

• Right-to-left intrapulmonary shunt (atelectasis)
• Mismatching of ventilation to perfusion (decreased functional
  residual capacity)
• Congestive heart failure
• Pulmonary edema (fluid overload, postobstructive edema)
• Alveolar hypoventilation (residual effects of anesthetics and/or neuromuscular blocking drugs)
• Diffusion hypoxia (unlikely if receiving supplemental oxygen)
• Inhalation of gastric contents (aspiration)
• Pulmonary embolus
• Pneumothorax
• Increased oxygen consumption (shivering)
• Sepsis
• Transfusion-related lung injury
• Adult respiratory distress syndrome
• Advanced age
• Obesity

Question 11

PAO2 formula

Answer 11

PAO2 = FiO2(PB - PH2O) - PaCO2/RQ

PAO2: alveolar oxygen pressure
Paco2: partial pressure of CO2 in arterial blood
FiO2: fraction of inspired oxygen
PB: barometric pressure (760 at sea level)
PH2O: vapor pressure of water (46 at sea level)
RQ: respiratory quotient (0,8)

Question 12

Normally, minute ventilation increases linearly by approximately … for every 1-mm Hg increase in Paco2

Answer 12

2 L/min

Question 13

How does the diffusion hypoxia can cause hypoxemia in the PACU?

Answer 13

Diffusion hypoxia refers to the rapid diffusion of nitrous oxide into alveoli at the end of a nitrous oxide anesthetic. Nitrous oxide dilutes the alveolar gas and produces a transient decrease in Pao2 and Paco2. In a patient breathing room air, the resulting decrease in Pao2 can produce arterial hypoxemia while decreased Paco2 can depress the respiratory drive. In the absence of supple- mental oxygen administration, diffusion hypoxia can persist for 5 to 10 minutes after discontinuation of a nitrous oxide anesthetic; therefore, it may contribute to arterial hypoxemia in the initial moments in the PACU

Question 14

Criteria for the Diagnosis of Transfusion-Related Acute Lung Injury: the American-European Consensus Conference Recommendations

Answer 14

1. Acute lung injury evidenced by:
   a. Acute onset of signs and symptoms
   b. Hypoxemia:
   - i. PaO2/FiO2 <300, or
   - ii. Room air SpO2 <90%, or
   - iii. Other clinical evidence of hypoxemia
   c. Bilateral infiltrates on chest radiography without cardiomegaly
   d. No clinical evidence of left atrial hypertension
2. No preexisting acute lung injury before transfusion
3. Onset of lung dysfunction within 6 h of transfusion
4. No temporal association of onset to alternative causes of acute
   lung injury

Question 15

Brief resume of TRALI

Answer 15

Transfusion-related lung injury is typically exhibited within 2 to 4 hours after the transfusion of plasma-containing blood products, including packed red blood cells, whole blood, fresh frozen plasma, or platelets.

TRALI occurs when recipient neutrophils become activated by constituents of the donor blood products. These neutrophils then release inflammatory mediators which initiate the cascade of pulmonary edema and resulting
lung injury via increasing the permeability of the pulmonary vasculature.

Given that presenting symptoms (sudden onset of hypoxemic respiratory failure) can appear up to 6 hours after the conclusion of the transfusion, the syndrome may develop during the patient’s stay in the PACU.

The resulting noncardiogenic pulmonary edema is often associated with fever, pulmonary infiltrates on chest radiograph (without signs of left heart failure), cyanosis, and systemic hypotension. If a complete blood cell count is obtained with the onset of symptoms, then documenting an acute drop in the white blood cell count (leukopenia) is possible, reflecting the sequestration of granulocytes within the lung and exudative fluid.

Treatment is supportive and includes supplemental oxygen and diuresis. It is estimated that up to 80% of patients will recover within 48 to 96 hours. Mechanical ventilation may be needed to support hypoxemia and respiratory failure. Vasopressors may be required to treat refractory
hypotension

Question 16

As a general rule, each liter per minute of oxygen flow through nasal cannula increases the FiO2 by …, with 6 L/min delivering an FiO2 of approximately …

Answer 16

0.04

0.44

Question 17

Factors Leading to Postoperative Hypertension

Answer 17

Preoperative hypertension
Arterial hypoxemia
Hypervolemia
Emergence excitement
Shivering
Drug rebound
Increased intracranial pressure

Increased sympathetic nervous system activity:
Hypercapnia
Pain
Agitation
Bowel distention
Urinary retention

Question 18

The surgical procedures most commonly associated with postoperative hypertension are …

Answer 18

carotid endarterectomy and intracranial procedures

Question 19

Differential Diagnosis of Hypotension in the Postanesthesia Care Unit

Answer 19

1) Intravascular volume depletion
Persistent fluid losses
Ongoing third-space translocation of fluid
Bowel preparation
Gastrointestinal losses
Surgical bleeding

2) Increased capillary permeability
Sepsis
Burns
Transfusion-related acute lung injury

3) Decreased cardiac output
Myocardial ischemia or infarction
Cardiomyopathy
Valvular disease
Pericardial disease
Cardiac tamponade
Cardiac dysrhythmias
Pulmonary embolus
Tension pneumothorax
Drug induced (β-blockers, calcium channel blockers)

4) Decreased vascular tone
Sepsis
Allergic reactions (anaphylactic, anaphylactoid)
Spinal shock (cord injury, iatrogenic high spinal)
Adrenal insufficiency

Question 20

The amount of volume loss tends to dictate clini- cal signs, as patients seem to be able to tolerate up to a …% blood volume loss, with tachycardia being the only sign, whereas when patients lose around …% of their total blood volume, clear signs of shock are evident (lactic acidosis,
severe hypotension, reduced cardiac output).

Answer 20

10

40

Question 21

Drugs Involved in Perioperative Anaphylaxis

Answer 21

1) Muscle relaxants: 69.2 p% (Succinylcholine, rocuronium, atracurium)

2) Natural rubber latex: 12.1% (Latex gloves, tourniquets, Foley catheters)

3) Antibiotics: 8% (Penicillin and other β-lactams)

4) Hypnotics: 3.7% (Propofol, thiopental)

5) Colloids: 2.7% (Dextran, gelatin)
Opioids: 1.4 (Morphine, meperidine)

6) Other substances: 2.9% (Propacetamol, aprotinin, chymopapain, protamine, bupivacaine)

Question 22

Myocardial ischemia after non-cardiac surgery (MINS) has been established as an entity in itself. MINS is defined as …

Answer 22

elevated postoperative troponin levels without any clinical symptoms or any changes in the ECG, provided there is no other nonischemic cause for the elevated troponin level (e.g., chronic troponin elevation, pulmonary embolism, sepsis, rapid atrial fibrillation)

Question 23

Common ventricular arrhytmias in the PACU and inicial management

Answer 23

Premature ventricular contractions (PVCs) and ventricular bigeminy commonly occur in the PACU. PVCs most often reflect increased sympathetic nervous system stimulation that may accompany tracheal intubation, pain, and transient hypercapnia. They commonly resolve on their own, but this can be facilitated by administering analgesics and ensuring proper ventilation

Question 24

The most commonly administered QT prolonging drugs in PACU are …

Answer 24

5-HT3 receptor antagonists (e.g., ondansetron, dolasetron), haloperidol, droperidol, albuterol, methadone, and amiodarone

Question 25

Differential diagnosis of postoperative renal dysfunction

Answer 25

Prerenal
- Hypovolemia (bleeding, sepsis, third-space fluid loss, inadequate volume resuscitation)
- Hepatorenal syndrome
- Low cardiac output
- Renal vascular obstruction or disruption
- Intraabdominal hypertension

Renal
- Ischemia (acute tubular necrosis)
- Radiographic contrast dyes
- Rhabdomyolysis
- Tumor lysis
- Hemolysis

Postrenal
- Surgical injury to the ureters
- Obstruction of the ureters with clots or stones
- Mechanical (urinary catheter obstruction or malposition)

Question 26

How to use FeNa and Ur/Cr in the context of renal dysfunction?

Answer 26

FeNa < 1% and Ur/Cr > 40 favors a prerenal condition

Question 27

Urinary retention can be defined as bladder volume greater than … in conjunction with …

Answer 27

600 mL

an inability to void within 30 minutes

Question 28

Normal IAP in a patient who is not obese is approximately …

Intraabdominal hypertension is graded into four categories: …

Answer 28

5 mm Hg

I: 12 to 15 mmHg;
II: 16 to 20 mmHg;
III: 21 to 25 mmHg;
IV: greater than 25 mmHg.

Question 29

Abdominal compartment syndrome definition

Answer 29

For research purposes, ACS is defined as a sustained intra-abdominal pressure >20 mmHg (with or without APP <60 mmHg) that is associated with new organ dysfunction.

For clinical purposes, ACS is better defined as IAH-induced new organ dysfunction without a strict intra-abdominal pressure threshold, since no intra-abdominal pressure can predictably diagnose ACS in all patients

Question 30

… pressure, an indirect assessment of IAP, should be measured in patients in whom intraabdominal hypertension is suspected to ensure the initiation of prompt intervention to relieve the pressure and therefore restore renal perfusion

Answer 30

Bladder

Question 31

How to mesure the bladder pressure?

Answer 31

Bladder pressure is measured at end expiration with the patient in the supine position and in the absence of abdominal muscle contractions

Question 32

Mechanism of postoperative shivering

Answer 32

Postoperative shivering is usually, but not always, associated with hypothermia. Although thermoregulatory mechanisms can explain shivering in the hypothermic patient, a number of different mechanisms have been proposed to explain shivering in normothermic patients.

One proposed mechanism is based on the observation that the brain and spinal cord do not recover simultaneously from general anesthesia.
The more rapid recovery of spinal cord function is thought to result in uninhibited spinal reflexes manifested as clonic activity. This theory is supported by the fact that
doxapram, a central nervous system stimulant, is somewhat effective in abolishing postoperative shivering.

Other proposed mechanisms include the action of kappa opioid, N-methyl-d-aspartate (NMDA), and 5-hydroxytryptamine receptors. The higher incidence of postanesthetic shivering in patients who receive high-dose remifentanil is thought
to be by the same mechanism that causes hyperalgesia in these patients—sudden opioid withdrawal resulting in the stimulation of NMDA receptors. Additional support for this theory comes from the same authors who found that a small dose of intraoperative ketamine reduced the incidence of remifentanil-induced postanesthetic shivering.

Tramadol, a weak μ-opioid receptor agonist, and norepinephrine and serotonin reuptake inhibitor, has been shown to be effective in preventing postoperative shivering while also contributing to analgesia.

Question 33

Shivering treatment

Answer 33

A number of opioids, ondansetron, clonidine, and ketamine have been shown to be effective in abolishing shivering once it starts. Of those, meperidine, 12.5-25 mg IV, is most commonly used in adults. The intraoperative infusion of dexmedetomidine
has been shown to be an effective prophylactic measure

Question 34

Negative effects of mild to moderate hypothermia

Answer 34

Mild to moderate hypothermia (33°C-35°C) inhibits platelet function, coagulation factor activity, and drug metabolism. It exacerbates postoperative bleeding, prolongs neuromuscular blockade, and may delay awakening.

Whereas these immediate consequences are associated with a prolonged PACU
stay, long-term deleterious effects include an increased incidence of myocardial ischemia and myocardial infarction, delayed wound healing, and increased perioperative mortality.

Question 35

Without prophylactic intervention, roughly … of patients who undergo inhalational anesthesia will develop PONV (range, …%)

Answer 35

one third

10%-80

Question 36

Apfel et al. identified … as independent risk factors for PONV.

In the Simplified risk score from Apfel et al to predict the patient’s risk for PONV, 0, 1, 2, 3, and 4 risk factors correspond to PONV risks of approximately …%, respectively

Answer 36

female gender, non-smoker, history of PONV/motion sickness, and the need for postoperative opioids

10%, 20%, 40%, 60%, and 80%

Question 37

Pediatric risk factors for PONV

Answer 37

Preoperative
- Age > 3 years
- History of PONV/motion sickness
- Family history of PONV
- Post-puberal female

Intraoperative
- Strabismus surgery
- Adenotonsillectomy
- Otoplasty
- Surgery > 30 min
- Volatile Anesthetics
- Anticholinesterases

Postoperative
- Long-acting opioids

Question 38

Postoperative delirium (POD) has been linked to multiple risk factors. These are commonly distinguished between predisposing factors (inherent to the patient) and precipitating factors (triggering the onset of delirium).

Major predisposing patient risk factors include …

In the perioperative context, …

Answer 38

(1) age greater than 65 years, (2) cognitive impairment, (3) severe illness or comorbidity burden, (4) hearing or vision impairment, and (5) presence of infection.

the performed surgical procedure acts as a physiologic stressor with the extent of surgery having a major impact on the likelihood of developing delirium

Question 39

If prevention of delirium has failed and the patient screens positive, prompt evaluation of possible precipitating factors should occur. These include …

Answer 39

uncontrolled pain, hypoxia, pneumonia, infection (wound, indwelling catheter and blood stream, urinary tract, sepsis), electrolyte abnormalities, urinary retention, fecal impaction, medications, and hypoglycemia

Question 40

Even after prolonged surgery and anesthesia, a response to stimulation in … minutes should occur.

If emergence has not taken place at that point, it is important to consider multiple different reasons as the possible underlying cause

Answer 40

60 to 90

Question 41

Most frequent cause of delayed emergence

Answer 41

Residual drug effects are the most frequent cause of delayed emergence and may occur after too much anesthetic has been given or in a patient who is susceptible to the side effects of certain medications due to age, underlying disease, or metabolic derangements.

The most common drugs to consider are benzodiazepines, opioids, and neuromuscular blocking drugs, however, after a very long anesthetic, propofol and volatile anesthetics can also cause a delay in emergence.

Furthermore, acute alcohol or illicit drug intoxication can be other culprits.

Another often overlooked drug effect is the central anticholinergic syndrome (CAS). Several drugs used during anesthesia can block the central cholinergic neurotransmission and therefore delay the wakeup.

Question 42

Non pharmacological causes of delayed emergence

Answer 42

Metabolic disturbances such as hypothermia (<33°C), electrolyte imbalances (e.g., hyponatremia, hypercalcemia, hypermagnesemia), hypo- or hyperglycemia, as well as underlying metabolic diseases (e.g., liver, kidney, or thyroid abnormalities) can delay emergence after anesthesia.
Neurologic complications such as cerebral hypoxia, seizures (with consecutive postictal state), elevated ICP, as well as any intracerebral event (hemorrhage,
thrombosis, embolus) should be considered

Question 43

Treatment of central anticholinergic syndrome

Answer 43

physostigmine 1 to 2 mg IV

Question 44

In the ambulatory surgery setting, postoperative … is the most significant
cause of delayed discharge and unplanned hospital admission

Answer 44

pain

Question 45

Criteria for Determination of Discharge Score for Release Home to a Responsible Adult

Answer 45

VITAL SIGNS (STABLE AND CONSISTENT WITH AGE AND PREANESTHETIC
BASELINE)
- Systemic blood pressure and heart rate within 20% of the preanesthetic level: 2
- Systemic blood pressure and heart rate 20% to 40% of the preanesthetic level: 1
- Systemic blood pressure and heart rate >40% of the preanesthetic level: 0

ACTIVITY LEVEL (ABLE TO AMBULATE AT PREOPERATIVE LEVEL)
Steady gait without dizziness or meets the preanesthetic level: 2
Requires assistance: 1
Unable to ambulate: 0

NAUSEA AND VOMITING
None to minimal: 2
Moderate: 1
Severe (continues after repeated treatment): 0

PAIN (MINIMAL TO NO PAIN, CONTROLLABLE WITH ORAL ANALGESICS; LOCATION, TYPE, AND INTENSITY CONSISTENT WITH ANTICIPATED POSTOPERATIVE DISCOMFORT)
Acceptability Yes: 2
Acceptability No: 1

SURGICAL BLEEDING (CONSISTENT WITH THAT EXPECTED FOR THE SURGICAL PROCEDURE)
Minimal (does not require dressing change): 2
Moderate (up to two dressing changes required): 1
Severe (more than three dressing changes required): 0

*** Patients achieving a score of at least 9 are acceptable for discharge

Question 46

Criteria for the Determination of Discharge Score for Release from the Postanesthesia Care Unit (Modified from Aldrete JA.)

Answer 46

ACTIVITY
Able to move four extremities on command: 2
Able to move two extremities on command: 1
Able to move no extremities on command: 0

BREATHING
Able to breathe deeply and cough freely: 2
Dyspnea: 1
Apnea: 0

CIRCULATION
Systemic blood pressure ≤20% of the preanesthetic level: 2
Systemic blood pressure is 20% to 50% of the preanesthetic level:1
Systemic blood pressure ≥50% of the preanesthetic level: 0

CONSCIOUSNESS
Fully awake: 2
Arousable: 1
Not responding: 0

OXYGEN SATURATION (PULSE OXIMETRY)
Greater than 92% while breathing room air: 2
Needs supplemental oxygen to maintain saturation >90%: 1
Less than 90% with supplemental oxygen: 0

** A score of 9 out of 10 was considered adequate for discharge from the PACU

Question 47

Risk factors for Ischemic Optic Neuropathy have been identified and include:

Answer 47

• male gender
• obesity
• use of Wilson frame
• long surgery/anesthesia (>6.5 hours)
• high EBL (>45% of estimated blood volume)
• lower percent colloid administration