Exam 2 Flashcards
Two most common reasons for spinal surgery
Spinal stenosis and intervertebral disc herniation
Which spine procedures can be done minimally invasive
perc endoscopic lumbar discectomy, vertebroplast and kyphoplasty, cervical discectomy and foraminectomy, intradiscal electrothermal therapy
What is the greatest anesthetic challenge of neuroskeletal surgery
positioning
What is the prone position’s effect on cardiac output
Reduced CO
Prone position’s effect on SVR and PVR
Increased
What occurs in the prone position when the patient’s head is rotated 60 degrees
Compression of the contralateral vertebral artery begins to constrain blood flow
What occurs in the prone position when patient’s head is rotated 80 degrees
Contralateral vertebral artery becomes completely occluded
Intraabdominal and intrathoracic pressures in the prone position are…
Increased
What hemodynamic parameters are decreased in the prone position
Stroke volume and cardiac index
What complication is associated with general anesthesia and prone positioning
Post operative vision loss
What are risk factors for postoperative vision loss
Male
Obesity
Use of Wilson Frame
Anesthesia duration >6 hr
Large blood loss
Intraoperative hypotension
Colloid administration
History of obstructive sleep apnea
Which type of surgery is most highly associated with POVL
prone spine
What are the two main causes of vision loss
Retinal vascular occlusion and ischemic optic neuropathy
What are the key features of POVL
typically bilateral, painless, no light perception, non-reactive pupil, decreased or absent color vision, occurs within 24-48 hours post op
When should an ophthalmologist be consulted
At the first sign that patient has altered vision after procedure
What positioning interventions can be done to prevent povl
5-10 degree reverse Tberg position during prone spine procedures
During Steep Tberg procedures, use a 5 minute supine rest stop at the 4 hour timeframe
Assess and document that the eyes are free of pressure throughout the prone procedure
Stage lengthy procedures performed with patient prone
Position the head in a neutral position with the face down and the head level with or higher than the heart to minimize venous outflow obstruction
What medication can be used when there is evidence of increased IOP
dorzolamide-timolol (cosopt) drops
Also can consider antiplatelet agents and steroids
What medications may be used as part of ERAS multimodal pain protocols
Acetaminophen, gabapentin, lidocaine, ketamine, mag, dexamethasone, dexmedetomidine
(But may not be able to use precedex or mag if neuromonitoring!)
What is an important factor in preop assessment for an anterior cervical discectomy and fusion (ACDF)
Airway assessment: important to assess cervical mobility and if they have pain while moving head/neck and where the pain/symptoms are
What techniques should be utilized for intubation for ACDF
passive immobilization, inline traction, video +/-
Avoid flexion, extension, and lateral rotation of the head when intubating
What is standard positioning for ACDF
supine, arms tucked, shoulder roll (to allow for better neck access)
Induction type for ACDF
GA with OET
Tape the ETT to the side opposite where the surgeon stands
If neuromonitoring, check baseline before and after intubation (soft bite blocks)
What structures can be potentially damaged during ACDF
RLN, major arteries, veins, esophageal perforation, pneumothorax
What medications should be avoided during ACDF if MEPs used
NMBA and magnesium
When should neurologic function be assessed after emergence from ACDF
Before leaving the operating room
What two complications should be assessed for after ACDF
RLN damage and hematoma
What is lumbar laminectomy indicated for
Symptomatic nerve root or spinal cord compression
Disc herniation usually at the L4 to L5 or L5 to S1 intervertebral space
What is an important preop aspect for lumbar laminectomy or fusion
Assess and document neurologic deficits of the lower extremities
What positions might be used for lumbar laminectomy or fusion
prone, lateral, or knee-chest
Most common anesthetic technique for lumbar laminectomy or fusion
GA
Local with sedation is also possible but not typical
Epidural for lumbar laminectomy or fusion requires analgesia to what level and what is the benefit of epidural
T7-T8
Reduces blood loss and shrinks epidural veins
What type of anesthesia CANNOT be used if using neuromonitoring
Regional
Which lumbar lami/fusion anesthetic technique is most likely to cause hypotension that can be accentuated with position changes
Spinal
How often should the face check be done and documented during lumbar lami/fusion
every 15 minutes
What is the most likely cause of sudden profound hypotension during lumbar lami/fusion
Major intraabdominal vessel (iliac, aorta) damage
What is the max dose of crystalloid that should be given in prone position in order to decrease the incidence of ischemic optic neuropathy
no more than 40 ml/kg
What position should extubation take place in for lumbar lami/fusion
Supine
What are the postop complication of lumbar lami/fusion
Hemorrhage
Neurologic deficits - assess and ensure they can move all extremities!
Visual loss
Surgery above what level requires a double-lumen ETT to collapse the lung on the operative side
T8
Which has greater risk of damage to the spinal cord, thoracic or lumbar fusion
Thoracic fusion
What is a source of anesthetic concerns for anteroposterior fusion
intraoperative position changes
When is surgery indicated for scoliosis
when curvature is severe - cobb angle greater than 40-50 degrees or rapidly progressing
What PFT results indicates that you may need to keep the patient intubated
Vital capacity is less than 40% of predicted
What is the main concern with controlled hypotension
compromising spinal cord blood supply
What are complications of a wake up test
Uncontrolled pt movement may have consequences
Forceful inspiratory efforts may provoke VAE
What is intervention if patient moves the hands and not the feet during a wakeup test
surgeon should decrease the spinal distraction
What spinal cord transection level is incompatible with survival
C2-C4
What disease process can cause spontaneous dislocation of C1 on the C2 vertebra
rheumatoid arthritis
What in the most frequent nontraumatic cause of spinal cord transection
Multiple sclerosis
Where are temperature regulation and spinal cord reflexes lost in spinal cord injuries
Below the level of injury
What is the initial product of spinal cord transection
Flaccid paralysis with total absence of sensation below the level of injury
What is the initial phase of spinal cord injury
Spinal shock: 1-3 weeks
What happens in the chronic phase of spinal cord injury
some regeneration of reflexes
What considerations should be given to succinylcholine in spinal cord injury
While ok from a potassium standpoint within the first 24 hours after injury, fasciculations may make the injury worse. Should probably be avoided
What type of patient should not receive ketamine for their spinal cord injury procedure
Trauma patient who also has a head injury
Injury above what level can cause autonomic hyperreflexia
T6
What precipitates autonomic hyperreflexia
cutaneous or visceral stimuli below the spinal cord lesion
Symptoms of autonomic hyperreflexia
severe HTN and severe bradycardia
Treatment for autonomic hyperreflexia
Remove the stimulus (see if BP and HR recover)
If it doesn’t then try diluted nitro
Emergence for spinal cord injury
Halo device or body jacket
Fully awake
Prevent coughing and bucking
Extubation criteria
Airway patency test
Nerve stimulator won’t be useful!
Postop consideration for SCI
Airway obstruction
Respiratory insufficiency
BLeeding
Neuro deficits
DVT
Pneumonia
What 4 types of injury/stress can impact evoked potentials?
Injuries to neural structures caused from heat (electrocautery)
Mechanical stress (retraction)
Ischemia (ligation, edema, vessel damage)
Loss of functional integrity (transection)
What is the elastic limit of nerves
20% - stretching further may produce irreversible damage
What 4 patient factors can affect evoked potentials?
hypothermia
hypotension
positioning
anemia
What represents the intensity of the evoked response
Amplitude
What is indicative of the time necessary for the evoked response to be measured in the brain
Latency
What % changes in amplitude and latency suggest possible ischemia
50% decrease in amplitude
or
10% increase in latency
Lipophilic agents that interfere with neuronal membrane conduction also interfere with…..
subcortical conduction
Lipophilic agents cause an increase in what aspects of neuromonitoring
Interpeak latencies
Control conduction time
What is the effect of inhalation and IV anesthetic agents on EP waveforms
They depress EP waveforms in a dose-dependent manner
Which has a greater depressant effect on EP waveforms, inhaled agents or IV agents
Inhaled
What effect does the combo on inhaled and IV agents have on SSEP waveforms
Synergistic
What pathway do SSEPs monitor?
Sensory pathway through the dorsal root ganglia and posterior column. They monitor the integrity of the posterior (dorsal) columns.
Which nerves are typically stimulated for SSEP monitoring?
Ulnar or median nerve for upper extremity.
Posterior tibial nerve for lower extremity.
What agents are SSEPs most sensitive to?
All inhalational agents and nitrous oxide
Which IV anesthetics increase SSEP amplitude
Ketamine and etomidate
Which medications decrease amplitude and increase latency of SSEPs
Halogenated agents
N2O
Barbiturates (ok to use when burst suppression on EEG)
Propofol (least pronounced, best iv agent to use with ssep)
Opioids (mildly, bolus more so than infusion, ok to use)
Which medication increases amplitude and latency of SSEPs
Etomidate
Which medications increases amplitude and causes no change in latency of SSEPs
Ketamine
Which medications have little effect on SSEPs
Benzos
What pathway is monitored by MEPs
The motor pathway - including the motor cortex, corticospinal tract, nerve root, and peripheral nerve - by transcranial electric (sometimes magnetic) stimulation of the motor cortex
Are MEPs or SSEPs more sensitive to the effects of anesthetic agents
MEPs
Which changes occur first, changes in MEPs or SSEPs
MEPs
Where are MEPs most susceptible to anesthetic agents
Motor cortex and anterior horn cells (alpha motor neurons and interneurons)
What are the effects of NMBAs on SSEP and MEP
SSEP = no effect
MEP = increased latency, decreases amplitude
What are the effects of precedex on SSEP and MEP
No effect on latency in either.
Decreases amplitude in both.
What 2 hormones are secreted by the thyroid gland
T3 - triiodothyronine
T4 - thyroxine
Where is the thyroid gland located
Anterior to trachea
Below (caudad to) the hyoid bone
Caudad to the thyroid cartilage
On top of the parathyroid glands
Between cricoid cartilage and suprasternal notch
Where does the thyroid gland receive its vascular supply
Superior and inferior thyroid arteries
What laterally borders each thyroid lobe and is commonly injured during procedure
Recurrent laryngeal nerves
What are the functional units of the thyroid gland
Follicles - contain colloid and are lined by epithelial cells
What makes up most of the colloid and is responsible for synthesis and storage of thyroid hormones
Thyroglobulin
What is the rate limiting step of thyroid hormone synthesis
iodine trapping
What are the effects of excess iodine
Decreased thyroid gland size and TH production
What hormone is responsible for iodine trapping
TSH (anterior pituitary)
Where are T3 and T4 synthesized and what is required for synthesis?
Synthesized in follicles.
Controlled by TSH.
Also requires tyrosine (on thyroglobulin) and iodine
What controls the release of T4 and T3
TSH
Which thyroid hormone makes up 93% of released hormone
T4
Which hormone makes up 7% of released hormone
T3
Which thyroid hormone has a longer half life
T4: 6-7 days
T3: 24 hours
Which thyroid hormone is the primary stimulus at the target tissue, is more potent, and is less bound in circulation
T3
What are the major functions of thyroid hormone
Increased cellular metabolic activity: vasodilation and increased blood flow to tissues.
Normal growth in infants and children: Brain development.
Direct and indirect excitability of the heart: HR and force of contraction.
Increase hormone secretion from other endocrine glands: insulin, digestive enzymes, appetite.
Where is thyroid regulating hormone (TRH) released from
Hypothalamus
What acts on the anterior pituitary to stimulate it to release TSH
Thyroid regulating hormone (TRH)
What mechanism controls the secretion of hormones from the anterior pituitary and hypothalamus
Inhibitory feedback by T4
What lab findings are expected in primary hypothyroidism
Increased TSH
Normal or Low T3/T4
What are common causes of primary hypothyroidism
Iodine abnormalities
Colloid goiter
Iatrogenic (surgery, radiation)
Amiodarone
Tyrosine kinase inhibitors
Lithium
(problem is actually within the thyroid gland)
What type of problem is hashimoto thyroiditis
Primary hypothyroidism
What lab findings are expected in secondary hypothyroidism
Decreased TSH
Decreased T3 and T4
Common causes of secondary hypothyroidism
Pituitary or hypothalamic disorders
(Occurs somewhere outside of the thyroid gland)
What cardiac symptoms should be expected with hypothyroidism
Bradycardia
Dysrhythmias
Cardiomegaly
Impaired contractility
Abnormal baroreceptor function
Heart failure
Labile BP
Noncardiac signs/symptoms of hypothyroidism
Goiter
Slowed metabolism
Intolerance to cold
Fatigue and depression
Joint and muscle pain
Dry, brittle hair/skin, puffy face
Treatment of hypothyroidism
Thyroid hormone replacement: synthetic T4
Careful monitoring of CV and thyroid status
What are 3 airway implications for a patient with hypothyroidism?
Goiter
Tracheal deviation/compression
Enlarged tongue (macroglossia)
Considerations for the patient with hypothyroidism
Consider concurrent adrenal suppression
May have slowed metabolism and clearance of meds
Depression of ventilatory responses to hypercarbia and hypoxia
Monitor body temp closely
Should be euthyroid prior to surgery
Should thyroid medication be given on day of surgery?
Yes!
What response to anesthetic agents might a patient with hypothyroidism have?
Exaggerated CNS depression
What are the signs of myxedema coma
Hypothermia, hypoventilation, hypotension, hyponatremia
Expected lab findings of myxedema coma
Hypoglycemia
Hypoxemia, hypercapnia
Hyponatremia
Prolonged QT, low voltage
Pericardial effusion
Precipitating factors of myxedema coma
Infection
Cold exposure
Stroke
Meds - amiodarone and lithium
Management of myxedema coma
Supportive - airway, rewarming
Hydrocortisone
Levothyroxine (T4)
May need IV thyroid medications
What is Grave’s disease
Autoimmune stimulation of thyroid gland by TSH-receptor antibodies (IgG)
Causes gland enlargement and excess T3/T4
Risk factors for Grave’s disease
Female
Genetics
Stress
Cigarette smoking
Causes of hyperthyroidism
Graves disease, nodules, pituitary tumor, thyroid cancer, and amiodarone (iodine rich)
Signs/symptoms of hyperthyroidism
Hypermetabolic state
Tachycardia
Warm, moist skin
Tremor
Diarrhea
Osteopenia
Muscle weakness
Weight loss
Anxiety
Heat intolerance
Ocular abnormalities
Expected lab values with primary hyperthyroidism
Low TSH
High T3/T4
Grave’s disease lab level alterations
Thyroid-stimulating immunoglobulins, alkaline phos, calcium
Expected lab values with subclinical hyperthyroidism
Low TSH
Normal T3/T4
Treatment of hyperthyroidism
Radioactive iodine: absorbed by the thyroid gland and destroys secretory cells
Antithyroid drugs and beta blockade: thionamides inhibit TH synthesis
Thyroidectomy: partial or total, for cancer or ineffective treatment
Risk factors for thyroid cancer
Female
Radiation exposure
Inherited syndromes
Relevant nearby structures regarding thyroidectomy
Anterior to larynx, pharynx, esophagus, trachea
Below thyroid and cricoid cartilage and hyoid bone
Relevant nearby vessels regarding thyroidectomy
Internal jugular veins
Carotid arteries
Thyroid veins/arteries
Relevant nearby nerves regarding thyroidectomy
Superior laryngeal nerve
Recurrent laryngeal nerve
Most common anesthetic choice for thyroidectomy
GETA
But can also use LMA, local and sedation: bilateral cervical plexus block
What is the purpose of intraop nerve monitoring for thyroidectomy
Assists with identifying, dissecting, and confirming function of recurrent laryngeal nerve.
Used to minimize nerve injury
What ett is used for nerve monitoring in thyroidectomy
EMG ETT aka NIM tube
Ensure the electrodes are in contact with the vocal cords via video laryngoscopy
Use a short acting NMBD (succ) for induction only
What adjunct medication can be given when using a NIM tube
Remifentanil, often used to suppress cough reflex
What medications should be avoided during thyroidectomy induction
Ketamine, vagolytics, pancuronium - agents that stimulate the SNS
Patient is often already baseline hyperthyroid
What anesthetic technique is usually used for thyroidectomy maintenance
TIVA (decreases PONV). Should decrease possibility of PONV when operating around the neck as it could result in ruptured sutures or hematoma
Direct vs. indirect acting vasopressors for thyroidectomy
Choose phenylephrine over ephedrine because the patient may have already high levels of circulating catecholamines at baseline
What are 3 priorities for extubation following thyroidectomy
Assess for airway compromise and laryngeal edema
Minimize coughing and bucking
Aggressive treatment of PONV
What is the intervention for bilateral recurrent laryngeal nerve injury
Reintubation
What would be expected in an acute hypothyroid state following thyroidectomy
Hypocalcemia, tingling in fingertips/lips, stridor, laryngospasm
When might thyroid storm mostly likely occur
6-18 hours postop thyroidectomy
Clinical manifestations of thyroid storm
Fever >38.5 degrees
Tachycardia
Confusion and agitation
Tremor
Weakness
Dysrhythmias
Nausea and vomiting
Hypertension
Heart failure
What medications should be avoided for cooling during thyroid storm
Salicylates (asa) - they can displace the t3 and t4 from their proteins and convert them to their active form. Choose acetaminophen instead
What is the curative treatment for thyroid storm
Antithyroid medications - PTU and methimazole
What is the function of the parathyroid glands
Produce parathyroid hormone which regulates calcium levels
What is the normal total serum calcium level
8.5-10.5 mg/dl
Does albumin affect total calcium or ionized calcium
Total
Does blood pH affect total or ionized calcium
Ionized
What is the effect of alkalosis on calcium-protein binding and ionized calcium
Increases calcium-protein binding and decreases ionized calcium
What is the effect of acidosis on calcium-protein binding and ionized calcium
Decreases calcium-protein binding and increases ionized calcium
Which form of calcium exerts physiologic effects
Only the ionized form
What are the functions of ionized calcium
Hemostasis (platelet aggregation, blood coagulation)
Hormone and neurotransmitter release
Muscle contraction
Bone formation
Cell division and function
Which has a greater affect on calcium levels, PTH or vitamin D
PTH
What are the effects of vitamin D on calcium
Promotes dietary absorption
Increases kidney reabsorption
Stimulates release from bone
What are the effects of PTH on calcium and phosphate
Increases calcium and decreases phosphate
What stimulates the release of PTH from the parathyroid gland
low ionized calcium states
What is activated by parathyroid hormone
Osteoclasts: to breakdown bone to release calcium and phosphate
Vitamin D: to promote absorption of calcium and phosphate from intestines
Increases calcium reabsorption and phosphate excretion in the kidney
What hormone is secreted from the thyroid parafollicular cells (C cells) in response to elevated serum ionized calcium
Calcitonin
What hormone opposes the actions of parathyroid hormone
Calcitonin - reduces serum calcium
What is the effect of calcitonin on osteoclasts
Inhibits osteoclasts
What lab finding is expected in hypoparathyroidism
Low serum calcium levels
(due to low PTH or resistance to PTH)
What are the symptoms of low serum calcium
Hyperexcitability of nerve and muscle cells
Muscle spasms, cramps, paresthesia, hyperactive deep tendon reflexes and tetany (trousseau sign and chvostek sign)
Stridor and laryngospasm
What is the treatment of hypoparathyroidism
Vitamin D
Calcium
Magnesium
Recombinant PTH
What lab findings are seen in hyperparathyroidism
Hypercalcemia
Elevated serum PTH
Causes of hyperparathyroidism
Hypersecretion of parathyroid adenomas
Hyperplasia
MEN (multiple endocrine neoplasia) syndrome
Carcinoma
Are these features of hyper or hypoparathyroidism:
Hypertension
Cardiac conduction disturbances
Shortened QT interval
Hyperparathyroidism
Are these features of hyper or hypoparathyroidism:
Prolonged QT interval
Hypotension
Decreased cardiac contractility
Hypoparathyroidism
What is the appropriate management of hypercalcemia in hyperparathyroidism
Isotonic saline: dilutes serum ca, increases GFR and excretion
Loop diuretics
What are three anesthesia implications for hyperparathyroidism
Management of hypercalcemia
Correction of electrolyte abnormalities (Mag and K)
Management of CV complications
After parathyroidectomy, should iPTH levels increase or decrease?
Levels should decrease
How many calories of energy are available from 1 gram of fat
9 calories
What are the terminal consequences of excessive adipose tissue
Insulin resistance
Inflammation throughout the body
Where can android fat be found
Central distribution - mostly upper body
Truncal, cushingoid, apple
Where can gynecoid fat be found
Peripheral distribution - hips, buttocks, thighs
Gluteal, pear
Which fat distribution is associated with increased o2 consumption, DM, and CV disease (LV dysfunction)
Android
Which fat distribution is less metabolically active and has less CV comorbidities
Gynecoid
What is the new standard used as a marker of abdominal obesity?
Waist circumference:
>102 cm (40.2 in) in men
>88 cm (35 in) in women
What risks are associated with waist circumference >40.2 in in men and 35 in in women
Increased risk for CV disease, DM II, HTN, dyslipidemia, and death
Formula for BMI
weight (in kg) / height (in meters)squared
What is the consequence of dosing a drug to total body weight in a morbidly obese individual
Overdose
What is ideal body weight
Ideal weight associated with maximum life expectancy for a given height
How do you calculate ideal body weight
Male: height (cm) - 100
Female: height (cm) - 105
What is the difference between the total body weight and fat mass
Lean body weight
How much is lean body weight increased in obese individuals
30%
Calculation for lean body weight
IBW x 1.3
Which body weight measurement will underestimate the dose for an obese patient
Ideal body weight
Which body weight is probably the best estimate of dose
Lean body weight
What calculation should be done for obese patient in the case of strongly hydrophilic drugs
Instead of calculated LBW, add 20% to the ideal body weight to account for the increase in lean body tissue content
What is the ideal metric for dosing in the case of strongly lipophilic drugs
Lean body weight
What 4 things effect the volume of distribution of a drug in an obese patient
Increased blood volume
Increased cardiac output
Altered plasma protein binding
Lipid solubility of a drug
What happens to the volume of distribution of hydrophilic and lipophilic drugs in an obese patient
Vd increases for both type of drugs, however the Vd of lipophilic drugs increases more
What is the effect of obesity on ventilation
Restrictive ventilatory effect
Decreased chest wall compliance
Difficulty getting air IN
What is the relationship between BMI and FRC
As BMI increases, FRC decreases at the same rate
When does small airway collapse occur
When FRC is less than closing capacity
What lung volumes are decreased in obesity
FRC = ERV + RV
IC = TV + inspiratory reserve capacity
VC = TV + IRV + ERV
ERV
Which lung volumes are increased in obesity
Closing volume
What are the most commonly reported abnormalities of pulmonary function in the obese patient
Decreased FRC and ERV
What is the most sensitive indicator of the effect of obesity on pulmonary function
ERV
What is the result of FRC falling below closing capacity in an obese patient
V/Q mismatch, shunt, hypoxemia (hypercapnia)
What is the most common blood gas abnormality in obesity and what causes it
Arterial hypoxemia resulting from atelectasis and R to L shunt
What constitutes apnea
Cessation of respiration for > or equal to 10 seconds
Define hypopnea
Any respiratory patterns that leads to increased CO2 accumulation (decreased volume or decreased rate)
What is obstructive apnea
Continued respiratory effort despite no air flow
What are the criteria for sleep apnea
Airflow reduced by 50% x 10 seconds for > or equal to 15 times
Per hour of sleep
Associated with snoring
4% decrease in SpO2
What can obesity hypoventilation syndrome lead to?
Central apnea - apnea without respiratory effort
What does central apnea reflect?
Desensitization of the respiratory centers to nocturnal hypercarbia
What are the characteristics of obesity hypoventilation syndrome
OSA
Hypercapnia
Daytime hypersomnolence
Arterial hypoxemia
Cyanosis-induced polycythemia (due to long term low pao2 levels)
Respiratory acidosis
Pulmonary HTN
R sided heart failure (from increased PVR)
Diagnostic criteria for obesity hypoventilation syndrome
BMI >30
Awake PCO2 > 45 (daytime hypoventilation)
Sleep-disordered breathing in the absence of other pathophysiology
Is CO increased or decreased in obesity
Increased
Is total body oxygen demand increased or decreased in obesity
Increased (primarily due to increased lean body mass)
Is cardiac preload increased or decreased in obesity
Increased
Is cardiac afterload increased or decreased in obesity
Can be either
Normotensive pts usually decreased, however prevalence of HTN is high due to chronic sympathetic activation which is attributed to chronic hypoxia of OSA
What is the effect of obesity on LV contractility
Impaired
There is increased LV wall thickness and chamber volume.
LV diastolic function is often impaired Expanded volume = greater demand on myocardium = increased stress on LV wall = LVH
Are RV preload and afterload increased or decreased in obesity
Increased leading to RV failure
How much is cardiac output increased in obesity
0.1 L/kg of excess body fat
What is the impact of obesity on total and relative blood volume
Total BV = Increased
Relative BV = Decreased (adipose tissue is poorly perfused)
what is the EBV for an obese individual
45 ml/kg
What factors contribute to the increased risk of thrombosis in obesity
Immobility
Polycythemia (increased red cell mass associated with chronic hypoxia leading to hyperviscosity)
Adipose tissue releases cytokines, chemokines, and hormones that promote pro-inflammatory state leading to CV disease)
High factor VIII
2 x greater risk of DVT
What makes obese patients a high risk for aspiration
90% have gastric volume >0.35ml/kg and gastric pH <2.5 (mendelson’s criteria)
Delayed gastric emptying
What are the diagnostic criteria for Metabolic Syndrome (Syndrome X)
Central obesity
Serum triglycerides >150 mg/dl
Reduced serum HDL
HTN (>135/85)
Elevated fasting serum glucose >110
*diagnosis requires 3/5
What is the single major predictor of problematic intubation in morbidly obese patients
Neck circumference
Is BMI an independent predictor of a difficult airway?
No
What are the induction implications of a decreased FRC and increased o2 consumption in an obese patient
Desaturation in 1/2 the time of a non-obese adult during apnea
What is the number 1 nerve injury related to bariatric surgery
Carpal tunnel
Followed by:
Ulnar
Brachial plexus
Radial
Peroneal
Sphenoid
Which position is best for diaphragmatic excursion in an obsese pt
lateral decubitus
Which position provides the longest safe apnea time during induction for an obese pt
Head-up (reverse Trend, Fowler’s)
What are the benefits of HELP (head elevated laryngoscopy position)
Improves view
Increases safe apnea time
Better position for rescue ventilation techniques such as bag-valve mask ventilation or insertion of LMA
What medications are first line for pain management in obese patients
NSAIDs
How do local anesthetic requirements change when using regional on an obese patient
LA requirements can be up to 20% lower than non-obese for neuraxial blockade due to decreased volume of the epidural space from intra-abdominal pressure
What is the fio2 goal to prevent atelectasis in an obese patient
fio2 <80% to prevent absorption atelectasis
What are the benefits of recruitment maneuvers
improves FRC, V/Q matching, and arterial oxygen
What is the only vent parameter shown to improve respiratory function in obese patients
PEEP
What is the optimal PEEP setting for obese patients
Around 20 cmH2O
How should vent settings be changed for obese patients
Still 6-8 ml/kg tidal volume (increasing TV can cause shear stress to lungs)
May need higher resp rate to maintain PaCO2
Increased PEEP
What is the most sensitive indicator of post-gastric bypass anastomotic leak
tachycardia (hr >120 should prompt investigation)
What is the most common cause of postop mortality after bariatric surgery
thromboembolism
