Obesity and Anesthesia

What is the waist circumference in patients with metabolic syndrome?
men: > 40in, women > 35in

What is one medication that will likely need to be increased with obesity anesthesia delivery?

What is the estimated blood volume in obese patients?

What is the change in pulmonary function/anatomy with obesity?
decreased ERV, which decreases FRC

What is the leading cause of morbidity and mortality in obese patients?
failure to intubate

What is the best predictor of difficult intubation in morbidly obese?
neck circumference. > 42cm. This associates with men, increased Mallampati, grade 3 laryngoscopy view, and OSA

What are several important drugs in obesity-related anesthesia pharmacology to dose by IBW?
propofol, vecuronium, rocuronium, remifentanil

Ultimately, what is the effect of impinged pulmonary ERV and FRC volumes? (2)
(1) V/Q mismatch with right->left shunting, (2) Rapid desaturation due to less reserve (normal FRC 46ml/kg, obese FRC ~ RV=23ml/kg, and oxygen consumption increases from 250mL/min to 375mL/min)

What physiologically happens to the respiratory drive with obesity hypoventilation syndrome?
increased reliance on hypoxic drive for ventilation due to loss of hypercarbic drive

What are the criteria for OHS?
coexisting lung disease and effects of chronic PHTN related to obesity

Pickwickian Syndrome has an associated compromise in what?
cardiac function; RV failure, secondary polycythemia, and biventricular failure

Describe Obesity Supine Death Syndrome.
pt. with pre-existing cardiac compromise placed supine, which acutely increases demand for cardiac output increase due to increased central blood volume. The LV cannot compensate, and pulmonary congestion and hypoxemia develops with acute LV failure.

Cardiac output must increase how much per 10kg body weight?

How much is SBP increased with 10kg body weight?
6 mmHg

How much is DBP increased with 10kg body weight?
4 mmHg

What is dangerous about induction with obese patients?
mimics exercise, and LV size and hypertrophy cannot compensate, leading to arrest on induction

Is an obese patient with hypertrophied LV safer or at greater risk than non-hypertrophied LV?
hypertrophied LV is more appropriate; compensation mechanisms have attempted to make up for body changes.

What ECG changes should be noted with obesity?
low voltage, right axis deviation r/t RVH, RBBB r/t PHTN

What metabolic effects are seen with obesity?
increased insulin secretion with resistance to insulin actions and decreased # of insulin receptors

What percentage of obese patients have Mendelson’s syndrome? Review what Mendelson’s is.
90%. 25ml gastric content @ pH <= 2.5 with higher risk of aspiration pneumonitis

What are recommended approaches to mechanical ventilation of obese patients?
5-6ml/kg IBW w/ 10 PEEP. Remember, the lungs are not obese

What are the safest considerations for ventilating an obese patient?
FiO2 < 60%, Vt < 6ml/kg, and plateau pressures < 30 cmH2O

How should neuraxial anesthetics be dosed in the obese?
75-80% of normal dose due to epidural vein engorgement

What is unique about attempting to reverse obese patients who have had a NMBA?
neostigmine may take 25 minutes to work

What aspect normally considered therapeutic post-op may actually mask apnea in the obese patient?
oxygen via nasal cannula. The increased PaO2 will reduce the respiratory drive because hypercarbic drive is lost

What is thiopental’s 1/2 life in obese patients compared to normal?
normal 6.3 hr half life, obese 27.8 hr half life

Is GI motility lower with opioids in obesity?

What is risky about using IV opioids in obesity?
decreased pharyngeal tone

What is the most common complication from Rou-En-Y procedure?
GI leak

What are important guidelines for post-op management of OSA patients?
no neuraxial opioids, use non-opioids for pain control, CPAP ASAP after surgery, recover in lateral, prone, or sitting position, continuous SpO2 until RA SpO2 > 90% asleep.

What are the 4 characteristics to OSA patients undergoing exercise test?
(1) lower exercise HR, (2) higher exercise DBP, (3) delayed SBP recovery time, (4) DBP tended to be higher after recovery

What is the leading mortality in obesity surgery?
pulmonary embolism

What is the time when a patient should stop smoking prior to surgery for recovery of some pulmonary physiologic mechanisms?
6 weeks

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