Obesity Quick Review

1170: What is the formula for BMI?

(Weight in Kg)/m2

3906: What are the principal cardiovascular considerations of obesity?

-Ischemic heart disease, hypertension, and heart failure -1 kg of fat = 0.1 L/min increase in CO -Chronic respiratory insufficiency --> increase in blood volume -Increased workload --> increased O2 consumption and CO2 production -Increased LV pressure and hypertrophy -Hypertension is more than twice as common in obese patients -Hypercholesterolemia is usually present -Arrhythmias occur as a result of hypoxemia, sleep apnea, electrolyte disorders, ventricular hypertrophy, and CAD

1851: What are the classifications of obesity based on BMI?

25-29.9 = Overweight 30-35 = obesity class 1 35-40=obesity class 2 40=morbid obesity 50=super obesity 60= super-super obesity

3873: How does the degree of obesity and the risk of pulmonary aspiration correlate?

An increase in the BMI by 3.5 increases the risk for pulmonary aspiration by 270%.

3814: How is the volume of distribution and elimination half-life of midazolam compare between obese and non-obese patients?

Both the volume of distribution and the elimination half-life are significantly increased in obese patients, resulting in prolonged duration of action in obese patients. A single intravenous dose should be based on total body weight, but a continuous infusion should be based on lean body weight.

3909: How does obesity affect chest wall compliance?

Compression of abdominal, diaphragmatic, and thoracic structures by adipose tissue results in thoracic kyphosis, lumbar lordosis, and fixation of the thorax in an inspiratory position which results in a decrease in chest wall compliance by about 35%.

3893: How does obesity affect pulmonary function?

FRC and ERV reduction are the most commonly reported abnormalities of pulmonary function in obese patients.

4919: What coagulation factors would be most likely to be elevated in obese patients?

Fibrinogen Factors VII, VIII, vWb factor Plasminogen activator inhibitor

3970: How does hyperinsulinemia contribute to cardiovascular disease in the obese patient?

Hyperinsulinemia -activates the sympathetic nervous system -causes sodium retention -results in an overall 50-60% increase in the incidence of HTN. Chronic HTN leads to: -concentric LV hypertrophy -an increase in the risk for CHF

3366: What is the usefulness of obtaining pre- and postoperative creatine kinase levels in morbidly obese patients?

It can help in diagnosing and managing rhabdomyolysis which occurs in 1-2 percent of morbidly obese patients undergoing surgery. Rhabdomyolysis occurs due to compression of deep tissues and can lead to acute renal failure.

613: What are the primary functions of adipose tissue?

It serves as a reservoir of readily convertible energy and serves as a heat insulator.

3887: What ECG changes are often seen in obese patients?

Low QRS voltage T-wave flattening in the inferior and lateral leads LVH criteria Left atrial enlargement Prolonged QT interval

1609: What is the formula for ideal body weight?

Male IBW = centimeters - 100 Female IBW = centimeters - 105.

4922: What are the diagnostic criteria for metabolic syndrome?

Metabolic syndrome: a cluster of conditions that increase the risk of heart disease, stroke, and diabetes. -waist circumference > 102 cm in men or 88 cm in women -triglyceride level > 150 mg/dL -HDL cholesterol < 40 mg/dL in men or < 50 mg/dL in women -a blood pressure > 130/85 mm Hg -a fasting glucose > 110 mg/dl.

3886: Why do liver enzymes tend to be elevated in patients with morbid obesity?

Morbid obesity produces fatty infiltration, inflammation, and necrosis of the liver. Abnormal liver function tests are present in about 1/3 of morbidly obese individuals. Clearance of drugs is usually not reduced, however. Increased alanine aminotransferase (ALT) is the most common abnormality.

3419: Should obese patients undergo rapid-sequence induction?

Studies differ with respect to whether all obese patients are at risk for pulmonary aspiration. It is generally accepted, however, that patients above a BMI of 50 should undergo awake intubation or intubation with propofol alone and no muscle relaxation.

3724: Name four anesthetic drugs whose induction or initial doses should be calculated according to total body weight in the obese individual.

Succinylcholine Neostigmine Sugammadex Dexmedetomidine Versed

3875: How should the procedure for epidural anesthesia be adjusted for an obese individual?

The obese patient should be in the sitting position when the epidural is placed to help in identifying landmarks. Because rostral spread of the anesthetic is more prevalent in obese patients and they are more prone to suffer respiratory symptoms as a result, you should have them sit up for a longer period of time after injection.

3258: How should positioning for induction of an obese patient be carried out?

The patient should have the shoulders and head ramped up with the head in sniffing position and the bed should be placed in reverse Trendelenburg to increase the FRC and allow large breasts to fall away from the neck. The acronym HELP may be used to remember 'Head Elevated Laryngoscopy Position' for obese patients.

3885: What are the gastrointestinal considerations in the obese patient?

The risk of GERD, cholelithiasis, and pancreatitis are substantially increased in the obese patient. Nonalcoholic fatty liver disease, which consists of steatosis, cirrhosis, hepatomegaly, abnormal liver enzyme levels, and impaired liver function may be present. The mortality rate of cirrhosis is approximately twice that in obese patients compared to normal weight patients.

3957: How does obesity hypoventilation syndrome (OHS) differ from the respiratory changes associated with simple obesity?

With simple obesity, the PaCO2, pH, and pulmonary compliance are still in the range of normal values. OHS is present when the morbidly obese patient exhibits: -inappropriate somnolence -sleep apnea -hypoxemia -hypercapnia -decreased alveolar ventilation -Polycythemia, enlarged heart, and cyanosis may also be present.

3888: How does obesity affect renal function?

increased GFR increased renal tubular resorption impaired sodium excretion --> worsens HTN

3312: What measurable characteristic best predicts the occurrence of a difficult airway in the obese patient? What factors are present in the obese airway that may result in a difficult airway?

Neck circumference is the single best predictor of a difficult airway. A neck circumference of 40 cm is associated with a 5% chance of difficult intubation while a neck circumference of 60 cm indicates a 35% chance of difficult intubation. Fat rolls around the neck restrict neck motion while fat in the airway tissue decreases the glottic opening. Other anatomic abnormalities that are often associated with obesity include reduced temporomandibular and atlantoaxial motion.

3169: How does obesity affect the choice of anesthetic?

No difference has been demonstrated in emergence following inhalation versus narcotic techniques. Many clinicians, however, recommend a 'light' general anesthetic combined with epidural anesthesia whenever possible as it reduces the need for opioids and facilitates coughing and deep breathing after surgery.

3876: What diagnostic parameter is the most sensitive indicator of the effect of obesity on pulmonary function?

Obesity decreases respiratory compliance due to the accumulation of fat on the chest wall, diaphragm, and abdomen resulting in a decrease in functional residual capacity, vital capacity, and total lung capacity. The reduction in functional residual capacity is due to a reduction in the expiratory reserve volume, which is the most sensitive indicator of the effect of obesity on pulmonary function.

4915: What anti-obesity agents are FDA-approved?

Orlistat, phentermine, buproprion-naltrexone, phentermine-topiramate, lorcaserin, and liraglutide are presently the only FDA-approved anti-obesity agents. Because phentermine is a noradrenergic amine, it can produce tachycardia, palpitations, and hypertension and should not be used for more than 3 months.

4987: A morbidly obese patient is undergoing general anesthesia with mechanical ventilation and has an oxygen saturation of 80%. Which ventilatory change would improve oxygenation the most?

PEEP is the only setting to consistently improve the respiratory function of morbidly obese individuals.

3908: What is the incidence of obstructive sleep apnea in obese patients? How does it affect cardiovascular status?

Patients with OSA typically develop: -Hypercarbia -Polycythemia (not anemia) -Pulmonary hypertension -Right-sided heart failure

3877: How does obesity affect the left ventricle?

Patients with morbid obesity have a larger total blood volume than non-obese patients to supply the excess adipose tissue. The excess blood volume and resulting increase in preload causes ventricular dilation and increased left ventricular wall stress (eccentric hypertrophy).

4989: What anesthetic drugs should be administered based on lean body weight in obese patients?

Propofol induction doses Sufentanil maintenance doses Remi Bolus Versed infusion

4988: What anesthetic drugs should be administered based on ideal body weight in obese patients?

Rocuronium vecuronium cisatracurium remifentanil infusion rates