Obesity and obstructive sleep apnea

1

Define obesity.

Obesity is defined using the body mass index (BMI) ( Table 49.1 ).

2

Describe the implications of obesity as they pertain to anesthetic management.

• Anesthetic Plan—Procedures that are normally performed under sedation and/or monitored anesthetic care may not be safe or feasible to perform in obese patients.

• Induction of Anesthesia—Decreased lung volumes (i.e., functional residual capacity [FRC]) and increased oxygen consumption because of body habitus, in conjunction with a short, fat neck, and decreased pulmonary compliance can make mask ventilation and intubation difficult.

• Relaxation—Procedures that usually do not require neuromuscular blockade may not be feasible in obese patients without it.

• Pulmonary—Decreased pulmonary compliance predisposes to hypoventilation and atelectasis, which increases the risk of hypercarbia and hypoxemia, respectively.

• Airway—High incidence of obstructive sleep apnea (OSA) and pulmonary complications, all of which is exacerbated by the respiratory depressant effects of anesthesia and opioids.

• Positioning—Procedures requiring Trendelenburg or lateral positioning can present challenges regarding patient safety and/or operating room equipment stability.

• Monitoring—Noninvasive blood pressure monitoring may be inaccurate or ineffective in obese patients necessitating invasive arterial blood pressure monitoring.

3

Discuss the cardiovascular considerations in patients who are obese.

Systemic and pulmonary hypertension, as well as left- and right-sided heart failure and coronary artery disease, can be found in obese patients. As body mass increases, so does oxygen consumption, causing a compensatory increase in circulating blood volume and cardiac output to meet increased demand. Chronic systemic hypertension, in the setting of compensatory increased cardiac output, can lead to left ventricular hypertrophy and left heart failure. Chronic hypercapnia and hypoxia, commonly associated with OSA, can increase pulmonary artery pressure (i.e., hypoxic pulmonary vasoconstriction), leading to right ventricular hypertrophy and right heart failure.

4

What are the main pulmonary abnormalities associated with obesity?

• Decreased pulmonary compliance (Δ V/ΔP)

• Decreased FRC

• Increased oxygen consumption ( $\stackrel{.}{V}{O}_2$ )

5

Review pulmonary and respiratory considerations in caring for patients with obesity.

Considerations include the possibility of a difficult airway, increased incidence of asthma, OSA, obesity hypoventilation syndrome (OHS), and pulmonary hypertension. Obesity is a major risk factor for hypoxemia in the perioperative environment.

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