Chapter 18-6: Obstructive Sleep Apnea

TEXTBOOK PRESENTATION

Patients with OSA often complain of daytime sleepiness or fatigue. Bed partners often note snoring or actual apneic episodes. Most patients are obese.

DISEASE HIGHLIGHTS

1. Characterized by repetitive episodes of complete or partial upper airway obstruction during sleep that results in desaturation in oxyhemoglobin and sleep fragmentation.

   1. An obstructive apnea is at least 10 seconds of cessation of ventilation accompanied by respiratory efforts.

   2. A hypopnea is at least a 30% reduction in airflow for 10 seconds or longer with at least a 4% reduction in oxygen saturation.

   3. A respiratory effort related arousal is an occurrence of disordered breathing that does not meet criteria for apnea or hypopnea but does cause arousal.

   4. The apnea-hypopnea index (AHI) is the total number of apneas plus hypopneas per hour; the respiratory disturbance index (RDI) includes apneas, hypopneas, and respiratory effort related arousals.

      1. OSA is defined as an AHI or RDI ≥ 5 with daytime somnolence, or an AHI or RDI ≥ 15 regardless of symptoms.

      2. Mild OSA is an AHI or RDI of 5–14; moderate is an AHI or RDI of 15–29, and severe is an AHI or RDI ≥30.

2. Prevalence of OSA

   1. When OSA is defined as an AHI ≥ 5 with symptoms or an AHI ≥ 15, the prevalence is 15% in men and 5% in women.

   2. The prevalence is 50% in referral populations.

3. Pathophysiology

   1. There are normal decreases in tonic pharyngeal muscle tone and compensatory reflex dilators during sleep.

   2. Patients with OSA have smaller upper airways due to increased parapharyngeal fat, tongue prominence, elongated palate, or thickened lateral pharyngeal walls, and are unable to maintain airway stability.

   3. During inspiration, the negative upper airway pressures close these narrowed airways, resulting in apneas or hypopneas.

4. Risk factors

   1. Obesity

      1. The strongest risk factor for OSA

      2. There is a 6-fold increase in the risk of OSA with a 10% weight gain.

      3. Enlarged neck circumference, a measurement of upper body obesity, is a predictor of OSA (>16 inches in women, >17 inches in men).

   2. Sex: OSA is 2–3 times more common in men than women.

   3. Menopausal status: 4-fold increase in risk in postmenopausal compared to premenopausal women.

   4. Craniofacial morphology, especially short mandibular length, may explain the presence of OSA in otherwise low-risk patients.

5. Consequences of OSA

   1. Increased rate of motor vehicle accidents (relative risk = 2.5–5)

   2. Hypertension (relative risk = 2.89)

   3. HF (relative risk = 2.38)

   4. Higher rates of mortality and adverse cardiac events in patients with coronary artery disease and untreated OSA.

   5. An association with impaired glucose tolerance has been observed.

   6. Long-standing, severe OSA can lead to cor pulmonale.

EVIDENCE-BASED DIAGNOSIS

1. History and physical exam

   1. Excessive daytime sleepiness is reported by about 35–40% of patients with OSA and by about 18% of patients without sleep-disordered breathing. Sleepiness can be assessed with the Epworth Sleepiness Scale and patients with a score > 10 should be tested for OSA.

   2. Lack of energy, ...