Sleep Medicine: Defining Apnea, Choosing Therapy
Diagnosis
Obstructive sleep apnea is defined by an apnea-hypopnea index (AHI) ≥5 with symptoms or comorbid conditions, or an AHI ≥15 with no symptoms at all. Hypopnea requires a ≥30% fall in airflow with desaturation or arousal, so differing scoring rules change the index - a common source of ambiguity. Screening tools like STOP-BANG generate pretest probability only; they never diagnose.
Central versus obstructive
Central sleep apnea shows absent respiratory effort, classically with Cheyne-Stokes respiration in heart failure. Adaptive servo-ventilation is contraindicated in heart failure with reduced ejection fraction <45% because mortality increased; this is a high-yield trap. Obesity hypoventilation syndrome requires BMI ≥30 plus waking PaCO2 >45 mmHg, and is treated with positive pressure ventilation and weight loss, not oxygen alone.
Treatment
CPAP is first-line for symptomatic OSA; adherence determines benefit. Alternatives include mandibular advancement devices for mild disease or CPAP intolerance, positional therapy, and hypoglossal nerve stimulation in selected patients. Weight loss, including surgical or pharmacologic, improves disease. Patients should be counseled about drowsy driving. Untreated OSA worsens hypertension, atrial fibrillation, and stroke.
Other disorders
Narcolepsy shows a mean sleep latency ≤8 minutes with ≥2 sleep-onset REM periods on MSLT after adequate sleep; cataplexy is specific. Restless legs syndrome is clinical and responds to iron repletion and dopamine agonists. Insomnia first-line therapy is cognitive behavioral therapy, not hypnotics.
Worked rule
AHI 6 with severe daytime sleepiness = treat OSA. AHI 6 without symptoms or comorbidity = do not commit to lifelong CPAP; address sleep hygiene and weight.