Sleep-Related Breathing Disorders
Definitions and scoring rules
Obstructive sleep apnea (OSA) requires documentation of obstructive events. An apnea is ≥90% airflow reduction for ≥10 seconds; a hypopnea uses the AASM rule of ≥30% reduction with ≥3% desaturation or an arousal (a common alternative rule uses ≥4% desaturation without arousal). The AHI = apneas + hypopneas per hour of sleep; the RDI adds respiratory effort-related arousals (RERAs). Severity thresholds: mild 5–15, moderate 15–30, severe >30 events/hour.
Central sleep apnea (CSA) shows absent airflow without respiratory effort. Cheyne-Stokes respiration is a crescendo-decrescendo pattern with central events, classically in heart failure. Treatment-emergent central apnea appears when obstructive events are eliminated and central events emerge.
Pathophysiology and consequences
OSA results from anatomic collapsibility (retrognathia, macroglossia, adenotonsillar hypertrophy) plus reduced pharyngeal dilator tone, worsened by REM atonia, supine position, alcohol, and sedatives. Consequences include sympathetic activation, hypertension, atrial fibrillation, stroke risk, and daytime sleepiness. Obesity hypoventilation is a separate diagnosis defined by awake hypercapnia (PaCO2 ≥45 mmHg).
Traps: equating snoring with OSA (snoring is neither sensitive nor specific); assuming a normal BMI excludes OSA (craniofacial features matter); and forgetting that a supine-predominant AHI can be missed if total-night AHI is used alone. Also remember that CPAP adherence is typically defined as ≥4 hours/night on ≥70% of nights.
Rule of thumb: AHI 5–15 plus symptoms or comorbidity still warrants treatment; AHI alone does not dictate management.
Worked example: A patient with AHI 12 but no symptoms and no comorbidity may not require treatment; the same AHI with resistant hypertension does.