Sleep-Related Breathing Disorders and Diagnosis
What the candidate must know
Understand the spectrum of sleep-disordered breathing: obstructive sleep apnea, central sleep apnea, mixed and complex patterns, and sleep-related hypoventilation. Know the apnea-hypopnea index (AHI) and oxygen desaturation index (ODI), and the severity thresholds: mild 5 to under 15, moderate 15 to under 30, severe 30 or more events per hour. Recognize that hypopnea scoring criteria differ between rule sets and that this affects reported AHI. Know that a home sleep apnea test typically measures airflow, respiratory effort, and oximetry but may underestimate disease, especially in patients with heart failure, significant cardiopulmonary disease, or suspected central apnea, where in-lab polysomnography is preferred.
Traps in questions
A frequent error is treating AHI as the sole measure of clinical significance; symptom burden, oxygen nadir, and comorbidities matter. Questions may blur the distinction between screening and diagnosis, or between a home test and attended polysomnography. Another trap: assuming central events are benign or that a mixed pattern is stable - complex sleep apnea can emerge on PAP and warrants physician reassessment. Also distinguish snoring without apnea from OSA; snoring alone is not a diagnosis. Remember that pediatric scoring criteria and thresholds differ from adult criteria.
Worked example / rule of thumb
A patient with AHI 22 and nadir oxygen saturation of 82% has moderate OSA by index but clinically important desaturation. Rule of thumb: report severity by AHI but interpret it alongside symptoms, oxygen nadir, and comorbidity. When a home test is negative but clinical suspicion is high, escalate to in-lab polysomnography rather than dismissing the concern.