Central Sleep Apnea and Hypoventilation Syndromes
Central apnea categories
Central sleep apnea (CSA) reflects absent respiratory effort. Causes include Cheyne-Stokes respiration in heart failure, opioid use, high-altitude exposure, and idiopathic central apnea. Treatment-emergent central apnea can appear when PAP resolves obstructive events but central events persist. Cheyne-Stokes breathing shows a crescendo-decrescendo pattern with a long cycle length; treatment targets the underlying heart failure, and adaptive servo-ventilation has a specific, limited role.
Hypoventilation syndromes
Obesity hypoventilation syndrome is defined by obesity (BMI 30 or more) with daytime hypercapnia (PaCO2 above 45 mm Hg) during wakefulness in the absence of other causes, often with sleep-related hypoventilation. Neuromuscular and chest wall disorders cause hypoventilation with preserved airway patency. Noninvasive ventilation (bilevel) is preferred over CPAP when hypoventilation dominates.
Traps
- Opioid-associated CSA may improve with reducing opioids; PAP mode choice matters.
- ASV is contraindicated in some heart failure with predominant central apnea and low ejection fraction (per major trial).
- Do not call hypoventilation OSA; the mechanism and therapy differ.
- Awake hypercapnia is the defining feature of OHS, not nocturnal alone.
Rule of thumb
If effort is absent, think central; if effort is present but ventilation is inadequate, think hypoventilation. Bilevel ventilation supports the latter.