Introduction Children with Down syndrome (DS) have a high incidence of obstructive sleep apnea (OSA) that is often associated with hypoventilation. Little is known, however, about the prevalence of sleep-associated hypoventilation independent of OSA in these children.

Methods Retrospective chart review of all children with DS under 18 years of age undergoing polysomnography at a tertiary care paediatric hospital during a 2-year period. Exclusion criteria were as follow: those requiring oxygen or positive-pressure ventilation; with tracheostomy, baseline hypoxia, unrepaired cyanotic heart disease, pulmonary hypertension, and cerebral palsy; or OSA with >5 obstructions/hour.

Results 86 children met inclusion criteria. 68 (79%) had ETCO₂values >50 mm Hg during sleep. 37 (43%) ranged 50–55 mm Hg, and 12 (14%) met American Academy of Sleep Medicine criteria for hypoventilation of ETCO₂ >50 mm Hg for >25% of total sleep time (TST). Average pulse-oximetry saturation (SpO₂) values during sleep were 97.8% (SD ±1; range: 95.1–99.9). Average percentage of TST with SpO₂ >92% was 99.89%.

Conclusion Mildly elevated ETCO₂ in the absence of OSA is common in children with DS. This may reflect underlying differences in autonomic control of ventilation in these children and may be considered a normal variant not necessitating intervention other than close monitoring for pulmonary hypertension.