A Simplified Approach to Diagnosing Sleep Disordered Breathing and Nocturnal Hypercapnia in Individuals with Spinal Cord Injury

The objective of this study was to to evaluate a strategy of home-based testing to diagnose sleep-disordered breathing and nocturnal hypercapnia (NH) in patients with spinal cord injury (SCI) though a case series design  of ninety-one adults with C1-T6 SCI. Subjects were eligible if ≥ 18 years old, with SCI of ≥ 3 months duration, living within 100 miles of the study site and not meeting exclusion criteria. Of the 161 individuals contacted from the SCI Model System database that were not enrolled, reasons were not interested in participating, change of location, prior PPV use or medical contraindication. Ten patients did not complete the study. The intervention was the  performance of an unsupervised home sleep apnea test (HSAT) combined with transcutaneous (tc) pCO2/SpO2 monitoring. This was measured through the prevalence of sleep disordered breathing and nocturnal hypercapnia. Clinical and physiologic variables were examined to determine which, if any, correlate with the severity of sleep-disordered breathing. Results showed that obstructive sleep apnea (OSA) was found in 81.3% of subjects, central sleep apnea (CSA) in 23.8%, and nonspecific hypopnea events (NSHE), where respiratory effort was too uncertain to classify, were present in 35%. Nonspecific hypopnea events correlated closely with CSA but weakly with OSA, suggesting that conventional sleep apnea test scoring may underestimate central/neuromuscular hypopneas. Nocturnal hypercapnia was present in 28% and oxygen desaturation in 18.3%. Neck circumference was the primary predictor for OSA, while baclofen use and O-AHI weakly predicted CSA. Awake tc-pCO2 and CSA were only marginally associated with NH.

Unsupervised, home sleep apnea testing with transcutaneous capnography effectively identifies sleep-disordered breathing and NH in SCI patients.