Re: SCI Sleep Disordered Breathing vs. Hypoventilation?

Simplified Approach to Diagnosing Sleep-Disordered Breathing and Nocturnal Hypercapnia in Individuals With Spinal Cord Injury

OBJECTIVE

To evaluate a strategy of home-based testing to diagnose sleep-disordered breathing and nocturnal hypercapnia in individuals with spinal cord injury (SCI).

DESIGN

Case series.

SETTING

Referral center.

PARTICIPANTS

Adults with C1-T6 SCI (N=81). Individuals 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 recruited from the SCI Model System database who were not enrolled, reasons were not interested in participating, change of location, prior positive pressure ventilation use, or medical contraindication. Ten individuals did not complete the study.

INTERVENTIONS

Performance of an unsupervised home sleep apnea test combined with transcutaneous partial pressure of carbon dioxide/oxygen saturation by pulse oximetry monitoring.

MAIN OUTCOME MEASURES

Prevalence of sleep-disordered breathing and nocturnal hypercapnia. Clinical and physiological variables were examined to determine which, if any, correlate with the severity of sleep-disordered breathing.

RESULTS

Obstructive sleep apnea (OSA) was found in 81.3% of individuals, central sleep apnea (CSA) was found in 23.8%, and nonspecific hypopnea events, where respiratory effort was too uncertain to classify, were present in 35%. Nonspecific hypopnea events correlated strongly 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, whereas baclofen use and obstructive apnea/hypopnea index weakly predicted CSA. Awake transcutaneous partial pressure of carbon dioxide and CSA were only marginally associated with nocturnal hypercapnia.

CONCLUSIONS

Unsupervised home sleep apnea testing with transcutaneous capnography effectively identifies sleep-disordered breathing and nocturnal hypercapnia in individuals with SCI.

Home-based overnight transcutaneous capnography/pulse oximetry for diagnosing nocturnal hypoventilation associated with neuromuscular disorders

OBJECTIVE

To determine the utility of home-based, unsupervised transcutaneous partial pressure of carbon dioxide (tc-Pco(2)) monitoring/oxygen saturation by pulse oximetry (Spo(2)) for detecting nocturnal hypoventilation (NH) in individuals with neuromuscular disorders.

DESIGN

Retrospective case series analyzed consecutively.

SETTING

Multidisciplinary neuromuscular respiratory failure (NMRF) clinic at an academic institution.

PARTICIPANTS

Subjects (N=35, 68.6% men; mean age, 46.9y) with spinal cord injury (45.7%) or other neuromuscular disorders underwent overnight tests with tc-Pco(2)/Spo(2) monitoring. Fifteen (42.9%) were using nocturnal ventilatory support, either bilevel positive airway pressure (BiPAP) or tracheostomy ventilation (TV).

INTERVENTIONS

A respiratory therapist brought a calibrated tc-Pco(2)/Spo(2) monitor to the patient's home and provided instructions for data collection during the subject's normal sleep period. Forced vital capacity (FVC), body mass index (BMI), and exhaled end-tidal Pco(2) (ET-Pco(2)) were recorded at a clinic visit before monitoring.

MAIN OUTCOME MEASURES

Detection of NH (tc-Pco(2) ≥50mmHg for ≥5% of monitoring time). Data were also analyzed to determine whether nocturnal oxygen desaturation (Spo(2) ≤88% for ≥5% of monitoring time), FVC, BMI, or daytime ET-Pco(2) could predict the presence of NH.

RESULTS

NH was detected in 18 subjects (51.4%), including 53.3% of those using BiPAP or TV. NH was detected in 43.8% of ventilator-independent subjects with normal daytime ET-Pco(2) (present for 49.4%±31.5% [mean ± SD] of the study period), and in 75% of subjects with an elevated daytime ET-Pco(2) (present for 92.3%±8.7% of the study period). Oxygen desaturation, BMI, and FVC were poor predictors of NH. Only 3 attempted monitoring studies failed to produce acceptable results.

CONCLUSIONS

Home-based, unsupervised monitoring with tc-Pco(2)/Spo(2) is a useful method for diagnosing NH in NMRF.