Low-concentration carbon dioxide is an effective adjunct to positive airway pressure in the treatment of refractory mixed central and obstructive sleep-disordered breathing.

Objectives: To assess the efficacy of added carbon dioxide as adjunctive therapy to positive airway pressure-refractory mixed obstructive and central sleep-disordered breathing, using a prototype device-the positive airway pressure gas modulator.

Design: Open-label evaluation of low concentrations of carbon dioxide added to a positive airway pressure circuit.

Setting: Physician-attended polysomnographic titration in a free-standing sleep laboratory with end-tidal and transcutaneous carbon-dioxide monitoring.

Patients: Six adult men (age 54 +/- 5.7 years) with severe poorly controlled mixed sleep-disordered breathing in the absence of renal or heart failure.

Interventions: Flow-independent addition of incremental concentrations of carbon dioxide during sleep.

Measurements And Results: The respiratory disturbance index before treatment was 66 +/- 14.5 events per hour of sleep, with a nocturnal desaturation low of 84.6% +/- 10.1%. Residual respiratory disturbance index on best treatment was 43 +/- 9 events per hour of sleep. There was an immediate (<1 minute) response to the addition of 0.5% to 1% carbon dioxide, and minimal changes were required to be made across the night. There was no discomfort, shortness of breath, palpitations, headache, or significant increase in respiratory or heart rate. The residual respiratory disturbance index on carbon dioxide, scored irrespective of desaturations, was in the normal range (< 5 / hour of sleep). Two subjects had a second night at the concentration of carbon dioxide determined to be efficacious, with no required concentration change. No adverse effects on overall sleep architecture were noted.

Conclusions: Low concentrations of carbon dioxide added to conventional positive airway pressure effectively control severe treatment-resistant mixed obstructive and central sleep-disordered breathing.