Background: Continuous positive airway pressure (CPAP) is effective therapy for the obstructive sleep apnea syndrome (OSAS). Automatic CPAP devices continuously adjust the positive pressure to the required levels.
Objective: To determine the efficacy of an automatic CPAP machine used with an estimated reference pressure value.
Design: A before-and-after, single-blind trial in which patients were randomly allocated to one of three modes of CPAP administration.
Setting: Referral-based sleep center in a public health care institution.
Patients: 36 outpatients with OSAS.
Intervention: Continuous positive airway pressure was given at a conventional fixed pressure (group 1), automatic CPAP was given at a measured reference pressure (group 2), and automatic CPAP was given at an estimated reference pressure (group 3). In group 1, the effective pressure was determined during a titration sleep study. In groups 2 and 3, the pressure interval was allowed to vary from 4 cm H2O below reference pressure to 3 cm H2O above reference pressure. In group 3, the estimated value of the reference pressure was determined according to individual anthropometric characteristics.
Measurements: Sleep studies were performed and measurements of diurnal sleepiness were obtained at each visit.
Results: Sleep and breathing disorders and hypersomnolence were alleviated similarly in the three groups. The apnea + hypopnea index remained abnormal in one patient in group 3 for whom the reference pressure had been underestimated. A strong negative correlation was found between the percentage of time spent below reference pressure during CPAP and the difference between the effective and estimated pressures.
Conclusion: Automatic CPAP can be used with an estimated reference pressure without doing a titration sleep study. The positive pressure trend can be used to determine whether treatment failure is caused by an inadequate pressure setting and to determine the amount of pressure to apply.