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Predicting Effective Continuous Positive Airway Pressure^*

^* From the Department of Medicine, St. Michael’s Hospital, and Center for Sleep and Chronobiology, University of Toronto, Toronto, Ontario, Canada.

Correspondence to: Victor Hoffstein, PhD, MD, FCCP; St. Michael’s Hospital, 30 Bond St, Toronto, ON, Canada M5B 1W8; e-mail: victor.hoffstein{at}utoronto.ca

Purpose: The purpose of this study was to compare the pressure required to abolish apneas as predicted from a previously derived algorithm (Ppred) with the true effective pressure (Peff) determined during a continuous positive airway pressure (CPAP) titration study.

Setting: Sleep clinic of a university hospital.

Methods: We prospectively studied 329 patients with sleep apnea undergoing CPAP titration. The following protocol was employed. Titration began at a pressure (Ppred) calculated from a previously derived equation based on body mass index, neck circumference, and apnea/hypopnea index (AHI). If AHI at Ppred was > 10, the pressure was increased in steps of 1 cm H₂O until AHI became < 10. If, on the other hand, AHI at Ppred was < 10, the pressure was reduced in increments of 1 cm H₂O until AHI became > 10. The lowest pressure that abolishes sleep apnea is defined as the Peff. Paired t tests, linear correlation, and distribution of (Ppred - Peff) were used to compare Peff and Ppred.

Results: Successful titration was accomplished in 276 patients (84%). Mean Ppred was similar to mean Peff (8.1 ± 2.2 vs 8.1 ± 2.6 cm H₂O, respectively). There was a significant correlation between these two pressures (r = 0.73; p = 0.0001). Examination of the distribution of (Peff - Ppred) revealed that in 63% of patients, Ppred was within ± 1 cm H₂O of Peff; in 83% of patients, the two measures were within ± 2 cm H₂O; and in 95%, within ± 3 cm H₂O.

Conclusion: We conclude that pressure predicted from an algorithm based on simple anthropometric and sleep variables constitutes a good starting point for CPAP titration, allowing the optimum pressure to be achieved with only a few incremental changes.

Key Words: continuous positive airway pressure • prediction • sleep apnea • titration

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