Predicting effective continuous positive airway pressure.
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 H(2)O until AHI became < 10. If, on the other hand, AHI at Ppred was < 10, the pressure was reduced in increments of 1 cm H(2)O 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 H(2)O, 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 H(2)O of Peff; in 83% of patients, the two measures were within +/- 2 cm H(2)O; and in 95%, within +/- 3 cm H(2)O. 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.