Optimal level of continuous positive airway pressure: Auto-CPAP titration versus predictive formulas

Abstract

Continuous positive airway pressure (CPAP) is the most effective treatment of obstructive sleep apnea hypopnea syndrome (OSAHS). The therapeutic level of CPAP is achieved by manual titration or an auto CPAP device, but an alternative way involves the use of mathematical equations.Aim of the work: to compare between CPAP pressure obtained by autoCPAP titration and that calculated from five different mathematical formulas. MethodsWe enrolled 30 patients with OSAHS. In addition to standard examination, anthropometric measurements and investigations, all patients underwent an over-night polysomnography (PSG) AutoCPAP (level II) to diagnose OSAHS. Manual scoring of polysomnographic data was performed according to criteria established by the American Academy of Sleep Medicine in 2012. All patients used AutoCPAP with pressure ranging from 4 to 20cm H2O. Information recorded was downloaded and the following data were retrieved: 1) P90% (90th percentile pressure delivered by the autoCPAP device and eliminated snoring, flow limitation and apnea), this pressure was chosen as the therapeutic pressure, 2) peak pressure level, 3) mean pressure level, 4) the estimated residual apnea hypopnea index (AHI), 5) P90%/mean pressure level ratio, which is an index of pressure variability, was calculated. Five predictive formulas were retrieved from published literature and calculated for all patients. ResultsThe mean±SD of AHI was 47.94±27.21events/h. OSAHS was mild in 5 patients (16.67%), moderate in seven patients (23.33%), and severe in 18 patients (60%). AutoCPAP P90% was 10.59±2.66cm H2O and showed significantly direct correlation with each of Epworth sleepiness scale (p=0.000), BMI (p=0.001), neck circumference (p=0.002), neck to height ratio (p=0.000), and AHI (p=0.000). Also it was found to show statistically significant inverse correlation with each of minimal (p=0.000), and average minimal oxygen saturation (p=0.032). The pressure calculated by Hoffstein et al. equation was significantly lower than autoCPAP P90%. There was no significant difference with pressure calculated by the other four formulas and P90%. The following model of predictive equation was derived from the studied sample: Predicted therapeutic pressure=4.740+68.575 X (N/H) – 0.153 X (Minimal SpO2). ConclusionsPredictive formulas might be useful as an alternative to autoCPAP. The model of predictive formula derived from the present small sample of Egyptian patients with OSAHS should be validated on a larger sample size.