Accuracy of CPAP prescription by different predictive equations in OSAS.

Usefulness of formulas to predict effective CPAP level for OSAS treatment is under debate.Inthisstudy,CPAPlevelscalculatedaccordingtofourdifferentformulas [StradlingJRetal,RespirMed(2004)98:152-4;HoheiselGBetal,AmJRespir CritCareMed(1994)149:A496;SérièsFetal,AmJRespirCritCareMed(2000) 162:94-7;HoffsteinVetal,AmJRespirCritCareMed(1994)150:486-8]were comparedtoeffectiveCPAPleveltitratedduringpolysomnography.CPAPtitration waspreformedin136OSASsubjects(22F,age54 ± 11 yrs,BMI34.6 ± 6.1 kg/m2 , AHI58 ± 22) bymeansofoneAPAPdevice(AutosetT,ResMed)applied duringapolysomnographicstudy.Aseffectivepressurewasconsideredthe95th centile pressureleveldeliveredbytheAPAP,correctedaccordingtotheanalysisof polysomnographicsignals.Correlationsbetween calculatedandeffectivepressures werealwayssignificant,butloose(r2 between 0.044and0.139).Differences <=2 cmH2O fromeffectivepressurewerefoundfor78%pressurevaluescalculated by Stradling'sformula,andfor19-46%valuescalculatedbytheotherformulas. Differencesbetween95th centilepressuresandcalculatedpressureswereslightly higher (64%pressurelevelsbyStradling'sformula,and14-32%bytheotherones, differing <=2 cmH2O from95th centilepressures).Differencesbetweeneffective pressureandpressurecalculatedbyStradling'sformularangedbetween-3.5and +6.5 cmH2O. Onlyvaluescalculatedbyoneofthetestedpredictiveformulas approximatedsufficientlytotherealeffectivepressureinahighpercentageof cases, butevenbythatformulaeffectivepressureisnotestimatedwithacceptable accuracyin1outof5cases.