Calculating intrinsic positive end-expiratory pressure from end-expiratory flow in mechanically ventilated children-A study in physical models of the pediatric respiratory system

RationaleThe high resistance of pediatric endotracheal tubes (ETTs) exposes mechanically ventilated children to a particular risk of developing intrinsic positive end-expiratory pressure (iPEEP). To date, determining iPEEP at the bedside requires the execution of special maneuvers, interruption of ventilation, or additional invasive measurements. Outside such interventions, iPEEP may be unrecognized.ObjectiveTo develop a new approach for continuous calculation of iPEEP based on routinely measured end-expiratory flow and ETT resistance.MethodsFirst, the resistance of pediatric ETTs with inner diameter from 2.0 to 4.5 mm were empirically determined. Second, during simulated ventilation, iPEEP was either calculated from the measured end-expiratory flow and ETT's resistance (iPEEPcalc) or determined with a hold-maneuver available at the ventilator (iPEEPhold). Both estimates were compared with the end-expiratory pressure measured at the ETT's tip (iPEEPdirect) by means of absolute deviations.ResultsEnd-expiratory flow and iPEEP increased with decreasing ETT inner diameter and with higher respiratory rates. iPEEPcalc and iPEEPhold were comparable and indicated good correspondence with iPEEPdirect. The largest absolute mean deviation was 1.0 cm H2O for iPEEPcalc and 1.1 cm H2O for iPEEPhold.ConclusionWe conclude that iPEEP can be determined from routinely measured variables and predetermined ETT resistance, which has to be confirmed in the clinical settings. As long as this algorithm is not available in pediatric ICU ventilators, nomograms are provided for estimating the prevailing iPEEP from end-expiratory flow.