The Effect of Inspiratory Effort on Circuit Compensation for Volume-Targeted Modes.

Abstract

Critical-care ventilators provide patient circuit compensation (CC) to counteract the loss of volume due to patient circuit compliance. No studies show the effect of inspiratory efforts (indicating maximal value of the muscle pressure waveforms [Pmax]) on CC function. The goal of this study was to determine how Pmax affects volume delivery with or without CC for both volume control continuous mandatory ventilation with set-point targeting scheme (VC-CMVs) and pressure control continuous mandatory ventilation with adaptive targeting scheme (PC-CMVa) modes on the Servo-u ventilator. A breathing simulator was programmed to represent an adult with moderate ARDS with different Pmax. It was connected to a ventilator set to VC-CMVs or PC-CMVa. The change in tidal volume (ΔVT) was defined as the difference between VT with CC on versus off. VT error was defined as the difference between the simulator displayed VT and the set VT with CC on versus off. For both VC-CMVs and PC-CMVa modes, ΔVT decreased as Pmax increased. The VT error decreased as Pmax increas-ed for VC-CMVs. In contrast, VT error increased on PC-CMVa mode as Pmax increased and peaked 39.0% for Pmax = 15 cm H2O. For both modes, the difference in VT errors for CC on versus CC off decreased as Pmax increased. CC corrected the delivered VT for volume lost due to compression in the patient circuit as expected. This compensation volume decreases as airway pressure drops due to patient Pmax.