Volume Targeted Patient Triggered Ventilation: Decreased Subject Effort and Improved Efficiency in an Animal Model of Respiratory Distress Syndrome† 1611

Abstract

We hypothesized that a fully-synchronized patient triggered mode of ventilation, assist-control (A/C), would reduce subject effort when compared to IMV and SIMV. Ten newborn piglets (1.9±0.40 kg) with saline lavage-induced lung injury (PaO2<100 torr at FiO2 1.0) were randomized to sequential 30 minute periods of IMVSIMVAC (n=5), or ACSIMVIMV (n=5) using time-cycled, pressure limited, volume targeted (15 mL/kg) ventilation (Drager Babylog®). Respiratory rate(RR) and minute ventilation (Ve) were determined as 1 minute moving averages every 15 seconds; tidal volume (Vt), mean airway pressure (MAP), and an esophageal pressure-time index (PE·RR) to estimate subject, not mechanical, work of breathing were determined for all breaths. PE·RR was defined as the area below baseline of the esophageal pressure-time curve× RR, and was recorded using a computer-assisted lung mechanics analyzer(VenTrak®). Blood gases were recorded every 30 seconds using an in-line continuous blood gas analyzer (Paratrend 7®); a/A was calculated. Vt variation was assessed using the coefficient of variation (V; SD/mean × 100). Data analysis used paired t-tests with Bonferroni correction. Wilcoxon rank-sum test was used for nonparametric data.Results: Subject work, estimated by PE·RR, was significantly lower with A/C. Statistically significant differences in A/C vs IMV and SIMV included higher pH, lower RR, and increased Ve and MAP. No differences in a/A were seen. Vt was always less variable during A/C. Conclusion: Fully-synchronized A/C ventilation produced the highest Ve and pH, and the most consistent Vt, with the lowest subject effort as estimated by PE·RR. This data suggests A/C is more efficient during spontaneous respiration than either IMV or SIMV, as it provides improved gas exchange with less inspiratory effort, Table