A method for monitoring and improving patient: ventilator interaction

To evaluate a new approach for monitoring and improving patient-ventilator interaction that utilizes a signal generated by the equation of motion, using improvised values for resistance and elastance obtained noninvasively.

Observational study in intensive care units in five European centers.

We studied 21 stable patients instrumented with esophageal/gastric catheters for a previous study and ventilated alternately with pressure support (PSV) and proportional assist (PAV) ventilation with a Tyco 840 ventilator.

Previously recorded digital files were analyzed in real-time by a prototype incorporating the new technology (PVI monitor, YRT, Winnipeg, Canada). Actual onsets (P_DI-T_ONSET) and ends (P_DI-T_END) of inspiratory efforts, ineffective efforts, and patient respiratory rate were identified visually from transdiaphragmatic or calculated respiratory muscle pressure. Monitor-identified T_ONSET occurred 0.107 ± 0.074 s after P_DI-T_ONSET, substantially less than trigger delay observed with conventional triggering (0.326 ± 0.086 s). End of effort was identified 0.097 ± 0.096 s after P_DI-T_END, significantly less than actual cycling-off delay during PSV (0.486 ± 0.307 s) or PAV (0.277 ± 0.084 s). The monitor detected 80% of ineffective efforts. There was excellent agreement between monitor-estimated respiratory rate and actual patient rate over a wide range (17–59/min) of patient rates (mean ( ± SD) of difference −0.2 ± 1.9/min for pressure support and 0.2 ± 0.9/min for proportional assist) even when large discrepancies existed (> 35/min) between patient and ventilator rates.

The proposed approach should make it possible to improve patient-ventilator interaction and to obtain accurate estimates of true patient respiratory rate when there is nonsynchrony.