Comparison of Respiratory Care Practitioner-Set Tlow and Autorelease Tlow in APRV

Abstract

Background: The time-controlled adaptive ventilation (TCAV) protocol for APRV states that T_high should be 90% of the respiratory cycle and T_low should transition to T_high at 75% of the peak expiratory flow (PEFR). Respiratory care practitioners (RCPs) use ventilator graphics to set T_low, but accuracy and consistency could be RCP dependent. A possible solution is to allow the ventilator to set T_low based on a PEFR% target, such as the AutoRelease feature on the Dräger Infinity V500. The study aimed to compare RCP-set T_low (RST) and AutoRelease T_low (AR) at 75% PEFR at varying levels of compliance and P_high. Methods: Participants were 25 RCPs from Michigan Medicine adult ICUs. A V500 ventilator was attached to a lung simulator (Michigan Instruments TTL). The ventilator was initially set to: P_high 25 cm H₂O (P25), P_low 0 cm H₂O, T_high 4 s, T_low 1 s, FIO₂ 1.0, and Slope 0.2 s. In the experimental group, the RCP adjusted T_low to achieve an end expiratory flow of 75% PEFR at compliances of 30 (C30) and 50 (C50) mL/cm H₂O. T_low was set back to 1 s, P_high was set to 35 (P35) cm H₂O, and the test was reproduced at C30 and C50. In the control group, AutoRelease was set at 75% for each condition and T_low was noted. Data was summarized in SPSS. Total PEEP (PEEP_tot) was measured post hoc for each condition at the average AutoRelease T_low and the min and max RCP-set T_low . Results: Mean ± SD T_low for RST vs AR at C30/P25: 0.56 ± 0.1 vs 0.63 ± 0.0, P < .01; C30/P35: 0.66 ± 0.1 vs 0.72 ± 0.0, P < .01; C50/P25: 0.82 ± 0.1 vs 0.95 ± 0.0, P < .01; and C50/P35: 0.92 ± 0.2 vs 1.1 ± 0.0, P < .01. When pressures were averaged for a given compliance, mean ± SD T_low for RST vs AR at C30/P25 and P35: 0.61 ± 0.1 vs 0.68 ± 0.0, P < .01; C50/P25 and P35: 0.87 ± 0.1 vs 1.0 ± 0.0, P < .01. When compliances were averaged for a given pressure, C30 and C50/P25: 0.69 ± 0.1 vs 0.79 ± 0.0, P < 0.01; C30 and C50/P35: 0.79 ± 0.1 vs 0.90 ± 0.0, P < .01. PEEP_tot for AR vs RST max and min at C30/P25: 8.9 vs 7.5-13.1; C30/P35: 12.8 vs 8.6-18.0; C50/P25: 10.4 vs 9.8-14.4; C50/P35: 14.6 vs 13.4-22.5. Conclusions: RST was statistically significant when compared to AR at each condition of compliance and P_high . Changing the compliance and the P_high independently yielded statistically significant results between methods of setting T_low. The differences in T_low may be clinically important in that PEEP_tot varied widely between those associated with AR and the RST min and max. A clinical trial should be conducted to determine the clinical impact.