Abstract
Background:
The time-controlled adaptive ventilation (TCAV) protocol for APRV states that Thigh should be 90% of the respiratory cycle and Tlow should transition to Thigh at 75% of the peak expiratory flow (PEFR). Respiratory care practitioners (RCPs) use ventilator graphics to set Tlow, but accuracy and consistency could be RCP dependent. A possible solution is to allow the ventilator to set Tlow based on a PEFR% target, such as the AutoRelease feature on the Dräger Infinity V500. The study aimed to compare RCP-set Tlow (RST) and AutoRelease Tlow (AR) at 75% PEFR at varying levels of compliance and Phigh.
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: Phigh 25 cm H2O (P25), Plow 0 cm H2O, Thigh 4 s, Tlow 1 s, FIO2 1.0, and Slope 0.2 s. In the experimental group, the RCP adjusted Tlow to achieve an end expiratory flow of 75% PEFR at compliances of 30 (C30) and 50 (C50) mL/cm H2O. Tlow was set back to 1 s, Phigh 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 Tlow was noted. Data was summarized in SPSS. Total PEEP (PEEPtot) was measured post hoc for each condition at the average AutoRelease Tlow and the min and max RCP-set Tlow .
Results:
Mean ± SD Tlow 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 Tlow 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. PEEPtot 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 Phigh . Changing the compliance and the Phigh independently yielded statistically significant results between methods of setting Tlow. The differences in Tlow may be clinically important in that PEEPtot varied widely between those associated with AR and the RST min and max. A clinical trial should be conducted to determine the clinical impact.
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