Effect of increased resistance on dynamic compliance assessed by two clinical monitors during volume-controlled ventilation: a test-lung study

Objective To evaluate the effect of increased respiratory system resistance (RRS) on dynamic compliance (Cdyn) assessed by the NM3 monitor (Cdyn(NM3) – Philips Respironics, USA) and the E-CAiOV module (Cdyn(ECAiOV) – GE Healthcare, USA). Study Design Prospective laboratory study. Methods A training test lung (TTL) simulated the mechanical ventilation of a mammal with 50 (50-mL) and 300 mL (300-mL) tidal volumes, in three conditions of RRS [normal (RBL), moderately increased (R1) and severely increased (R2)] and a wide range of clinically relevant Cdyn. Simulations at increased RRS were paired with simulations at RBL with the same static compliance for comparisons. Pearson’s correlation coefficient and concordance correlation coefficient between the measurements at RBL with the ones with increased RRS were calculated. Bland-Altman plots were also used to evaluate the agreement of Cdyn(ECAiOV) and Cdyn(NM3) at RBL (control values) with their paired values at R1 and R2. Relative bias and limits of agreement (LOA) were calculated and LOA larger than 30% were considered unacceptable. Trending ability of Cdyn(NM3) and Cdyn(ECAiOV) were evaluated by polar plots. Values of p < 0.05 were considered significant. Results The effect of increased RRS was more pronounced for Cdyn(ECAiOV) than Cdyn(NM3). Unacceptable agreement was only observed in Cdyn(NM3) at R2 in the 300-mL simulation (bias = -18.3% and lower LOA = - 45%). For Cdyn(ECAiOV), agreement was unacceptable for all tested RRS in both simulations, being the worst at R2 in the 300-mL simulation (bias = -54.7% and lower LOA -100.2%). Both levels of increased RRS caused poor trending ability for Cdyn(ECAiOV), while the same effect was only observed for Cdyn(NM3) at R2. Conclusions and clinical relevance In the presence of increased RRS, Cdyn estimated by the NM3 monitor presented better capability to distinguish between changes in RRS from changes in respiratory system compliance.