Effect of increased resistance on dynamic compliance assessed by two clinical monitors during volume-controlled...

To evaluate the effect of increased respiratory system resistance (R_RS) on dynamic compliance (C_dyn) assessed by the NM3 monitor (C_dyn(NM3)) and the E-CAiOV module (C_dyn(ECAiOV)).

Prospective laboratory study.

A training test lung (TTL) simulated the mechanical ventilation of a mammal with 50 and 300 mL tidal volumes in three conditions of R_RS [normal (R_BL), moderately increased (R₁) and severely increased (R₂)] and a wide range of clinically relevant C_dyn. Simulations at increased R_RS were paired with simulations at R_BL with the same static compliance for comparisons. Pearson's correlation coefficient and concordance correlation coefficient between the measurements at R_BL with the ones with increased R_RS were calculated. Bland-Altman plots were also used to evaluate the agreement of C_dyn(ECAiOV) and C_dyn(NM3) at R_BL (control values) with their paired values at R₁ and R₂. Relative bias and limits of agreement (LOAs) were calculated and LOAs larger than 30% were considered unacceptable. Trending ability of C_dyn(NM3) and C_dyn(ECAiOV) were evaluated by polar plots. Values of p < 0.05 were considered significant.

The effect of increased R_RS was more pronounced for C_dyn(ECAiOV) than for C_dyn(NM3). Unacceptable agreement was only observed in C_dyn(NM3) at R₂ in the 300 mL simulation (bias = -18.3% and lower LOA = -45%). For C_dyn(ECAiOV), agreement was unacceptable for all tested R_RS 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 R_RS caused poor trending ability for C_dyn(ECAiOV), whereas the same effect was only observed for C_dyn(NM3) at R₂.

In the presence of increased R_RS, C_dyn estimated by the NM3 monitor presented better capability to distinguish between changes in R_RS from changes in respiratory system compliance.