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 (R) on dynamic compliance (C) assessed by the NM3 monitor (C) and the E-CAiOV module (C).

STUDY DESIGN

Prospective laboratory study.

METHODS

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

RESULTS

The effect of increased R was more pronounced for C than for C. Unacceptable agreement was only observed in C at R in the 300 mL simulation (bias = -18.3% and lower LOA = -45%). For C, agreement was unacceptable for all tested R in both simulations, being the worst at R in the 300 mL simulation (bias = -54.7% and lower LOA = -100.2%). Both levels of increased R caused poor trending ability for C, whereas the same effect was only observed for C at R.

CONCLUSIONS AND CLINICAL RELEVANCE

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