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 _RS ) on dynamic compliance (C _dyn ) assessed by the NM3 monitor (C _dyn(NM3) ) and the E-CAiOV module (C _dyn(ECAiOV) ).
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 _RS [normal (R _BL ), moderately increased (R ₁ ) and severely increased (R ₂ )] 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 R ₁ and R ₂ . 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.
Results: 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 R ₂ 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 R ₂ 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 R ₂ .
Conclusions and Clinical Relevance: 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.
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