Effect of tidal volume and end tracheal tube leakage on end-tidal CO(2) in very low birth weight infants

OBJECTIVE: To examine the extents to which low tidal volume (VT) and endotracheal tube (ETT) leakeage influence the accuracy of ETCO(2) for estimating arterial PCO(2) (PaCO(2)) in very low birth weight (VLBW) infants with mechanical ventilation. STUDY DESIGN: An observational study. We evaluated a total of 287 paired ETCO(2) and PaCO(2) values as well as VTs obtained from 22 VLBW infants with ventilation. Deming regression, quadratic discriminant analysis, and Bland–Altman analysis were performed. RESULT: ETCO(2) and PaCO(2) were correlated (r(2) = 0.5897, p < 0.0001). A quadratic discrimination analysis of the VT and the percentage of leak yielded 70.4% [95%CI, 65.1 to 75.7] discrimination for the agreement between ETCO(2) and PaCO(2). ETCO(2) was strongly correlated with PaCO(2) in the discriminant function Z > 0 group (r(2) = 0.7234, p < 0.0001). CONCLUSION: Our results indicate that ETCO(2) is a good surrogate for PaCO(2) when VT is high and ETT leak is low.