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.