End-tidal carbon dioxide monitoring in very low birth weight infants: Correlation and agreement with arterial carbon dioxide

Objective We aimed to determine the correlation and the agreement between end-tidal carbon dioxide (ETCO 2) and partial pressure of arterial carbon dioxide (PaCO 2) in very low birth weight infants (VLBWI); furthermore, we assessed factors that could affect the ETCO 2- PaCO 2 relationship. Methods Simultaneous end-tidal and arterial CO 2 pairs were obtained from ventilated VLBWI who were monitored by mainstream capnography and had umbilical arterial catheter. Correlation and agreement between ETCO 2 and PaCO 2 were evaluated by using Spearman test and Bland-Altman method, respectively. Results A total of 143 simultaneous ETCO 2-PaCO 2 pairs were analyzed from 45 ventilated VLBWI. There was a significant correlation (r = 0.69; P < 0.0001) between ETCO 2 and PaCO 2 values. The ETCO 2 value was lower than the corresponding PaCO 2 value in 94% pairs, with a mean bias of 13.5 ± 8.4 mmHg (95% agreement levels, -3.0 to 29.9 mmHg). Mean PaCO 2-ETCO 2 bias was similar between ELBWI (13.1 ± 7.7 mmHg; 95% agreement levels, -1.9 and 28.2 mmHg) and infants with birth weight 1,001-1,500 g (14.8 ± 9.7 mmHg; 95% agreement levels -4.3 and 33.8 mmHg). The bias between ETCO 2 and PaCO 2 was significantly increased with increasing FiO 2, mean airway pressure and oxygenation index. Within each patient, there was a positive correlation (r = 0.78, P < 0.0001) between the changes in PaCO 2 and the simultaneous changes in ETCO 2. Conclusions In ventilated VLBWI, the correlation between mainstream ETCO 2 and PaCO 2 is good, but the agreement is poor and negatively influenced by the severity of pulmonary disease. Capnography is feasible in ELBWI. ETCO 2 should not replace PaCO 2 measurements in ventilated VLBWI, but may have a role to detect trends of PaCO 2. Pediatr Pulmonol. 2012; 47:367-372. © 2011 Wiley Periodicals, Inc.