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 (ETCO2) and partial pressure of arterial carbon dioxide (PaCO2) in very low birth weight infants (VLBWI); furthermore, we assessed factors that could affect the ETCO2-PaCO2 relationship. Methods: Simultaneous end-tidal and arterial CO2 pairs were obtained from ventilated VLBWI who were monitored by mainstream capnography and had umbilical arterial catheter. Correlation and agreement between ETCO2 and PaCO2 were evaluated by using Spearman test and Bland-Altman method, respectively. Results: A total of 143 simultaneous ETCO2-PaCO2 pairs were analyzed from 45 ventilated VLBWI. There was a significant correlation (r = 0.69; P < 0.0001) between ETCO2 and PaCO2 values. The ETCO2 value was lower than the corresponding PaCO2 value in 94% pairs, with a mean bias of 13.5 +/- 8.4 mmHg (95% agreement levels, -3.0 to 29.9 mmHg). Mean PaCO2-ETCO2 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 ETCO2 and PaCO2 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 PaCO2 and the simultaneous changes in ETCO2. Conclusions: In ventilated VLBWI, the correlation between mainstream ETCO2 and PaCO2 is good, but the agreement is poor and negatively influenced by the severity of pulmonary disease. Capnography is feasible in ELBWI. ETCO2 should not replace PaCO2 measurements in ventilated VLBWI, but may have a role to detect trends of PaCO2. Pediatr Pulmonol. 2012; 47:367-372. (C) 2011 Wiley Periodicals, Inc.