Correlation of end tidal and arterial carbon dioxide levels in critically Ill neonates and children

AIM OF THE STUDY: End tidal carbon dioxide (EtCO(2)) monitoring is considered to reflect real-time estimation of partial pressure of carbon dioxide in arterial blood (PaCO(2)) noninvasively. However, knowledge about its relationship with PaCO(2) in critically ill pediatric and neonatal patients is limited. The primary objective was to evaluate predictive capability of end tidal carbon dioxide monitoring and secondary objective was to determine the influence of severity of lung disease on EtCO(2) and PaCO(2) relationship. MATERIALS AND METHODS: This was a prospective, nonrandomized, consecutive enrollment study carried out in neonatal and pediatric intensive care units of a tertiary care children hospital. It was conducted in 66 neonates and 35 children receiving mechanical ventilation. Severity of lung disease was estimated by ventilation index and PaO(2)/FiO(2) (P/F) ratio. Simultaneous recording of EtCO(2) and PaCO(2) levels was done and data were analyzed for correlation and agreement. RESULTS: In neonates, 150 EtCO(2) and PaCO(2) pairs were recorded. The mean weight ± SD of patients was 2.1 ± 0.63 kg. PaCO(2) had a positive correlation with EtCO(2) (r = 0.836, 95% CI = 0.78-0.88). P/F ratio <200 adversely affected relationship. In infants and children, 96 pairs were recorded. Mean age ± SD of patients was 4.20 ± 4.92 years and mean weight ± SD was 13.1 ± 9.49 kg. PaCO(2) had an excellent correlation with EtCO(2) (r = 0.914, 95% CI = 0.87 and 0.94). P/F ratio <200 adversely affected relationship. CONCLUSION: EtCO(2) monitoring displayed a good validity to predict PaCO(2). Correlation was affected by low P/F ratio (<200); hence, it is recommended that blood gases be measured in these patients until such time that a good relation can be established between end tidal and arterial CO(2) values.