Introduction: Continuous noninvasive monitoring of the partial pressure of arterial carbon dioxide (PaCO2) in ventilated neonates would help clinicians to reduce arterial blood sampling. Our objective was to determine the correlation and agreement between end-tidal carbon dioxide (EtCO2) and PaCO2 in newborns ventilated for various clinical situations.
Methods: This prospective study was undertaken over 15 months in a teaching hospital. Simultaneous end-tidal and arterial CO2 pairs were obtained from ventilated neonates who were monitored by mainstream capnography and had indwelling arterial catheter. The correlation coefficient and degree of bias between EtCO2 and PaCO2 were assessed for various clinical situations.
Results: A total of 133 end-tidal and arterial CO2 pairs were analysed from 32 ventilated newborns. The mean gestational age was 34.6 +/- 3.8 weeks and birth weight was 2,200 +/- 780 g. The overall coefficient of correlation (r) was 0.73 (p-value is less than 0.001). The EtCO2 value was lower than the corresponding PaCO2 value in 86.5 percent pairs, with a mean bias of -6.65 +/- 7.54 mmHg (95 percent CI, - 7.9 to - 5.35). The r-value was more than or equal to 0.92 in neonates ventilated for sepsis, asphyxia and apnoea of prematurity, 0.67 in hyaline membrane disease (HMD) and 0.69 in meconium-aspiration syndrome. In HMD, neonates who received surfactant had a better r-value than those who did not (0.76 vs. 0.6).
Conclusion: The correlation between mainstream EtCO2 and PaCO2 is good. Neonates with pulmonary disease will have a lower correlation. Surfactant therapy improves the correlation. EtCO2 monitoring is helpful in trending or screening for abnormal PaCO2 values.
Keywords: arterial carbon dioxide monitoring, end-tidal carbon dioxide monitoring, mainstream capnography, mechanical ventilation, neonate ventilation
Singapore Med J 2008; 49(3):199-203
