Partial pressure measures could be used in neonates after surgery

Sep 10 2012

By Piriya Mahendra, medwireNews Reporter

End tidal carbon dioxide (Et_CO2) and transcutaneous carbon dioxide (Tc_CO2) could be useful to monitor partial pressure of arterial CO₂ (PaCO₂) in neonates after surgery, a study shows.

"This study suggests that both Tc_CO2 and sidestream Et_CO2 are reliable methods to describe PaCO₂ trends in the postoperative period," remark David Tingay (Royal Children's Hospital, Melbourne, Australia) and colleagues.

The study of 50 mechanically ventilated neonates without lung disease revealed that the respective mean PaCO₂, Et_CO2, and Tc_CO2 values were 43.6 mmHg, 39.4 mmHg, and 44.3 mmHg, respectively, with Et_CO2 being significantly lower than PaCO₂ and Tc_CO2.

Overall, Et_CO2 underestimated PaCO₂, with a PaCO₂-Et_CO2 bias of 4.1 mmHg. Tc_CO2 approximated PaCO₂, but with wider limits of agreement bias that were independent of PaCO₂.

Overall, 56.1% of Et_CO2 values and 60.6% of Tc_CO2 values were within 5 mmHg of PaCO₂. Only 27.3% and 35.6% of Et_CO2 and Tc_CO2 values were within 2 mmHg of PaCO₂.

Subgroup analysis revealed that tidal volumes of 10 mL or more, or 4.5 mL/kg or more, resulted in better agreement between both Et_CO2 and Tc_CO2 with PaCO₂.

The authors explain that the benefit of continuous CO₂ monitoring in ventilated neonates was previously well established, but not universally applied.

Indeed, although Tc_CO2 is widely used to monitor PaCO₂ in the neonatal intensive care unit (NICU), it is rarely used during or after surgical procedures. Et_CO2 is also rarely used in the NICU due to variable accuracy in preterm neonates and neonates with severe respiratory failure.

"To our knowledge, this is the largest comparative study of noninvasive CO₂ monitoring in ventilated neonates, and the first to selectively identify a population in which neither Et_CO2 nor Tc_CO2 has significant technical disadvantages," Tingay et al conclude in the Archives of Diseases in Childhood: Fetal and Neonatal Edition.

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