Transcutaneous CO₂ versus end-tidal CO₂ in neonates and infants undergoing surgery: a prospective study

Aim: End-tidal CO₂ (Et_CO2) is the standard in operative care along with pulse oximetry for ventilation assessment. It is known to be less accurate in the infant population than in adults. Many neonatal intensive care units (NICU) have converted to utilizing transcutaneous CO₂ (tcP_CO2) monitoring. This study aimed to compare perioperative Et_CO2 to tcP_CO2 in the pediatric perioperative population specifically below 10 kg, which encompasses neonates and some infants. Methods: After IRB approval and parental written informed consent, we enrolled neonates and infants weighing less than 10 kg, who were scheduled for elective surgery with endotracheal tube under general anesthesia. P_CO2 was monitored with Et_CO2 and with tcP_CO2. Venous blood gas (Pv_CO2) samples were drawn at the end of the anesthetic. We calculated a mean difference of Et_CO2 minus Pv_CO2 (Delta Et_CO2), and tcP_CO2 minus Pv_CO2 (Delta tcP_CO2) from end-of-case measurements. The mean differences in the NICU and non-NICU patients were compared by t-tests and Bland-Altman analysis. Results: Median age was 10.9 weeks, and median weight was 4.4 kg. NICU (n=6) and non-NICU (n=14) patients did not differ in Pv_CO2. Relative to the Pv_CO2, the Delta Et_CO2 was much greater in the NICU compared to the non-NICU patients (-28.1 versus -9.8, t=3.912, 18 df, P=0.001). Delta tcP_CO2 was close to zero in both groups. Although both measures obtained simultaneously in the same patients agreed moderately with each other (r =0.444, 18 df, P=0.05), Bland-Altman plots indicated that the mean difference (bias) in Et_CO2 measurements differed significantly from zero (P<0.05). Conclusions: Et_CO2 underestimates Pv_CO2 values in neonates and infants under general anesthesia. TcP_CO2 closely approximates venous blood gas values, in both the NICU and non-NICU samples. We, therefore, conclude that tcP_CO2 is a more accurate measure of operative Pv_CO2 in infants, especially in NICU patients.