Transcutaneous CO(2) versus end-tidal CO(2) in neonates and infants undergoing surgery: a prospective study

Aim: End-tidal CO(2) (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 CO(2) (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.