An End-Tidal Carbon Monoxide Nomogram for Term and Late-Preterm Chinese Newborns

Abstract

Objective: To establish a reference nomogram for end-tidal CO corrected for ambient CO (ETCOc) levels in term and late-preterm Chinese newborns and then assess its efficacy to identify hemolytic hyperbilirubinemia.

Study design: We conducted a prospective study by measuring concurrent ETCOc and total serum bilirubin (TSB) or transcutaneous bilirubin (TcB) levels collected postnatally at 12, 24, 48, 72, 96, and 120 hours of age. ETCOc at the 25th, 50th, 75th, and 95th percentiles at each epoch were used to construct the reference nomogram. We then explored the ability of predischarge ETCOc and TSB/TcB metrics to predict the development of hyperbilirubinemia requiring phototherapy in early postnatal period and jaundice readmission in late postnatal period.

Results: Our nomogram, based on 990 measurements from 455 infants who were not nonhemolytic, displayed a steady line within 3 postnatal days, followed by a subsequent decline. From a cohort of infants with a serial ETCOc measurements (n = 130) and those readmitted (n = 21), we found that ETCOc and TSB/TcB ≥75th percentile can identify most hemolytic hyperbilirubinemia between 12 and 72 hours after birth with an area under the curve (AUC) of 0.741. An ETCOc ≥1.7 ppm alone between 96 and 120 hours after birth can identify most hemolytic hyperbilirubinemia with an AUC of 0.816. In addition, 90.5% of readmitted infants had an ETCOc ≥75th percentile.

Conclusions: An ETCOc reference nomogram during the first 5 postnatal days in nonhemolytic term and late-preterm newborns can be used to identify hemolytic hyperbilirubinemia requiring phototherapy in the early postnatal period and readmission in the late postnatal period.

Keywords: bilirubin production; end-tidal carbon monoxide; hemolysis; hyperbilirubinemia; nomogram.