Phototherapy increases hemoglobin degradation and bilirubin production in preterm infants

OBJECTIVE: To compare hemoglobin degradation and bilirubin production before and during phototherapy in preterm infants. BACKGROUND: Hemoglobin is catabolized into globin and heme, which is degraded by microsomal heme oxygenase into equimolar carbon monoxide and biliverdin. Biliverdin is then reduced into bilirubin. CO is excreted exclusively by the lungs; therefore, end-tidal carbon monoxide, corrected for inhaled CO (ETcoc), reflects hemoglobin degradation and total bilirubin production. METHOD: A prospective study design was used, including a study group of 24 preterm infants requiring phototherapy. Infants with hemolytic diseases, sepsis, recent blood transfusions, and infants on mechanical ventilation were excluded. ETcoc was measured in preterm infants before and during phototherapy. Hemoglobin degradation and bilirubin production were calculated by measuring ETcoc. RESULTS: The (mean ± SD) birth weight of 24 preterm neonates was 1975 ± 613 gm, gestational age was 32.7 ± 2.3 weeks, hematocrit was 47.5 ± 6.2 volume%, and peak bilirubin was 13.1 ± 3.2 mg/dl. First ETcoc measurements were done at 59.6 ± 22.2 hours of age immediately before starting phototherapy. The second ETcoc measurements were taken at 13.7 ± 7-9 hours after starting phototherapy. The second measurement of 2.6 ± 0.6 ppm (mean ± SD) was significantly higher than the first ETcoc of 2.1 ± 0.6 ppm (p < 0.05). CONCLUSION: Phototherapy increases hemoglobin degradation and bilirubin production in preterm infants.