Phototherapy and Photo-Oxidation in Premature Neonates

Abstract

Objective: The potential for photo-oxidation during phototherapy in premature neonates was assessed by measuring parameters reflective of photo-oxidation. Methods: Blood was sampled from premature neonates prior to, and after 4 and 24 h of phototherapy, respectively. Total plasma bilirubin (TPB), blood carboxyhemoglobin corrected for inspired carbon monoxide (COHbc) (a sensitive index of heme catabolism), blood thiobarbituric acid reacting substances (TBARS) (a measure of lipid peroxidation), and plasma protein carbonyls (representative of protein oxidation) were determined. Study measurements were compared with baseline values both for the entire study group, and also individually for subgroups < and ≧1.5 kg birthweight, respectively. The percentage difference (%δ) between baseline and the 24-hour measurement was calculated for each parameter. Results: Forty-one premature neonates (mean [± SD] gestational age 30.5 ± 2.7 weeks and birthweight 1,499 ± 448 g) were studied. Mean TPB values decreased from a baseline of 9.1 ± 2.3 to one of 7.2 ± 2.8 mg/dl, p < 0.01, during the first 24 h of phototherapy. For the entire patient sample, neither COHbc, TBARS or protein carbonyl values increased significantly over baseline measurements: COHbc: 0.90 ± 0.26% vs. 0.92 ± 0.32%; TBARS: 19.0 ± 5.6 vs. 18.0 ± 4.5 nmol/ml, and protein carbonyls 7.73 ± 3.78 vs. 7.63 ± 3.56 U/ml (baseline and 24-hour samples only are shown in the abstract). Similarly, for the entire group, %δ (mean, interquartile range) were not significantly different between COHbc [–3.77 (–15.89–17.65)%], TBARS [–7.47 (–17.37–7.38)%], and protein carbonyls [–1.47 (–28.51–43.48)%], respectively. For subgroup analysis of neonates < or ≧ 1.5 kg birthweight, respectively, no significant increases in COHbc, TBARS or protein carbonyls were documented. A significant increase in %δ for COHbc in the <1.5 kg birthweight subgroup compared with those ≧1.5 kg, possibly indicative of hemolysis, was not matched by similar changes in %δ for TBARS or protein carbonyls, and may therefore not be a result of photo-oxidation. Conclusions: Except for changes in %δ in COHbc alone and in the smallest babies only, overall, short term phototherapy in premature infants was effective in reducing TPB concentrations without associated evidence reflective of photo-oxidation.