[Disorders of acid-base equilibrium in neonatal physiologic jaundice]

38 healthy term jaundiced infants were tested. On 3rd day of life we obtained a blood sample from a peripheric vein to determine red blood cells and reticulocytes count, serum albumin, total, conjugated and unconjugate bilirubin. On 3rd, 4th, 5th, 6th day of life 4 standard heparinized microtubes were filled after lancing the heel: 2 microtubes to estimate the mean value of total bilirubin, 2 for the mean value of pH. The urine pH was evaluated every morning. The results of total bilirubin (T.B.), pH, pCO2 and Base Deficit were analyzed using T-test. All tested infants were free-bilirubin jaundiced. Infants treated with phototherapy had a T.B. ranging from 15.2 mg/dl on 3rd day of life to 10.5 mg/dl on 6th, while in controlled infants T.B. never exceeded 10 mg/dl. In treated infants the pH was higher than in controlled ones: p was less than 0.001 on 4th day, less than 0.005 on 5th day and less than 0.001 on 6th day. In both groups the urine pH ranged from 5 to 6.5 every day. The marked increase in respiratory rate during phototherapy is a well known side effect. But a significant decrease in pCO2 was present before starting phototherapy. A mixed disturbance of acid-base balance could be suspected: an already existing mild metabolic acidosis in phototherapy group with respiratory alkalosis due to anion gap variety, with unknown determining causes. We relate the initial metabolic acidosis to the depressed oxidative phosphorylation (with lactic acidosis) in the neonatal liver.(ABSTRACT TRUNCATED AT 250 WORDS)