Hypernatraemia in preterm infants born at less than 27 weeks gestation

Aims: To study the incidence of hypernatraemia (plasma sodium > 145 mmol/L), identify predisposing factors to and associated complications of hypernatraemia in preterm infants born less than 27 weeks gestation in the first 5 days of life. Methods: Preterm infants less than 27 week gestation over an 18-month period were studied by retrospective analysis of patient records. Data were collected on gestation, birthweight, sex, antenatal steroid use, phototherapy, incubator humidity, time of transfer to incubator, plasma sodium, urea and creatinine. Actual fluid and sodium intake was calculated for the first 5 days of life. Data were collected on chronic lung disease, patent ductus arteriosus, intraventricular haemorrhage, necrotising enterocolitis and death. Results: In this study 46 (69.7%) of 66 infants studied developed hypernatraemia (> 145 mmol/L), occurring most frequently between 24 and 48 h of age. The median gestation of hypernatraemic babies was significantly lower. There was no significant difference in median birthweight, or factors associated with increased insensible water loss between the hypernatraemic and the non-hypernatraemic groups. Fluid intake was significantly higher on days 2, 3 and 4 in the hypernatraemic group. There was no difference in sodium intake between the two groups. More hypernatraemic babies compared with controls developed chronic lung disease, patent ductus arteriosus, significant intraventricular haemorrhage, necrotising enterocolitis and died, but was not significant. Conclusion: Hypernatraemia occurs commonly in preterm infants less than 27 weeks gestation and was not associated with significant morbidity. The more immature infants developed hypernatraemia and all cases resolved after increasing fluid intake.