Early neonatal hyperkalaemia in the extremely premature newborn infant

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Abstract
The incidence of hyperkalaemia in 43 consecutive infants born at less than 28 weeks gestation and cared for in our neonatal intensive care unit was documented. Plasma K levels were related to indices of renal function as well as to the degree of illness in the infants. The mean gestational age was 26.0 weeks (range 24-27 weeks) and the mean birthweight was 815 g (range 395-1170 g). Twenty-six of infants (60%) had at least one plasma K > 5.5 mmol/L and 13 (30%) had a maximum plasma K > 7 mmol/L. The mean postnatal age at which the plasma K exceeded 7 mmol/L was 25 h (range 10-39 h). Five infants with plasma K > 7 mmol/L developed cardiac arrhythmias and four died to this complication. Only one infant had a large intraventricular haemorrhage. Only two of 16 infants with an initial plasma K < 5 mmol/L had a maximum plasma K > 7 mmol/L, compared with eight of 10 with an initial plasma K > 6 mmol/L (P < 0.005). Plasma K also correlated directly with plasma urea (P < 0.001) and plasma creatinine (P < 0.025), and inversely with urine volume (P < 0.05). Plasma K did not correlate with K intake, arterial pH, presence of asphyxia, severity of respiratory illness, gestation or birthweight. The rapidity with which the plasma K concentration reached potentially hazardous levels in some infants makes it imperative to measure plasma K within 6 h of birth and to continue to monitor levels at least every 6 h for the first 48 h in all infants born at less than 28 weeks gestation.