Early onset hyperkalemia in extremely low birth weight infants.

The incidence of hyperkalemia and associated clinical features in extremely preterm infants were determined by reviewing medical records of 32 infants with birth weights of less than or equal to 800 g born during a 1-year period. Hyperkalemia, defined as serum potassium concentration of greater than 6.5 mEq/L, occurred in 12 infants on the first day of life and in four others on the second day. Six infants (38%) had electrocardiographic abnormalities associated with hyperkalemia. Infants with hyperkalemia were less mature than infants with normal potassium levels. All infants of less than 25 weeks' gestation developed hyperkalemia. Fluid intakes and urine flow rates were lower and body weight loss greater during the first 24 hours of hospitalization for hyperkalemic infants. Hyperkalemia frequently occurs within the first 48 hours of life in extremely immature infants. Serum potassium should be monitored closely to avoid life-threatening cardiac arrhythmias in these infants.