Métabolisme du potassium chez le prématuré

Abstract

During the first days of life, hyperkalemia can affect 30 to 60% of very low birth weight infants free of acute renal insufficiency (i.e. nonoliguric hyperkalemia). The place of the kidney in the regulation of the potassium homeostasis of VLBW remains badly specified. Objective To evaluate the rate and the mechanisms of hyperkalemia in infants born at less than 32 weeks' gestation. Methods A prospective study was conducted in 33 preterm infants (BW = 1289 ± 382 g; GA = 28.8 ± 1.7 weeks). Fifteen consecutive 8-hour urine collections were performed for each infant from the 8th hour of life (495 periods). A plasma sample was obtained at the end of each urine collection. Sodium, potassium and creatinine were measured in urine and blood samples as often as possible. Results Plasma potassium concentrations varied significantly over the 15 successive periods with an initial value (P1) of 4.55 ± 0.80 mmol/l, a peak on P3 (4.94 ± 0.81 mmol/l) and the lowest value on P13 (3.88 ± 0.42 mmol/l). Hyperkalemia (plasma potassium > 6.0 mmol/l) was observed in 4 infants (12%) and in 1.2% of the periods. The cumulative potassium balance (output-input) was negative over the first 7 periods (–1.97 mmol/kg), and afterwards became positive (from P8 to P15: + 1.57 mmol/kg). Over the first 3 days, plasma potassium concentrations were positively correlated ( p < 0.01) with urinary excretion of potassium, clearance of potassium, fractional excretion of potassium, and negatively with endogenous creatinine clearance. Conclusion In the first days of life, very low birth weight infants present an increase in kalemia associated with a negative potassium balance indicating a intracellular to extracellular potassium shift rather than a lower renal potassium excretion.