The possibility that negative potassium balance may occur in critically ill preterm neonates is suggested by factors such as the usual provision of minimal potassium intake, increased plasma aldosterone concentrations, increased prostaglandin synthesis, and the frequent use of diuretic agents. In order to assess the relationship between potassium balance and renal prostaglandins, nine infants with respiratory distress syndrome (mean birth weight 1,264 g, mean gestational age 30.6 weeks) were studied sequentially with timed-urine collections during the first four postnatal days and values were compared with those of 18 preterm infants without respiratory distress syndrome. Mean plasma potassium concentrations decreased significantly from 4.87 ± 0.19 mEq/L (mean ± SEM) on day 1 to 3.83 ± 0.18 mEq/L on day 4, (P < 0.05), and cumulative potassium balance was -4.07 ± 0.95 mEq/kg or 10% of estimated total body potassium. Urinary excretion of prostaglandin E, on day 1 in infants with respiratory distress syndrome was significantly greater than in those without respiratory distress syndrome (22.0 ± 4.9 v 8.3 ± 1.6 ng/mg of creatinine) and varied directly with urinary potassium excretion (r = .66, P < .001). These studies suggest that consideration be given to the importance of providing sufficient potassium to prevent hypokalemia in the stressed preterm infant and that pharmacologic agents that alter prostaglandins or potassium excretion should be used with caution.
Phenomenological analysis of renal regulation of sodium and potassium balance