Postnatal diuresis and respiratory distress syndrome in infants receiving mechanical ventilation

Measurements of body water homeostasis and pulmonary function were obtained in 24 infants with respiratory distress syndrome requiring mechanical ventilation during the first five days of life to determine the relationship of diuresis to improvement in pulmonary function. Initial diuresis (output intake ratio greater than 0.8) occurred at 24 hours, maximum diuresis (output intake ratio greater than or equal to 1.6) at 40 hours, and initial improvement in pulmonary function (fall in AaDO2 greater than 50 mm Hg) at 48 hours. Urine flow rates over four-, eight-, or 12-hour periods were quite variable and correlated poorly with improvement in pulmonary function. Reduction in body weight was a more accurate indicator of total changes in body water than urine output, output intake ratio, or fractional excretion of sodium. Although there was a temporal relationship of loss of body water and improvement in pulmonary function by analysis of means, no cause-and-effect relationship could be found on a case-by-case analysis. Five of 24 infants demonstrated improvement in pulmonary function prior to diuresis or reduction in body weight. Nine infants had a diuresis more than 24 hours prior to pulmonary improvement, and two infants had a diuresis without pulmonary improvement during the five-day study period. These data indicate that factors other than body water are associated with improvement in pulmonary function in infants with respiratory distress syndrome.