July 1982 The Journal of P E D I A T R I C S 103 Changes in pulmonary function during the diuretic phase of respiratory distress syndrome To evaluate the relationship between improvement in pulmonary function and spontaneous diuresis in respiratory distress syndrome, nine premature infants requiring mechanical ventilation for RDS were studied at a mean age of 11.9 hours prior to the onset of diuresis, at onset of diuresis, at maximum urine output (mean age 44.9 hout:9), and at 24 hours after maximum urine output. Prior to diuresis functional residual capacity decreased from mean +_SEM of 16.2 +_ 2 to 13.3 ++_ 1.2 ml/kg, and dynamic lung compliance decreased from 2.5 +_ 0.3 to 1.8 + 0.3 ml/cm 1t20 (P < 0.05), indicating that the respiratory disease was worsening. There was no significant change in alveolar-arterial oxygen gradient, peak inflating pressure, or rate of intermittent mandatory ventilation over this period. At the time of maximum urine output, however, FRC had increased 36% (P < 0.05), CL had increased by 60% to 2.8 +_ 0.4 ml/cm HeO (P < 0.025), Aaoo 2 had decreased from 246 +- 27 to 184 +_ 30 torr (P < 0.005), and PIP had decreased from 14.9 +_ 2.2 to 11.3 + 2.l cm/HeO (P < 0.05). On follow-up study 24 hours after maximum urine output, there was no further significant improvement in FRC, CL, or PIP, but IMV rate and AaDo: continued to decrease. These data show that the pulmonary functio n in RDS deteriorates until the onset of diuresis, after which it rapid(y improves. This diuresis may represent the removal of excess lung liquid and seems necessary for improvement in RDS. David P. Heaf, M.B., M.R.C.P., Jaques BeUk, M.D., Alan R. Spitzer, M.D., Michael H. Gewitz, M.D., and William W. Fox, M.D.,* Philadelphia, Pa. TRANSUDATION of fluid from the pulmonary capillaries is an important pathophysiologic finding in the early stages of neonatal respiratory distress syndrome:~. 2 The resultant excess fluid in the alveolar and interstitial spaces impai~:s pulmonary gas exchange, lowers lung compliance, and reduces functional residual capacity. 3 Previous studies have demonstrated that infants with RDS have a spontaneous diuresis near the time of maximal improvement.4-6 There are conflicting theories about the cause of this diuresis and whether the spontaneous diuresis or the clinical improvement occurs first. CorP and Torrado et al 5 concluded from their studies that diuresis followed From the Divisions of Neonatology and Cardiology of The Children's Hospital of Philadelphia, and the Department of Pediatrics of the University of Pennsylvania School of Medicine. *Reprint address: Division of Neonatology, The Children's Hospital of Philadelphia, 34th Street and Civic Center Boulevard, Philadelphia, PA 19104. improvement in oxygenation and resulted from improved renal function. In contrast, recent studies6.7 showed that diuresis preceded improvement in alveolar-arterial oxygen Abbreviations used AaDO2: C~: FRC: IMV: PDA: PIP: RDS: PEEP: alveolar-arterial oxygen gradient dynamic lung compliance functional residual capacity intermittent mandatory ventilation patent ductus arteriosus peak inflating pressure respiratory distress syndrome peak end expiratory pressure gradient and may represent removal of interstital lung edema. Diuretics have been used to reduce pulmonary edema in RDS and two studies have shown improvement in pulmonary function shortly after the induced diuresiS. 8,9 However, other studies have failed to confirm these results?0. ~, 0022-3476/82/070103+05500.50/0 9 1982 The C. V. Mosby Co. Vol. 101, No. 1, pp. 103-107