Comparison of respiratory function and fluid balance in very low birthweight infants given artificial or natural surfactant or no surfactant treatment

Exogenous surfactant administration improves respiratory function. The spee d of improvement appears greater if a natural rather than an artificial sur factant is used, our aim was to determine if that effect was explained by d ifferences in fluid balance, evidenced by the timing of the diuresis onset tie. output greater than input). Thirty infants (median gestational age 29 weeks), 10 given an artificial surfactant (Exosurf), 10 a natural surfactan t (Survanta) and 10 no surfactant (controls) were studied. During the first three days, compliance and functional residual capacity were measured dail y, arginine vasopressin (AVP) levels estimated on days 1, 3 and 5 and, in 8 -hourly intervals, the median arterial/alveolar ratio was calculated for ea ch individual and urine output and fluid input recorded. Throughout the thr ee-day period, the median arterial/alveolar ratio was always significantly higher in the control compared to the two surfactant groups (p < 0.05). On day 3 the Exosurf-treated babies had lower compliance and functional residu al capacity (p < 0.05) than the other two groups. Neither the timing of diu resis onset, timing of the maximum diuresis nor the AVP levels, however, di ffered significantly between the groups. Only surfactant treatment and type of surfactant, but not the timing of the onset nor of the maximum diuresis , related significantly to changes in lung function. These results do not s upport the hypothesis that differences in fluid balance explain differences in the lung function improvement rate following natural and artificial sur factant.