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The pool size of intra-alveolar surfactant lipids is about 100 mg/kg in healthy neonates and in babies with RDS only about 10 mg/kg. From this data it would seem that the minimum dose requirement of a baby with established RDS should amount to at least 90 mg/kg, and probably more to compensate for uneven distribution of the exogenous material and the inhibitory activity of serum proteins leaking into the airspaces. This calculated dose level is somewhat larger than the quantity of natural surfactant necessary to prevent RDS in premature lambs, about 50 mg/kg, and much larger than the estimated amount of surfactant lipid required to coat the total alveolar surface with a monolayer, about 3 mg/kg.
Estimates of normal surfactant pool size in adult humans, made by extrapolation from animal data, range from 3 to 15 mg lipid/kg body weight. Because of the need to overcome various inhibitors present in injured lungs, higher doses must be used in children and adults. Suggested optimal dose varies from 50 to 300 mg/kg.
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