Insensible water loss (IWL) was determined from measurements of insensible weight loss during the first 7 weeks of life on 30 immature and nine small-for-gestational age, low birth weight infants. Under standard conditions (single-walled incubator, infant nude, gavage feeding), 10 infants with birth weights less than 1,250 gm, gestational age < 230 days (32 weeks) and postnatal age <10 days lost >2.5 gm/kg/hr (equivalent to 60-120 ml/kg/day), considerably higher than previously reported. Studies following the insertion of a plastic heat shield revealed a 25% reduction in IWL.

The heat shield facilitates achievement of neutral thermal environment and reduced water losses in low birth weight infants. IWL measurements in infants with birth weights >1,500 gm and those small-for-gestational age were similar to previously reported studies. Because of the known limited ability of small immature infants to increase metabolic rate, these extremely high losses are believed to represent disproportionately larger water losses from skin. Skin factors predisposing to large water loss in immature infants include thinner epidermis, increased water content, and increased permeability.

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