Radiant warmer power and body size as determinants of insensible water loss in the critically iii neonate

Twelve critically ill neonates mechanically ventilated for respi-ratory failure (mean weight 1.33 kg, mean gestation 31 wk) were studied to quantitate the effects of radiant power from a radiant wanning device, body weight, and body surface area on insensible water loss. Radiant power density (Mw/cm²) was measured using a wattmeter and thermopile transducer. Insensible water loss was measured using a Potter Baby Scale. Weight correlated inversely with insensible water loss, (r = —0.86, P < 0.001). Radiant power density correlated inversely to weight, (r = —0.71, P < 0.001). There was a significant increase in insensible water loss as radiant power density increased, (r = 0.54, P < 0.05). Net radiant power received (W/kg) by infants over their exposed surface area, correlated directly to insensible water loss, (r — 0.67, P < 0.01) irrespective of body weight. Critically ill neonates ventilated for respiratory failure and nursed under radiant warmers incurred greater insensible water losses than peviously reported for well infants. The magnitude of this increastd insensible water loss is inversely related to body size and is determined directly by the radiant power density required to maintain body temperature. Speculation: Quantitative measurement of radiant power density delivered to critically ill newborn infants nursed under servocontrolled radiant warmers facilitates estimation of insensible water loss. Used in conjunction with body mass and surface geometry, quantitative radiant power assessment is clinically applicable to monitoring insensible water loss. Calculation of parenteral fluid requirements might be enhanced using this technique.