Insensible Water Loss in the Critically Ill Neonate: Combined Effect of Radiant-Warmer Power and Phototherapy

To quantitate radiant power and insensible water loss under phototherapy, 12 neonates were studied under radiant warmers for one hour each with and without phototherapy. Warmer power was measured by wattmeter and thermopile. Power density received from phototherapy was 4.4 mW/sq cm. Addition of phototherapy to the servocontrolled warmer caused a decrease in power density received from the warmer However, the total radiant-power density received with phototherapy and the warmer combined (17.3 mW/sq cm) did not differ from net power density received without phototherapy (17.1 mW/sq cm). Insensible water loss, measured with a metabolic balance, increased from 2.54 to 3.73 mL/kg/hr, with addition of phototherapy. Since the total radiant-power density did not change, mechanisms other than increased radiant-power delivery must exist to explain the increased insensible water loss observed with phototherapy.