A WARMING MATTRESS FOR PREMATURE INFANTS

Abstract

We measured temperatures and metabolic rate of healthy infants (gestational age 28-33 wks and postnatal age 2-26 days) in contact with a heated water mattress. Infants were randomized with/without the mattress ≥8 hrs in a single wall forced convection incubator, unrestrained, diapered and supine. Tmattress (35.2±.1°C) was regulated by continuous circulation of H2O through a thermostatically controlled bath. Mid-inc air temp (Ta) was within the thermoneutral range. No humidity was added to inc. Heating effects measured q half hrly: skin temp at 6 sites → mean skin temp (Ts), esophageal temp (Te), heart rate (HR), resp rate (RR) and O2 consumption (VO2) at the end of each period. N=10 patients. Results(mean±SD): No mattress vs mattress p value by paired t-test: Ta (°C) 32.4±1.3 vs 31.6±0.9 p<0.05; Ts (°C) 35.3±0.3 vs 36.3±0.3 p<0.01; Te (°C) 36.5±0.3 vs 37.2±0.4 p<0.01; HR (beats/min) 155±8 vs 161±10 p<0.01; RR (breaths/min) 41±6 vs 48±8 p<0.01; VO2 (ml/kg/min) STPD 5.33±1.4 vs 4.94±1.55 NS. Results indicate that heat storage occurred due to alteration of balance between body heat production and losses. To determine the rate of dry (sensible) heat exchange we used a metabolic simulator, an electrically-heated 10 cm diam sphere. At a representative incubator Ta of 31.5°C and simulator Ts of 35°C, the dry heat loss was reduced from 60 W/m2 to 35 W/m2 on the heated pad. This was brought about by a combination of heat conduction to the simulator and decreased radiation losses from the simulator to the surrounding mattress.