Quantifying heat balance components in neonates nursed under radiant warmers in neonatal intensive care

Abstract

Neonatal intensive care units use radiant warmers (RW) to maintain stable body temperatures in many newborns. This study examined whether the rate of radiant heat required for heat balance (Rreq) is equal to the rate of radiant heat provided by the RW (Rprov). A systematic evaluation of time‐dependent changes in heat balance components was conducted in 10 newborns (mass: 2829±636 g; age: 9.2±11.0 days; BSA: 0.19±0.03 m2) nursed under RW. Metabolic rate, evaporative heat loss, convective and conductive heat flow, rectal temperature (Trec) and mean skin temperature (Tsk) were measured continuously for 105 min. The rate of body heat storage (S) was calculated using a two‐compartment model of ‘core’ (Trec) and ‘shell’ (Tsk) temperatures. Mean Rprov (1.28±2.59 W) and Rreq (1.25±2.51W) were not significantly different (P=0.63). However, while the resultant mean change in body heat content after 105 min was low (+0.46±2.79 kJ) and not significantly different from zero (P>0.05), an acute time‐dependent change in body heat storage was evidenced by a mean positive heat storage component of +6.64±2.98 kJ and a mean negative heat storage component of −6.17±2.64 kJ. Accordingly, the mean difference between maximum and minimum values for Trec and Tskwere 0.71±0.37°C and 2.18±0.81°C respectively. In conclusion, while RW maintain astable core temperature over a prolonged period, they induce acute bouts of heat imbalance.Supported by a NSERC Discovery Grant (O. Jay) & a CHEO Dept. of Surgery Research Grant (S. Chou).