An evaluation of a healthy participant laboratory model of epidural hyperthermia: a physiological study.

BACKGROUND: Hyperthermia complicates 21% of cases of intrapartum epidural analgesia, but the mechanism is unclear. One hypothesis is that blockade of cholinergic sympathetic nerves prevents active vasodilation and sweating, thus limiting heat loss. Because labour increases heat production, this could create a situation in which heat production exceeds loss, causing body temperature to rise. This physiological study tested a novel laboratory model of epidural-related hyperthermia, using exercise to simulate the increased heat production of labour and surface insulation to simulate the effect of epidural analgesia. METHODS: Twelve healthy non-pregnant participants (six female) cycled an ergometer for two hours at 20 Watts (W) on two occasions: once with surface insulation (intervention) and once without (control). Core temperature, skin temperature (eight sites), and heat loss (eight sites) were recorded. Mean body temperature and heat production were calculated. Values are mean (SD). RESULTS: Exercise increased heat production on both visits (intervention 38 (18) W; control 37 (31) W; P = 0.94). Total heat loss was less on the intervention visit (intervention 115 (19) W; control 129 (23) W; P = 0.002). Core temperature increased on both visits (intervention 0.21 (0.37)°C; control 0.19 (0.27)°C; P < 0.001). The increase in mean body temperature was greater on the intervention visit (intervention 0.47 (0.41)°C; control 0.25 (0.19)°C; P = 0.007). CONCLUSIONS: This laboratory model predicts that labour epidural analgesia limits heat loss by >14 W. Once the model is validated, it could be used to test the efficacy of potential interventions to prevent and treat epidural-related maternal hyperthermia.