Resting energy expenditure and thermal balance during isothermic and thermoneutral haemodialysis—heat production does not explain increased body temperature during haemodialysis

Background. During routine haemodialysis (HD) body temperature increases, which contributes to haemodynamic instability. The relative roles of increased heat production and/or incomplete heat transfer are not fully elucidated. Concomitant measurement of heat production and heat transfer may help to assess the factors determining thermal balance during HD. Methods. Thirteen stable non-diabetic maintenance HD patients were investigated during two HD procedures (isothermic, dT = 0, no change of body temperature; thermoneutral, dE = 0, no energy transfer between blood and dialysate), using a blood temperature monitor (BTM) in active mode. Energy transfer, blood and dialysate temperature, and relative blood volume change (dBV) were continuously recorded, and resting energy expenditure (REE; Deltatrac Datex) was measured repeatedly during each procedure. Fourteen healthy persons served as controls for REE comparison. Results. In isothermic HD, median energy removal was 218 kJ/4 h HD (= heat flow −15.1 W). This cooling correlated with dBV induced by ultrafiltration (ρ = 0.731, P < 0.01). There was no difference in dBV between isothermic (7.7%) and thermoneutral (8.1%) HD. Predialysis REE was 82.8 W/1.73 m2, not different from controls. No variation in REE during HD was observed, except a small and transient increase after a light meal (5 and 4%). In the time course of REE, no difference between the procedures was found. Conclusions. Our findings suggest that stable maintenance HD patients have REE not different from healthy controls, that HD procedure per se does not significantly increase REE and that neither isothermic nor thermoneutral regimen has any influence on metabolic rate. Therefore, body temperature elevation during routine HD may rather be due to decreased heat removal. With the use of BTM in active mode, body temperature can be kept stable (isothermic HD), which requires active cooling. This negative energy transfer is proportional to decrease in blood volume induced by ultrafiltration.