Effect of dialysate temperature on energy balance during hemodialysis: Quantification of extracorporeal energy transfer

An impaired vascular response is implicated in the pathogenesis of dialysis -induced hypotension, which is at least partly related to changes in extrac orporeal blood temperature (Temp). However, little is known about changes i n core Temp and differences in energy balance between standard and cool dia lysis. In this study, core Temp and energy transfer between extracorporeal circuit and patient, as well as the blood pressure response, were assessed during dialysis with standard (37.5 degrees C) and cool (35.5 degrees C) Te mp of the dialysate. Nine patients (4 men, 5 women; mean age, 69 +/- 10 [SD ] years) were studied during low- and standard-Temp dialysis, each serving as his or her own control. Bicarbonate dialysis and hemophane membranes wer e used. Energy transfer was assessed by continuous measurement of Temp in t he arterial (T-art) and venous side (T-ven) of the extracorporeal system ac cording to the formula: c.rho.Qb*(T-ven - T-art)*t, where c = specific ther mal capacity (3.64 kJ/kg*degrees C), Qb extracorporeal blood flow, rho = de nsity of blood (1,052 kg/m(3)), and t = dialysis time (hours). Core Temp wa s also measured by Blood Temperature Monitoring (BTM; Fresenius, Bad Hombur g, Germany). Core Temp increased during standard-Temp dialysis (36.7 degree s C +/- 0.3 degrees C to 37.2 degrees C +/- 0.2 degrees C; P < 0.05) despit e a small negative energy balance (-85 +/- 43 kJ) from the patient to the e xtracorporeal circuit. During cool dialysis, energy loss was much more pron ounced (-286 +/- 73 kJ; P < 0.05). However, mean core Temp remained stable (36.4 degrees C +/- 0.6 degrees C to 36.4 degrees C +/- 0.3 degrees C; P = not significant), and even increased in some patients with a low predialyti c core Temp. Both during standard and cool dialysis, the increase in core T emp during dialysis was significantly related to predialytic core Temp (r = 0.88 and r = 0.77; P < 0.05). Systolic blood pressure (RR) decreased to a greater degree during standard-Temp dialysis compared with cool dialysis (4 3 +/- 21 v 22 +/- 26 mm Hg; P < 0.05), whereas diastolic RR tended to decre ase more (15 +/- 10 v 0 +/- 19 mm Hg; P = 0.07). Core Temp increased in all patients during standard-Temp dialysis despite a small net energy transfer from the patient to the extracorporeal system. Concluding, Core Temp remai ned generally stable during cool dialysis despite significant energy loss f rom the patient to the extracorporeal circuit, and even increased in some p atients with a low predialytic core Temp. The change in core Temp during st andard and cool dialysis was significantly related to the predialytic blood Temp of the patient, both during cool- and standard-Temp dialysis. The res ults suggest that the hemodialysis procedure itself affects core Temp regul ation, which may have important consequences for the vascular response duri ng hypovolemia. The removal of heat by the extracorporeal circuit and/or th e activation of autoregulatory mechanisms attempting to preserve core Temp might be responsible for the beneficial hemodynamic effects of cool dialysi s. (C) 1999 by the National Kidney Foundation, Inc.