Isothermic hemodialysis and ultrafiltration

Abstract

The increase in patient temperature during hemodialysis is explained by hemodynamic compensation during ultrafiltration and hypovolemia that leads to peripheral vasoconstriction and reduced heat losses. We analyzed 51 stable high-efficiency hemodialysis treatments in 27 patients during isothermic dialysis in which body temperature was maintained at a constant level (±0.1°C) using the temperature-control option of the Blood Temperature Monitor (BTM; Fresenius Medical Care, Bad Homburg, Germany). Hemodialysis was delivered using ultrapure water (limulus amebocyte lysate test < 0.06 endotoxin units/mL) at mean blood flows of 410 ± 40 mL/min. During treatments lasting 178 ± 23 minutes, 4.8% ± 1.4% of postdialysis body weight (W%) and 9.5% ± 2.5% of postdialysis body water were removed using mean ultrafiltration rates of 1.1 ± 0.3 L/h. Dialysate temperatures significantly decreased from 35.9°C ± 0.3°C to 35.6°C ± 0.6°C during hemodialysis. During these treatments, 187 ± 69 kJ of thermal energy were removed from the patients through the extracorporeal circulation using cool dialysate. Extracorporeal heat flow was 17 ± 6 W. Energy expenditure (H) estimated from anthropometric data was 65 ± 12 W. Thus, 28% ± 10% of estimated energy expenditure (H%) was removed during isothermic dialysis. A highly significant correlation was observed between H% and W% (H% = –5.6 * W%; r2 = 0.91; P < 0.0001). This result is in support of the volume hypothesis of intradialytic heat accumulation and provides a rule of thumb to estimate extracorporeal cooling requirements for isothermic dialysis. Approximately 6% of H must be removed through the extracorporeal circulation for each percent of ultrafiltration-induced body-weight change. The importance of body temperature control during hemodialysis increases with increased ultrafiltration requirements.