Background: Haemodynamic stability is better maintained during isolated ultrafiltration (i-UF) than during combined ultrafiltration/haemodialysis (UF + HD). This difference might be explained by differences in thermal energy balances. In this study we compared the thermal energy balance of i-UF with UF + HD at different dialysate temperatures (Td) and determined the Td at which the thermal energy balance during UF + HD is similar to the thermal energy balance during i-UF.
Methods: In the first part of the study, 10 chronic haemodialysis patients were compared during three different treatment sessions, i-UF, UF + HD at Td of 35.5 degrees C and UF + HD at Td of 37.5 degrees C. The second part of the study consisted of one session of 1 h of UF + HD (UF + HD ET-set) with a pre-set energy transfer (ET) at the same level of ET found for that particular patient during i-UF in the first part of the study.
Results: First part of the study: body temperature (BT) decreased significantly during i-UF (-0.25 +/- 0.25 degrees C, P<0.05) and UF + HD 35.5 degrees C (-0.24 +/- 0.18 degrees C, P<0.05) and increased significantly during UF + HD 37.5 degrees C (+0.18 +/- 0.19 degrees C, P<0.05). The differences between the change in BT during UF + HD 37.5 degrees C compared with the other treatments were significant (P<0.05). ET gave a significantly more negative value during i-UF (-30.8 +/- 3.1 W, P<0.05) than during UF + HD 35.5 degrees C (-23.6 +/- 4.1 W, P<0.05). A slightly positive ET was found during UF + HD 37.5 degrees C (+0.4 +/- 4.7 W, P=not significant). Second part of the study: there was a slight, but not significant, decrease in BT during UF + HD ET-set (-0.17 +/- 0.26 degrees C). The changes in BT did not differ significantly between i-UF and UF + HD ET-set. After 1 h of UF + HD ET-set, the mean Td was 34.75 degrees C (34.0-36.0 degrees C). The correlation between pre-dialysis BT and Td during UF + HD ET-set was significant (r=0.764, P<0.05).
Conclusion: ET gives a more negative value during i-UF than during UF + HD 35.5 degrees C and than during UF + HD 37.5 degrees C. To obtain the same thermal ET during UF + HD as that achieved during i-UF, a mean Td of 34.75 degrees C is needed, depending on the pre-dialytic BT of the patient. The results of this study may be of relevance in relation to future clinical investigations which can elucidate whether differences in vascular response between i-UF and UF + HD are only related to differences in thermal balance.