Circadian variations in body temperature during dialysis.

BACKGROUND: Thermal changes during dialysis strongly influence intra-dialytic hemodynamics. The mechanisms behind the increase in body temperature during hemodialysis (HD) are still not completely understood. The objective of this retrospective observational cohort study is to assess the effect of circadian variation on body temperature changes during HD by comparing results in patients treated on different treatment shifts. METHODS: Data from the Renal Research Institute, New York, clinical database encompassing patients treated in six states in the USA were used. Data from January and August 2008 were used for analysis. Body temperature changes during HD were categorized by dialysis shifts. Patients with morning shifts (n = 1064), afternoon shifts (n = 730) and evening shifts (n = 210) were compared. RESULTS: Pre-dialysis body temperatures were significantly different among the different shifts [morning, 36.41 (95% confidence interval: 36.39-36.43 degrees C), afternoon, 36.47 (36.45-36.49 degrees C), evening, 36.67 (36.64-36.70 degrees C), P < 0.001]. In August, but not in January, intra-dialytic increases in body temperature were significantly different between patients treated during morning [0.07 (0.058-0.082 degrees C)], afternoon [0.03 (0.016-0.044 degrees C)] and evening shifts [-0.01 (-0.032 to 0.012 degrees C); P < 0.001 analysis of variance], although in January, treatment shift was a significant predictor of the intra-dialytic increase in body temperature. The intra-dialytic change in body temperature was related not only to the pre-dialysis body temperature (r(2) = 0.31; P < 0.001) but also to microbiological dialysate quality, treatment time and dialysate temperature. The intra-dialytic change in blood pressure (BP) was significantly related to changes in intra-dialytic body temperature irrespective of the study month. CONCLUSIONS: Both pre-dialytic body temperature as well as changes in body temperature are significantly related to the timing of the dialysis shifts, in phase with the circadian body temperature rhythm. Due to the relationship between body temperature changes and changes in intra-dialytic BP, these findings might be of additional relevance in the pathogenesis of intra-dialytic hypotension.