Cooling effect of continuous renal replacement therapy in critically ill patients

Hypothermia is reported to increase intensive care unit (ICU) mortality. Th e heat loss that occurs during continuous renal replacement therapy (CRRT) favors the development of hypothermia. In an effort to assess the influence of CRRT on body temperature, we reviewed the records of 72 consecutive ICU patients treated with CRRT and further prospectively studied the temperatu re in the inlet and outlet lines for blood and dialysate of 27 other patien ts at various flow settings during continuous venovenous hemodialysis (CVVH D). Among the 72 retrospective cases, 36 episodes of hypothermia (core body temperature <35.5 degrees C) occurred and persisted for a mean of 2.6 +/- 1.8 days. It was more frequent during venovenous than arteriovenous modalit ies (31 of 67 v 5 of 20, respectively); no patients developed hypothermia d uring arteriovenous slow continuous ultrafiltration (AVSCUS), whereas 48% o f the patients undergoing CVVHD became hypothermic, occurring earlier in th e therapy course (days 2 to 4). Mean arterial pressure (MAP) tended to incr ease after CRRT initiation, but absolute changes were not statistically sig nificant. In the prospective arm, the CVVHD circuit temperatures were direc tly measured. Whereas no attempt was made to change body temperature, stepw ise changes in blood (Qb) and dialysate flow rate (Qd) produced venous circ uit temperature changes: the higher the Qb, the smaller the arteriovenous t emperature differences independent of changes in Qd (P < 0.001). Also, Veno us circuit temperature varied directly with Qd at fixed Qb (P < 0.001). Thi s relationship also held for temperature conversion to lost energy units pe r minute. Using room temperature dialysate, CRRT may significantly lower pa tients' core temperatures. Although the clinical significance of this effec t is not clear at this point, energy loss during CVVHD may be important in hemodynamic stability or patient prognosis. (C) 1998 by the National Kidney Foundation, Inc.