On-line temperature monitoring in continuous hemodialysis (CVVHD): a feasibility study

Thermal Balance in patients undergoing CVVHD has never been studied. The blood temperature monitor (BTM) is a device implemented in the Fresenius 2008H machine, allowing for the calculation of access recirculation, thermal energy balance and body temperature control. BTM has only been used at blood and dialysate flows typical for conventional hemodialysis. In this study we evaluate the possible use of the BTM in CVVHD. The study was conducted in vitro using a modified 2008H machine. The machine was calibrated at 37.0°C with dialysate flows (Qd) of 500 and 100 ml/min. Accuracy of temperature (T) setting was then checked at Qd of 300,200,100 ml/min. Results displayed the best accuracy at 200 ml/min. At 100 ml/min wide fluctuations could be observed (±12%). At 300 ml/min, actual T never reached the set T (average delta &le -0.6°C). BTM could not be used in T control mode because of delay in the effects of thermal boli utilized for recirculation measurement. T variations in blood occurred beyond the detection time of the BTM (4 minutes). BTM could calculate automatically the total energy balance during a CVVHD session (8 hours measurement time) and it could be used in thermal energy control mode (TECM) to maintain a constant flux of energy across the hemodialysis membrane with values varying from - 100 to + 100 Kj/h). In conclusion, BTM can be used in CVVHD to measure thermal energy balance and to control the flux of energy delivered or withdrawn from the patient during treatment. This features of the BTM is of great interest for the critically ill patient. Patients may frequently be hyperthermic and may require a progressive cooling to improve hemodynamic stability and prevent thermal damage. On the other hand, when large volumes of fluid are exchanged, the risk of a negative thermal balance is highly enhanced. For all these aspects, the use of BTM in the acute renal failure should be investigated and future application of these monitors in CRRT machines may be advantageous.