Patients on continuous ambulatory peritoneal dialysis (PD) are encouraged to warm dialysate to 37°C before peritoneal infusion; main international PD guidelines do not provide specific recommendation, and patients generally warm dialysate batches partially or do not warm them at all. Warming of dialysate is a time-consuming procedure, not free from potential risks (i.e. degradation of glucose), and should be justified by a clear clinical benefit. The investigators designed a single blind randomized controlled trial where PD patients were randomized to receive a peritoneal equilibration test either with dialysate at a controlled temperature of 37°C (intervention group) or with dialysate warmed with conventional methods (control group). Primary end-point was a higher peritoneal creatinine clearance in patients in the intervention group.

Peritoneal dialysis (PD) currently represents the main choice for home renal replacement treatment for patients with end stage renal disease. One of the limitations of PD technique is represented by the difficulty in achieving target dialytic clearances and PD adequacy for some patients, especially with increasing PD vintage. A potentially relevant issue in PD clearances is the effect of dialysate temperature on depuration. Indeed, it is common for clinicians to advise patients in Continuous Ambulatory Peritoneal Dialysis (CAPD) to warm the dialysate before infusion into the peritoneal cavity, with different methods (microwave oven, warming cabin, warming pad). Nevertheless, main international PD guidelines do not provide specific recommendations on this topic. Only guidelines from the British Columbia Renal Agency (Canada) dedicate a specific chapter to the temperature of dialysate, recommending its warming to 37°C before peritoneal infusion, mainly in order to avoid an "uncomfortable lowering of body temperature". On the other hand, warming of PD batches could lead to hot spots formation inside the batch, especially with microwaves, and to degradation of glucose leading to the formation of toxic glucose degradation products (GDPs). Also, notable differences in room temperature exist according to geographical latitude and year season, and there are no clear and detailed reports in the literature regarding intolerable effects of the infusion of dialysate at room temperature. It must be acknowledged that it is common practice for patients to warm dialysate batches only partially or not to warm them at all. Moreover, warming pads that are most commonly used by CAPD patients do not effectively warm the dialysate up to 37°C. In the Peritoneal Dialysis Unit at Azienda Ospedaliero-Universitaria di Modena, it was recently observed that average dialysate temperature at infusion was 31.1°C, even if the pad was calibrated to 37°C [unpublished data]. With respect to the effects on toxins clearances through the peritoneal membrane, a higher dialysate temperature could theoretically favor vasodilation of peritoneal membrane microcirculation, potentially increasing the passage of substances. Severe microcirculatory dysfunction has been reported in PD patients and any intervention designed to ameliorate microcirculatory flow at peritoneal level could be beneficial. Surprisingly, reports regarding the effects of dialysate temperature on peritoneal clearances in PD in humans are surprisingly scarce. In 1967 Gross et al reported an increase in the exchange of substances between peritoneal fluid and blood upon warming of the PD fluid to 37°C (compared to 20°C) in a patient treated with intermittent peritoneal dialysis; the increase in urea clearance with the 37°C solution was 35% on average. In contrast, Indraprasit et al did not encounter differences in peritoneal creatinine clearance utilizing dialysate at room temperature (27-31°C) and warmed at 37°C in a group of 18 patients in PD. Confirmation of the effects of dialysate temperature on peritoneal clearances would be of great interest in order to maximize the depurative potential of PD and to justify patients' effort to warm the batches.

In order to determine the real effects of dialysate temperature on peritoneal clearances and transport characteristics, abdominal discomfort and vital signs, the investigators designed a randomized controlled trial comparing two strategies of peritoneal dialysate warming.

Study design and participants PD patients, both in CAPD and automated PD, in regular follow-up at the Nephrology Unit of the University Hospital of Modena, were randomized to receive a single dialysis exchange, either with dialysate at a controlled temperature of 37°C (intervention group) or with dialysate at warmed with conventional methods at uncontrolled temperature (control group). Randomization was generated through the use of the Random Allocation software11.

Primary end-point of our study was peritoneal creatinine clearance. Secondary end-points were: peritoneal urea clearance, creatinine and urea mass transfer area coefficient (MTAC), abdominal discomfort, blood pressure and body temperature.

A power analysis was performed while designing the study using the few data available in the literature; setting the alpha-error level at 0.05 for a 2-tailed t-test with a statistical power of 95% (beta-error 0.05) the estimated sample needed was 14 patients (7 per group).

Inclusion Criteria:

• age > 18 years
• ability to give informed consent
• peritoneal dialysis (PD) treatment
• PD vintage of more than 3 months
• absence of signs of active acute systemic or localized infections at least four weeks apart from the trial

Exclusion Criteria:

• pregnancy