Data are reported in the case of normal distribution as mean �� standard deviation, otherwise as median with selleck chemical 25th and 75th percentiles. Differences between data, obtained on days when the water supply was disinfected and on disinfection-free days, were compared using non-parametric (Mann-Whitney U-test) or parametric tests (two-tailed Student’s t test for unpaired data), as appropriate. P < 0.05 was regarded as statistically significant.ResultsIn 52 patients (27 male, 25 female, mean age 73 years, range 52 to 89 years, mean weight 77 �� 17 kg, mean height 167 �� 9 cm), 241 sessions of either extended hemodialysis or hemodiafiltration were performed between 1 February 2008 and 31 January 2009 with a mean duration of 466 �� 138 minutes. Of these dialysis sessions, 34 were performed on days when the hospital water supply was disinfected.

During dialysis, 706 arterial blood gas analyses were carried out, 89 of them on the days of water disinfection.The results of the methemoglobin measurements are presented in Table Table1.1. The evaluation of the 241 measurements, taken for final analysis, revealed a significantly increased methemoglobin fraction during hemodialysis/hemodiafiltration on the days of water disinfection, compared with disinfection-free days, with a maximal value of 12.2%. In 21 dialysis sessions, performed on days with water disinfection, the methemoglobin fraction increased above 2%. Also, all methemoglobin values greater than 2.0% (n = 22) were measured on days of water disinfection, except for one (methemoglobin fraction 2.2%).

The mean hemoglobin concentration of patients during extended hemodialysis/hemodiafiltration was slightly, but statistically significantly, lower on days with water disinfection (Table (Table1).1). Spot checks on the hydrogen peroxide concentrations in the water supply, the permeate and dialysate, using a semi-quantitative test, demonstrated levels between 10 and 25 mg/l during water disinfection. Control measurements before and after extended hemodialysis/hemodiafiltration did not indicate hydrogen peroxide, thus excluding the formation of hydrogen peroxide in the circuit of the dialysis machine independently of the water disinfection procedure.

Table 1Maximum methemoglobin fraction and hemoglobin concentration during each session of extended hemodialysis/hemodiafiltration between 1 February 2008 and 31 January 2009The review of the administration of drugs with oxidizing properties (local anesthetics, nitroglycerine, sulfamethoxazole) revealed that one patient, who Brefeldin_A received all hemodialysis/hemodiafiltration sessions on disinfection-free days, had been treated with sulfamethoxazole. A nitroglycerine infusion had been administered in four patients during five sessions of hemodialysis/hemodiafiltration, all of which were on disinfection-free days.