Conventional hemodialysis (CHD) administered thrice weekly for 3- to 4-hour sessions and peritoneal dialysis (PD) are the 2 most commonly delivered dialysis modalities. Patients treated with CHD are subject to short periods of rapid fluid and solute removal accompanied by brisk electrolyte shifts followed by long intervals when these substances reaccumulate. In contrast, PD uses the patient's peritoneal membrane to allow for continuous and gradual removal of fluid and uremic toxins.
A typical CHD schedule results in 2 one-day intervals and 1 two-day interval between dialysis sessions. The 2-day interval usually occurs from Saturday through Sunday or Sunday through Monday. Among CHD recipients, the period immediately following the 2-day interdialytic interval (either Monday or Tuesday) has recently been associated with an increased risk of death compared with other days of the week.1 The increased mortality risk may be mediated via significant fluid gain and electrolyte disequilibrium that occurs during the 2-day hiatus from dialysis. Since PD occurs daily, we hypothesized that mortality rates should be stable across different days of the week among PD recipients compared with those receiving CHD.
We used the Canadian Organ Replacement Register (CORR),2 a national registry that captures more than 95% of all dialysis and solid organ transplant recipients in Canada, to identify all incident patients receiving PD between 2001 and 2010.
We determined the number of deaths among PD patients for each day of the week and used a χ2 test to compare differences between the observed number of deaths per day of the week and those expected in the absence of any weekly variation. Among patients receiving PD, deaths occurring after transfer to CHD or after kidney transplantation were excluded. This study was approved by the St Michael's Hospital research ethics board.
Between 2001 and 2010, 8 855 patients initiated PD, of whom 169 died during the PD course (24.5%); 1390 underwent kidney transplant (15.7%); and 2488 transferred to CHD (28.1%). Among PD patients who died, there was no difference in the observed and expected number of deaths by day of the week. (P = .16) (Figure).
Our study of all patients undergoing PD in Canada over a 10-year period found no difference in the risk of all-cause mortality by day of the week during the PD course. These findings contrast with the results of Foley and colleagues,1 who found a higher risk of death among CHD patients in the days immediately following the long intradialytic interval.
Although observational data would suggest that overall long-term survival among patients treated with either PD or CHD are similar, these studies have failed to account for potential differential risks of mortality according to the day of the week for patients receiving PD vs CHD.3 Compared with CHD, PD might avoid extreme fluctuations in uremic toxin levels, electrolyte concentrations, and fluid accumulation. It is likely that these fluctuations are important contributors to the increased mortality observed after the long 2-day interval among those treated with CHD.4
Our work is limited to the Canadian setting and may not be generalizable to dialysis populations in other countries. However, the CORR registry is pan-Canadian, has been validated for cause and time of death, and performs similarly to other national administrative data sets, including The United States Renal Database.2,5,6
The variation in mortality risk by day of the week among CHD but not PD patients highlights an opportunity to improve survival among individuals receiving CHD. Further prospective study is needed to evaluate clinical outcomes using alternative hemodialysis strategies that eliminate the long interdialytic interval.
Correspondence: Dr Harel, St Michael's Hospital, 61 Queen St, Seventh Floor, Toronto, ON M5B 1W8, Canada (harelz@smh.ca).
Author Contributions: Dr Na takes full responsibility for the accuracy of the data and analysis. Study concept and design: Perl, Wald, Bell, and Harel. Analysis and interpretation of data: Perl, Wald, Na, Bell, and Harel. Drafting of the manuscript: Perl, Na, Bell, and Harel. Critical revision of the manuscript for important intellectual content: Perl, Wald, Bell, and Harel. Statistical analysis: Na and Harel. Obtained funding: Perl. Administrative, technical, and material support: Perl, Wald, and Harel. Study supervision: Perl and Bell.
Financial Disclosure: None reported.
Additional Contributions: We are grateful for the thoughtful input of Louise M. Moist, MD.
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