Bloembergen WE, Port FK, Mauger EA, Wolfe RA
A comparison of mortality between patients treated with hemodialysis and peritoneal dialysis and a comparison of causes of death (two back-to-back papers)

J Am Soc Nephrol (Aug) 6:177-191 1995

These papers use the enormous USRDS database to compare mortality rates between HD and PD. Previous studies from different countries on this topic have shown conflicting results. Bloembergen et al, however, show a significantly higher mortality on PD with a relative risk of 1.19 compared to HD. This is after correction for age, race, sex and diabetes. The excess risk is only significant at age over 55 and is most marked in diabetics and females. It is most marked for deaths from infection and cardiovascular disease. Overall, the excess mortality represents 4 deaths per 100 patient years.

These studies have some notable features. Firstly, they have enormous statistical power with 170,000 patient years and 42,000 deaths from 1987 to 1989. Secondly, they deal with the difficult issue of modality switches by treating each patient as a member of a new cohort at the start of each year. This approach, which has obvious advantages, contrasts with that in other studies which ignore or censor modality switches.

These studies may have a detrimental effect on PD, particularly in the US. A number of points should be noted, however, before they are overinterpreted. Firstly, Bloembergen et al adjust for age, sex, race and diabetes, but not for other comorbidities. It is possible that the latter explain the excess mortality on PD. Registry data are not controlled trials, modality selection is not random and unmeasured characteristics of the population directed to PD in the US may explain the higher mortality. Such a view is supported by data from the recently published 1993 Canadian Registry showing a significantly lower mortality on PD than on HD with relative risks of .89 and .76, under and over age 65, after correction for sex, age, time and diabetes. Modality selection in Canada is unlike that in the US and the striking differences in relative outcomes suggest case mix may be confounding all these analyses.

A second point is that the practice of both PD and HD is constantly changing. PD practices were not optimal in the US during the period covered by the Bloembergen studies. 'Flush before fill' giving sets were less widely used than in Canada or Europe and a high proportion of patients received less than 8 liters of dialysate daily. It may be relevant that data from the multicenter, CANUSA, PD adequacy study to be presented at ASN 1995 show over 10% higher mortality at 2 years in he US as compared to Canada, even after correction for demographics, comorbidity, dialytic dose and nutritional indices. This again suggests either a case mix difference not picked up by the parameters for which the data were corrected or, alternatively, a persisting problem with PD practice in the US. Examples of such a problem might be greater noncompliance with exchanges or less widespread use of newer, betterŒgiving sets.

In summary, there are reasons to justify some scepticism about how applicable the findings of Bloembergen et al are in the mid 1990's inside and, particularly, outside the US. It would be unjustifed to conclude that PD is an inferior therapy to HD. Nevertheless, these studies are an incentive to give attention in PD to issues such as dialytic dose, newer giving sets, compliance, volume overload, malnutrition, dyslipidemia and appropriate use of automated PD. A randomized trial comparing PD and HD may one day be done although many doubt it's feasibility. For now, both modalities should be viewed as complementary and in need of constant improvement. (Blake)

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CRF: Problem Areas : Outcomes (Morbidity, Mortality)