We love to come up with health care prescriptions that work for everyone. But, that rarely happens. It’s how drugs get abused- we know the drug solves this problem in one cohort, so we apply it to another cohort. The problem is the second cohort has other associated maladies that interact negatively with the drug.
It seems the same principle applies when we try to proscribe blood pressure management for dialysis patients. We have long known that mortality for ESRD (end stage renal disease) patients is high; cardiovascular disease the primary cause of death (many patients have what could be termed uncontrolled hypertension). Yet, we have set the targets for blood pressure based upon our knowledge of the general population, and not directly for or from ESRD issues. This is true because ESRD patients have never been included in studies concerned with blood pressure management.
It seems that the relationship between blood pressure and mortality among ESRD patients may be U-shaped: one group has higher mortality at low blood pressure, while another has problems at high blood pressure (but moderate pressures [140/90 mm Hg] are probably good for everyone). These results were discussed in a study funded by DCI (Dialysis Clinics, Inc.) led by Dr. Philip Zager (joint appointment with DCI and University of New Mexico Health Sciences), to be published shortly in the Journal of the American Society of Nephrology (advance copy posted). This six-year study examined 16,283 patients (6250 died during the course of the research), all of whom survived at least 150 days from first outpatient dialysis treatment (to ensure that the dialysis treatment was successful). One key fact resulted from this study: Systolic blood pressure correlated better with mortality than did diastolic pressures. The other significant finding was that ESRD patients with diabetes had higher mortality risks with lower systolic pressures.
Low systolic pressure was linked with elevated mortality, but this correlation was even more pronounced with the elderly or those patients also suffering from diabetes. For patients 50 y of age or older, systolic pressures below 140 mm Hg were detrimental; pressures exceeding 160 were not associated with elevated mortality. On the other hand, for the younger patients, systolic BP of 160 mm Hg or higher were a problem, while the 140 mm Hg or lower were not a problem (diabetes and race did not affect these results).
ESRD patients manifest different relationships from the normal population. ESRD patients in their 30’s had similar relationships with “normal” between systolic blood pressure and mortality. For each decade increase in age, mortality related to low systole increased and that for high systole decreased for ESRD patients (but not for the general population). This may be related to the fact that organ perfusion is affected (higher systole would tend to augment blood flow to the various organs of the body) when the patients have non-compliant blood vessels and other arterial diseases. [It should be noted that cardiac disease was not monitored as part of the study (and one would expect it to manifest increased incidence with age).]
In an accompanying editorial by Drs. Crews and Powe, it was suggested that, with the purported desire of Congress (American Recovery and Reinvestment Act of 2009) to have the Institute of Medicine define national priorities for effectiveness research, “determining which treatment works best, for whom, and under what circumstances”, a new study be funded. The aim should be to determine the desired approaches for the treatment of cardiovascular disease and ESRD; one that would more clearly define the desired intervention in the case of blood pressure management.
