Low diastolic blood pressure associated with higher mortality in chronic kidney disease

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1.  Among US veterans with non-dialysis dependent chronic kidney disease, diastolic blood pressure lower than 70 mm Hg was associated with higher mortality even when systolic blood pressure was within the ideal range. 

Evidence Rating Level: 2 (Good)            

Study Rundown: The association between high blood pressure (BP) and increased risk for cardiovascular disease and death has been well established in the general population. Current hypertension treatment guidelines in both chronic kidney disease (CKD) patients and patients with normal renal function emphasize tight control of systolic blood pressure (SBP) without much regard to diastolic blood pressure (DBP). However, recent studies have shown that low DBP, independent of SBP, may be a risk factor for higher mortality. This research is especially relevant in CKD patients, whose unique vascular physiology often results in high pulse pressures and low DBP. This study showed that non-dialysis dependent CKD patients with BP in the range of 130-159/70-89 mmHg had the lowest mortality rates.  That is, despite mild systolic hypertension, patients who maintained their DBP above 70 mm Hg had the best outcomes.  “Normal” blood pressure (<130/80 mmHg) was actually associated with the highest risk of mortality because of the inclusion of patients with DBP<70 mmHg.  A key major limitation is observational nature of this nature, and thus, causal relationships cannot be established from these results.  Furthermore, the study is limited by its population, which was comprised of primarily white males. Nonetheless, results of this study suggest that achieving ideal SBP at the expense of low DBP may increase risk of mortality in patients with non-dialysis dependent CKD.

Click to read the study in the Annals of Internal Medicine

Relevant Reading: Association between pulse pressure and mortality in patients undergoing maintenance hemodialysis

In-Depth [retrospective cohort study]: This study analyzed data from 651,749 US veterans with non-dialysis dependent CKD, available BP measurements, and sufficient follow-up for survival analysis between 2005 and 2012. They divided the cohort into 96 categories based on all possible combinations of SBP and DBP from lowest (<80/<40 mm Hg) to highest (>210/>120 mm Hg) in 10-mm Hg increments. The authors used time-dependent Cox models to determine the association between SBP-DBP combination and all-cause mortality, adjusting for age, sex, race, diabetes mellitus, cardiovascular and cerebrovascular disease, chronic heart failure, Charlson Comorbidity Index scores, medication use, eGFR’s, and blood cholesterol levels.

238,640 patients in the study cohort died during a median follow-up of 5.8 years. When analyzed separately, both SBP and DBP showed a U-shaped association with mortality, with higher mortality associated with lower and higher BP values. The best outcomes were associated with SBP of 140-160 mm Hg or DBP of 80-90 mm Hg. When SBP and DBP were analyzed as combinations, BP’s of 130-159/70-89 were associated with the lowest mortality rates in adjusted analyses. Interestingly, combinations of lower SBP and DBP were associated with lower mortality only when DBP was greater than approximately 70 mm Hg, regardless of how low the patient’s SBP was kept.  For example, when comparing a combination BP of 130-139/70-79 to 110-119/60-69, the mortality HR increased from 1.01 to 1.48.

By Sarah Chuzi and Aimee Li, MD

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