Bicarbonate Concentration, Acid-Base Status, and Mortality in the Health, Aging, and Body Composition Study

Abstract

Background and objectives Low serum bicarbonate associates with mortality in CKD. This study investigated the associations of bicarbonate and acid-base status with mortality in healthy older individuals.Design, setting, participants, & measurements We analyzed data from the Health, Aging, and Body Composition Study, a prospective study of well functioning black and white adults ages 70-79 years old from 1997. Participants with arterialized venous blood gas measurements (n=2287) were grouped into ,23.0 mEq/L (low), 23.0-27.9 mEq/L (reference group), and $28.0 mEq/L (high) bicarbonate categories and according to acid-base status. Survival data were collected through February of 2014. Mortality hazard ratios (HRs; 95% confidence intervals [95% CIs]) in the low and high bicarbonate groups compared with the reference group were determined using Cox models adjusted for demographics, eGFR, albuminuria, chronic obstructive pulmonary disease, smoking, and systemic pH. Similarly adjusted Cox models were performed according to acid-base status.Results The mean age was 76 years, 51% were women, and 38% were black. Mean pH was 7.41, mean bicarbonate was 25.1 mEq/L, 11% had low bicarbonate, and 10% had high bicarbonate. Mean eGFR was 82.1 ml/min per 1.73 m 2 , and 12% had CKD. Over a mean follow-up of 10.3 years, 1326 (58%) participants died. Compared with the reference group, the mortality HRs were 1.24 (95% CI, 1.02 to 1.49) in the low bicarbonate and 1.03 (95% CI, 0.84 to 1.26) in the high bicarbonate categories. Compared with the normal acid-base group, the mortality HRs were 1.17 (95% CI, 0.94 to 1.47) for metabolic acidosis, 1.21 (95% CI, 1.01 to 1.46) for respiratory alkalosis, and 1.35 (95% CI, 1.08 to 1.69) for metabolic alkalosis categories. Respiratory acidosis did not associate with mortality.Conclusions In generally healthy older individuals, low serum bicarbonate associated with higher mortality independent of systemic pH and potential confounders. This association seemed to be present regardless of whether the cause of low bicarbonate was metabolic acidosis or respiratory alkalosis. Metabolic alkalosis also associated with higher mortality.

Serum Bicarbonate Is Associated with Heart Failure in the Multi-Ethnic Study of Atherosclerosis

“…Finally, we did not have a complete description of the acid-base status of the patients (pH, PCO2 and bicarbonate level) and thus we do not know if the patients with higher serum bicarbonate levels were alkalemic. Studies have shown that patients can have alkalemia or acidemia with various serum bicarbonate concentrations [18] and future studies should obtain a complete acid-base profile.…”

“…Recent studies have also found that metabolic acidosis results in activation of the renin-angiotensin aldosterone system and vascular endothelial dysfunction [3]. Epidemiologic studies have found that lower serum bicarbonate concentrations are associated with incident and prevalent hypertension [4–6], insulin resistance [7,8], kidney disease progression [9–16] and mortality [14–18]. Collectively these data suggest that metabolic acidosis may be a risk factor for CVD.…”

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“…This study showed a U-shaped association between S-bicarbonate and mortality as well as ICU length of stay. Another recently published study investigated the associations of bicarbonate and acid-base status with mortality in healthy older individuals [3]. This study showed that metabolic alkalosis was associated with higer mortality.…”