Serum bicarbonate levels and kidney outcomes in critically ill patients: a prospective cohort study

The interplay between serum bicarbonate levels and kidney outcomes is not fully understood. We conducted a prospective cohort study in three intensive care units (ICUs) to evaluate the association of serum bicarbonate levels with acute kidney injury (AKI) and kidney function recovery in critically ill patients.

A prospective cohort study in three intensive care units (ICUs) was performed. The serum bicarbonate level in the first 24 h after ICU admission was categorized as low (< 22 mEq/L), normal (22-26 mEq/L), or high (> 26 mEq/L). Serum creatinine (SCr) levels according to the KDIGO AKI guideline were used for defining AKI within the first 7 days of ICU stay. At ICU admission, SCr ≥ 1.1 for women and ≥ 1.3 mg/dL for men were indicative of impaired kidney function. Mortality outcome was tracked up to 28 days, and kidney function recovery was assessed at hospital discharge.

A total of 2732 patients (66 ± 19 years and 55% men) were analyzed, with 32% having impaired kidney function at ICU admission. Overall, 26% of patients had low bicarbonate levels, while 32% had high bicarbonate levels. Notably, patients with preserved kidney function showed a lower prevalence of low bicarbonate levels compared to those with impaired kidney function (20% vs. 39%, p < 0.001), while higher rates were observed for high bicarbonate (35% vs. 24%, p < 0.001). Compared with patients with normal serum bicarbonate levels, those with low bicarbonate were 81% more likely to develop AKI (OR = 1.81; 95% CI 1.10-2.99), whereas those with high bicarbonate were 44% less likely (OR = 0.56; 95% CI 0.32-0.98) in the adjusted model for confounders. Neither those with high nor low serum bicarbonate levels were associated with an increased risk of mortality (HR = 1.03; 95% CI 0.68-1.56 and 0.99; 95% CI 0.68-1.42, respectively). In subgroup analysis, regardless of the kidney function at ICU admission, serum bicarbonate levels were not associated with the development of AKI and all-cause mortality. Regarding kidney function recovery, higher non-recovery rates were found for those with low bicarbonate.

In critically ill ICU patients, low bicarbonate levels were associated with the more likely development of AKI and subsequent non-recovery of kidney function, while high bicarbonate levels showed no such association. Therefore, low bicarbonate levels may be considered a risk factor for adverse kidney outcomes in critically ill patients.