Critically ill patients with acute kidney injury (AKI) who, at hospital admission, had low sodium levels and concurrently high potassium levels are at increased risk for death, investigators reported in BMC Nephrology.

Among patients with serum sodium levels below 136 mmol/L, a serum potassium level of 4.8 mmol/L or higher was associated with a 45% increased risk of 90-day mortality, the study’s primary outcome, Fang-fang Zeng, PhD, of Jinan University in China, and colleagues reported.

“Across different sodium strata, a higher admission serum potassium level was associated with increased risk of mortality among patients with lower sodium levels, whereas the effects of hypernatremia seemed to be independent of serum potassium,” the authors wrote.

Dr Zeng’s team grouped 13,621 ICU patients with AKI (mean age 65.3 years) into tertiles of serum sodium and potassium levels at hospital admission. The study population included 7543 men and 6078 women.

Both serum sodium and potassium were independently associated with survival in a U-shaped curve. In multivariable Cox models, patients with hyponatremia or hypernatremia at hospital admission had 38% and 56% excess mortality risks, respectively, and patients with hypokalemia or hyperkalemia had 12% and 25% excess mortality risks, respectively, compared with patients with mid-range serum sodium and potassium values (136.0 to 144.9 mmol/L and 3.7 to 4.7 mmol/L, respectively).

“This finding shows that the risk for mortality is higher not only for those with clinically abnormal potassium levels, but also for those with potassium levels in the normal range of 3.5–3.7 mmol/L and 4.8–5.0 mmol/L,” Dr Zeng and peers explained.

The authors noted that, to their knowledge, the study is the first to examine the association between serum sodium and potassium levels among patients with AKI. The study included a large number of hospitalized patients, “allowing a relatively higher power to get precise exploration of the independent or joint prognostic effects of admission serum sodium or potassium levels.”

Limitations of the study included its retrospective design and inclusion of patients from just a single center. Consequently, the investigators were only able to establish associations rather than causal relationships.

Reference

Gao XP, Zheng CF, Liao MQ, et al. Admission serum sodium and potassium levels predict survival among critically ill patients with acute kidney injury: a cohort study [published online August 8, 2019]. BMC Nephrol. 20:311. doi:10.1186/s12882-019-1505-9