Serum potassium level, variability and in-hospital mortality in acute myocardial infarction

Abstract

Objective: Clinical guidelines recommend an optimal serum potassium concentration between 4.0 and 5.0 mmol/L in patients with acute myocardial infarction (AMI), which was based on lower-quality evidence from more than 20 years ago. Therefore, it is essential to re-evaluate the range of optimal potassium levels in patients with AMI in intensive care unit (ICU).

Methods: This was a retrospective study based on Philips eICU Collaborative Research Database, which covered 9776 patients with AMI between 2014 and 2015. All patients had more than or equal to 2 serum potassium measurements and were categorized by the mean serum potassium level (<3.5, 3.5-4.5, 4.5-5.5, ≥5.5 mmol/L) and potassium variability (1st, 2nd, and ≥3rd standard deviation (SD)). Binary logistic regression was used to determine the association between mean potassium levels, variability and in-hospital mortality in AMI.

Results: Of all 9776 AMI patients in ICU, 8731 (89.3%) patients were included. A total of 69847 potassium measurements were performed in these patients. There was a J-shaped relationship between mean serum potassium level and in-hospital mortality. The lowest mortality (mortality rate, 7.2%; 95% CI, 6.57%-7.76%) was observed in patients with mean potassium level between 3.5 and 4.5 mmol/L and a low potassium variability within the 1st SD. Logistic regression showed that the risk of in-hospital mortality is highest when the mean potassium level ≥5.5 mmol/L (57.6%; 95% Cl, 45.02%-70.24%; multivariable adjusted OR, 14.8; 95% CI, 8.4-26.2) compared to the reference group of 3.5-4.5 mmol/L and potassium variability within the 3rd SD (16.5%; 95% Cl, 15.19%-17.88%; multivariable adjusted OR, 3.3; 95% CI, 2.7-4.1) compared to 1st SD. Several sensitivity analyses confirmed these results.

Conclusion: Among AMI patients in ICU, the minimum risk of in-hospital mortality was observed in those with mean potassium levels between 3.5 and 4.5 mmol/L or a minimal potassium variability compared to those who had higher or lower values.

Keywords: ICU; acute myocardial infarction; mortality; potassium; potassium target; potassium variability.