Purpose: To investigate the association between potassium concentration at the initiation of critical care and all-cause mortality.
Methods: We performed a retrospective observational study on 39,705 patients, age ≥18 years, who received critical care between 1997 and 2007 in two tertiary care hospitals in Boston, Massachusetts. The exposure of interest was the highest potassium concentration on the day of critical care initiation and categorized a priori as 4.0-4.5, 4.5-5.0, 5.0-5.5, 5.5-6.0, 6.0-6.5, or ≥6.5 mEq/l. Logistic regression examined death by days 30, 90, and 365 post-critical care initiation, and in-hospital mortality. Adjusted odds ratios were estimated by multivariable logistic regression models.
Results: The potassium concentration was a strong predictor of all-cause mortality 30 days following critical care initiation with a significant risk gradient across potassium groups following multivariable adjustment: K = 4.5-5.0 mEq/l OR 1.25 (95 % CI, 1.16-1.35; P < 0.0001); K = 5.0-5.5 mEq/l OR 1.42 (95 % CI, 1.29-1.56; P < 0.0001); K = 5.5-6.0 mEq/l OR 1.67 (95 % CI, 1.47-1.89; P < 0.0001); K = 6.0-6.5 mEq/l OR 1.63 (95 % CI, 1.36-1.95; P < 0.0001); K > 6.5 mEq/l OR 1.72 (95 % CI, 1.49-1.99; P < 0.0001); all relative to patients with K = 4.0-4.5 mEq/l. Similar significant associations post multivariable adjustments are seen with in-hospital mortality and death by days 90 and 365 post-critical care initiation. In patients whose hyperkalemia decreases ≥1 mEq/l in 48 h post-critical care initiation, the association between high potassium levels and mortality is no longer significant.
Conclusions: Our study demonstrates that a patient's potassium level at critical care initiation is robustly associated with the risk of death even at moderate increases above normal.