Ion shift index as a promising prognostic indicator in adult patients resuscitated from cardiac arrest

Several studies reported that disturbances in cellular ion homeostasis occur following ischaemia, the magnitude of which was proportional to illness severity. The changes in serum electrolyte levels following ischaemia were minor compared with the changes in ion concentrations in the extracellular fluid. To amplify the serum electrolyte changes, we devised a new index (ion shift index), which could be calculated using commonly measured serum electrolyte levels, and explored its prognostic value in adult cardiac arrest patients. This retrospective observational study included adult cardiac arrest survivors treated at a tertiary university hospital between January 2014 and December 2017. Using the first available serum electrolyte levels, the ion shift index was calculated as follows: ion shift index = (potassium + phosphate + magnesium) / calcium. The primary outcome was poor outcome at hospital discharge (cerebral performance categories 3–5). The area under the receiver operating characteristic curve (AUC) of ion shift index for predicting poor outcome was 0.878 (95% confidence interval [CI], 0.849–0.907). The AUC of ion shift index was greater than those of individual electrolytes (all p