ECG
Chem 10 (including potassium, magnesium, and phosphorus)
Consider point-of-care lab testing for more rapid result
Consider ABG/VBG to evaluate pH
Consider point-of-care lab testing for more rapid result
Changes NOT always predictable and sequential
6.5 - 7.5 mEq/L: peaked T waves, prolonged PR interval, shortened QT interval
7.5 - 8.0 mEq/L: widened QRS interval, flattened P waves
10 - 12 mEq/L: sine wave, ventricular fibrillation, heart block
Based on lab testing (>5.5 mEq/L), although ECG may provide earlier information
Consider pseudohyperkalemia (e.g. from hemolysis)
Hyperkalemia
Pseudohyperkalemia: hemolyzed specimen, prolonged tourniquet use prior to blood draw, thrombocytosis or leukocytosis
Hyponatremia
Redistribution 
Hypernatremia
Acidemia 
Hypokalemia
Cellular breakdown: see Rhabdomyolysis/Crush syndrome, electrical/thermal burn, hemolysis, see Tumor lysis syndrome