The electrolyte concentration that has the potential to precipitate dysrhythmias and cardiac arrest in a client is Serum potassium of 7.2 mEq/L (7.2 mmol/L). Hyperkalemia causes dysrhythmias and cardiac arrest. The normal serum potassium concentration ranges between 3.5 and 5.0 mEq/L (7.2 mmol/L) indicates hyperkalemia. The normal concentration of sodium in the serum ranges between 135 and 145 mEq/L . The normal chloride concentration ranges between 96 and 106 mEq/L and the normal serum calcium level ranges between 9 and 10.5 mg/dL.