Figure 323

Approach to hyperkalemia: hyperkalemia without total body potassium excess. Spurious hyperkalemia is suggested by the absence of electrocardiographic (ECG) findings in patients with elevated serum potassium. The most common cause of spurious hyperkalemia is hemolysis, which may be apparent on visual inspection of serum. For patients with extreme leukocytosis or thrombocytosis, potassium levels should be measured in plasma samples that have been promptly separated from the cellular components since extreme elevations in either leukocytes or platelets results in leakage of potassium from these cells. Familial pseudohyperkalemia is a rare condition of increased potassium efflux from red blood cells in vitro. Ischemia due to tight or prolonged tourniquet application or fist clenching increases serum potassium concentrations by as much as 1.0 to 1.6 mEq/L. Hyperkalemia can also result from decreases in K movement into cells or increases in potassium movement from cells. Hyper-chloremic metabolic acidosis (in contrast to organic acid, anion-gap metabolic acidosis) causes potassium ions to flow out of cells. Hypertonic states induced by mannitol, hypertonic saline, or poor blood sugar control promote movement of water and potassium out of cells. Depolarizing muscle relaxants such as succinylcholine increase permeability of muscle cells and should be avoided by hyperkalemic patients. The mechanism of hyperkalemia with p-adrenergic blockade is illustrated in Figure 3-3. Digitalis impairs function of the Na+-K+-ATPase pumps and blocks entry of potassium into cells. Acute fluoride intoxication can be treated with cation-exchange resins or dialysis, as attempts at shifting potassium back into cells may not be successful.

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