Hyperkalemia is a common electrolyte abnormality following cardiac surgery which can result in serious complications. Potential causes of hyperkalemia are listed in Table 169.1. While evaluating patients for clinical sequelae from this disturbance; these underlying causes should be carefully considered.

Decreased Clearance of Potassium. Preexisting renal insufficiency or evolving acute tubular necrosis is the most concerning cause of hyperkalemia in the postoperative period. Cardiopulmonary bypass (CPB) is characterized by altered renal blood flow because of non-pulsatile pump flow and intraoperative hypotensive episodes. Vasodilatation induced by CPB and systemic inflammatory response syndrome (SIRS) may result in diminished renal flow, pooling of blood in venous capacitance vessels, and capillary leakage with resulting hypotension. Shear forces of CPB may cause red cell destruction resulting in intravascular hemolysis, which in turn can lead to hemoglobinurea, hyperkalemia and renal failure. Management strategies include the restoration and maintenance of normovolemia, renal blood flow, and perfusion pressure to limit further insult.

ACE inhibitors are known to result in potassium retention secondary to a lowering of plasma aldosterone levels and thus a decrease in potassium clearance. This phenomenon is note to occur in individuals with other risk factors for hyperkalemia, including disruption of homeostasis or congestive heart failure. Furthermore, ACE inhibitors may also contribute to renal insult in situations where MAP falls below 50-65 mmHg, hypovolemia, or inadequate cardiac output. Therefore prior to treatment of hyperkalemia with potassium wasting diuretics, you must make certain that the patient is adequately resuscitated so as not to contribute to ongoing renal insult.