A client with chronic kidney disease (CKD) has a serum potassium (K+) level of 6.8 mEq/L. Based on the ECG shown below, which medication should the nurse anticipate administering FIRST to protect the myocardium?

Emergency management of severe hyperkalemia with ECG changes

Hyperkalemia is a potentially life-threatening electrolyte disorder frequently encountered in the emergency department. A serum potassium (K+) level of 6.8 mEq/L indicates severe hyperkalemia and places the client at immediate risk for cardiac toxicity^[1].

Hyperkalemia is dangerous to the heart because it alters membrane potentials. Normally, the potassium gradient across the cell membrane is the key determinant of the resting membrane potential. As serum potassium rises, the resting membrane potential becomes less negative (partial depolarization). Initially this may transiently increase myocardial cell excitability, but as potassium climbs higher, sodium channels remain inactivated and both excitability and conduction velocity fall sharply. The result can be dysrhythmias and cardiac arrest^[1][2].

Treatment priority: protect the myocardium

Management of hyperkalemia follows three broad steps. First, stabilize the myocardial cell membrane to prevent immediately life-threatening dysrhythmias. Second, shift potassium from the vascular space into the cells to temporarily lower the serum level. Third, remove excess potassium from the body^[1].

The critical detail in this item is the presence of ECG changes. ECG abnormalities indicate that cardiac toxicity from hyperkalemia has already begun, so the first intervention must be myocardial protection. Calcium gluconate raises the threshold potential of myocardial cells, restoring the normal gap between the threshold and the depolarized resting membrane potential. This action does not lower the serum potassium, but it immediately restores electrical stability and prevents progression to lethal dysrhythmias. It is therefore the first-line drug in severe hyperkalemia accompanied by ECG changes^[1].

Role of the other treatment options

The remaining options are all used in hyperkalemia, but they shift or remove potassium and rank below myocardial protection in priority.

Regular insulin with dextrose and sodium bicarbonate drive potassium into the cells and temporarily lower the serum concentration. Insulin activates the Na+/K+-ATPase pump to promote cellular uptake of potassium, and sodium bicarbonate corrects metabolic acidosis, producing a similar shift through hydrogen–potassium exchange. However, these agents take time to work and do not stabilize the myocardial cell membrane itself, so they cannot be the first priority when ECG changes are present^[1].

Furosemide and Kayexalate remove potassium from the body. Furosemide is a diuretic that increases renal potassium excretion, and Kayexalate is a cation exchange resin that exchanges potassium for sodium in the bowel and eliminates it in the stool. These measures are important for definitive potassium removal, but their onset is very slow and they do not provide emergency cardiac protection^[1].

ECG abnormalities from severe hyperkalemia can progress to lethal conduction disturbances such as atrioventricular block. In one case report, severe hyperkalemia in a client with end-stage renal disease produced complete atrioventricular block with a heart rate as low as 15–20 beats per minute along with hypotension^[2]. Cases like this clearly illustrate why prompt administration of a calcium preparation for myocardial protection is the top priority in a hyperkalemic client with ECG changes.