A 45-year-old man is evaluated in the surgical intensive care unit on postoperative day 1 … — USMLE Step 2 CK

A $45$ -year-old man is evaluated in the surgical intensive care unit on postoperative day $1$ following a $14$ -hour complex pelvic exenteration for an advanced rectal malignancy. His surgical history is significant only for this recent procedure. Over the past $6$ hours, his urine output has precipitously declined to $15 \text{ mL/hr}$ , and the fluid in the Foley catheter tubing is noted to be dark reddish-brown. Vital signs are blood pressure $110/70 \text{ mmHg}$ , heart rate $118 \text{ beats/min}$ , respiratory rate $18 \text{ breaths/min}$ , and temperature $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ). Physical examination reveals diffuse muscle tenderness in the lower extremities, which were positioned in prolonged lithotomy during the surgery. Stat laboratory testing reveals a serum potassium level of $7.9 \text{ mEq/L}$ , serum creatinine of $3.4 \text{ mg/dL}$ , and a creatine kinase level of $52,000 \text{ U/L}$ . An emergent $12$ -lead electrocardiogram demonstrates peaked T waves, a widened QRS complex, and loss of P waves. Arrange the following interventions in the correct chronological sequence for the optimal management of this acute postoperative emergency.

1Administer intravenous calcium gluconate to antagonize the membrane effects of hyperkalemia.
2Administer intravenous regular insulin concurrently with $50\%$ dextrose to shift potassium intracellularly.
3Initiate aggressive intravenous fluid resuscitation with isotonic crystalloids to address myoglobinuric acute kidney injury.
4Administer an intravenous loop diuretic to promote the renal excretion of potassium and myoglobin.
5Consult nephrology for emergent hemodialysis if medical therapy fails to correct the electrolyte derangements.

Answer

The correct chronological sequence is to first stabilize the cardiac membrane with calcium gluconate, followed by intracellular shifting of potassium with insulin and dextrose, volume resuscitation with intravenous fluids to address the underlying myoglobinuria, forced renal elimination with loop diuretics, and finally, hemodialysis if medical management fails.

The management of severe hyperkalemia with electrocardiographic changes follows a strict chronological protocol to prevent fatal arrhythmias and treat the underlying cause. The first and most critical step is the administration of intravenous calcium gluconate to stabilize the myocardial cell membrane. This antagonizes the depolarizing effects of hyperkalemia without actually changing the serum potassium level. Once the myocardium is protected, the next step is to temporarily shift potassium from the extracellular space into the cells using intravenous regular insulin, with dextrose to prevent hypoglycemia. After the acute life-threatening risk is mitigated, the focus shifts to addressing the underlying rhabdomyolysis and permanently eliminating potassium. Aggressive intravenous fluid resuscitation is required to flush the myoglobin from the renal tubules and restore glomerular filtration. Once the patient is adequately volume-resuscitated, loop diuretics are administered to force the renal excretion of potassium and wash out myoglobin casts. Finally, if these conservative measures fail or if the patient remains anuric due to severe acute kidney injury, emergent hemodialysis is indicated for definitive extracorporeal removal of potassium.

Step-by-Step Solution

Administer intravenous calcium gluconate.

The resting membrane potential of the cardiac myocytes is stabilized.

To prevent lethal ventricular arrhythmias caused by severe hyperkalemia.

Administer regular insulin and

50\%

dextrose.

Potassium is rapidly shifted from the extracellular to the intracellular space.

To acutely lower the serum potassium concentration while preventing hypoglycemia.

Initiate aggressive intravenous crystalloid resuscitation.

Intravascular volume is expanded and renal perfusion is restored.

To treat the underlying rhabdomyolysis and prevent myoglobin deposition in the renal tubules.

Administer an intravenous loop diuretic.

Tubular flow is increased, promoting the excretion of potassium and myoglobin.

To actively eliminate excess potassium from the body once the patient is volume-replete.

Prepare for emergent hemodialysis.

Extracorporeal removal of potassium and uremic toxins is achieved.

Indicated as a last resort if hyperkalemia is refractory or if oliguric acute kidney injury persists.

Key Concept

The stepwise management of severe hyperkalemia secondary to rhabdomyolysis involves immediate cardiac membrane stabilization, followed by intracellular potassium shifting, and finally, definitive potassium elimination from the body.

Estimated Time:2m 0s

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