Hyperkalemia
A 59-year-old man presented to the ED complaining of generalized weakness, the onset of which he stated had developed gradually over the previous 3 days. He denied chest pain, shortness of breath, or nausea and vomiting. His medical history was significant only for renal insufficiency. The patient was on no medications and denied alcohol or tobacco use.
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On physical examination, the patient had normal vital signs, including normal pulse oximetry. Similarly, the heart, lung, and abdominal examinations were all normal. On neurological examination, the patient had 5/5 motor strength in all four extremities and exhibited a normal gait.
The EP ordered an ECG, complete blood count (CBC), basic metabolic panel, urinalysis, and a chest X-ray (CXR). Laboratory evaluation showed an elevated potassium level of 6 mEq/L. The results of the CBC, urinalysis, and CXR were all reported as normal. (Unfortunately, there was no published information on the results of the BUN, creatinine, serum bicarbonate, or ECG findings.)
Based on the patient’s elevated potassium level, the EP ordered sodium polystyrene (Kayexalate) orally and arranged for admission to the hospital. The sodium polystyrene was administered to the patient approximately 1 hour after it was ordered. While waiting for an inpatient bed, the patient experienced a cardiac arrest and died in the ED.
The family sued the EP and hospital for failure to properly respond to the patient’s elevated potassium level. The hospital denied any negligence, and the defense argued that the death was not related to any electrolyte abnormality, but was due to a respiratory arrest that led to the cardiac arrest. The defendants also maintained the sodium polystyrene had been administered in a timely manner. At trial, a defense verdict was returned.
Discussion
Hyperkalemia has been variably defined as serum potassium concentrations >5 mEq/L, >5.5 mEq/L, or >6 mEq/L.1 Symptoms of hyperkalemia include generalized muscle weakness (as seen in this patient), muscle cramps, paresthesias, nausea, vomiting, and/or diarrhea. However, it is the cardiac manifestations (eg, ventricular arrhythmias, complete heart block, asystole) associated with hyperkalemia that are most concerning.
There are numerous causes of hyperkalemia, including medications, renal failure, digitalis toxicity, and metabolic acidosis. Therefore, it is important for the EP to identify the etiology in order to definitively treat the hyperkalemia.
Traditionally, it has been taught that hyperkalemia only requires treatment if abnormalities on the ECG are noted. Classic findings seen on ECG include prolonged PR interval, peaked T waves,2 shortened QT interval, QRS widening, and a sinusoidal wave pattern. Once fictitious or hemolysis has been ruled out as the etiology, most EPs will initiate treatment above a specific threshold value (frequently 6 mEq/L),
Since it is the cardiac effects of hyperkalemia that can result in death, the initial treatment must be directed toward cardiac membrane stabilization. This is best accomplished by the administration of calcium gluconate 10% IV. This medication has a rapid onset of action (typically 1-3 minutes) and helps prevent the development of cardiac arrhythmias. Additional measures, which involve moving potassium intracellullarly, include sodium bicarbonate IV and insulin with glucose IV.
Actual removal of potassium from the body involves either the administration sodium polystyrene sulfonate or hemodialysis. Sodium polystyrene sulfonate, which is an ion-exchange resin designed to exchange sodium for potassium in the colon, can be given either orally or as an enema. Even though sodium polystyrene sulfonate has been approved for the treatment of hyperkalemia since 1958, it does not take effect for 1 to 2 hours after administration; there is also growing evidence questioning its efficacy and safety.3 In addition, sodium polystyrene sulfonate can exacerbate volume overload due to the associated increase in serum sodium. Therefore, hemodialysis is the most effective treatment for hyperkalemia, and is the treatment of choice for unstable patients with hyperkalemia and acute or chronic renal failure.