Hyperkalemia: Clinical

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Hyperkalemia: Clinical

USMLE® Step 2 questions

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USMLE® Step 2 style questions USMLE

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A 63-year-old man comes to the emergency department because of severe weakness and nausea. His suffered a heart attack a month ago and has recently been placed on aspirin, carvedilol, and atorvastatin. An ECG is obtained and the readout is shown below:

Of the available options, which one is most likely to help this patient's condition?


With hyperkalemia, there’s too much potassium in the extracellular fluid, generally over 5 mEq/L.

Common causes include metabolic acidosis; a hyperglycemic hyperosmolar state; the use of medication, like potassium sparing diuretics; and tissue breakdown, like with a crush injury.

In addition, individuals with acute or chronic kidney disease, can develop hyperkalemia when there’s a high potassium intake.

Hyperkalemia is often asymptomatic, but it can cause symptoms like palpitations, paresthesias, and muscle weakness.

Ultimately if hyperkalemia is severe enough, it can lead to a flaccid paralysis that starts in the lower extremities and ascends upward.

In addition, severe hyperkalemia can affect renal function - causing a person to become oliguric- meaning their daily urine output can fall below 400 milliliters.

Whenever potassium levels are above 5 mEq/L, the first to do is an EKG.

If the EKG is normal and the individual doesn’t have symptoms of hyperkalemia, and if there’s no apparent cause of hyperkalemia, then it may be due to pseudohyperkalemia. This happens when potassium moves out of the cells during or after a blood draw.

For example, potassium gets released from muscle cells during muscle contraction, so if a person repeatedly clenches their fist during the blood draw, then potassium levels can rise - in fact, they can go up by up to 2 mEq/L in that forearm!

Also during blood drawing, some of the red cells can be harmed and release potassium.

Pseudohyperkalemia can also happen when there’s thrombocytosis or leukocytosis.

For example in chronic lymphocytic leukemia, the lymphocytes are frail, so they break easily and release potassium. The key is to simply repeat the serum potassium level and to obtain a CBC.

If pseudohyperkalemia is ruled out, then there’s a true hyperkalemia.

There may be EKG changes, but they don’t always correlate with the severity and progression of hyperkalemia.

Oftentimes, a potassium level between 6 and 7 mEq/L, will cause peaked T waves with a narrow base in the precordial leads V1 through V6.


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