Practice Perfect 875
A Primer on Hypokalemia
A Primer on Hypokalemia
Surgery is an important aspect of the podiatric profession. As such, it is necessary that we understand perioperative medicine well. In fact, it is rarely the localized foot and ankle problem that creates delays when starting surgical cases, especially in the hospital. More commonly, medical issues that could have been predicted or treated before surgery cause delays.
In my own experience, most delays have occurred because of the following:
- Uncontrolled hyperglycemia
- Continued anticoagulation
- Electrolyte disorders, especially hyperkalemia and hypokalemia
Situations like abnormal ECGs and cardiac risk evaluation, although highly important, always seem to be taken care of before the surgery, and do not typically cause delays. It is probably obvious to speculate that it is because cardiac complications are so significant that this is worked up before the surgery.
I had a recent experience in which a patient that I was about to take to surgery had a preoperative potassium value of 3.1 mEq/L. As a result, a very nervous anesthesiologist held the case for an hour while a stat potassium was drawn. In the end, the patient was allowed to be brought to the operating room with this potassium level, and he did just fine. As you will see in a moment, a 3.1 mEq/L potassium is not particularly significant and is unlikely to cause complications. However, this situation sparked the question, how important is perioperative hypokalemia? Let’s take a quick look at hypokalemia to answer the question.
- Potassium is the primary intracellular cation.
- Regulated at the cellular level via the sodium–potassium ATPase pump (sodium out, potassium in).
- Potassium also regulates extracellular hydrogen ion production.
- Potassium intake = 100 mEq/day.
- Potassium urinary excretion = 90 mEq/day (90% urine)
- Fecal potassium excretion = 10 mEq/day (10% stool).
- Potassium levels in bone, liver, muscles, red blood cells, extracellular fluid all affect potassium.
- Kidneys are primarily responsible for potassium balance, taking several hours to adjust.
- Short-term potassium buffering occurs via movement in and out of muscle.
⇨ Look for urine and GI causes of potassium loss when investigating hypokalemia.
Definition of Hypokalemia
- Normal potassium equals 3.5-5.0 mEq/L
- 2.5-3.5 mEq/L = mild to moderate hypokalemia
- < 2.5 mEq/L = severe hypokalemia
- Every 1 mEq/L decrease potassium = potassium deficit 200-400 mEq.
Causes of Hypokalemia: Generally decreased intake or increased urine excretion or GI loss of potassium. GI loss is most common.
- GI loss: Diarrhea, laxatives
- Intracellular shift: Insulin, beta-2 agonists (albuterol, terbutaline), thyrotoxicosis
- Renal potassium losses: Cushing's, primary hyperaldosteronism, renal tubular acidosis, hypomagnesemia
- Drugs: Thiazide, loop, osmotic diuretics; laxatives; antipseudomonal penicillins; theophylline
How Important Is Perioperative Hypokalemia?
Hirsch, et al performed a prospective observational study that examined 447 patients undergoing major cardiac or vascular operations. They checked serum potassium levels immediately preop. They then stratified the patients based on the severity of potassium deficits and looked for various types of arrhythmias in this high risk population. They were unable to find any relationship between hypokalemia or the incidence of perioperative arrhythmias . Since their definition of severe hypokalemia was less than or equal to 3.0 mEq/L, it appears we really do not need to worry much about hypokalemia unless it is significantly low.
One additional effect we should consider in these perioperative patients is that muscle relaxants during anesthesia may provoke a paralytic ileus in patients with hypokalemia. Interestingly, in the case I mentioned above, my anesthesiologist gave the patient succinylcholine during the surgery with the intent that it would increase the patient's potassium level but could have led to perioperative ileus.
Treatment of Hypokalemia
There are 4 aims to consider:
- Decrease potassium losses.
- Increase serum potassium levels.
- Evaluate the patient for potential toxicities.
- Determine the cause of hypokalemia.
One very important consideration that is common to many of the hospitalized patients podiatrists see is diabetes. Keep in mind that insulin drives potassium into the cell, which may lead to hypokalemia. This was actually the cause of my own patient’s hypokalemia, and in this case, was nothing to worry about.
Potassium levels 2.5-3.5 mEq/L = oral replenishment with potassium chloride.
Potassium levels less than 2.5 mEq/L = IV potassium, and ECG, close follow-up, and serial potassium levels, in addition to determining the cause of the hypokalemia.
Additionally, it is recommended to check and correct magnesium levels as needed.
A little extra knowledge about our friend potassium, always in flux, especially in diabetic patients, is very helpful for best patient care and to help prevent perioperative delays. Lord forbid, we may actually start a hospital surgery on time!
Jarrod Shapiro, DPM
PRESENT Practice Perfect Editor
Hirsch IA, Tomlinson DL, Slogoff S, Keats AS. The overstated risk of preoperative hypokalemia. Anesth Analg. 1988 Feb;67(2):131-136.
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