Hypokalemia

I got a little excited today when my patient had hypokalemia and the anesthesiologist asked me for a possible differentials. Don't get me wrong, I haven't been bored on Anesthesiology and I am actually enjoying it more than I thought I would. They have been letting me intubate patients which is beneficial for my future career. I just miss running through differentials! The most obvious reason for the patient's hypokalemia was redistribution from her respiratory alkalosis, but unfortunately we can't work up a pt in surgery like we can on the wards. Still, I wanted to revisit this topic today. 

First, check to make sure that the patient is not having any changes on EKG. If the patient is stable, you can go ahead and work up the cause for the hypokalemia. Second, check the metabolic acid base status. 

Normal Metabolic Acid Base

This category includes hypokalemia from redistribution or extrarenal losses. Redistribution occurs when there is an increase in exchange of potassium from extracellular to intracellular space. Redistribution occurs in the following situations...

• Catecholamine excess
• Alkalosis (resp alkalosis in my patient)
• hypokalemic periodic paralysis
• Insulin administration
• Albuterol inhaler or beta 2 agonist
• Barium poisoning

Extrarenal losses include...

• Simply, decreased potassium intake
• Laxative abuse

Metabolic Acidosis

Divide this category into if the urine potassium is < 20 (not a problem with the kidneys) or > 20 (problem with the kidneys). 

Urine potassium < 20 - This tells you that the kidney is doing its job holding onto the potassium and that the losses are extrarenal . These losses include...

• Diarrhea
• Laxative abuse - you can have both a normal or met acidosis with laxative abuse

Urine potassium is > than 20 - This tells you that something is wrong with the kidneys because if your body was experiencing hypokalemia, than the kidneys should be doing their job reabsorbing the potassium to help correct the hypokalemia. Causes include...

• Renal Tubular Acidosis - See other post on RTAs
• Carbonic anhydrase inhibitors
• organic acidosis

Metabolic Alkalosis

Check the urine K and the urine chloride. If the urine K is < 20 think of vomiting as a likely cause. If the urine chloride is > 20, you divide the categories into if the patient has a normal BP or high BP. 

Normal BP

• Bartter's syndrome
• Diuretics

High BP

• Hyperaldosteronism
• Essential HTN with diuretic use
• Hypercortisol
• Mineralcorticoid ingestion (licorice, Liddle's syndrome)

Treatment - Always check the Mg level in the patient as Mg will stabilize the nephron and reduce the urinary loss of K. If the patient is asymptomatic, give potassium supplementation (10 meq roughly will increase the serum K by 0.1 meq/L). The equation used to calculate the potassium deficit is...

(Goal K - Serum K)/Serum Cr x 100 = Total meq of K required

Don't use D5W or fluids with high glucose as glucose will cause an increase in insulin which will further drive K intracellularily and exacerbate the hypokalemia. Most common fluids to use for repletion are KCL, KHCO3 and can also use KPO3 depending on the coexisting deficits.