Today, I review, link to, and excerpt from The Cribsiders‘ #117: This Lab is Bananas, B-A-N-A-N-A-S: Hyperkalemia in the Acute Setting. * August 14, 2024 | By Sam Masur.
*Zhang AY, Symons JM, Masur S, Chiu C, Berk J. “#117 This Lab is Bananas, B-A-N-A-N-A-S Hyperkalemia in the Acute Setting”. The Cribsiders Pediatric Podcast. https:/www.thecribsiders.com/ August 14, 2024.
All that follows is from the above resource.
Summary:
We’ve all been there – you’re woken up by a critical page and a bright red potassium number blares at you from the computer screen. How do you make sense of the number? What does it mean for a potassium to be hemolyzed? And what are the steps to treating it? Dr. Jordan Symons (Seattle), walks us through all this and more as we learn all about hyperkalemia.
Acute Hyperkalemia Pearls
- The causes of hyperkalemia can be divided into several buckets – from most to least common, it’s defects in excretion, transcellular potassium shifts, and excessive intake
- Treatment of hyperkalemia involves stabilizing the cardiac membrane with calcium, pushing potassium intracellularly with insulin and/or albuterol, and augmenting potassium excretion with furosemide or a potassium resin binder.
- When you’re working up a patient with hyperkalemia, in the acute setting it’s important to get an ECG to look for peaked T waves, as well as blood and urine specimens.
Hyperkalemia Pt. 1: Notes
Why is potassium so important? Potassium is essential for maintaining a resting cell potential for nerves and muscles. Defined normal ranges of potassium are generally 3.5-5.5 meq/mL or mmol/L, and for infants this can be a little higher, likely due to kidney immaturity. When it’s high, it can change how cells depolarize and repolarize – most importantly, this can cause arrhythmias.
Hyperkalemia can be asymptomatic, but symptoms can include muscle weakness (e.g. periodic paralysis, which can also happen with hypokalemia).
Causes of Hyperkalemia
Expert pearl: These can be roughly divided into the following categories – too much in (uncommon); shifting of K (common); defects in excretion (most common)
A defect in excretion is the most common reason, due to low GFR with acute kidney injury and/or chronic kidney disease, renal tubule dysfunction (eg RTA type 4), sickle cell patients (chronic sickling sequelae on kidney), hypovolemia, low mineralocorticoid activity (CAH, primary hypoaldosteronism)
Another cause is transcellular movement of potassium. Most potassium should stay within cells. Potassium serum level will rise when potassium leaves cells, either via cell destruction (tumor lysis, cell necrosis/injury, rapid hemolytic anemia), or transcellular shifts for pH balance (e.g. metabolic acidosis)
Especially in pediatrics, watch for pseudohyperkalemia – an artificially elevated lab test, usually due to hemolysis. The hemolysis can be due to the lab draw technique (e.g. very small needles in infants, or finger/heel poke), or if the patient has marked leukocytosis or thrombocytosis, as these cells can break down en route to the lab. If in doubt, always repeat the lab (but don’t necessarily wait for it to result if you’re concerned).
Finally, a more uncommon cause of hyperkalemia is excessive intake. Usually kidneys adapt to intake of potassium, but occasionally in the patient with otherwise normal renal function, they can be overwhelmed if given too much potassium (e.g. in TPN, IVF, large amounts of RBC transfusions). Generally, marked intake of potassium will not result in hyperkalemia unless the patient has existing, usually chronic, kidney injury.
Workup
Lab workup
Blood/serum
- full chem panel including BUN/Cr
- CBC to check for number of blood cells for breakdown
- Check CK (if relevant history)
- Could check aldosterone levels (most useful in acute setting)
Urine
- Urinalysis including urine sodium, creatinine, osmolality, potassium
- If hyperkalemic in serum, urine potassium should be low, aka <20, unless there was renal dysfunction, or massive input from extensive cell breakdown)
- Can use these values in algorithm like the transtubular potassium gradient
- Low urine sodium = intravascularly deplete
Imaging/Other
- Expert opinion – don’t forget the ECG as one of the first tests to obtain! “Peak your Ts, lose your Ps, widen your QRS”
- Peaked T is early (NOT tall), pinched at base, pointy at top – different than tall T waves in adolescents
- P waves shorten and disappear
- Bladder scan, renal ultrasound – these can both wait until medical stability
Management
Start here.
