A cardiac arrest arrives to the Emergency Department in January. During the resuscitation it is discovered that the patient is severely hypothermic, and rewarming is begun. A serum potassium results. Which potassium level would prompt you to terminate resuscitative efforts?

A. < 1 mmol/L

B. > 3 mmol/L

C. > 6 mmol/L

D. > 12 mmol/L

Answer: D. You may have heard the common phrase in EM: “the patient isn’t dead until they’re warm and dead.” And it is true that a hypothermic patient may often appear dead with stiffness that resembles rigor mortis and fixed pupils. Resuscitative efforts and rewarming should continue unless there are obvious signs of irreversible death (i.e. a frozen noncompressible body) or serum potassium >12 mmol/L which would indicate that continued CPR is likely futile.

Brown DJ, Brugger H, Boyd J, Paal P. Accidental hypothermia. N Engl J Med. 2012 Nov 15;367(20):1930-8. doi: 10.1056/NEJMra1114208. Erratum in: N Engl J Med. 2013 Jan 24;368(4):394. PMID: 23150960.