Of all the things about which I am called as a critical care specialist, I think I am called/notified about serum potassium levels the absolute most. For some reason, if the serum potassium level is below 4.0, I am expected to do something about it, even if it is within the normal range for serum potassium.
From where did this come? From where is the literature that every patient - not only in the ICU but seemingly the entire hospital - needs to have potassium levels above 4.0? The literature is mainly derived from acute MI, where studies have shown that mortality is lowest when the potassium is above 4. Yet, the studies are also conflicting, with some showing lowest mortality between 4.0 and 4.5, and
others showing lowest mortality between 3.5 and 4.5.
In heart failure, a study showed that outcomes were the same between those with serum potassium levels less than 4 and those between 4 and 4.5. Yet, it seems that this literature has been extrapolated to everyone.
What is the concern about having a low potassium? Mainly it is the development of significant arrhythmias, which can become life-threatening. And so, I was ecstatic to see the TIGHT K randomized trial.
This was a randomized trial out of the UK and Germany, and it tested whether relaxed potassium supplementation rules were "noninferior" to tight potassium supplementation rules with respect to the development of atrial fibrillation after cardiac surgery. Atrial fibrillation is quite common after cardiac surgery, and it can lengthen hospital stays and place patients at risk for the development of stroke.
They found that, if you replace potassium only when the level decreases to below 3.6 (which was the lower limit of normal in the study), those patients do not develop more atrial fibrillation than those who got potassium replacement when the level decreased below 4.5.
What's more, the relaxed potassium strategy saved about $112 per patient, according to the study. This quickly adds up when it is applied across large populations, and this is a very easy way to preserve precious resources in the healthcare system.
I am so happy these researchers published this trial! It shows that it is OK to have a potassium that is below 4.0 but still within the normal range. I hope these authors do more studies like this in more patient populations, so we can finally stop giving potassium - which is not benign, by the way - to patients who do not need it.
