HyperK and Shades of Grey: Myths and Facts about Hyperkalemia Part I

Happy New Year everybody!

We start 2013 with a continuation of our discussion about the field treatment of hyperkalemia. 

It might be helpful to review the first part of the discussion," HyperK and Shades of Grey" here

We are fortunate to have as a guest contributor Dr. Brooks Walsh of the Mill Hill Ave Command blog. An advocate of prehospital medicine, Dr. Walsh offers shares "Myths and Facts" of hyperkalemia with us. My sincerest thanks him for his valued contributions! 

I asked Dr. Walsh why he thought hyperkalemia presented such a challenge for EMS providers. Here is what he had to say:

"The recognition and treatment of hyperkalemia is one of those areas in medicine where, despite strong & clinically relevant results in the literature, the "usual practice" keeps kicking along. This is like a lot of areas in medicine, true.

But rather than curse the darkness, I wanted to go over some newer perspectives on hyperkalemia. Now, I don't want to simply reiterate all the great material that Dr. Weingart talked about on EMCRIT, so you really ought to download his great podcasts on the treatment of hyperkalemia and on why Kayexalate is likely ineffective, if not outright dangerous. The podcasts are real short, so just play them right now.

With that said, I'd like to review a few topics in hyperkalemia that deserve more attention:

 

Myth: Dialysis patients tolerate hyperkalemia better than other people.

Medicine is funny. I mean, there are "facts" that "everyone knows," but that are surprisingly hard to prove in studies. This is sort of one of those kind of facts, with very little evidence, and plenty of "real world" experience. Should we continue to believe it?

Maybe. It kind of depends on what we mean by "tolerate." If we mean "don't show ECG signs of hyperkalemia," then maybe dialysis patients do "tolerate" hyperkalemia better than other people. 

It's kind of hard to answer this definitively, though, since ECG signs of hyperkalemia, especially in the moderate range (e.g. < 6.5), are often absent on the ECG on all patients. We just don't see that many patients, dialysis or no, with severe hyperkalemia. Even in a study that looked only at dialysis patients, the vast majority had a K < 5.2, and ECG changes were accordingly infrequent.

But it may also be that dialysis patients, in fact, do show fewer signs of hyperkalemia on the ECG than do other people. A study done back in 1967 looked at dogs that received IV potassium slowly or quickly (but ending up at the same blood level). The faster infusions caused more ECG and hemodynamic effects. It is possible that ESRD patients, with a presumably slow increase in potassium levels, show fewer ECG changes than, say, a patient with acute rhabdomyolysis.

But the ability to avoid ECG changes isn't the "tolerance" we care about in hyperkalemia - we really care about the potential for patients to go into cardiac arrest. Hyperkalemia, regardless of ECG signs, puts the patient at risk for fatal arrhythmias. If you have either lab results or ECG evidence of hyperkalemia, that patient needs to be treated immediately – on that, most experts agree. I couldn't find any mention in the literature that suggests otherwise. For example:

                   "We emphasize that despite the absence of ECG changes of hyperkalaemia in ESRD, hyperkalaemia is still a     potentially life-threatening condition." –Aslam 2002

Or

"Some experts advocate calcium administration in patients whose serum potassium is >6.0–6.5 mm, even in the absence of EKG changes." –Putcha 2007 

 

Myth: If the ECG doesn't show QRS widening, then the patient is at low risk.

Some clinicians are under the impression that you can wait to treat the hyperkalemia until the QRS is "incredibly widened," showing huge sine-waves.  An ECG that shows "just T-waves" is presumably at lower risk, in this view.

Except that's not how it works, according to the experts. As these nephrologists explain:

                 "Five medical textbooks (two nephrology, two internal medicine, and one emergency medicine) advocate calcium gluconate in all hyperkalemic patients with EKG changes. "

Or this critical-care nephrologist:

                "It is apparent that neither the EKG nor the [potassium level] alone is an adequate index of the urgency of hyperkalemia,… hyperkalemia should be treated emergently for 1) K > 6.5 mmol/L or 2) EKG manifestations of hyperkalemia regardless of the [level]." –Weisberg 2008 "Management of severe hyperkalemia"

We asked Dr. Smith about his experiences with this topic, whether he has seen patients arrest without going through the ECG transition to widened, sine wave ECGs. His response as well was that "I have seen v-fib with peaked T waves only" on the ECG.

Stay tuned for "Myths and Facts Part II"!

 

4 Comments

  • Here's a clinically relevant finding that expands upon the second myth:

         "Young subjects, with otherwise normal hearts, seem able to retain a normal QRS duration with even high levels of potassium [e.g., 8.0 - 8.9 meq/L]; whereas the elderly widen their QRS complexes and sometimes lose all sign of a distinct ST segment so that a virtual straight line–from nadir of S to apex of T–results in a 'Z-fold' pattern"  (1)

    Source / Reference:
    1.  Marriott HJL. Emergency Electrocardiography. Naples: Trinity Press, 1997, p. 112-113.

  • David Baumrind says:

    Excellent finding…thanks Jason!

    Definitely expands upon the myth!

     

  • Brooks Walsh says:

    It's the first I've heard of the role of age in the ECG manifestations of hyper-K.
    My first thought is "I have two books by Marriott; he's a smart guy!" My second thought is that there are so many confounding variables beteen the young and old patients (etiology of hyperkalemia, degree of chronic renal impairment, comorbidities, etc.) that it would be almost impossible to directly test the hypothesis.
    I don't have that particular book by Marriott – does he give a reference to a study?
    Thanks for reading!

  • Sorry Dr. Walsh.  Unfortunately Dr. Marriott did not cite any evidence-based publication.  It's entirely possible this may have been an independent observation he made throughout the course of his long medical career.  I tried to find any reference to this claim in all of his other textbooks but was unable to find any.  It should be noted that the ages of the "young" patients in Dr. Marriott's ECGs were 29 and 30-years-old.

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EMS 12-Lead

Cardiac Rhythm Analysis, 12-Lead ECG Interpretation, Resuscitation
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Tony
59 year old male: chest pressure – Conclusion
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