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

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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"!

 

Posted by on December 31, 2012 • Filed under: ems-health-safety, ems-topics, patient-management, Training, training-development • Tagged: , , , , , , ,

Top 10 myths about prehospital 12 lead ECGs

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A recent thread at JEMS Connect has reminded me how many myths are circulating about prehospital 12 lead ECGs.

1.) If you're close to the hospital, performing a prehospital 12-lead ECG is a waste of precious time.

The prehospital 12-lead ECG is an important triage tool. The closest hospital is not necessarily the closest appropriate hospital! In addition, just because you're close to a PCI hospital doesn't mean you can't save 15 minutes of ischemic time by giving the hospital early notification that you've identified a STEMI patient.

2.) Prehospital 12-lead ECG monitors are incapable of capturing diagnostic quality 12 leads.

As long as the low frequency (high pass) filter is set to 0.05 Hz (which happens automatically when you capture a prehospital 12-lead ECG) then you will record accurate ST segments. A more important issue is data quality and lead placement, which is a training issue (and a credibility issue).

3.) It's important for the ED staff to perform another 12 lead ECG to confirm that it's really a STEMI.

I don't care if the ED staff performs another 12 lead ECG as long as the cath lab has already been activated based on the prehospital 12-lead ECG and they are already taking advantage of parallel processing (for those patients who show obvious STEMI in the field). However, there's nothing "magic" or "special" about the ED's 12 lead ECG. Serial ECGs can be extremely important, but mostly for suspected ACS patients with nondiagnostic (or borderline) ECGs on initial presentation. If they're waiting for their own 12 lead ECG before activating the cath lab, then they're wasting valuable time.

4.) If ST segment elevation resolves by the patient's arrival at the hospital, then it's not a STEMI, and the patient doesn't need an emergent cath.

Should you wait for the cardiac biomarkers to come back positive before sending the patient to the cath lab? I'm not sure that's a good idea. The case I posted last month shows that even when ST segment elevation resolves by arrival at the hospital, the patient can still have an occlusive thrombus in an epicardial coronary artery.

5.) Nitroglycerin is contraindicated for patients with suspected right ventricular infarction.

Not all patients with inferior STEMI have RV involvement, and not all patients with RV involvement develop the hypotensive syndrome. Consider the vital signs, the heart rhythm, and the physical exam, and treat accordingly. Sometimes the patient just needs a preemptive fluid bolus.

Update: The new 2010 AHA ECC Guidelines say to use NTG "with extreme caution, if at all" in the setting of suspected right ventricular infarction. It's not quite "contraindicated" but that's a strong statement! What do I say? "Use your brain!"  There's no substitute for sound clinical judgment! 

6.) Prehospital 12-lead ECGs are important tools to help distinguish between VT and SVT with aberrancy.*

If you're using QRS morphology to "rule in" VT, then be my guest! If you're using it to justify giving a CCB to a patient with a wide complex tachycardia, then I think you're crazy. That's not to say that I don't capture 12 lead ECGs for all patients who present with cardiac arrhythmias, because I do. Documenting the arrhythmia is very important. Sometimes it even helps with the diagnosis. But I do not base my treatment decisions on QRS morphology and neither should you.

7.) If the hospital ignores the prehospital 12-lead ECG then there's no point in performing one.

I'm sympathetic to this view, but it's a defeatist attitude. You should capture a prehospital 12-lead ECG with the first set of vital signs, prior to oxygen and nitroglycerin. That way, when you "clean up" the 12 lead ECG prior to arrival, you can hand them a picture of what the patient looked like prior to your intervention. It's hard to imagine that a board certified EM physician would ignore that. In any case, the ECG should be made a part of the patient's record, because the cardiologist may care.

8.) It's easy to identify STEMI on the prehospital 12-lead ECG.*

Technically this isn't a myth. It is easy to identify a home run STEMI on the prehospital 12-lead ECG. However, that should not be interpreted to mean that reading a 12 lead ECG is easy, or that just because you've been taught to identify an obvious STEMI with reciprocal changes that you can read an ECG as good as a physician. You might be able to, but you probably can't. Identifying ST segment elevation on the 12 lead ECG is easy! Differentiating between true STEMI and the STE-mimics can be difficult. Sometimes very difficult.

9.) It's impossible to identify STEMI in the presence of LBBB.

Sure you can. You can use a modified form of Sgarbossa's criteria and you can perform serial ECGs. A moving ST segment suggests dynamic supply vs. demand characteristics consistent with ACS. Is it difficult? It's more difficult. Impossible? Hardly.

10.) Axis determination is "nice to know" information but you don't really "need to know" it.

That's like saying "paramedics don't really need to know how to read a 12 lead ECG." That's fine, if that's really your opinion. Just don't complain when you're asked to transmit the ECG for physician interpetation.

* Technically not a myth but requires qualification.

Posted by on April 21, 2009 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , ,