Month: January 2015

One Troponin is All You Need

The newer, highly-sensitive troponin assays have their pitfalls.  Specifically, specificity.  However, most of the issues associated with diminished specificity are iatrogenic – transitioning from use of troponin as a dichotomous test that used to tell us “yes” to one that does a better job of telling us “no”.

This is a pre-planned substudy as part of a prospective evaluation of patients with chest pain and non-diagnostic ECG, prospectively evaluated for acute coronary syndrome.  These authors looked at hsTnI, but, rather than using the 99th percentile as their cut-off for “negative”, they evaluate the utility of an undetectable hsTnI – which, for this Siemens assay, was <0.006 µg/L.  Based on 1,076 patients evaluated, 647 had an undetectable troponin at initial presentation.  Of these, 4 patients had a subsequently detectable troponin and were adjudicated as acute MI, 3 of which had coronary artery disease and received revascularization.

What was special about those four patients?  Each of them presented within 2 hours of symptom onset.  All told, 399 patients presented more than 2 hours after the onset of symptoms, had an undetectable troponin, and were free of MACE at 7 and 30 days.  These results are generally consistent with other work looking at the sensitivity of the (duh) highly-sensitive troponin assays – capable of conferring an excellent instant rule-out.

So, if you’re asking the question – does this patient have an acute MI? – you’re in good shape.  However, if you’re using highly-sensitive troponin assays, you’ll also need to be smart about appropriately interpreting the indeterminate range – or your patients will ultimately suffer as a result of decreased specificity and downstream over-testing.  Lastly, this is only valid as a diagnostic tool for acute MI – the extent to which it provides prognostic or diagnostic information regarding acute coronary syndromes, coronary artery disease, or ischemic heart disease is still being refined.

“Does undetectable troponin I at presentation using a contemporary sensitive assay rule out myocardial infarction? A cohort study”
http://www.ncbi.nlm.nih.gov/pubmed/25552547

Opiates Are a Gateway Drug … to Opiates

By definition, essentially, all prescription drug abuse starts with a prescription.  Diversion and misuse cannot occur without a physician – well-meaning or not – at the start of the chain.  And, not only are physicians the pipeline for maintaining supply in the community – they’re also one of the sources for minting new abusers.

This simple retrospective study looked at Emergency Department patients receiving treatment for an acutely painful condition.  Patients were then distilled down into those without prior use of opioids within the previous one year – the so called “opioid naive” for the purposes of this classification.  Approximately half of these patients received an opiate prescription at discharge.

Two interesting observations:

  • Those receiving, and filling, a prescription for opiates were far more likely than those who did not receive a prescription – 17% vs. 10% – to fill another prescription for opiates in a 60-day time period one year later.
  • Those receiving, but not filling, a prescription for opiates had only an 8% prevalence of filling another prescription for opiates a year later.

Within the limitations of the selection biases inherent to a such a retrospective evaluation – the message is reasonable: beware the downstream harms of every opiate prescription provided.

“Association of Emergency Department Opioid Initiation With Recurrent Opioid Use”
http://www.ncbi.nlm.nih.gov/pubmed/25534654

Your Lungs Will Not Explode

Gas laws dictate the relationship between pressure and volume.  As pressure decreases, the volume of a gas increases.  If that volume of gas is a pneumothorax … the Aerospace Medical Association and the British Thoracic Society feel such hypobaric conditions, e.g., commercial air travel, are absolutely contraindicated.

But, does the small difference in atmospheric pressure – ~550mmHg versus 760mmHg – truly induce clinically important changes, such as tension physiology?

These clinicians in Salt Lake City enrolled patients with recently-treated traumatic or iatrogenic pneumothorax and subjected them to 2-hours of simulated air travel using a hyperbaric and hypobaric chamber.  Twenty patients were included, 14 of whom received tube thoracostomy for their pneumothorax, with 11 still having residual pneumothorax visible on chest x-ray.  Two types of simulated flights were performed – an initial 554mmHg phase intended to simulate aircraft cabin pressure, and a second phase using 471 mmHg, intended to compensate for the low baseline barometric pressure of 645 mmHg present in Murray, UT.

Did the volume of pneumothoracies increase as atmospheric pressure decreased?  Yes.  Did lungs explode?  No.  Did patients require emergency needle decompression?  No.  Did patients have any change in vital signs?  No.  And, all pneumothoracies returned to their baseline size following return to baseline atmospheric pressure.

Is this durable, generalizable, slam-dunk data regarding prospective guidance for air travel following small pneumothoracies?  No.  But, it’s a lovely bit of dogmalysis demonstrating an unnecessarily absolutist approach certainly is inappropriate, and doesn’t accurately describe the true individualized risks.

“Cleared for takeoff: The effects of hypobaric conditions on traumatic pneumothoraces”

A Happy New EMLitOfNote Year!

Hello, New York City!  You win – with a commanding lead, 4.4% of all visitors to the site, over the past year.  But, after NYC, you have to go down to #5 to get to another U.S. city, and only 4 of the top 10 are ‘merican:

  • New York
  • Sydney
  • Melbourne
  • London
  • Chicago
  • Houston
  • Brisbane
  • Philadelphia
  • Perth
  • Toronto

Australia, I love you too.

What were some of the top posts of the past year?

Pre-Hospital Furosemide – No, No, Also No
It’s almost certainly net harmful for paramedics to give furosemide in the pre-hospital setting.

TMJ Dislocations: A Better Mousetrap?
The syringe technique for relocating mandible dislocations.  Cool.

The Scandal of Dabigatran – A Summary
Unless you’ve been living under a rock, you know we’ve been lied to about Pradaxa.

Azithromycin, the World’s Most Effective Antiviral
What’s more insane than one mostly useless treatment for influenza?  Trying to prove the value in adding an antimicrobial to the mix.

Go Ahead, Age-Adjust the D-Dimer
If you’re going to use D-Dimer to rule-out PE, you probably won’t miss much if you use higher cut-offs in the elderly.

The tPA Cochrane Review Takes Us For Fools
The updated tPA Cochrane Review is just another biased document failing to acknowledge the limitations of the underlying data.

My ACEP tPA Policy Critique
The ACEP Clinical Policy regarding use of tPA was controversial, to put it mildly.

Bayesian Statistics: We’re Dumb as Rocks
How many patients have a disease with prevalence 1/1000, given a test with 5% false positives?  Banana.

Of course, a few great posts from the past couple months simply haven’t had enough of an internet lifetime to accumulate pageviews, including Jerry Hoffman Debates Greg Albers on tPA, the ARISE study, and MR-CLEAN.

Also, a special thanks to Anand Swaminathan, Rory Spiegel, and William Paolo for their guest posts this year.

Thanks for visiting!  I hope you enjoy keeping up and poking holes in the newly published literature as much as I do in 2015!