Shattering Urban Legends in Emergency Medicine.

Presented by Dr. Anand Swaminathan, NYU/Bellevue.

MEGACASE: 75 yo F with history of ESRD on HD presents to your E.D. after a looooong bus ride with unilateral leg swelling, shortness of breath, hemoptysis, and a recent history of hip surgery. Your thorough history further reveals that the patient has asthma, a severe shellfish allergy, and has had contrast reactions in the past. To make matters worse, the patient is writhing in pain on the stretcher complaining of right flank pain radiating to the groin and a history of renal calculus last year. And for some reason, this patient is still finding the time to tell you she has a “sore throat,” with fever, cough, tonsillar exudate and cervical lymphadenopathy. Oh yeah, and her throat snaps shut like a bear-trap if she has penicillin.

You just finished prepping the exam room, when…

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1.) Do patients with ESRD need emergent dialysis after receiving IV contrast?

NO

There may be a slightly increased risk of pulmonary edema with iodinated contrast secondary to higher molecular weights, but most hospitals use non-iodinated contrast now. Patients may continue their current dialysis schedule so long as they are dialysed within 24-72 hrs post-contrast administration, regardless of anuric/oliguric status. Check out wha t the American College of Radiology says:
“… Unless an unusually large volume of contrast medium is administered or there is substantial underlying cardiac dysfunction, there is no need for urgent dialysis after intravascular iodinated contrast medium administration.” ACR, version 9, pg 26. (http://www.acr.org/quality-safety/resources/contrast-manual)

2.) Is pretreatment necessary/effective in preventing adverse reactions to IV contrast?

NAH

“The efficacy of corticosteroid and/or antihistamine prophylaxis is unknown, though some have suggested this practice. However, given the likely differing mechanisms between acute and delayed reactions, as well as the extreme rarity or nonexistence of severe delayed reactions, premedication prior to future contrast-enhanced studies is not specifically advocated in patients with solely a prior history of mild delayed cutaneous reaction.” ACR, version 9, page 40. (http://www.acr.org/quality-safety/resources/contrast-manual)

3.) Ok, ok, how about flomax for renal stones? Everybody’s doing it.

Take it or leave it.

Most studies are equivocal showing no benefit. However, one recommendation that pervades the literature is that if you are going to use it, save it for distal stones. (http://www.ncbi.nlm.nih.gov/pubmed/21149761)

4.) I’ve heard pen allergic patient’s should never, ever get cephalosporins because the rate of cross-reactivity is 10%. This has to be true.

Listen, pal…

Well, when penicillins and cephalosporins were first produced, the were often made in the same factories – this 10% figure is more likely related to cross-contamination during the production process, not cross-reactivity. The actual rate is closer to 1-3%. There may be higher rates with 1st or 2nd generation cephalosporins, but 3rd generation or higher seem to be fine. Furthermore, the proportion of patients claiming to have a PCN allergy, that actually have a true PCN allergy, is 3%. Overall, the rate of anaphylaxis to cephalosporin in patient’s with a history of anaphylaxis to PCN in 0.001%.

Remember the rule of 3’s: 3% actually have it, 3% will have a reaction and 3rd gen cephalosporin or higher is best. (http://www.ncbi.nlm.nih.gov/pubmed/21742459)

Brian Hayes of UM puts it best on ALiEM:
http://academiclifeinem.com/busting-the-myth-the-10-cephalosporin-penicillin-cross-reactivity-risk/

5.) I know antibiotics can’t prevent PSGN. I get it, I know. But what about for Acute Rheumatic Fever (ARF)?

This one’s gotta be right.
As it turns out: not really. The rate of ARF is so low in industrialized nations, that the CDC does not track incidence of the disease any more. (In aboriginal populations, older thinking still holds strong; ARF remains problematic and necessitates antibiotic therapy). The risk of sequela from the disease is significantly and statistically low, and it is a self-limiting process. A Cochrane review demonstrated “resolution and improvement of pain in participants with sore throat” when comparing the efficacies of steroids and antibiotics. (http://www.ncbi.nlm.nih.gov/m/pubmed/23076943/)

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