It’s time we start to take a closer look at commonly held misconceptions and rules perceived as law!

 

1. Seafood allergy = iodine allergy = contrast allergy

1. A seafood allergy is to the tropomyosin protein (more concentrated in shellfish and crustaceans), not iodine concentration
2. Contrast allergy is a misnomer, it’s an idiosyncratic (unpredicatable, non-IgE mediated) reaction which is anaphylactoid and has, to date, resulted in no deaths

1. Schabelman & Witting. The Relationship of Radiocontrast, Iodine, and Seafood Allergies: A Medical Myth Exposed. The Journal of Emergency Medicine, 2010 39:5 701-707

1. Insurance companies do not pay for AMA

1. THEY DO!  Don’t use this as a scare tactic because it is false
2. Widger, et al (doi:10.1016/j.annemergmed.2009.11.024) did a chart review to bust this one

1. Ketamine cannot be used in head injured patients

1. Early studies proposed this myth in the 1940s and were on un-intubated patients who likely had respiratory depression, resultant increased pCO2 inducing increased ICP
2. Some studies currently posit a neuroprotective effect of ketamine!

1. CJEM 2010;12(2):154-157

1. Anesthetic with epinephrine causes ischemic necrosis in areas of non-dual blood flow

1. Tissue ischemia takes hours to set in, and is irreversible at 6-12h (think of torsed testicles, ovaries, amputated appendages, etc)
2. The half-life of epi is considerably shorter than this time period

1. Droperidol should not be used because of it’s high incidence of QT prolongation and severe side effect profile and blackbox warning!

1. Insapsine (droperidol) is a cousin of haldol and highly effective in treating acute agitation states, nausea, and psychosis
2. To date, no study has shown a direct causal relationship between the reported QTp and droperidol
3. More concerning, all claims of this effect were reported to the FDA within 48h of each other and none were reported thereafter!

1. Dig-toxic patients CANNOT receive calcium!!!

1. 161 patients with digoxin toxicity in one hospital over 17.5 years, 23 received calcium, and no one developed stone heart, whatever the hell that is!
2. Dig-toxic pt w/ hyperkalemia NEEDS calcium!!!

1. Levine M, Nikkanen H, Pallin D. The effects of intravenous calcium in patients with digoxin toxicity. Journal of Emergency Medicine. 2011; 40(1):41-46

1. Magnesium levels are accurate predictors of true cellular concentrations

1. Mag is an intracellular ion, therefore serum concentrations have no bearing on intracellular levels and cannot be used to predict total body volume
2. When in doubt, just give some Mag, it helps for SO MANY things!

1. Creatinine and GFR are real-time indicators of renal function

1. Creatinine is similar to Hb, it represents renal function 10-12h ago, and most GFR is simply an estimated calculation from Cr and does NOT accurately correlate with real-time renal function  

1. Flat or Trendelenburg positioning with a shoulder bump correctly positions a patient for direct laryngoscopy

1. Actually, a patient in the semi-Fowlers position (sitting up at about 20 degrees) with their head tilted (external auditory meatus in line with sternal notch) correctly approximates an optimal viewing angle

1.  aVR is a useless lead and should not be interpreted

1. STE in aVR has high specificity for proximal LAD occlusion >85%

1.  S1Q3T3 is pathognomonic for acute PE

1. Sens/spec of this finding for APE are extremely poor

1. Prog Cardiovasc Dis 1975 Jan-Feb;17(4):247-257)

1. Negative T waves in leads III and V1 allows APE to be differentiated simply but accurately from ACS in patients with negative T waves in the precordial leads

1. Am J Cardiol 2007;99:817– 821

1. Consider PE if 3 of following:  RBBB especially with ST elevation or T inversion in V1, prominent S waves in I or AVL, shift of transition zone to V5, Q waves in III or aVF, RAD or indeterminate axis, low QRS voltage in the limb leads, T wave in inversions in III, aVF or V1-4. 

1. Sreerama, et al. Am J Cardio 1999, 4:73

1. The most sensitive signs were tachycardia and incomplete RBBB (late R wave in aVR.  S1Q3T3 was equally present in those with and without PE 

1. AM J Cardiology 86:2000

1.  PO/IV contrast increase diagnostic accuracy of appendicitis, diverticulitis, etc.

1. Unenhanced vs enhanced CT sensitivity for appendicitis was similar (95% vs. 92%) as was specificity (97% vs. 94%) and accuracy (97% vs. 89%)
2. Numbers are about the same for diverticulitis

1.  Ultrasound has no role in the evaluation of adults with a concern for appendicitis because it is insensitive

1. Formal US: sens 89-98.5%, spec 95-99%, PPV 86-98%, NPV 96-98% (Dilley, et al; Baldisserotto et al)
2. When surgeons performed both the US and the clinical examination, they attained a sensitivity of 98
3. 2x the incidence of perforation found at time of CT as compared with US

1. Avg time of appy dx w/ CT is 7.9hrs vs US at 64min

1.  Blood at the urethral meatus is an absolute contraindication to Foley catheter placement

1. This came from an opinion piece by a Urology professor in 1955 and has lived on as dogma ever since, never to be corroborated with facts…
2. Treatment for a urethral tear is a Foley, urethral tear or dislocation seldom presents with blood at the meatus, forceful Foley placement is more likely to cause urethral damage than gentle placement in the face of known urethral injury!
3. You can attempt gentle placement once before obtaining imaging (J Trauma 2007;62(2):330)