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I’m finally getting around to the some of the good articles on ED pain management that appeared this summer. The first was in the August 2006 Annals of EM, an article by Gallagher, Esses et al. entitled, “Randomized Control Trial of Morphine in Acute Abdominal Pain.” The authors tested the oft-repeated dictum that morphine affects diagnostic accuracy, measuring pain on a 0-100mm visual scale in a prospective double-blind random trial, giving 0.1 mg / kg of IV Morphine sulfate or placebo (ouch!) with an endpoint of “diagnostic accuracy” (ie, comparing the provisional diagnosis made by an emergency physician in 15 minutes after the agent is given, vs. diagnosis at six or more weeks of followup.)

They randomized 78 patients into the morphine arm, 73 into the placebo group. After fifteen minutes, the patients who got morphine changed their pain rating from 98 to 65, on average, whereas the placebo group went from 99 to 97. Diagnostic discordance occurred 11 times in each group, meaning that accuracy wasn’t affected by analgesia.

The dictum to avoid analgesia in abdominal pain dates to a 1921 proclamation by Sir Zachary Cope — a good example of emminence-based medicine. Maybe this warning was appropriate in the age before antibiotics and CT scanners, but we now have eleven trials in the last twenty years showing that Cope doesn’t cut it.

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Drs. Nelson, Baumlin and Basavaraju wrote up an interesting case that was featured in the Correspondence section of the September 2006 Annals of Emergency Medicine (Vol. 48, No. 3, pp339-340). The letter was titled, Sonographic Diagnosis of Axillary Artery Aneurysm Presenting As Painful Axillary Mass and features some vivid photos. The summary is excerpted below:

Although the assessment of abdominal aortic aneurysms has long been a standard indication for bedside ultrasound, this case represents a previously unreported presentation (possible abscess) of a rare condition (axillary artery aneurysm). In this case, rapid assessment using bedside ultrasonography was able to unequivocally exclude abscess from the differential diagnosis, and allow the proper consultants to become involved earlier in the course of the ED visit. Furthermore, identification of the axillary artery aneurysm led to obtaining a computed tomography scan which revealed a larger and potentially lethal aortic aneurysm. Although it is unlikely that an emergency physician would have attempted to incise and drain a pulsatile “abscess,” it is useful to distinguish a mass impinging on a vessel from a mass which is a vessel.

Incidentally, the letter to Annals immediately following this one is from a former classmate. It is indeed a small EM world.

Given our recent guest speaker and spirited discussion, I thought it would be worthwhile to discuss a review from the September ‘06 Annals: the Use of Noninvasive Ventilation in ED Patients with Acute Cardiogenic Pulmonary Edema. We know ACEP will soon be publishing a new clinical policy on heart failure, it’ll be interesting to see how their interpretation of the literature squares with that of Collins et al.

And, even though we’ve all seen these masks in action, it’s probably worth repeating that CPAP is continuous positive airway pressure, regardless of inspiration or expiration. CPAP has been shown to reduce the work of breathing and decrease LV afterload, while maintaining cardiac index.

Noninvasive positive pressure support — sold under the trade name BiPAP – works similarly, but with less positive pressure during exhalation; it’s inspiratory pressure support plus PEEP (this variant called C-Flex kind of demonstrates it, but with an exhalation pression of zero). In theory, BiPAP should reduce the work of breathing even more than CPAP, and physiologically would seem to be of more benefit in obstruction airway disease (asthma, COPD).

For a more in-depth review of the mechanisms, indications and contraindications, check out this eMedicine article. For a practical guide with some key citations, see EMCrit.org. Basically, both CPAP and BiPAP work in part by raising intrathoracic pressure, which decreases preload AND afterload (which probably benefits patients with cardiac dysfunction). Neither therapy is definitive for cardiogenic pulmonary edema; they’re temporizing measures while your nitrates and diuretics kick in.

Previous studies have shown that CPAP decreases intubation rates in patients with acute cardiogenic pulmonary edema (ACPE). A systemic review in 1998 bolstered the claim, but that review included trials with non-ED patients.

The first big BiPAP study (Mehta, 1997) showed an increase in respiratory function and hemodynamic improvement compared to CPAP, but similar rates of mortality in hospital, and similar intubation rates. Plus, notably, the BiPAP patients experienced more MI! (it’s worth noting that that arm of the study received, by chance more patients complaining of substernal chest pain, and a 2004 study comparing CPAP and BiPAP showed no difference in MI).

Since then, many small trials between CPAP and BiPAP suggested no difference between these noninvasive ventilatory modes compared to standard-of-care, which other studies suggested a decrease in intubation and mortality. But this paper is the first systematic review of CPAP and BiPAP in ED ACPE patients.

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