Monthly Archives: March 2014

There’s an app for that

When you’re out in the sticks, you want to travel light. This limits the amount of diagnostic supplies you can carry, and generally wilderness medics trend towards carrying supplies that can do multiple jobs. Thus, necessity being the mother of invention, these authors wanted to use an item they already carry in a novel way.

Most of us diagnose fractures with radiography. While x-ray machines may be portable, I’ve yet to see any manufacturers produce an off-road version. Prior studies have shown relatively decent sensitivity and specificity using tuning forks and stethoscopes, by way of listening for a difference in vibratory transmission down the length of the bone. The idea is that a fracture will stop propagation of the waves, or at least reduce them significantly. Then you can compare to the unaffected side and identify an occult fracture.

Since carrying a tuning fork in your pack adds weight without a large amount of utility (maybe you can make a mouth harp out of it at the campfire), the authors tried to find another commonly carried object that could reliably produce a constant vibration. What they came up with was an iPhone 3S using the iVibe app. Not wanting to break the bones of alive patients, they used a cadaver model for the fractures, and a convenience sample of 27 EM residents and 1 EM attending.

Sadly, they weren’t very accurate, with a sensitivity of 73% and specificity of 83%. This is lower than the multiple tuning fork studies, and would probably be even lower in the austere environment, with outside noise, and clothed patients. The authors themselves say this is a pilot study that needs further validation. I would argue that as more people carry ultrasound devices, it will supersede the utility of lower sensitivity testing.

I wouldn’t go out planning on using them for that purpose, but if needed, it is better than nothing. And hey, if it keeps you from calling a helicopter to evacuate someone, or allows you to call one appropriately, then maybe it is worthwhile. At least you’re already carrying the phone and the stethoscope.

Novel Approach to the Diagnosis of Fractures in an Austere Environment Using a Stethoscope and a Cellular Phone
http://www.ncbi.nlm.nih.gov/pubmed/24393702

So you’ve pulled off a deer tick

What’s the next step? Perhaps you know the recommendation for a single dose of 200mg of doxycycline for prevention of Lyme disease, but is it based on solid evidence?

Well, the study at hand enrolled 506 patients, which they then pared down to 482 that had the ticks positively identified by an entomologist. They had this many because their power calculations determined they would need a sample size of 129, but once their data indicated that nymphal ticks were highly correlated with erythema migrans, they extended the study to the point it lasted almost 10 years. Due to the length of the study, 6 patients were enrolled twice due to being bitten in separate years.

Even with the large sample size only 9 patients developed EM, with 8 of these occurring in the placebo group. This allowed statistical significance even with relatively low prevalence. This gives them an efficacy rate of 87%, but unfortunately the 95% CI is 25-98%.

It seems like it works, and the theoretical risk of a single dose of antibiotics is fairly low. However, 30% of the doxy group had side effects from that single dose, usually nausea and vomiting.

Based on this study, giving 200mg of doxycycline as a single dose within 72 hours of tick removal appears sensible. You diminish the risks of developing erythema migrans, while also preventing a prolonged course of antibiotics. My only warning would be to tell patients to continue to watch for symptoms of Lyme, as prophylaxis is not 100%.

Prophylaxis with single-dose doxycycline for the prevention of Lyme disease after an Ixodes scapularis tick bite
http://www.ncbi.nlm.nih.gov/pubmed/11450675