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Thursday, September 5, 2013

One more word on needling the chest.

Of course, no sooner had I posted 4 things to know before you needle the chest, when I found a new article from Australia, just published, describing how new EMS guidelines and education improved their approach to tension pneumothorax. It describes a "new" approach to tension PTX, but also has some of the limitations of the older studies. 

"Improvement in the prehospital recognition of tension pneumothorax: The effect of a change to paramedic guidelines and education."

The authors of this study out of Melbourne had been concerned by the number of patients with a unrecognized tension PTX being brought into their hospital by EMS. Their guidelines for needle decompression evidently placed a certain amount of emphasis on certain physical signs for the diagnosis of progression to tension; e.g. tracheal tugging, subcutaneous emphysema, and JVD, amongst others. 

Realizing that these indications for decompression were vague and difficult to use in the field, they re-wrote the guidelines with an emphasis on the clinical situation most likely to present with a tension - an intubated patient with chest trauma.

On top of this, they made 7.5 cm IV needles available, as well as a 10 cm-long commercial device:

This Cook device comes with a crossguard, for effective parrying.
Fewer unrecognized tension PTXs
So the new guidelines and education worked. The rate of tension PTX that was treated by EMS went from about 66% to 90%. Put another way, the number of unrecognized tension pneumos went from 10 in one year, to 4

Since the EMS service had also started doing RSI intubations for trauma, the absolute number of tension PTXs also went up - this one EMS agency needled 81 patients in one year! (BTW, what the heck is going on in Melbourne?! That's a lot of serious trauma.)

Imagine what they could do if they had guns!

The limitations
So, how do we know that the paramedics were sticking needles into true tension pneumothoraces? 

Short answer: we don't, not for sure.

Longer answer: This has been the problem with older studies that merely reported, for example, a rate of needle decompression by medics, with no attempt at verification.  One prior study, however, used the subsequent presence of an air leak from a chest tube as a surrogate for tension PTX, and found a very low rate of "true" tension PTX - just 14% of the patients that were "needled" by EMS. An ultrasound-based study also casts doubt on the prehospital diagnosis of tension PTX.

The authors of the current paper used a "case definition" to identify tension PTX. That is, they went over all the clinical records and imaging studies, and made a best guess about what the patient had in the field. As you might imagine, this is an imperfect method, and we can only guess at the accuracy of the paramedics' diagnoses.

The bottom line
Despite these concerns about accuracy, there were fewer patients brought into the ED with a tension PTX, even as the rate of RSI, and thus positive-pressure ventilation, increased over the study period. That's a good thing, and it seems as though there was no large increase in complications. 

In the meantime, if anyone is planning a large prehospital study to look at PTXs, it sounds like Melbourne is the place for you!