Monday, September 29, 2014

Brought In By Ambulance, #2: Needle Decompression

You are on your first ride along of your EMS rotation. The first couple of trips are low acuity patients. While hanging out in the captain's chair in the darkened back of the truck as your unit patrols the streets, the steady rocking back and forth begins to lull you to sleep...

Tones drop. The call comes in, and seconds later the lights and sirens are at full blare. A few minutes of tense waiting as the ambulance courses through the neighborhood and then the rig screeches to a halt. You hear the EMS providers get out of the cab and raised voices outside. You mobilize the monitor and supply bag and wait for the back doors to open to jump out. However, when they do open, the medics & first responders quickly load up a 20-something female who reportedly was shot in the chest.

Once loaded, the EMT calls out vitals -- HR 60, BP 70/40, RR 22, O2 sat 99%. You begin your ATLS exam. Airway: midline, patent. Breathing: clear on the left, no appreciable breath sounds on the right. You palpate weak pulses in the bilateral radial wrists. You remove the patient’s undergarments and note a gunshot wound to the right parasternal area. The paramedic confirms your findings and instructs you to needle decompress the chest. “You know where to do it, right? Second intercostal space, mid-clavicular line. Here is the needle.” As you are about to impale the patient with a 14-gauge angiocatheter, you can't help but wonder why we place a needle in the anterior chest, but place the definitive treatment (a thoracostomy tube) in the lateral chest.

Clinical Question:

What is the optimal location for needle decompression of traumatic pneumothorax?

Literature Review:

For the majority of EMS agencies, it has long been standard practice to needle decompress those patients with a tension pneumothorax to allow air to evacuate -- effectively converting a tension pneumothorax to an open pneumothorax and thereby restoring respiratory and circulatory function. Currently, ATLS guidelines call for a 5cm angiocatheter device to be inserted at the second intercostal space, mid-clavicular line (2-MC). There are no validated studies supporting this practice as the optimal management. Failure is commonly reported, with published failure rates anywhere from 25-50% in cadaveric, radiologic, and clinical studies. In these studies, the vast majority of failures were attributed to excessive chest wall thickness, user error (including failure to identify to proper anatomic site), and catheter malfunction or obstruction. 

Several lines of questioning are currently being pursued in the EMS, trauma, and EM literature. As our population becomes more obese and thus the distance the needle/catheter must traverse before entering the pleural space becomes longer, can a 5cm catheter reliably reach the pleural space along the 2-MC? Does decompression at this site lead to excessive risk of damaging vital underlying structures? Is there a more appropriate site for needle decompression? Specifically, should more consideration be given to performing needle decompression at a similar site to that used during tube thoracostomy, roughly the 5th intercostal space, anterior axillary line (5-AA)?

Before beginning any such discussion, it must be noted that although a provider may know the proper site, that does not mean he/she can find it. This unfortunate fact was confirmed in a 2005 study by Ferrie et al that included 25 emergency medicine physicians, 21 of whom were ATLS certified. Twenty-two (88%) EP’s named the standard location (2-MC), but only 15 (60%) were able to accurately identify it on a human volunteer.

This is particularly worrisome given the high density of physiologically relevant and sensitive structures found in close proximity to the 2-MC. In 2003, Rawlins published a case series of 3 patients who presented with pneumothorax and were needle decompressed in the 2-MC which subsequently lead to life threatening intra-thoracic hemorrhages. The concern was that this location is very close to the subclavian vessels and internal mammary artery with its medial branches, and thus the 5-AA may be a safer approach. However, Wax et al conducted a study in which CT scans of 100 patients were reviewed and distances from potential needle insertion points to proximate soft tissue and vascular structures were calculated. They concluded the safer site was actually the anterior chest, not the lateral chest.

A further concern is that as patients become larger, the standard catheter length may longer be adequate to ensure entry into the pleural space. A study by Stevens in 2009 calculated chest wall thickness at the 2-MC in 110 trauma patients using CT scans. They concluded that using a standard 4.4cm angiocatheter would result in unsuccessful needle decompression in 50% of trauma patients in their cohort. Inaba et al took this idea one step further, comparing chest wall thickness at the 2-MC to the 5-AA. Using a 5cm needle, 42.7% of needle decompressions would be expected to fail at the 2-MC compared to 16.7% at the 5-AA. There was, on average, 1.3cm less tissue to penetrate at the 5-AA site before reaching the pleural cavity. Unfortunately, the evidence is again conflicting. Another study of chest wall thickness using CT scan data was published by Sanchez et al in 2011. A review of CT scans from 159 patients revealed potential failure rates of 33.6% at 2-MC, 73.6% at the 4th intercostal space, mid-axillary line (4-MA), and 55.3% at the 5th intercostal space, midaxillary line (5-MA), assuming a 5cm device was used. 

If switching from the anterior chest to the lateral chest would not be expected to improve success of decompression based on radiographic studies, perhaps the answer is using a longer device. A study by Chang et al in 2014 again used retrospectively-obtained CT data from a trauma cohort to estimate success of a 5cm angiocatheter versus an 8cm device, based on measured chest wall thickness as well as distance to the closest vital structure. They compared the 2-MC to the 4th intercostal space, anterior axillary line (4-AA). The chest wall thickness at the 4-AA was significantly thinner than that at the 2-MC, though in their study this did not lead to significantly different theoretical rates of success. The 8cm device was theoretically capable of reaching the pleural cavity in 96% of subjects at either location, and the 5cm device was gauged to have 66% success at the 2-MC and 81% at the 4-AA (a nonsignificant difference in this cohort). Interestingly, these authors also looked at theoretical chance of the angiocath reaching a sensitive anatomic structure. They even tried to take into account improper insertion technique by measuring distance from the chest wall to the nearest anatomic structure, even if this was not expected to be injured if the needle followed the proper course perpendicular to the chest wall. They found a relatively high theoretical risk (32%) of striking a vital structure when using the 8cm catheter at the 4-AA location -- even more concerning that this structure is actually the left ventricle. This rate fell to 9% if the distance was measured perpendicular to the chest wall, though this is still a worryingly high chance of hitting the LV even if your catheter is inserted correctly. 

All of these studies have significant limitations, most notably that their calculated success and failure rates are purely theoretical, based on idealized calculations using CT measurements of tissue depth in which "correct" anatomic positioning is assured. Thus validity of their conclusions for a provider caring for a crashing penetrating trauma patient in the chaotic prehospital environment is minimal. There is a distinct lack of real-world data regarding the practice of needle decompression. No randomized controlled trials or even prospective observational studies appear to exist in the literature.

Even taking this into account, the documented high rates of failure of "traditional" needle decompression and the theoretical advantage -- or at the least, viability -- of a lateral approach have prompted several organizations to specifically list it in their recommendations as an "alternate" site for needle decompression. Most notably, the Committee for Tactical Combat Casualty Care (TCCC), authors of guidelines for trauma care of US servicemen and women injured in combat, adopted the 4/5-AA as an alternate site in their manuals beginning in 2012. The Tactical Emergency Casualty Care (TECC) guidelines, which were created to adapt to the TCCC guidelines to tactical EMS care in the civilian realm, share this recommendation.

Take home:

- There is no validated study to support the use of the 2-MC as the optimal location for needle decompression.
- Needle decompression at the 2-MC is associated with a high failure rate, 25-50% in some studies.
- Radiologic studies confirm the viability of needle decompression using a lateral approach.
- Lack of real-world studies of needle decompression limit application of radiologic conclusions to prehospital care.
- Several trauma organizations have adopted a lateral approach for needle decompression into their guidelines and manuals.
- Use of an 8cm rather than the standard 5cm catheter may improve chance of reaching the pleural cavity, but may also increase chance of injuring vital structures such as the left ventricle.
- Prehospital providers likely need more education, preferably with high-fidelity simulators, to ensure proper understanding of anatomic positioning in both anterior and lateral approaches.

1) Emerg Med J. 2003 Jul;20(4):383-4.
2) Anesth Analg. 2007 Nov;105(5):1385-8.
3) Prehosp Emerg Care. 2009 Jan-Mar;13(1):14-7.
4) Arch Surg. 2012 Sep;147(9):813-8.
5) Acad Emerg Med. 2011 Oct;18(10):1022-6.
6) J Trauma Acute Care Surg. 2014 Apr;76(4):1029-34.
7) Needle Decompression of Tension Pneumothorax Tactical Combat Casualty Care Guidelines Recommendation 2012-05. July 6, 2012.
8) J Special Operations Medicine. 2011 Summer/Fall;11(3):104-22.

Submitted by Daniel Kolinsky, PGY-2 with additions from C. Sam Smith, PGY-3.

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