Forensic medicine: Gun Shot Wounds

Depending on where you are working, gun shot wounds (GSWs) may be a rarity or so common that almost everyday you will see a patient with a GSW in the emergency room. GSWs generally have a bad prognosis with a high incidence of gangrene and anaerobic infection. On top of that there is likely to be a criminal investigation regarding the shooting, so knowledge of how to describe a lesion and preserve evidence is incredibly important. 

When talking about GSWs you first need to consider the construction of the bullet and the mechanics of gunfire. Projectiles are most often made of lead and may be jacketed or not, the jacket is often made of an alloy like brass (copper and zinc alloy). Here in Italy, unjacketed projectiles are illegal.

The bullet contains the projectile, jacket and a small amount of gunpowder which produces the explosion behind which propels the projectile.  The gunpowder usually contains the following chemicals; Barium, Antimony and Lead. These chemicals are what forensics pathologists look for when they look for evidence, they can sometimes even type the gun with knowledge of the chemical ratio.

On pressing the trigger there is a small explosion and most of the gunpowder is burnt to produce gas, however some powder will not burn and be fired along with the projectile.

So when the bullet exits the muzzle of the gun, gas and small fragments of unburnt powder also exits the gun like a kind of small pepper spray, there is also residue and grease from the barrel that is fired along with everything else.

A shotgun bullet is slightly different in that the projectile is actually a collection on small pellets (the shot) as the pellets leave the barrel of the gun they spread out so a GSW from a close range shotgun shot (it forms a large hole) is different to a long range shotgun shot (many small holes).

Bullets may penetrate the body and may exit or stop within the body. They can ricochet off bone and some are actually made to bounce more in the body cavities (nasty). The bullet entry hole is usually much bigger than the actual bullet because as the bullet travels through the air it spins and oscillates (again some are designed to do this more, for more damage). It can sometimes be very difficult to tell the difference between the entrance and exit wound because of this. Bullets may even break and leave multiple exit wounds from a single a entry point or multiple entries. Usually an entrance wound is a round discontinuation with no loss of tissue. The residues from the gun will be on the skin surface around the entrance wound. Its important to use tape or a stub to collect the residue from the skin surface. In fact you should keep anything used to clean the wound and the victims clothes as well as they will contain very important residue.

There are four things you can see with a GSW and it depends on the distance of the victim from the gun.

•        Entry/exit wound

•        Tattooing

•        Smoke stains

•        Burns.

At long distance there will be only the entry and exit wounds from the bullet. As the victim is closer to the attacker tattooing can be seen caused by small pieces of unburnt gunpowder that produce small black spots (penetrating skin) or red spots (excoriations).

At even closer range the smoke from the gun can produce smoke stains on the skin, colouring the skin around the entry wound black. At even closer range than this the flame from the gunshot can burn the skin.

All these residues are collected and mapped and compared often with shooting experiments to determine firing range and gun type (each gun has its own distinct pattern of residue spread).

If the gun is fired at point blank on contact with the skin, a so called contact wound is produced. This is often stellate in shape, the flaps are caused by the pressure of air as it escapes around the gun, it can look like a blunt force injury so be careful in your description.

If the bullet penetrates a flat bone it can be easy to spot the entry and exit side from bevelling of the bone edge (the bone will be bevelled on the exit side of the bone and diameter of the hole as the entry side has a smaller diameter to the exit side. Exit wounds can be very messy and may sometimes look like a blunt force injury, sometimes if the victim is against a surface where the bullet exits eg. A wall, material from the wall behind can be found in the wound. 

In terms of treatment, GSWs must be treated with thorough debridement and delayed primary suture in the same way as battle injuries (future post). It must never be closed straight away! The debridement should be extra thorough taking extra care to remove fragments of clothing and soil from the wound. 

Clinically you can divide GSWs into low velocity and high velocity injuries. Low velocity injuries can cause little soft tissue damage as long as they remain stable (remember that oscillation and cartwheeling of the bullet will cause more damage). High velocity injuries act like a small explosion and many tissue planes are separated providing easy access for infections. There is often foreign material in the wound further enhancing chance of infection. 

St Emlyn's Emergency Medicine Blog

Shout out to this fantastic blog! Based out of the Manchester Royal Infirmary, St Emlyn's is an emergency medicine blog full of great insights into life as an EM doctor. There are lots of #FOAMed resources for those who are jumping on the social education bandwagon (a more modern version of medical education).
I particularly enjoyed this recent post about the risks of training in EM and why some Dr's quit and how to avoid those lows. @baombejp brings up the following points:

• Dont expect results too fast, take the SMART approach
• Dont fear failure, there are three ways you can react to a setback: you fly, you dive, you thrive
• With regards to the future find the right balance between competence and confidence when progressing and be careful of the unknown'unknowns (the things you dont know you dont know ha)
• Have a life! why have a job if you don't have a life
• There will be ups and downs, find someone to talk to about it

The blog is full of great posts, I enjoyed reading this morning about this consultant dealing with his junior knowing more than him and the following teaching tips. 

Pseudoaneurysms

Interesting case in the emergency theatres today. 40yr old male with a large hematoma in the left thigh. One week ago he underwent a cardiac procedure that required the use of an intra-aortic balloon pump.
Have an idea yet?
Insertion of an IABP is through a catheter in the femoral artery, if this puncture is misplaced or compression afterwards to close the wound is insufficient then the artery can continue bleeding into the thigh and form a pseudoaneurysm.
This chap had a pseudoaneurysm for exactly that reason, in fact you could see on doppler-ultrasound the hole was in the superficial femoral artery. The superficial femoral artery is a common origin of pseudoaneurysms because when you apply compression to the leg after cath lab or interventional radiology procedures for hemostasis, the femoral bone is not behind (as it would be for a standard common femoral artery puncture), so compression is ineffective.

What is a pseudoaneurysm?
Usually the result of injury to an arterial wall a pseudoaneurysm is an aneurysm lacking all three normal elements of an arterial wall. Pulsatile flow from the ruptured artery dissects the neighbouring tissues and forms a false lumen or sac containing the hematoma.

Risk factors: are any intra-arterial puncturing procedure, which increases in proportion to the size of catheter (larger catheters having higher rates of pseudoaneurysm formation). The risk is increased when the puncture site is not the common femoral artery eg. external iliac, superficial femoral and profunda femoral arteries.

How do you diagnose a pseudoaneurysm?
Most common presentation is pain and swelling in the groin area. Often the pain is disproportionate to the pain expected from the procedure. Large hematomas can compress neighbouring nerves and veins, and even cause skin necrosis.
Conduct peripheral pulse examination, ankle-brachial index and ultrasound scan of the area.
The best intial diagnostic test is a duplex ultrasound scan (7mhz linear probe). you can find and measure the diameter of the pseudoaneurysm neck.
If a doppler US scan cannot be performed the next step is a CT scan with contrast.

Management and treatment
So after support and resuscitation (a ruptured pseudoaneurysm can lead to catastrophic bleeding).
there are four main treatments:

1. Observation: for small pseudoaneurysms, less than 2cm. these will often spontaneously heal within a few weeks. keep monitoring with regular ultrasound scans. disadvantages include prolonged hospital stays and restricted activity.
2. US-guided compression: very variable success rates, the compression has to be maintained for at least 15minutes, aim for 20minutes. the probe can be used to target the pseudoaneuryms neck accurately. disadvantages include the fact that it not tolerated well and can be challenging. 
3. Percutaneous thrombin injection: guided by US thrombin is injected into the pseudoaneurysm cavity for immediate thrombosis. the real risk of embolism limits the procedure to pseudoaneurysms with a neck smaller than 4mm. often a well tolerated and successful procedure it does require anticoagulation therapy. 
4. Open surgical repair: Best for patients with complications or contraindicated to non-surgical management. open surgical repair allows direct visualization and control of the bleeding with suturing of the puncture site or patch angioplasty. hematoma can be evacuated and compression symtoms relieved. there are of course risks with any surgical procedure with  wound infction, lymphocele, radiculopathy and myocardial infarction topping the list. (make sure you check both sides of the artery).

So our patient had intially complained of a small thigh hematoma a few days after the cardiac procedure, he was infact in ITU with respiratory problems (complicated history). The surgeon had a look and since it was small and also considering the state of the patient, opted for the observation approach. so four/five days later the hematoma had expanded rapidly and considering the blood loss and size, open surgical repair was the best option. Operation went well, chap is doing fine. the hole was easily controlled with a controlled stitch and the hematoma evacuated from the anterior thigh and inguinal area. 

(pseudoaneurysm after arterial puncture to the superficial femoral artery)

Haematemesis

Haematemesis (vomiting blood) can present as either bright red in appearance (a medical emergency, suggesting an acute bleed) or a dark granular so called 'coffee grounds' (suggesting the bleeding is modest or has already ceased).

Causes of Haematemesis:

• Peptic ulcer disease: most common cause, often epigastric pain a well. Most often due to Helicobacter infection or NSAID use. 
• Upper GI malignancy: patient will often have fatigue, weight loss, anorexia and early satiety accompanying symptoms. 
• Varices: formed with portal hypertension when blood is trying to find routes to avoid the liver, most commonly with hepatic cirrhosis.
• Mallory-Weiss tear: characteristic history of forceful vomiting with haematemesis following (intial vomiting clear of blood). 90% of these will heal spontaneously.
• Gastritis/Duodenitis: consequence of Alcohol abuse or NSAID overuse. nausea and epigastric pain common.
• Oesophagitis: consequence of GERD. History of heartburn typically. 
• Dieulafoy’s lesion: developmental lesion, an unusually large (5-10mm) submucosal artery in the stomach wall. The pulsatility of which causes it to eventually erode through the stomach wall and perforate into the stomach. 
• Aorto-duodenal fistula: history of recent aortic surgery. 

Management, what to do:

The priority is resuscitation, patients with haematemesis may present in shock. So ABCDEs first. If a patient does present with shock or bright red haematemesis then after they are stabilised they need urgent upper GI endoscopy.
Get urgent CBC, U+E, coag screen, cross match and LFTs 
Varices have a high mortality rate and may be suggested by known chronic liver disease or characteristic signs if liver disease.
If patient has characteristic history of a Mallory-Weiss tear then endoscopy is not needed.
If active bleeding is not suspected and patient is stable, then take a full clinical history and exam. Suspect first gastritis, duodenitis or oesophagitis and pay attention to signs of malignancy.
If the diagnosis is not obvious consider inpatient endoscopy.