6 - Gunshot Wounds Flashcards
Key learning points
- Understand ballistic principles of GSW
- Interpret how missile ballistics influence the pathophysiology of a GSW
- Discuss basic guidelines for management of projectile wounds
Epidemiology
223 million firearms in the US in the last century
o 2/3 of American households have a gun
Civilian injuries are common
o 115,000 GSW in 1993
o 40,000 deaths
o Second episode increased from 26% in 1987 to 43% in 1990
1 million civilians killed since 1933 ( more than in all wars combined)
Many civilian GSW are in the extremities
o 30% noted by Demetriades @ LA County Medical Center
Low or mid range velocity
o Trend is higher power and faster delivery
o Trend is for more numbers of wounds
Close range
Simpson et al – A synopsis of urban firearm ballistics (2003)
- Review of police records
- Review of cost data
- 57% of confiscated weapons were semi automatic, 11% shotguns
- 23% of surrendered weapons were semiautomatic
- Evolution between 1970 and 2000:
o More firepower
o Faster delivery - Average cost $15,000 for treatment, $40,000 for rehab per incident
Ballistics
Internal Ballistics - Bullet in the barrel
o Bullet and casing design
o Caliber
External Ballistics - Bullet flight in the air o Spinning due to riffling of the barrel o Yaw o Range o Velocity
Terminal Ballistics - Bullet hitting the target
o Anatomic site
o Tissue density
Wounding variables
- KE of projectile (velocity, mass, range)
- Transfer of energy to the tissue (design of projectile, jacketed, hollow point)
- Density of the tissue (Increased density = increased energy transfer)
More energy = bigger injury?
It’s not that easy
- KE = (M x V2) / 2
Parameters controlling ballistics
- Casing size
- Propellant
- Projectile material
- Projectile design
- Velocity
- Range
- Contact tissue density
How does a gun work?
Cartridge
o Case
o Gun powder
o Primer
Powder is ignited when the firing pin of the gun hits the primer
Hot gas expansion accelerates the bullet through the barrel
o The longer the barrel the faster the bullet
o The barrel may be rifled to induce spin of the bullet and stabilize its flight
Bullet projectile materials
- Most bullets are lead due to the high specific gravity
- Some bullets have other substances such as glues or coatings
- Bullets are non-explosive and cause damage directly by projectile energy and transfer of that energy at tissue contact
- Explosive rounds are “shells”
Projectile design - unjacketed
o Soft material is exposed leading to more deformation therefor more energy transfer
Projectile design - fully jacketed
o Bullet stays intact
o Passes through tissue
o Less energy transfer
Projectile design - hollow point
- Designed specifically to mushroom at impact
- Transfers more energy to the tissues
- Deformation at contact increases energy transfer to tissue
- Exit wound averages 27 times larger than entrance
Projectile design - soft point
o Same as hollow point
Velocity
- Velocity: this definition is completely arbitrary but is widely used to describe GSW – You must know the definition & also understand the reality and new research
- Low Velocity 2500 feet/second (30/30, 3006, 9 mm, m-16 (7.62) and other military rifles)
Range
- Energy is dissipated over time of flight
- Close range injury has higher projectile energy
- Burns may occur due to hot gasses at very close range
Tissue damage (BE PREPARED TO DISCUSS THESE PRINCIPLES)
Direct
o Laceration
o Crush
o Contusion
Indirect
o Concussion zone
o Cavitation
o Secondary missiles
Velocity
o Lower velocity allows pushing of vital structures aside
Temporary cavity
- Out ward explosion of the tissues occurs as the KE is transferred from the missile to the tissues
- Happens in both high and low velocity wounds but is greater with higher velocity
- Cavity 30 x the bullet diameter is created momentarily
- Collapse can create a vacuum
- The higher the KE and the denser the tissue the more energy is transferred
- Bullet design also has an effect
General management rules
- ABC’s
- Vascular Evaluation
- Bullet Removal
- Debridement
- Antibiotics
- We should no longer treat based solely on velocity of firearm - Transfer of energy to the tissues is multifactorial (velocity, design, tissue density)
LA County/USC Medical Center Survey
For life threatening GSW:
o Rapid transit to definitive care facility is the most important determinant of survival
o For every 10 minutes of delay, 10% reduction in survival
o Patients transported by non-medical personnel did better than those who waited for EMS
o Minimal on scene treatment seemed to improve outcomes
Injury severity scores – Reconstruct vs. amputate
- Mangled Extremity Severity Score (MESS)
- Injury Severity Score (ISS)
- Predictive Salvage Index (PSI)
- Limb Salvage Index (LSI)
- Hanover Fracture Scale (HFS-97)
- NISSSA
Multiple studies unable to scientifically validate any of the current severity scores
- Lower Extremity Assessment Project (LEAP) JBJS 2001
- Ly et al, JBJS 2008
- Togawa et al, JBJS 2005
Vascular injury
- Indication for angiography is the indication for exploration
- “Routine angiography (another time consuming invasive procedure) is no longer the standard of care in extremity GSW.” Cornwell, CORR 2003
Antibiotics
- Bullet injuries are contaminated (bullet is not sterilized upon firing, external contamination dragged inward, cavitation vacuum)
- Debridement and wound care is the most important part of preventing infection, more important than antibiotics
- When fracture is present follow open fracture protocol
Efficacy of antibiotics in low velocity gunshot fractures – Dickey et al (1989)
- Prospective investigation of antibiotics vs. wound care alone for GSW
- 73 fractures divided into the two groups
- No high velocity or shotgun wounds
- Level 2
- 1 infection in each group
- Found no value for antibiotics for low velocity GSW
Antibiotic therapy in GSW injuries – Simpson et al (2003)
- Systematic Review
- Level 1
- Antibiotic prophylaxis indicated for high energy, shotgun, and intra-articular injury
o 48 hours of therapy
o Drug choice based on injury pattern - Now distinct advantage in low velocity injury
Bullet removal
- Bullet becomes encapsulated by fibrous tissue
- Lead intoxication is not common
- Remove if:
o Intra articular
o Adjacent to vital structures
o Expected functional compromise
Debridement
- Previous recommendation was to widely excise the entire cavity for all high energy wounds
- Staged debridement similar to open fracture management is now recommended
- Appropriate debridement is the cornerstone of therapy
Shotgun wound
- Low velocity but high energy
o 1000-1500 ft/sec
o Large combined mass of “shot”
o Large amount of gun powder
o Pellets act as a single missile within 8-10 feet
o Varies with the choke design of the barrel - Contamination of the wadding
- Twice the mortality of other fire arms
- Treatment is based on principles of high energy wounds
Shot (pellets)
00 “Buckshot” o Largest (eight pellets per once) o Caries higher energy longer distance
9 “Birdshot”
o Smallest (585 pellets per once)
o Loses energy very quickly
Materials
o Most common is lead
o Water fowl shot is steel
“Choke” of the barrel
o Determines the spread pattern of the shot
Shotgun wound classification
Type I
o Penetrating Subcutaneous
o > 7 yard range
o Small shot (buckshot can penetrate at longer distance)
Type II
o Perforating below fascia
o 3-7 yard range
Type III
o Massive
o Point blank
CASE STUDY 1
- Small caliber
- Entry and exit are the same size, so full metal jacket
- Less energy transfer means that it has energy left when it exits
- Need x-ray – always
- Need to know the principles of open fracture in order to treat gunshot wounds (essentially the same thing)
True or false… More energy = bigger injury?
- It is more complicated than this
- If it goes right through a very low density area, it may not have a big injury
- Need to know velocity, mass, range
- Transfer of energy into tissue is the key factor
- The more energy that gets transferred into the tissue, the bigger the injury
CASE STUDY 2
- Very small caliber
- Exit wound is much bigger than entry wound
Hollow point bullet
- Deformation at contact increases energy transfer to tissues
Bullet design
- Tumbling bullets
- Bigger caliber, went all the way through
- So much bone damage because it is higher density energy transfer and a temporary cavity was formed
- When the round hits the bone, it causes internal explosion of the bone, expansion of cavity
- Temporary cavitation zone
- Entry and exit wounds are small, but there can be devastating damage due to cavitation
CASE STUDY 3
- Comminuted fracture of the 3rd metatarsal
- Fragmentation of metal
- Secondary missile into the toe
Classification systems for GSW
- Low vs high = no
- Gustillow and Anderson = no
- There are many different classification systems, many of which are not useful clinically
- **BEST classification system is the Red Cross Classification on War Wounds **
BEST classification = Red Cross Classification on War Wounds
- Incorporates all the important, relevant factors in treating a GSW
- ** Entry, exit, cavity, fracture, vital structures, metallic products **
CASE STUDY 4
- Entry = huge, large caliber weapon with a lot of high energy transferred to tissue
- Exit = same (huge)
- Cavitation = high cavitation due to size of cavity within the foot, much larger than the bullet itself, so we know there has been cavitation
- Fracture = yes
- Vital structures = 2nd and 3rd toes are blue due to compromised vasculature
- Metallic = bullet retained
Treatment plan for case study 4
- X-ray first
- Debride the wound
- Get all contaminated tissue out
- I & D is the first thing for treatment
- Remove all necrotic tissue
- Do not initially do a large amputation, wait and see what tissues will survive and which ones will need to be amputated – you may be able to save more tissue this way
- At 48 hours, take the 2nd toe off because it is necrotic
General evaluation
Patient o ABCs o Vascular o Tissue damage o Fracture via x-ray
Management
o Abx
o Deridement
o Bullet removal
Vascular injury
- If you have a patient with GSW and clinical evidence for compromised vasculature need vascular surgery right away, not necessarily
CASE STUDY 5
- No exit
- All energy from the bullet was transferred to the tissue
Treatment for case study 5
- Debridement
- Antibiotics for 48 hours
- Then we wait – we don’t’ widely excise
- We wait and see if it demarcates
Debridement
- Monitor and wait for tissues to demarcate
- Excessive removal of tissue initially is unnecessary
Antibiotics
Are antibiotics necessary for GSW?
o Yes if it is an open fracture
o Open fracture protocol is antibiotics for 48 hours
No if there is just soft tissue damage
o Don’t necessary need to
Bullet removal
- Bullets become encapsulated over time
- Reasons to remove it (Depends on location - in subtalar joint, you would want to remove it)
- You don’t go looking around for something because it will not release lead
- Don’t need to go in after each individual tiny piece
CASE STUDY 6
- High energy injury
- Lots of soft tissue damage locally
- Entry and exit all the same wound
- A lot of cavitation
- Certainly have fracture and compromised vital structures
Treatment for case study 6
- Conservative I & D
- Try to leave it and limit it to a hallux amputation
- Final debridement with flap once found out what would live and what would not
Summary
Energy and velocity
o How much energy has been transferred to tissue?
o Soft tissue damage is the basis of healing and infection
Ballistic principles include: o Velocity o Missile design o Contact tissue density o Range
Test questions
- All of the things that are on the test are in the prep work
- There are pictures on the exam
