Wound Management – Infection

Despite the overwhelming number of pathogenic microorganisms in the environment, and on the skin itself, there are some surprises when we look at the epidemiology of wound infection.

Leaving surgical wounds aside, most wounds occur in unsterile traumatic conditions. And yet, there is still a surprisingly low incidence of infection.

Clinical studies performed in emergency departments show a rate of infection for simple lacerations between 4.5% and 6.3%.

A large enough portion of wounds occur as bites to make it worth mentioning. Bites have a much higher potential and higher incidence of infection than the simple uncomplicated wound. The potential for infection varies considerably with the anatomical region involved and with the source of the bite. The hand for example, is much more likely to be infected than say, the lip or the cheek. The rate of infection also vary considerably with the species doing the biting! Cats are, surprisingly, much more dangerous than dogs, with an infection rate more than 10 times higher according to some studies! In all cases, early consideration should be given to the possibility of rabies exposure.

Of course, this is a battle we would never win if the presence of bacteria alone lead inevitably to infection. Fortunately, there are a number of modifiable factors that affect the likelihood of infection. Preventing the bacterial count from reaching an infective level by controlling these modifiable factors should always be one of our primary goals in wound management.

Characteristics of the Wound

When did the wound occur?

One of the most effective predictors of infection is the time elapsed between the injury and the cleaning and repair of the wound.

As a general rule, the chances of infection rise with every passing hour but there are many factors at play and many wounds remain candidates for primary closure (taped, stapled or sutured) even after several hours. Those that are relatively clean and not visibly devitalized, especially those in highly vascular areas such as the scalp, can be safely repaired 12 to 24 hours after injury. Other wounds occur in areas that are much more prone to infection, such as the hands, and need to be closed much sooner if infection is to be avoided.

Where is the wound?

There are several clinical studies that show a correlation between infection rates and specific body regions. For example, the highest rates of infection occur in the lower leg with the arms and hands in a close second place. Meanwhile, facial lacerations result in relatively few infections, probably because of the high vascularity. Perhaps surprisingly, one of the lowest rates of infection is associated with scalp injuries. Again, this is probably because of the high vascularity of the region despite the coincidentally higher bacteria count in regions with hair.

What is the mechanism and extent?

A final characteristic to consider is the mechanism of injury and the extent of the resultant tissue damage. Injuries that result in extensive tissue damage and devitalization have a particular propensity for infection. This is partly due to the anaerobic conditions that occur in these extensive injuries. Our bodies rely on the phagocytic and bactericidal activity of leucocytes to control infection but the activity of leucocytes is drastically compromised in an anaerobic environment. Crush injuries are perhaps the most illustrative example of this effect, they frequently result in extensive tissue damage and devitalization as well as profoundly anaerobic conditions. 

Characteristics of The Patient

Most of our data in this respect comes from studies of post surgical wounds but it is probably reasonable to extrapolate. We know that patients with diabetes, those receiving corticosteroids, those over the age of 50, and those suffering from malnutrition, have much higher incidence of wound infection following surgeries. It is therefore reasonable to remain especially vigilant if these circumstances exist in association with traumatic wounds as well.

Management of the Wound & Infection

Cleaning the wound is an important first step, but it’s important to consider what we are using. Cleaning a wound isn’t as straightforward as cleaning a surface in our home or even as straightforward as washing our hands. While we want to reduce bacterial count in all of these scenarios, when cleaning a wound, it is important to preserve the body’s ability to fight infection. For example, it is common to use ionic detergents, a hexachlorophene surgical scrub or a povidone iodine scrub to clean one’s hands. But, if used to clean a wound, there is evidence that these compromise our ability to resist infection.

It’s also common when repairing wounds, to use local anaesthetics with epinephrine (adrenaline). Epinephrine is used for its vasoconstrictive properties to achieve haemostasis during the repair. But, anecdotally, we know that areas with better vascularization and perfusion do a better job of resisting infection. Perhaps unsurprisingly, there is evidence that use of vasoconstrictors in these circumstances compromise resistance to infection.

Dressing wounds provides a physical barrier to prevent contamination. However, the efficacy and importance of this barrier is actually not well-established. But, in the first 72 hours wounds do appear to be more susceptible to contamination with staphylococcus aureus or E. coli. There is no reason to think that dressing the wound causes any harm. So, it is probably reasonable to apply clean or sterile dressings over the wound in the early hours. After 72 hours the importance of these dressings is probably diminished in terms of her preventing infection. There is still a role for dressings in protecting the injury and preventing re-injury.

Wound closure and repair technique can have considerable impact on the incidence of infection as well. The accumulation of haematoma or ischaemia due to poor haemostasis or a poorly planned procedure can provide a good medium for bacterial growth. Wounds that can be closed by less invasive means such as taping tend to be less prone to infection. There is also some evidence that staples have a lower infection rate than suturing. If suturing is required, it is important to monitor suture tension as excessive tension causes compression at the edges of the wound and subsequently causes ischaemia in the tissues.  The ischaemia causes an inflammatory response and damage to the tissues that cannot only increase the rate of infection but can also lead to scarring. Of the nonabsorbable sutures, monofilament nylon and polypropylene appear to cause the least amount of inflammation. Among the absorbable sutures, polyglycolic acid sutures are associated with the least infection.

References

Rutherford W. and Spence R.; Infection in Wounds Sutured in the Accident and Emergency Department. Ann Emerg Med 9:350-352, 1980.

Lindsey D. et al; Natural Course of the Human Bite Wound: Incidence of Infection and Complications in 434 Bites and 803 Lacerations in the Same Group of Patients. J Trauma 27:45-48,  1987.

Aghababian R. and Conte J.; Mammalian Bite Wounds. Ann Emerg Med 9:79-83, 1980