By Dr. Becker
Most of us don’t give much thought to how wounds heal, so it may surprise you to learn that it’s actually quite an intricate process. As soon as an area of the skin is injured, a series of complex biochemical events kick off to repair the damage.
Your pet’s body heals a wound in four sequential, overlapping phases:
- Hemostasis is a process that causes the bleeding to stop
- Inflammation produces the white blood cells necessary to remove bacteria and cell debris from the wound
- Proliferation is the phase in which new tissue develops
- Remodeling is a process in which collagen is remodeled and realigned along tension lines
As the final remodeling phase progresses, the tensile strength of the tissue in and around the wound increases. At three months post-injury, the strength is about half that of normal tissue, and will continue to increase to as much as 80 percent of normal tissue.
As the final phase of healing winds down, the wound becomes less red as the extra blood vessels needed for repair are removed by apoptosis (programmed cell death).
Given the complexities and fragility of the process of wound healing and the opportunities at every stage for interruption or failure, the more we can do to support the activity as it occurs naturally, the better the chances of avoiding a non-healing, chronic wound.
Negative Pressure Wound Therapy: State-of-the-Art Wound Treatment
Negative pressure wound therapy (NPWT) is a state-of-the-art wound treatment using controlled suction to remove secretions, reduce swelling, and promote growth of granulation tissue (a type of collagen-rich tissue that forms at the site of an injury). The technique is also called vacuum-assisted closure (VAC).
NPWT is typically used in the early stages of wound healing to promote recovery. It delivers continuous negative pressure to the wound at a substmospheric level.
NPWT applies two different kinds of pressure to a wound -- “macrostrain” and “microstrain” -- that support the growth of granulation tissue. Macrostrain pulls the edges of the wound closer together, causing enough slack in the skin to ultimately allow the wound to close. Microstrain develops at the cellular level and promotes accelerated growth and division of wound fibroblasts, which are cells that form the structural framework of connective tissue.
For Certain Types of Wounds, NPWT Can Replace Wet-to-Dry Bandages
For certain types of injuries, NPWT can be used in place of wet-to-dry bandages, which are used to “debride” a wound. Debridement simply means to remove dead tissue so healing can occur. Applying a wet-to-dry dressing involves putting a piece of moist saline gauze directly onto the wound. As it dries, it adheres to wound tissue. Once the gauze is dry, it’s removed, which often requires force. As you can imagine, this causes tremendous pain for the animal. In fact, it’s not uncommon for patients to be anesthetized for bandage changes.
To make matters worse, often the therapy must be repeated every 4 to 6 hours. In addition to being one of the most painful procedures imaginable for patients, wet-to-dry bandages are non-selective, meaning they harm healthy tissue while removing dead tissue. They are also bacteria magnets.
The bandages used with NPWT can stay in place for 2 to 3 days, while also permitting frequent removal of wound secretions. One study with dogs showed that formation of an adequate amount of granulation tissue, which took from 6 to 7 days using wet-to-dry bandages, took just 3 to 4 days using NPWT.
NPWT can also offer other advantages over wet-to-dry bandages, including providing a continuous moist wound healing environment, and promoting blood flow to the injury.1
Wounds That Are Good Candidates for NPWT
Not every type of injury should be treated with negative pressure wound therapy. Good candidates include clean, debrided open wounds in the early stages of healing; immediate postoperative incisions and skin grafts; and open peritoneal drainage.
Other considerations for this type of therapy are that the pet typically must be hospitalized over the course of the NPWT treatment (which should be no longer than 7 days). Also, NPWT doesn’t debride the wound – debridement must be done surgically before the bandage is applied and then as needed during the course of treatment.
If, heaven forbid, your own furry family member should be injured or develop a significant wound requiring treatment, you might want to discuss the feasibility of negative pressure wound therapy with your veterinarian.