After completing this unit the student should be able to:

• Recognize and understand the stages of wound healing

• Know various clinical states in patients that affect their ability to heal

• Know the basic classifications of wounds

• Recognize the various types and causes of wounds that animals experience

• Understand how the wound classification determines wound care

• Know the steps taken in wound care

• Understand the methods of wound closure

• Identify passive vs. active types of drains

• Understand the indications for drain use

• Remove a drain properly

• Understand the indications and use of wound dressings

• Recognize complications in wound healing

In this unit, we will be reviewing concepts about wounds and basic wound care. The veterinary technician plays an integral role in wound care, not only at the time the animal is first presented, but also throughout the healing process. The technician is also often expected to provide client education regarding wound management.

Click on the photos to see an enlargement of the images.

Sutures and bandages are covered in a separate section.

McCurnin D and Bassert J: Clinical Textbook for Veterinary Technicians 6th edition, Chapter 4,  pp. 1230-1235, 1243-1250, and 1001.

Writing assignment is at the end of the lesson.

Stages of Healing- The stages of healing occur sequentially but may overlap in time. Healing may also occur at different rates in various regions of the same wound. The stages of healing are the inflammatory, debridement, repair, and maturation phases:

• Inflammatory phase (6-8 hours)- There is immediate vasoconstriction and then vasodilation. A clot is formed at the site of injury and some plasma like fluid is produced. Erythema, swelling, heat and pain develops to some degree.

• Debridement phase (6 hours to 5 days)- The inflammatory process stimulates cellular activity that results in the production of exudate and there will be a discharge from the wound. Necrotic debris, white blood cells, and tissue fluid are removed from the wound by this activity and so the discharge has a cleansing effect. The "pus" may be sterile or may indicate bacterial infection. Cytology may be performed to differentiate normal discharge from infectious discharge to determine proper wound care at this stage.

• Repair phase (starts at 3-5 days and lasting 3-6 days)- Granulation tissue forms to fill the defect and epithelium begins to form along the edge of the wound. The granulation tissue starts to contract and the wound becomes smaller and smaller in diameter.

Granulation tissue fills the wound defect and enables epithelialization. New epithelium can be seen initially along the edge of the wound as a white or light pink smooth border:

    Day 6

    Day 11

Although we like to see granulation tissue, many owners are very disturbed by its appearance. Healthy granulation tissue is red and shiny and bleeds easily, but it is not painful and infection is unlikely to occur. However, to a lay person, granulation tissue looks like something bloody and slimy that is seen on a monster in a horror movie. Therefore, many technicians prefer to change a bandage out of the owner’s sight until they are sure that the owner knows what to expect. Technicians often have the role of comforting the owner while explaining the optimistic meaning of granulation tissue and showing the owner where the epithelium or "new skin" is forming along the edge.

• Maturation phase (starts at 17-20 days and lasting up to 2 years)- the collagen fibers in the connective tissue are realigned and the capillaries decrease. The scar becomes pale and less noticeable.

Wound strength (Figure 4-1 in McCurnin)

• 0-5 days- There is very little strength during inflammatory and debridement phases

• 5-21 days- Strength increases during the repair and maturation phases

• 21+ days- Strength may increase slightly during the later maturation phase as the scar matures. But the final strength is usually about 20% weaker than the original tissue.

How long after surgery are sutures removed from veterinary patients?

What degree of wound strength do you think the wound has developed by the time the sutures are removed?

And does this mean the animal has enough wound strength to resume normal activities?

Wound care is dictated by the condition of the tissue at the time of presentation. The major classifications of wounds are clean, clean/contaminated, and infected.

• Clean- An example of this type of wound is a planned surgical incision. The wound is made under very controlled conditions with minimal trauma and in a very clean or sterile environment. Wounds of this nature are sutured soon after they have been created.

• Clean/contaminated- An example of this type of wound is a laceration less than a few hours old. There is some trauma to the tissues, and the conditions are non-sterile. The tissues are contaminated with environmental bacteria, either from the object causing the wound or from the normal flora of the animal. Wounds of this nature are prepared and sutured if the presentation is close to the "golden period" before bacteria have had a chance to proliferate in the tissue.

Example of a contaminated wound that is relatively clean.

• Contaminated- An example of this type of wound is one that is clearly soiled or heavily contaminated with bacteria, such as an animal that has been hit by a car and then dragged or thrown to the ground during the accident after being wounded. The wound often has been exposed for longer than 6-8 hours. This type of wound requires aggressive cleansing and staged treatment techniques to prevent complications.

Example of contaminated wounds that are heavily soiled with mud.

• Infected, or "dirty"- An example of this type of wound is one that has formed an abscess that has occurred as a result of an infection, usually bacterial growth. The discharge varies in character and color; it may be mucopurulent, caseous, or bloody, but often has an unpleasant odor. Gram stain cytology and culture and sensitivity are recommended before treatment is begun. This type of wound often requires aggressive cleansing, surgical debridement, and treatment techniques using drains.

Example of a necrotic infected wound.

Types of wounds- The cause of a wound is also a factor in the choice of specific wound treatments. The most common types of wounds animals experience are

• Abrasions
• Lacerations
• Crushing injuries
• Gunshot wounds
• Perivascular injections with secondary tissue slough
• Burns- sources are chemical, thermal, or electrical

An example of a burn wound.

• Puncture wounds- sources can be sticks, wires, nails, or bite wounds. These wounds often have a small opening yet the subcutaneous tissue damage can be extensive. The opening often heals much more rapidly than the deeper tissues still undergoing necrosis and debridement. Thus, abscesses are a common sequela.

Examples of puncture wounds

• Degloving injuries- This occurs when the animal is hit by a car and dragged across pavement.

An example of a degloving injury

• Pressure necrosis- improperly applied bandages, casts, or collars, and decubitus ulcers

Pressure necrosis of skin around the neck can be caused by a device like a tight elastic collar or a rubber band

All wounds, regardless of cause or tissue conditions, go through the same basic phases of healing. If closure via suturing can be done, this will enhance wound healing and lessen the size of the scar, but not all wounds can or should be closed on presentation.

During many injuries, surrounding tissue is also damaged, compromising the blood supply. If there is devitalization and necrosis of tissue, surgical repair is more challenging with likely complications. Often treatment may be performed in stages, or delayed to reduce contamination and infection. Delaying closure allows time for devitalized tissue to become obvious in appearance so surgical debridement is more effective. Sometimes there is so much tissue missing that surgical reconstruction is not an option, and long term wound management is required.

The term "healing by first or second intention" are actually categories of wound closures:

• Primary closure or first intention healing- For clean or clean/contaminated wounds, closure of the wound is done with sutures soon after injury. If there are no complications, healing occurs rapidly within a few days using this method of closure.

• Delayed primary closure- For contaminated or heavily traumatized wounds, the closure is delayed for a couple of days, before granulation occurs. Or sometimes the delay occurs because the animal has other injuries and is not stable enough to withstand sedation for wound repair the first day of the injury.

• Secondary closure- The closure occurs after granulation tissue is established. This method is chosen often for heavily contaminated wounds with large defects requiring surgical debridement and reconstruction, or for skin graft techniques.

• Second intention healing- The wound is allowed to heal naturally, often because tissue damage is extensive, heavily contaminated, or infected, and surgical reconstruction is not elected because it is not possible or complications would be likely. If this method is chosen, it usually requires long term wound care which may last weeks or months.

Factors that influence wound healing include characteristics of both the wound and the host, or animal.

Wound factors that delay healing are:

• Poor blood supply
• Edema
• Dead space with accumulation of fluid- exudate, hematoma, seroma
• Infection
• Foreign bodies or debris present

Host factors that contribute to delayed healing are:

• Geriatric age
• Malnutrition- low protein levels
• Systemic disease- liver or kidney failure
• Endocrinopathy- hypothyroidism, diabetes mellitus, Cushing’s disease
• Obesity
• Cancer and cancer treatments
• Self trauma- excessive licking or chewing of sutures or the wound site

The goals of wound care are to prevent contamination and protect the tissues. The treatment emphasis will change depending on the phase of healing that is present and the conditions of the tissues and patient.

• Immediate- Patient evaluation for patent airway, shock and hemorrhage is done first, then the wound is evaluated. Hemorrhage from a wound is best treated by direct pressure, not tourniquets. Prevent contamination of the wound by covering the wound temporarily with a clean towel or bandage material. Wet saline wraps may be used to prevent dessication of exposed tissues. Once life threatening injuries are addressed, the wound can be prepared for cleaning. Since manipulation may be painful, the patient may need to be sedated or local anesthetic applied. The wound is clipped to remove hair from the edge and the area around the wound. Avoid getting hair into the wound. If the wound is infected, a Gram stain and specimen collection for culture and sensitivity should be performed before treatment.

• Lavage- The wound is mechanically flushed with fluids under moderate pressure to remove debris and bacteria. Warm isotonic solutions are preferred. Hypertonic solutions may be used if edema is present. Soaps, antiseptics, and antibiotics are not recommended because they are irritating to the tissues and delay healing. However, to reduce bacteria, commonly used lavage solutions for infected wounds are dilute chlorhexidine, dilute povidone-iodine, or rarely used-- hydrogen peroxide.

• Debridement- The site is surgically prepared for debridement and repair. The wound is repacked so prep materials, such as antiseptic soaps and alcohol, do not get into the wound. Surgical debridement of necrotic or devitalized tissue is done either layer by layer or excised in one large section (en bloc) before the closure method is performed.

• Closure/repair- The wound is sutured, or suturing temporarily delayed for later closure, or left to heal by second intention, depending upon the type of wound. A drain may be placed at this time for certain wounds. And a bandage may be applied post operatively.

Drains are commonly made of flexible nonabsorbable tubing, and placed in a wound to:

• prevent the accumulation of fluids or exudates in potential dead space
• establish drainage of fluids from a dead space
• maintain drainage of fluids during the debridement phase of healing
• drain exudate from an infected wound.

One or two openings at or near the wound site is maintained for the placement of the drain into deeper tissues. The drain is sutured in place where it emerges at these openings. Often gentle lavage is performed at the drain sites.

There are two main types of drains: passive and active. Passive drains accomplish drainage by gravity.

The Penrose drain, a commonly used passive drain.

Drains sutured in place.

Active drains accomplish drainage by some sort of aspiration. The part of the drain that resides in the wound is fenestrated, so that fluid is collected from throughout the wound space. The drain is attached to a device such as a syringe or a Vacutainer-type tube which collects the fluid from the site through the drain. Commercially prepared closed suction devices are also available.

Removal of drains

Drain removal is often done by the technician. Drains are usually not left in a wound for any longer than 4 days because granulation tissue may start to form around the drain by 5 days. If left in too long, the body may heal around the drain and form a fistulous tract.

In this scenario, the drain is under a suture line and exits at two points on either side of the suture line.There are anchor sutures at each end. The steps for correct removal of a drain are demonstrated in the following mock set up:

Example of a mock drain set up.

At one end, the suture holding the drain in place is cut and removed.

The freed end of the drain is trimmed to the level of the opening.

The suture holding the drain is place at the opposite end is cut and removed.

The protruding free end of the drain at the second opening is grasped and pulled out straight so that friction against the skin opening is avoided.

Although it is a quick procedure, drain removal sometimes appears to be uncomfortable for the animal, so take appropriate precautions.

Dressings are medications or materials that are applied directly to a wound in order to enhance healing. They are often part of the primary layer of the bandage. The type of dressing used will vary depending on the phase of healing and the objective of the wound treatment. Hydrotherapy, or wound lavage with water or isotonic fluids is often done before applying a new dressing and bandage to an open wound.

  A protective material applied to an open wound. A drain is also present.

• Debridement- Trypsin preparations are sometimes used to enzymatically debride tissues over a period of time rather than as a single surgical procedure

• Debridement and granulation stimulation- Hydrotherapy is a simple yet effective method.

• Granulation and wound contraction stimulants- Examples of wound healing stimulants are Aloe vera extracts (acemannan), bovine collagen, hydrogels.

• Wound contraction inhibitors are used to prevent excessive scar formation and contracture deformity. Examples of medications that inhibit contraction include corticosteroids, silver sulfadiazine, hydrocolloids. Grafting techniques are also used in selected cases.

• Infection or prevention of infection- antibiotic ointments, antiseptic ointments

• Large contaminated wounds- Sugar or honey!! (Yes it is true and it works- see the references)

The following problems indicate that complications have occurred and the veterinarian should be notified so that treatment can be modified.

• Edema- The tissue becomes puffy or spongy and pale, and may leak clear watery fluid. The tissue may retain a fingerprint for a few moments after it has been pressed; this is called pitting edema

• Devitalized tissue- When blood supply is lost the tissue displays abnormal coloring such as blue, purple, white, gray, green, or black discoloration. This color change often is sharply demarcated from the normal tissue. It is possible to confuse a bruise with devitalized tissue. A bruise will discolor the tissue a bluish purple, and as the blood is metabolized in the tissues, a green color will result. In a few days, devitalized tissue undergoes necrosis and may liquify, or becomes dry and leathery and curl up away from the tissue beneath it, whereas bruised tissue will return to normal. When the tissue becomes black and leathery, it is termed an "eschar".

Devitalized skin is in the center of the wound.

Dehiscence- The wound repair breaks down and the wound becomes open again. If there is swelling around the sutures, sometimes the suture will actually cut through the tissue as it swells, weakening the repair. Sometimes dehiscence can be prevented if problems with the incision site are addressed early.

Dehiscence

• Exhuberant granulation tissue/proud flesh- This occurs mostly in horses on the distal limb. The granulation tissue is above the level of the skin edges and becomes progressively larger, nodular, and tumor like. It can protrude so far above the skin surface that it is virtually impossible for epithelium to migrate over its surface and heal the wound. Surgery may be required.

• Infection- There is inflammation and a discharge containing bacteria that is often malodorous. Usually the first thing that gives it away is the change in odor and color of the exudate. Gram stain cytology confirms the type of bacteria present.

• Fluid accumulation (seroma, hematoma, abscess)- A fluctuent swelling or mass containing fluid can be palpated. The nature of the fluid is not known until a needle aspirate and cytology is performed.

• Fistula- There is a persistent non-healing opening that may produce some exudate.

• Contracture deformity- As the wound contracts and undergoes maturation, the scar tissue may tie down tissue and restrict the range of motion. This most commonly occurs around joints.

• Hypertrophic scar- Instead of becoming less obvious over time, a scar becomes more obvious. The scar is raised, thickened, and prominent.

Maggot debridement therapy- Have you ever seen an animal infested with maggots? It is not a pretty sight! Here is a website about maggot debridement therapy- information on what have been termed the "world’s smallest surgeons" and how they are purposely cultivated and used for wound debridement. Note that there are important differences between different types of maggots- some can be beneficial and some are not.

Leech therapy- information on the resurgence of using leeches in wound therapy with venous congestions and skin grafts:

http://www.leeches.biz

World Wide Wounds- lots of information on wounds and wound care

http://www.smtl.co.uk/world-wide-wounds 

Matthews KA and Binnington AG: "Wound Management Using Honey" The Compendium on continuing Education for the Practicing Veterinarian:Small Animal January 2002 volume 24(1):53-60

Matthews DA and Binnington AG: "Wound Management Using Sugar" The Compendium on continuing Education for the Practicing Veterinarian:Small Animal January 2002 volume 24(1):53-60

McCurnin D and Bassert J: Clinical Textbook for Veterinary Technicians 5th edition WB Saunders, Philadelphia, 2002, pp. 102-106, 114-116, 600-01

Swaim SF and Gillette RL: "An Update on Wound medications and Dressings" The Compendium on Continuing Education for the Practicing Veterinarian:Small Animal October 1998 volume 20(10):1133-1145

Swaim SF, Hinkle SH, and Bradley DM: "Wound Contraction: Basic and Clinical Factors" The Compendium on Continuing Education for the Practicing Veterinarian:Small Animal January 2001 volume 23(1):20-34

Wilson, D: "Wound Management" Veterinary Technology presentation, Northern Virginia Community College, Sterling, Virginia, 2003.

Wormack BH: "Wound Management: Treatment & Patient Care" Veterinary Technician November 2001 volume 22(11):599-605

Acknowledgement: Many thanks to the doctors and staff of Alexandria Animal Hospital for wound photo contributions.

Writing assignment

When you have completed your study of the lesson, please answer the following questions and submit your answers via e-mail.  You may answer the questions directly in an e-mail or you may download the Word file, fill in your answers and return the Word file as an attachment.

Send to Dr. Bidwell: abidwell@nvcc.edu  

Wounds and Wound Care Lesson Writing Assignment MS Word file

Some students have reported having difficulty finding answers to the following questions - 5, 14, 15 and 26. If you can't find those answers please leave them blank and those answers will be provided.

1. What happens to a wound during the inflammatory phase?

2. What happens to a wound during the debridement phase?

3. What happens to a wound during the repair phase?

4. What happens to a wound during the maturation phase?

5. What roles do growth factors serve in wound healing and where do they come from?

6. Describe the appearance of poor quality granulation tissue.

7. Why would a topical corticosteroid ointment be contraindicated for a wound dressing?

8. What is "dead space" and how does it form?

9. Name two commonly used materials for surgical wound repair that increase inflammation.

10. Which surgical wound will likely heal in the shortest amount of time--electroscalpel, electrocoagulation, or steel blade?

11. Let’s pretend I have a pet who is getting chemotherapy and radiation treatments for cancer. Explain to me why a simple cut on his foot is taking over a month to heal.

12. What techniques of immediate open wound care are used to prevent the introduction of hair into the wound?

13. What is the "golden period"?

14. Which wound closure method would likely result in the largest scar?

15. Why is an abrasion so painful?

16. What is an avulsion?

17. Explain the difference between first, second, third, and fourth degree burns.

18. Name two iatrogenic causes of burns in the animal hospital setting.

19. What is "strike through"?

20. Why are drains often placed for the repair of puncture wounds?

21. Devitalized tissue, especially that of degloving injuries, may take up to how long to undergo recognizable changes?

22. What are decubitus ulcers?

23. Explain why decubitus ulcers are difficult to heal.

24. What is "proud flesh" and where is it commonly found?

25. Name some methods of controlling proud flesh.

26. What vaccination is often given to horses at the time of initial wound treatment?

27. Name two types of agents that should not be used in lavage fluids.

28. What are some devices that can be used for wound lavage technique?

29. What is the difference between active and passive drains?

30. What is the difference between primary closure, delayed primary closure and secondary closure?

31. When is granulation tissue usually seen (ie, how many days after the initial wound?)

Answers to wound strength questions

On average, most sutures are removed around 10 days post op. Looking at figure 4-1 this would mean that the wound strength is still fairly low, less than 50%. How do we get away with this and not see more problems post op? Take into account that with a surgical wound that is sutured, the time frames for the early healing phases are markedly decreased because the skin edges are apposed and there is very little defect to fill. Epithelialization of a sutured incision can occur as early as within 48 hours, compared to 4-5 days in an open wound that is not sutured. Therefore, wound strength is developed at a faster rate in a sutured surgical incision and is in the maturation phase at the time of suture removal. While it may support wound strength to leave the sutures in longer than 10 days or so, most technicians find that the longer sutures are present, the more likely the sutures act as foreign bodies, causing an inflammatory reaction that is counterproductive to wound healing and maturation. For common elective surgeries, we often find that many animals resume normal activities on their own before suture removal, but most doctors prefer to restrict activity until the incision is healed and in the maturation phase. Of course, activity recomendations will differ depending on the surgery, especially if rehabilitation is required post op.