Molly Varga
4. emodelling: collagen is remodelled from type 3 to type 1 (increasing in tensile strength) and
realigned in response to tissue forces. The tensile strength of the wound increases until it approaches that of undamaged tissue.
A practical approach to wound repair is outlined in Figure 11.2. Wound repair can be accomplished in various ways:
• rimary intention: wound edges are in good anatomical apposition and healing progresses rapidly with minimal scar formation, e.g. surgical repair. This minimizes scarring and maximizes chances of tissue functionality
• econdary intention: wound edges are not in apposition and granulation tissue formation is allowed. This produces a broader scar and slower healing. Functionality may be
compromised. Typically seen in large infected wounds. Ongoing wound cleaning and debridement may be required to allow granulation tissue to form
• elayed rimary or secondary intention: the wound is cleaned and debrided for several days prior to closure, or is left purposefully open (e.g.
to receive a tissue graft).
The rate of healing can vary with tissue type, e.g.
skin heals rapidly while tendons may take up to a year to be fully repaired.
A practical approach to wound management.
11.2
• The ideal for wound healing is rimary intention healing, allowing return to maximum function in minimum time. The criteria for this are: accurate apposition of tissue, usually achieved by suturing; and lack of infection. Surgical wounds most closely approximate this ideal; however, traumatic wounds can fall into this category as long as measures are taken to prevent infection and t ere are n si ni cant tiss e de cits eas res t pre ent infection include careful wound cleaning and debridement, sensitive apposition of tissue so that there is no excess tension on the wound, suitable choice of suture material and antibiosis.
• For grossly infected wounds, either secondary or delayed rimary intention healing is more appropriate. In practice, infected wounds should be thoroughly debrided and cleaned and then consideration given to how best to maintain healthy granulation tissue.
• ne c nsiderati n speci c t ra its is t at su cutaneous a scesses. They are one of the commonest presenting problems and can cc r sec ndar t tin in partic lar r t s in tra a of any kind. The confounding factor in the rabbit is the consistency of the pus, which is thick, sticky and tenacious. This means that t e traditi nal appr ac lancin s in and placin a drain does not work, and is indeed contraindicated. Ideally, subcutaneous abscesses would be removed intact without dist r in t e r s a scess caps le and t e nd c ld t en be allowed to heal by primary intention. However, this is not always possible and other solutions must be sought. The general approach is to resect as much of the abscess capsule as possible and to marsupialize the edges of the capsule to the skin surface and allow healing by secondary intention. This effectively allows the abscess to heal from the inside out (see also Chapter 29).
• For both grossly infected wounds and initial treatment of cutaneous abscesses, the author advocates the use of collagen matri dressings s t red ti tl n t t e nd r at least t e rst 3 days after debridement. This allows granulation tissue to form in a protective moist environment while wicking away any purulent exudates. Essentially, the pus gets locked into the dressing away
from the wound. Packing the wound tightly appears to enhance this process without causing additional discomfort to the rabbit.
nce t e dressin is re ed s cient ran lati n tiss e as formed to allow direct cleaning of the wound (see Operative Technique 11.1).
• An alternative option is the use of classical et to dry dressings using swabs moistened with sterile saline that are applied to the wound and allowed to dry in situ. As the dried swabs are removed this provides gentle wound debridement. Once infection is controlled and the granulation bed has formed, the decision can be made as to whether healing should continue by secondary intention or whether delayed primary closure should be attempted.
• oney has been advocated as a bactericidal wound dressing (there are several proprietary formulations, but unpasteurized Manuka honey is also suitable). While it has been shown to be less effective than some other compounds, the advantages of a non-toxic effective wound dressing are obvious. The mechanism of action is via production of hydrogen peroxide within the wound, which then kills the bacteria present (this is also cytotoxic) so healing relies on effective phagocytosis. This is well accepted by rabbits.
• Once a healthy bed of granulation tissue has formed, the skin de cit can e left o en, allowing the owner to clean (and thereby gently debride) the area once or twice daily. As rabbit wounds heal pri aril nd c ntracti n and epit eliali ati n t e s in de cit can red ce rapidl ten 1 1 da s r a 3 c 2 c de cit
• ecision making is ased n t e a nt tiss e de cit et er ap r ad ance ent pr ced res can e e pl ed ell infection is controlled, the requirement for full return to function, and the projected long-term effect on the patient.
• Rabbits are generally good candidates for a or skin advancement rocedures as t eir s in is er e i le and t e lack of collagenous attachment between the dermis and deeper tissues means it is practically easy to accomplish. This can be a useful tool for large skin wounds once infection has been addressed.
kin re aration
Rabbit skin is very fragile and the hair is dense, mak-ing it difficult to clip without causmak-ing skin damage.
The best option is to use new/sharp clipper blades it s all ine teet t is sensi le t a e ra it nl ’ clippers t at are n t l nted d and cat hair. Gentle tension should be placed on the skin and clipping should be done slowly and against the direction of hair growth, with the clipper blades as near parallel to the skin as possible. Even with care-ful clipping, iatrogenic damage can occur. This can cause skin irritation, leading to self-trauma.
Some authors have suggested plucking hair for s aller pr ced res e er in t e a t r’s e per ience, this can cause significant skin irritation and can lead to tearing. Hair removal creams have also been advocated; however, these are not widely used at this time and appear to have fallen out of favour.
Once the hair has been removed, skin cleaning and disinfection needs to be undertaken. This includes scrubbing with antiseptics such as chlor-hexidine or povidone–iodine, and final preparation with surgical spirit. Excessive scrubbing can cause postoperative irritation and increase the potential for discomfort and self-trauma. Single-application products should be considered, e.g. chlorhexidine
PRACTICAL TIP
Adhesions may be prevented by:
• Minimizing tissue handling and using gentle surgical technique
• Paying careful attention to haemostasis
• Keeping tissues moist, irrigating frequently and using wet gloves and moistened swabs
• Minimizing surgical time
• Using the smallest suitable suture material, with swaged-on needles.
or povidone–iodine in surgical spirit, as these may prove less irritant; however, in cases where there is gross skin contamination they may not be appropriate.
In small individuals it is sensible to try to reduce heat loss by removing the least amount of hair that is practical, and consistent with good surgical access, and minimizing the amount of skin that is wet (the hair at the edges of the prepared area should be slicked down away from the incision line).
Tissue handling
Rabbits have been used extensively as models for postsurgical adhesion formation, due to their propensity to form fibrous adhesions after any tissue damage, whether surgical or traumatic (Gordon et al., 1974). In humans, as many as 80%
of patients have clinical problems related to adhe-sion formation in the 2 years after abdominal surgery (Steinleitner et al., 1989, 1990). It is likely that as many, if not more, rabbits suffer in a similar way. From a surgical perspective, postoperative adhesion formation is significantly increased by rough or traumatic tissue handling. While adhesion formation can cause significant functional prob-lems for the rabbit patient, the important point is that they frequently cause discomfort, if not pain.
d esi ns are internal scars’ t at r et een viscera. Trauma to the visceral surface (e.g. surgical intervention or handling) causes fibrin to be depos-ited on to the damaged tissues. This acts to seal the injured area (fibrinous adhesion). Normally fibrino-lytic enzymes act to limit the extent of adhesion for-mation. If the availability of these enzymes is compromised (e.g. due to the disease process) then the adhesion matures. Fibrinolysin levels are lower in rabbits than in cats and dogs. Macrophages, fibroblasts and blood vessels penetrate the fibrinous tissue and lay down collagen, forming a permanent fibrous adhesion.
Fat necrosis can also lead to adhesion formation and this is often seen in the fat of the broad ligament after ovariohysterectomy (see Chapter 12).
n t e a t r’s e perience lac appr priate intraoperative haemostasis can also contribute to adhesion formation; for example, failure to ligate or cauterize the vessels in the broad ligament so that blood clots are left within the abdomen, which may eventually become adhesions. Equally, the use of inappropriate ligatures (e.g. catgut) for haemostasis can also result in adhesion formation.
In practical terms, the use of instruments rather than manual manipulation of tissue is advocated.
This is mainly because powder from gloves can encourage adhesion formation. Manipulation using instruments is also more precise, and the tips of surgical instruments are significantly smaller than fingertips, which means that a smaller area of tissue is damaged; this way of working is therefore far less likely to cause significant adhesions. Sterile cotton buds can be helpful for haemostasis, again because their small size means less tissue is contacted.
Tissue desiccation is also a factor in adhesion formation; the use of instruments (meaning more
viscera are kept inside the body cavity) as well as frequent irrigation of tissue exposed to air for any length of time will mitigate this. The use of mois-tened swabs rather than dry ones also helps to reduce adhesion formation, by reducing the likeli-hood of lint from the swab remaining on the tissue surface and by helping to keep the tissue moist.
Many rabbit surgeons also advocate flushing the surgical site prior to closure.
One possible consequence of laparoscopic sur-gery in rabbits is the creation of a pneumoperito-neum with attendant tissue drying; this is dependent on the length of time the procedure requires.
isk of haemorrhage
The clotting time in rabbits is shorter than that in many other species (Perry-Clarke and Meunier, 1991); however, intraoperative haemorrhage may still present the surgeon with problems. The blood volume of the rabbit is approximately 57 ml/kg body -weight (5.7% of total body-weight; therefore signifi-cantly less than the 10% estimate for a dog and 8%
estimate for a cat). Loss of 15–20% of this volume (around 30–40 ml in a 3.5 kg rabbit) can lead to significant tachycardia, arterial vasoconstriction and redistribution of blood away from less essential areas such as gut and skin. Loss of blood in excess of this amount can prove critical or fatal. In practice, rabbits can be seriously affected if they lose a volume of blood that would be tolerated by a cat or a dog. Venous access and fluid support throughout surgery can mitigate blood losses, and maintenance of blood pressure during surgery can make visual ization of potential bleeds easier.
Good surgical technique will minimize blood loss, although haemorrhage is sometimes unavoid-a le runavoid-aditi nunavoid-all li unavoid-ati n leeders’ sin suture material has been the method of choice;
however, the use of electrocautery or radiosurgical instrumentation can be very helpful. It is worth considering that the use of electrocautery causes inflammation within the surrounding tissues, but so does the swabbing-up of blood and placing liga-tures. Vessel-sealing handpieces (e.g. Ligasure) may also be used. Good knowledge of blood vessel anatomy will allow the surgeon to be spe-cific in sourcing and correcting the origin of a bleed. Ligatures of absorbable monofilament suture are least reactive and minimize inflamm-ation and adhesion forminflamm-ation in the longer term (McFadden, 2011).
Instrumentation
Most rabbit surgery can easily be accomplished using normal surgical kits of suitable size. For most rabbits a cat-sized kit is appropriate, while for larger individuals (>7 kg) a dog-sized kit may be neces-sary. When surgery on very young or small individu-als is contemplated, ophthalmic or microsurgical instrumentation may be helpful. Rabbit-specific sur-gical kits are available commercially. The smallest instruments that are practical should be selected.
incised or injured tissue in apposition so that it can heal. The suture material needs to provide enough tensile strength and for long enough to allow healing to be completed (Figure 11.3). Different tissues heal at different rates, so sutures need to stay in position for varying amounts of time. Bladder and uterine tissue heal rapidly (normal tensile strength achieved in 14–21 days), whereas fascia can take in excess of 42 days to repair. Within the gut, small intestine heals significantly faster than large intestine (14 versus 28 days).
The ideal suture material exhibits knot security, resistance to infection, and no inflammatory, immu-nological, or carcinogenic reactions. Such material does not exist, so a compromise must be made based on knowledge of healing and suture material characteristics.
As rabbits are commonly used experimental animals, much information has been generated on the reaction to and persistence of various suture materials in this species. In general, non-absorbable sutures that remain in tissues cause a persistent inflammatory response. Biological absorbable mat-erials (e.g. catgut/chromic catgut) cause a greater inflammatory response than synthetic ones. Bio-logical sutures are broken down by phagocytosis whereas synthetic ones are broken down by hydro-lysis to simple molecules which are then absorbed and metabolized by the body (McFadden, 2011).
Rabbits form excessive granulation tissue in response to foreign material such as sutures. Suture selection is therefore very important, as suture reactions are a common postoperative complication.
• Monofilament suture materials are more resistant to infection than multifilament ones, and tend to cause less tissue reaction. The use of
monofilament absorbable suture material for internal sutures (e.g. polydioxanone (PDS)) is recommended.
• External sutures should be non-absorbable but preferably also monofilament (e.g. monofilament ty ical surgical kit should include:
• Small (iris) scissors
• Long (Metzenbaum) scissors
• A pair each of dressing forceps and atraumatic or rat-toothed forceps
• A scalpel handle
• 3× artery forceps
• 4× towel clamps
• A pair of needle-holders.
100
80
60
40
20
0 Day 0 Day 7 Day 14 Day 21 Day 28 Day 42
Polydioxanone
Tensile strength (%) Polyglactin 910
Polyglyconate Polyglycolic acid Polyglecaprone 25 Deterioration in tensile strength (as a percentage of original strength) in a variety of commonly used sutures.
(Data from McFadden, 2011) 11.3
In all kits it is useful to have DeBakey atraumatic forceps; these have ridged ends without the points that are found on rat-toothed forceps, allowing very good grip with minimal tissue damage. Magnification loupes are helpful for smaller patients and radio-surgical units may also be useful, particularly where haemostasis may be an issue. Sterilized cotton buds are another helpful addition.
Non-powdered gloves are preferable as they can reduce the potential for adhesion formation (see above).
Suture materials and patterns
Selection of an appropriate suture material is critical to the success of any surgery. The general princi-ples applied to cats and dogs are also true for rabbits. The role of a suture is to maintain surgically
nylon). Surgical steel staples are also suitable, but often less well tolerated from a comfort point of view, leading to self-trauma of the wound. In cases where exuberant granulation or fistulous tracts are formed secondary to suture
placement, surgical excision may be necessary.
Cyanoacrylate tissue glue may also be used for skin closure. However, a significant exothermic reaction occurs as it cures, which can cause skin necrosis in severe cases, so it should be used with caution.
• One possible use for catgut is in infected
wounds, where the sutures can then be removed by phagocytosis along with any associated bacteria (Harcourt-Brown, 2002). This, however, can potentially prolong the inflammatory phase of wound healing and increase the potential for excessive formation of granulation tissue.
continuous suture pattern is used, the knots at each end of the incision must be secure and several extra throws placed at each end.
Absorbable monofilament or braided sutures are suitable (e.g. PDS or polyglactin 910 (e.g. Vicryl)).
The size should be suitable for the size of patient, e.g. 1.5 metric (4/0 USP) for a 2 kg rabbit.
• u cuticular sutures are ordinarily made in a simple continuous pattern; however, for wounds with a large skin deficit, it can be easier to place several interrupted subcuticular horizontal sutures to ensure the skin is where it is intended to be, prior to placing a full subcuticular suture.
Ideally, the knot at the end of the subcuticular suture should be buried (Aberdeen knot, Figure 11.4). Either monofilament or braided absorbable sutures are suitable in this location (e.g. PDS, Vicryl); the size should be the smallest suitable for the patient, e.g. 1.5 metric (4/0 USP) for a 2 kg rabbit.
• For skin the pattern chosen depends on the type of wound and the amount of subcuticular support already provided. Horizontal mattress, cruciate or simple interrupted suture patterns are all suitable.
Stainless steel skin staples could also be used.
PRACTICAL TIP
The size of the suture material has more effect on adhesion formation than the suture material itself (McFadden, 2011); therefore, the finest practical suture material should be chosen.
The Aberdeen knot is a buried knot suitable for the end of a subcuti cular suture pattern. Its main advantage is that the knot is secure but small and the end is buried in a tunnel of tissue rather than cut off short, potentially allowing it to poke through the suture line.
1. At the end of the subcuticular suture, keep the last loop of suture aterial l se and place a nal stitc
2. Loop the end of the suture material nearest to your hand through the last suture.
3. Pull the loop so that the last suture is tightened, then pull the end of the suture nearest you again through the remaining loop to make a third loop.
4. Place tension on the third loop so that the second loop is tightened.
5. Repeat this process for at least four to six throws and on the last t r pass t e ree end t e s t re t r t e nal l p and pull tight to secure the knot.
6. Tunnel the end of the suture material for a short way under the skin and up through the surface.
7. Pull it tight and cut off close to the skin surface, allowing the knot to pull back under the skin when released.
The Aberdeen knot. (Photos courtesy of Geraldine Hunt and reproduced from BSAVA Manual of Canine and Feline Surgical Principles: a Foundation Manual)
11.4 For most wound closures it is desirable not to
create any tension on the wound and the suture pattern chosen should reflect this.
• For closure of the gut, simple interrupted non-crushing suture patterns are advised. The submucosal layer of the gut is the most important for healing, as it contains the most collagen. It is important not to evert or invert the edges of rabbit intestine but to bring them into direct apposition without crushing the tissue. This is in contrast to similar surgery in dogs and cats, where serosal contact and inverting sutures are indicated.
Single-layer closures are acceptable as double-layer closures will reduce gut lumen and
functionality; however, the former are more prone to breakdown. The lack of a large, freely motile omentum means that intestinal wounds cannot be supported in this way. Inverting suture patterns will cause lumen stenosis and, particularly in the large intestine, can affect the function of the haustra. The most suitable suture material in this situation is a monofilament absorbable suture such as polydioxanone (PDS) 1 or 1.5 metric (5/0 or 4/0 USP).
• For the uterus or ladder continuous inverting suture patterns such as Lembert or Cushing would be suitable. Penetration of the bladder lumen should be avoided, as it can cause calculus formation for the duration of the life of the suture. Therefore sutures that do not
penetrate the wall fully are advocated, using 1 or 1.5 metric (5/0 or 4/0 USP) absorbable
monofilament materials (e.g. PDS).
• The a dominal all is closed in a single layer of either simple interrupted or simple continuous sutures (see Operative Technique 11.2). If a
Potential complications and their prevention
Common presenting problems, their potential causes, and actions that should be taken to address them are summarized in Figure 11.5.
ound reakdo n
The correct placement and choice of suture are vital for the prevention of wound breakdown, as are the tension placed on the wound, the tightness of the suture and the sterility of the procedure. However, regardless of the care and planning undertaken, breakdown can still occur. Revision surgery is often necessary and consideration must be given to:
• e patient’s c rt
• The immediate support the wound requires
• Addressing any infection
• Whether a second attempt at primary closure is warranted or whether delaying primary closure may be a more viable option.
ound infection
Sterile technique and judicious use of antibiosis should reduce the likelihood of wound infections sig-nificantly. Equally, careful clipping, gentle tissue handling, and suitable suture selection with sutures
that are not too tight will all reduce the likelihood of inflammation, tissue necrosis and self-trauma. Signs that a wound is infected include pain, swelling, red-ness, heat and the presence of purulent discharge.
Pus in rabbits is thick and sticky in consistency due to the mucolytic and proteolytic enzyme levels found in heterophils (a relative deficiency in myeloperoxidase means there is not enough of this enzyme to break down dead cells into thinner pus) (Baggiolini et al., 1969, 1970). This presents a significant problem to the surgeon, as rabbit pus does not flow; so drain placement, a traditional way of dealing with infected wounds in other species, does not help and is even contraindicated as the drain itself can act as a nidus for further infection (Harkness et al., 2010). Wounds that become infected may be dealt with by planning for healing either by delayed primary intention or by secondary intention. The area should be thoroughly and exten-sively debrided and cleaned repeatedly prior to con-sidering delayed closure. Most rabbit surgeons advocate treating abscessed wounds as radically as one would a tumour (see Operative Technique 11.1).
dhesions
d esi ns can e t t as internal scars’ t at form between soft tissues after any tissue trauma (e.g. surgery). They are commonly recognized
resenting ro lem ossi le causes ctions
Wound red r al ealin in a ati n sel tra a leedin Check wound. Assess antibiosis and pain relief. Check clotting ability if necessary
Wound swollen r al ealin in a ati n ser a r ati n sutures too tight; infection; abscessation; suture reaction
Check wound. Consider drain placement if seroma formation.
Consider culture and sensitivity testing (NB pus may be a poor sample for culture). Review antibiosis and pain relief. Revision surgery may need to be considered
Wound open Self-trauma; lack of exercise restriction; suture failure Review antibiosis and pain relief. Revision surgery may need to be considered
Purulent discharge Wound infection or abscessation; secondary to suture
reaction; secondary to self-trauma Review antibiosis and pain relief. Revision surgery must be considered. Obtain sample from pyogenic membrane for culture.
Consider delayed primary intention healing, addressing infection and causative factors prior to revision surgery and closure Not eating or
defecating after surgery
Wound infection or breakdown; inadequate pain relief;
reduced mobility due to incisions; acquired dental disease secondary to a period of anorexia related to the surgery or the reasons for it; reasons unrelated to surgery
Perform a full clinical examination (including a dental examination). Examine external wounds. Review antibiosis and pain relief. For abdominal surgery, consider either
abdominocentesis or ultrasonography to look for free peritoneal id and p tential nd rea d n r ide s pp rti e care incl din ids and assisted eedin a e a l d sa ple (blood glucose level may help to assess prognosis) Abdomen swollen cess id r as it in t e cess ree id it in
peritoneal cavity; abnormal abdominal mass formation (abscess or tumour growth)
Perform a full clinical examination including auscultation for gut sounds. Use abdominocentesis or ultrasonography to look for
ree perit neal id and a n r al ass r ati n e ie antibiosis and analgesia. Treat any abnormalities aggressively.
Revision surgery is likely to be required Lack of expected
return to function (of area operated on)
Continued pain; adhesion formation; wound contracture affecting mobility of area in question;
continued wound infection affecting healing
Perform full physical examination and compare current function with normal. Review antibiosis and pain relief. Revision surgery may be indicated. Consider physical therapy to aid in adhesion breakdown. Consider medical therapy for prevention of adhesion re-formation
Trouble-shooting guide for potential complications associated with wound healing.
11.5