Wound management forms an important part of small animal practice and is an area that is continually reassessed in light of new techniques and recommendations. Regardless of the dynamic approaches to managing wounds, the aims of such management are to repair the wound, relieve pain and distress, use financially viable procedures that are time efficient and to recognize delayed healing and take prompt action (Anderson, 1996). These aims apply whether the wound was caused by a surgical incision or trauma, and whether primary or secondary healing is deemed appropriate. In addition to pre-operative preparation, veterinary nurses also play a fundamental role in the post-surgical management of the wound, both of which contribute greatly to reducing wound infection rates. Veterinary nurses should also extend their role by educating and supporting owners in managing the wound appropriately at home.
Literature review
Primary closure should theoretically only be used where the wound has been created in an aseptic manner (Anderson, 1997) and this technique is therefore appropriate for clean surgical wounds, such as those involved in routine neutering. Depending on the degree of initial contamination, primary closure may also be deemed appropriate in certain cases, such as a recently lacerated pad. However, in this study, only routine ovariohysterectomy cases were used to assist in controlling variables. Three suture materials were involved: Polyglactin 910 (Vicryl, Ethicon, Livingston, Scotland); AK Catgut (Animus Surgical Ltd, Suffolk) and Nylon (Nylon, Ethilon, Ethicon). Polyglactin 910 and AK Catgut are both absorbable suture materials; polyglactin 910 is degraded by hydrolysis, whereas enzymes and phagocytosis degrade catgut (Niles and Williams, 1999). Nylon is non-absorbable although it is affected by slow hydrolysis (Niles and Williams, 1999). Therefore polyglactin and catgut can be used for subcutaneous and muscle suture while nylon is suitable only for skin closure.
Surgical wound healing can be affected by a variety of factors including infection (Cimino Brown et al, 1997; Eugster et al, 2004) and the infection risk has been found to be increased by the duration of anaesthesia (Beal et al, 2000), anaesthesia and surgery time combined (Nicholson et al, 2002), degree of wound contamination and general health of the patient (Cimino Brown et al, 1997). Eugster et al (2004) found that surgical wounds were more susceptible to becoming infected with increased surgical time, increasing numbers of staff in theatre and a contaminated surgical site. Eugster et al (2004) also found that surgical wounds were more susceptible to inflec-tion/infammation with an increased duration of anaesthesia, duration of time in an intensive care unit (ICU), degree of wound drainage, increased patient weight, contaminated surgical site and prophylactic antibiotics. The criteria used by Eugster et al (2004) to assess wounds is included in Table 1.
| Infection | Infection/inflammation |
|---|---|
| Purulent drainage | Signs of infection present |
| Abscess formation | Redness |
| Fistula formation | Swelling |
| Pain | |
| Heat | |
| Serous discharge | |
| Wound dehiscence |
Adapted from: Eugster et al (2004)
N.B. A wound was described as being ‘infected/ inflamed’ when infection was present or when three or more of the signs of ‘infection/infammation’ were present.
The research objectives of this study were to assess case histories to identify factors that may affect wound healing success and assess the effect that each factor has on wound healing in cats and dogs admitted for routine ovariohysterectomy. As this study uses retrospective data, no animals were specifically anaesthetized or underwent surgery for research purposes. As a result, there are no ethical issues involved with completion of this clinical audit. Clinical audits are completed to make improvements in practice (Viner, 2009); this research was completed to provide recommendations for the practice in an attempt to reduce the incidence of unsuccessful wound healing.
Methods
A clinical audit of 285 patients over a period of 18 months, from 2008–2009, was completed at one veterinary practice; veterinary staff were interested in determining which factors may have increased the risk of unsuccessful post-surgical wound healing. The mixed sample population comprised 115 dogs and 170 cats admitted for routine ovariohysterectomy. The veterinary staff carrying out the study suspected that the use of polyglactin 910 for skin sutures was associated with wound healing complications at this practice, so this was compared with nylon, the only other material used for suturing skin layers. This retrospective cohort study selected patients based on their exposure to the suture material under investigation. There were no other exclusion factors. To add more power to the study, an approximate 3:1 ratio was used in selecting suitable cases: of the total 285 patients, polyglactin 910 was used in 212 patients and nylon was used in 73 patients as the skin suture material of choice. Patients were initially grouped according to the skin suture material used, but further analysis was completed by investigating the suture materials used for muscle and subcutaneous layers.
Data collected from case histories included the date of procedure, age, species and breed of the patient. Specific data in the form of the suture materials used for muscle, subcutaneous and skin closure were recorded, as was whether an Elizabethan collar was used, antibiotics were prescribed and whether there were any problems with wound healing.
For the purpose of statistical analyses, data were grouped according to the potential factors affecting wound healing such as suture material used and patient age, and then according to whether there was complicated or uncomplicated healing.
Statistical analyses included risk ratio (RR) analysis, Chi square test and Fisher's exact test. Data were analyzed using the statistical programs Genstat 13th edition and Win Episcope 2.0. In all analyses, p≤0.05 indicates statistical significance.
Results
Incidence of healing complications when polyglactin 910 or nylon were used as the skin suture material
When polyglactin 910 was used as the skin suture material, 15/212 (7%) patients experienced healing complications, compared with 8/73 (10.9%) when nylon was used. Risk ratio analysis at the 95% confi-dence level was insignificant, RR=0.646 (0.285–1.462; p>0.05). There was no significant difference in the incidence of healing complications when polyglactin 910 and nylon were used as the skin suture material.
Subcutaneous suture material and incidence of healing complications
RR analysis produced a RR of 3.764 (1.061–13.350; p≤0.01). The use of catgut as the subcutaneous suture material was shown to significantly increase the risk of healing complications by almost four times that seen with polyglactin 910 sutures (Figure 1).
Muscle suture material and incidence of healing complications
The use of catgut as the muscle layer suture material was shown to significantly increase the risk of healing complications by almost eight times that seen with pol-yglactin 910, RR=7.636 (1.621-35.970; p≤0.01) (Figure 2).
Incidence of healing complications: effect of the veterinary surgeon
Veterinary surgeons who used catgut in the muscle and/or subcutaneous layers were shown to be five times more likely to experience healing complications than those who did not, RR=5.468 (1.287–23.238; p≤0.05). Initially, this analysis identifed certain veterinary surgeons as being associated with increased healing complications. However, more in-depth analysis identified that these veterinary surgeons were the ones who used catgut in the muscle and/or subcutaneous layers. It is therefore important to note that healing complications were due to the suture material and not the veterinary surgeon included in this study.
Species of patient and incidence of healing complications
Fisher's exact test, at the 95% confidence level, indicated that there were significantly more canine patients that experienced healing complications when compared with feline patients (p<0.001) (Figure 3).
Age of the patient and the incidence of healing complications
Fisher's exact test, at the 95% confidence level, indicated that there was no significant difference in the incidence of healing complications between feline patients aged less than 3 years and those aged 3 years or more (p=0.656) (Table 2).
| Cats aged <3years | Cats aged ≥3 years | |
|---|---|---|
| Healing complications | 4 | 0 |
| Uncomplicated healing | 151 | 15 |
Fisher's exact test, at the 95% confidence level, indicated that there was no significant difference in the incidence of healing complications between canine patients aged less than 3 years and those aged 3 years or more (p=0.063) (Table 3).
| Dogs aged <3years | Dogs aged ≥3 years | |
|---|---|---|
| Healing complications | 17 | 4 |
| No complications | 56 | 38 |
The use of an Elizabethan collar and the incidence of healing complications
When an Elizabeth collar was worn, 9/70 (12.8%) patients experienced healing complications, compared with 14/201 (6.9%) when an Elizabethan collar was not worn. RR analysis at the 95% confidence level was insig-nificant, producing a RR of 1.974 (0.897–4.346; p>0.05). There was no significantly increased risk of healing complications if an Elizabethan collar was not worn.
The use of post-surgical antibiotics and the incidence of healing complications
When post-surgical antibiotics were prescribed, 0/3 (0%) patients experienced healing complications, compared with 23/259 (8.88%) when post-surgical antibiotics were not prescribed. At the 95% confi-dence limit, Fisher's exact test confirmed that there was no significant association between the use of post-surgical antibiotics and complications in wound healing (p=0.612). However, all patients received a pre-surgical subcutaneous injection of clavulanic acid (35 mg/ml) and amoxicillin (140 mg/ml) (Synulox, Pfizer Animal Health, Kent) at a dose of 8.75 mg/kg.
Discussion
This clinical audit has identified a range of factors which may influence healing success in cats and dogs, and the findings are of importance to both veterinary surgeons and veterinary nurses. Veterinary surgeons could use the findings to help them decide which suture material to use, or even to change practice protocol as some practices have a standard protocol for routine neutering. The findings are important to veterinary nurses who are likely to be assessing wounds and who should therefore be aware of the potential healing complications associated with particular suture materials.
This study found that catgut increases the risk of healing complications by almost four times when used subcutaneously, and increases the risk almost eight times when used in muscle compared with polyglactin 910. Catgut is associated with a mild to severe inflammatory reaction, which is a result of breakdown by phagocytosis (Niles and Williams, 1999) whereas polyglactin 910 initiates a lesser inflam-matory response due to hydrolysis (Hochberg et al, 2009). This may explain the results relating the subcutaneous and muscle suture material. The increased risk of healing complications when catgut is used subcutaneously or in muscle may be explained by a higher antigenicity, which increases the likelihood of infection (Campbell and Marks, 1985). However, it is entirely possible for some individuals to react favourably to suture materials regarded as being more reactive, and for some individuals to respond poorly to suture materials regarded as being less reactive. In both the subcutaneous and muscle layers, polyglactin 910 was associated with a lesser risk of complications. However, there was no statistically significant advantage in terms of healing complications of polyglactin 910 over nylon when used as a skin suture material.
The findings indicate that dogs are more susceptible to healing complications than cats. However, there are many factors that could have influenced this result. In this study, all cats were ovariohysterec-tomized via a flank incision and in bitches, a midline incision was made. In addition, nurses will be aware that, typically, ovariohysterectomy in the cat is of a shorter duration than in the bitch. As duration of anaesthesia and surgery has been previously identi-fied as a risk factor of post-surgical infection (Beal et al, 2000), this may provide a partial explanation as to why dogs appeared more at risk from healing complications than cats; shorter surgery in the cat may contribute to lowering the risk.
The findings for the effect of wearing an Elizabethan collar were statistically insignificant in this study. However, it may be possible that owners of dogs were more likely to remove the Elizabethan collar at an earlier time, or indeed not use it at all, than owners of cats. This may be because owners find it practically difficult managing a dog wearing an Elizabethan collar. However, no data were recorded on whether owners kept the collars on the animals. Väisänen et al (2004) found that although wearing an Elizabethan collar did not affect post-operative signs or behaviour in dogs after soft tissue surgery, many owners believed that it caused the animals discomfort. This could also have occurred in this study, and may contribute to the fact that dogs appeared more at risk from complications if owners removed the collars. Recommendation of the use of an Elizabethan collar is based on clinical experience, and as a result, the authors encourage Elizabethan collars to be used to prevent self-mutilation until more research is completed despite the findings of this study.
There was so significant relationship between the effect of patient age and incidence of healing complications. However, the results are approaching signifi-cance so it may be possible that a larger scale study could identify a relationship.
There appears to be no published research regarding different suture patterns in cats and dogs. However, there is evidence that surgical wounds in gold-fish heal differently according to the suture pattern chosen when polyglyconate suture material was used (Nematollahi et al, 2010); subcuticular sutures produced the mildest inflammatory reaction and gave the best cosmetic appearance when compared with interrupted horizontal mattress sutures and simple interrupted sutures. It may therefore be possible that differences in wound healing complications were in-fluenced to some extent by the suture pattern used.
The duration of anaesthesia and surgery was also not recorded in this study. Beal et al (2000) found that for each minute of additional surgery, there was a 0.5% increase in the infection risk and also found that extended anaesthesia increases susceptibility to infection. It is therefore possible that healing complications were present in animals that had been anaesthetized for longer and/or those in which surgery time had been extended.
Six veterinary surgeons had completed the 285 procedures included in this study. The results indicate that the risk of healing complications is increased when catgut was used. This explains the differences in the number of healing complications associated with each veterinary surgeon, depending on which suture material was chosen. It may be beneficial for veterinary surgeons to consider using an alternative suture material to catgut, such as polyglactin 910 or polydioxanone. However, further research is needed to directly compare the incidence of healing complications in a large sampe size when using a variety of different suture materials.
Finally, nurses completing a clinical audit on wound healing complications in practice, would obtain further useful information if healing complications were graded according to their severity. This study did not grade complications in this way, meaning that factors influencing severity could not be identified. This is an area of importance because mild inflammation is clinically less important than complete wound breakdown. Clinical audits are a useful tool and nurses should strive to ensure that all information is recorded carefully and thoroughly, allowing for meaningful data to be collected for use in such studies.
Limitations of the study
The main limitation of this study is that the data collected did not include which anaesthetic agent was used for each individual patient. Lee et al (2010) found that, in experimental rats, prolonged exposure to sevoflurane affected the expression of growth factor, therefore affecting the inflammatory stage of wound healing. Demetriou and Stein (2011) state that while healing complications are multifactoral, the use of several growth factors appears to have a positive effect on wound healing.
This study did not consider the suture patterns used in each individual procedure. As a result, it is possible that patterns used differed according to the veterinary surgeon performing the operation.
Data collection did not consider the type of antibiotics prescribed to animals post operatively, only whether antibiotics were given. This is a limitation in that different antibiotics may be more effective in reducing the likelihood of wound infection due to the differing efficacy of particular antibiotics against different bacteria.
Data were not collected regarding the veterinary surgeons included in the study. Although analysis identified that healing complications were associated with the suture material selected for use, it would have also been beneficial to have collected data on the experience of each veterinary surgeon such as the number of years they had been qualified; although there appear to be no published data, it may be likely that less experienced veterinary surgeons take longer to complete procedures, therefore potentially increasing the risk to the patient caused by a prolonged anaesthetic. It was impossible to standardize the way in which owners managed the animals once discharged, although in the discharge consultation, advice would have been given on suitable care. There is a good possibility that this affected the results, even though statistical analysis for the effect of Elizabethan collars on wound healing was insignificant. Nurses in practice will be aware that not all owners follow recommended guidelines when using Elizabethan collars, typically with some owners removing them before advised. The fact that it will not have been the same veterinary nurse discharging the animal could have also introduced variation to the way the animals were managed post operatively; some nurses may recommend for owners to try the animal without the Elizabethan collar whereas other nurses may recommend keeping the collar on until suture removal.
In addition, exclusion factors did not remove animals from the study with concurrent systemic disease, and these were not considered.
Suggestions for further research
Further research needs to be completed investigating the incidence of healing complications when a range of suture materials are used for different suture patterns. This research could then provide evidence-based guidelines recommending that certain suture materials are not suited to certain patterns and vice versa.
Due to data distribution regarding the age of patients and effect on wound healing, it would be bene-ficial for further research to be completed with a more equal distribution of patient ages. This information could be used to possibly highlight ages when patients may be more at risk of healing complications. Further investigation into the use and effectiveness of antibiotics after routine neutering is required. There appears to be a considerable degree of difference between veterinary surgeons and practices as to whether antibiotics are prescribed post neutering.
The effect of Elizabethan collars on healing success post neutering would be a worthy research area, although a rigorous study design would be needed to ensure all animals were managed exactly the same. If Elizabethan collars were proven to have a beneficial effect on wound healing, this finding could be explained to owners to encourage them to comply with advice given. Further research in this area may also identify the points in the healing process where it is especially important for Elizabethan collars to be worn.
Conclusions
When compared with polyglactin 910, the use of catgut in muscle and subcutaneous tissue was shown to increase the risk of healing complications in cats and dogs. Dogs appeared to be more at risk of healing complications, although confounding factors are likely to have affected this. No statistically significant difference to healing was identified when polyglactin 910 was used for skin sutures compared with nylon. In addition, age, the use of an Elizabethan collar, administration of post-surgical antibiotics and which veterinary surgeon completed the research did not appear to significantly alter wound healing.