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EQUINE VETERINARY EDUCATION / AE / JANUARY 2017


when hypotension was treated but did report a decrease in severity. Bidwell et al. (2007) reported that 3 cases with post- anaesthetic myopathy necessitating euthanasia were in horses that had undergone procedures lasting three or more hours. In the current study there was no significant relationship between duration of anaesthesia or bodyweight and the incidence of myopathy or neuropathy. The presence of hypotension during anaesthesia was not examined but this may be useful in future studies. The prevalence of thrombophlebitis doubled in the


current study from 1% to 2% and univariate analysis found a significant positive relationship between increasing age and occurrence of thrombophlebitis. Previous studies have reported thrombophlebitis in 8–13% horses undergoing colic surgery (Morton and Blikslager 2002; Gazzerro et al. 2015). This may not be an appropriate comparison due to an increased incidence of coagulation abnormalities following abdominal surgery. Previous studies have examined putative risk factors: poor insertion technique, prolonged catheterisation, catheter used for induction of anaesthesia, debilitation of the horse and injection of irritants (Lankveld et al. 2001; Divers 2003). To our knowledge, links to nonabdominal procedures have not been tested. Gazzerro et al. (2015) found that geriatric horses were less likely than mature horses to have thrombophlebitis (odds ratio 0.68), which contrasts with our findings. However, previous studies have found increased co-existing systemic disease with increasing age in horses (Fermaglich and Horohov 2002; Vasto et al. 2006), which may explain the greater propensity for this complication. Wound infection was recorded in 1/92 horses in the most


recent data set. This is likely to be an underestimation of the actual rate. In the current study the criteria for identification of wound infections involved a swab being taken for culture and sensitivity and a purulent or seropurulent discharge. In reality, the majority of horses were treated with antibiotics and only if the infection was nonresolving would a swab be taken. Freeman et al. (2012) previously defined post- operative infection as the persistent (>32 h) drainage of serous, purulent or serosanguinous fluid from the incision, more than 48 h after the post-operative period, and local or systemic treatment. Further studies using less stringent criteria may yield very different results, highlighting the importance of defining morbidities. Pyrexia may arise from inflammation or infection following


surgery. In the current study, pyrexia was reported in 7/92 horses compared with 1/194 in the 2004–5 data. The reason for this increase is unknown. No changes in the use of nonsteroidal anti-inflammatory use had been implemented. No previous studies have examined the incidence of pyrexia following nonabdominal surgery in horses, but in human patients incidences vary from 9.3% to 18% (Galicier and Richet 1985; Garibaldi et al. 1985; Petretta et al. 2013). Many of these studies failed to find a cause for the pyrexia and not all patients developed an infection. Likewise, in horses, previous studies have shown that pyrexia is not necessarily associated with infection (Freeman et al. 2012). Further studies may aid identification of contributing factors. Previous morbidity studies have investigated risk factors or


predictors of survivability with respect to different morbidities. Common factors were: drug use, breed, procedure performed, intraoperative complications, re-laparotomy and personnel. Future studies investigating changes in morbidity with these factors may be useful. However, in order to draw


© 2016 EVJ Ltd


firm conclusions large numbers of horses are required, necessitating a multicentre study with similar methods of recording post-operative morbidities. Several limitations became apparent when analysing the


results of this study. In the initial study by Senior et al. (2007), 194 anaesthetics were examined. This contrasts with the current study’s data in several ways. First, the data from 2013– 4 were taken over 12 months compared to 14 months in the 2004–5 data set. Ideally these data would have been matched to the exact time period and the time of year. In addition, many of the records from 2004–5 were incomplete with respect to case background, which led to the inclusion of full data for only 101/194 horses. This introduced bias as the records of animals with significant morbidities are more likely to be complete due to the importance of maintaining legal records when complications occur. It may also be that other morbidities are more likely to be identified if the horse already has a complication, owing to more frequent examination. A further concern was the binary nature of recording, i.e. morbidity present or absent, which does not reflect the subtleties of mild, moderate or severe clinical signs. The decision as to what is included in definitions of morbidity is subjective and disputable (Johnston et al. 1995). In conclusion, increases in the prevalence of morbidities


were found between 2004–5 and 2013–4 following nonabdominal procedures. The expectation was that improvements in clinical practice over time would lead to a decrease in the prevalence of morbidities. Reasons for the overall increase in the prevalence of morbidities are likely to be multifactorial and may include better recording practices, a change in the population of horses or a change in clinical practice. In light of the requirement from the Royal College of Veterinary Surgeons to audit clinical practice, accurate identification of morbidities is essential. Further studies would be useful to formally define each morbidity with the goal of standardising reporting. Ideally a large scale study would be conducted to identify influencing factors that may have been missed when analysing relatively small numbers of cases.


Authors’ declaration of interests No conflicts of interest have been declared.


Ethical animal research


Ethical approval for the study was received by the Veterinary Ethical Review Committee at the University of Edinburgh.


Acknowledgements We thank Dr Mark Senior for sharing the data from the original study.


Manufacturer's address 1Minitab, State College, Pennsylvania, USA.


References


Andersen, M.S., Clark, L., Dyson, S.J. and Newton, J.R. (2006) Risk factors for colic in horses after general anaesthesia for MRI or nonabdominal surgery: absence of evidence of effect from perianaesthetic morphine. Equine Vet. J. 38, 368-374.


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