EQUINE VETERINARY EDUCATION / AE / JANUARY 2017
time was statistically significantly longer in procedures conducted in the most recent time period (103 min, compared to 87 min in 2004–5, P = 0.003) and the number of emergency cases was statistically significantly greater in the more recent data set (29%, compared with 21%; P<0.001).
Orthopaedic surgery was carried out in the majority of
cases (54/92, 59% in 2013–4 and 58/101, 57%). The majority of the orthopaedic cases involved arthroscopy with lavage while soft tissue cases largely comprised upper airway surgery and castration.
Morbidities The overall prevalence of post-operative morbidities was 13.4% when prolonged recovery was excluded in the 2004–5 data. This compares with 25% in the 2013–4 data meaning that the overall prevalence of morbidities had increased. The prevalence of PAC, thrombophlebitis, pyrexia and neuropathy, myopathy, and post-operative lameness increased over time. PAC increased in prevalence from 7.7% to 18.5% (P = 0.01). In the study by Senior et al. no horses experienced post-operative lameness, myopathy or neuropathy in comparison to 3% of horses in the 2013–4 data set (P = 0.06) and the proportion of horses with thrombophlebitis increased from 1% to 2% (P = 0.053). Horses classified as pyrexic increased from 0.5% in 2004–5 to 7.6% (P = 0.002). No horses had a fracture in the post-operative period in either dataset. Fewer horses suffered from diarrhoea in the 2013–4 dataset (2% vs. 1%, P = 0.92). Similarly, in the 2004–5 dataset 1.5% of horses were described as being in respiratory distress compared to 0% in the 2013–14 dataset (P = 0.563). One horse (0.5%) in the 2004–5 dataset had wounds in recovery in comparison to 0% in the 2013–4 dataset (P = 0.490). Wound infections were not reported in the 2004–5 data set while one horse was reported to have a wound infection in the 2013–4 data.
Binary regression analysis Univariate analysis revealed a statistically significant association (P = 0.045) between the duration of anaesthesia and the prevalence of PAC in horses. Duration of anaesthesia was not found to be significantly associated with the other morbidities reported. No statistically significant association was found between colic and sex (P = 0.390), time in hospital (P = 0.816), bodyweight (P = 0.169), age (P = 0.403) or emergency status (P = 0.075). Multivariable univariate logistic regression revealed no statistically significant associations between bodyweight or emergency status, and PAC. Univariate analysis of all horses revealed a statistically
significant association (P = 0.036) between age and thrombophlebitis: the odds ratio indicated its likelihood increased by 1.20 (95% confidence interval 1.01–1.41) for every year of the horse’s life. No statistically significant relationships were found for wound infections or pyrexia.
Discussion
The purpose of the current study was to test the null hypothesis that the prevalence and type of morbidity at a single centre did not change over time. The null hypothesis was rejected as the overall prevalence of morbidities increased.
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Post-anaesthetic colic, after nonabdominal surgery,
increased from 7.7% (2004–5) to 18.5% (2013–4), which is statistically significant and clinically important. Additionally, there was a significant association between PAC and the duration of anaesthesia, which had not been identified previously. The prevalence of PAC was greater than that found in other studies, which ranged from 2.8% (Mircica et al. 2003; Senior et al. 2004, 2007; Andersen et al. 2006; Nelson et al. 2013) to 10.5% (Jago et al. 2015). The reasons for the increase in prevalence are not known.
The current study did not investigate PAC with respect to administration of drugs, personnel or out-of-hours surgery. Emergency status was not associated with an increased risk. In previous studies, the risk factors identified included morphine administration and out-of-hours surgery (Senior et al. 2004), decreased faecal output following surgery, the Arabian breed and increasing blood lactate (Nelson et al. 2013). Morphine was found to lead to no increased risk of colic, in contrast to the use of isoflurane and benzylpenicillin or ceftiofur (Andersen et al. 2006). Jago et al. (2015) found that PAC following nonabdominal surgery was significantly associated with breed, perioperative microbials and administration of butorphanol. Senior et al. (2007) stated that the morbidities reported in the 2004–5 study were believed to be minimums and that ‘mild’ cases of colic may not have been reported. Senior et al. (2007) also found large variations in the PAC in different centres. The increase in prevalence may have been due to reporting of more ‘mild’ cases or a different population of horses. In the original data from Senior et al. (2007), horses were analysed for signs of colic 72 h following surgery whereas the most recent data included horses that displayed colic until discharge. This may go some way to explain the increase in prevalence. Given the stated risk factors in previous studies, further work investigating drugs used, faecal output and the proportion of surgeries during the out-of-hours period may be useful. The significant association between increasing
anaesthesia time and the prevalence of PAC highlights the importance of minimising time spent under anaesthesia. The confidential enquiry into post-operative equine fatalities found that the likelihood of death increased as the duration of anaesthesia increased beyond 61 min, with the greatest risk being operations lasting longer than 241 min (Johnston et al. 1995). Minimising anaesthesia time involves maximising efficiency of surgical preparation, ensuring optimal communication between anaesthesia and surgical teams and provision of sufficient personnel to reduce surgery time. The results presented reinforce the evidence that minimising the time spent by horses under anaesthesia is an important consideration for surgical intervention. No cases of neuropathy or myopathy were recorded in
horses undergoing nonabdominal procedures during the 2004–5 sampling period in contrast to 3 (out of 92) cases recorded from 2013–2014. Previous studies have examined the incidence of post-anaesthetic lameness. Richey et al. (1990) reported an incidence of post anaesthetic lameness of 6.4%, Franci et al. (2006) reported this morbidity in 0.98% of horses following surgery and Young and Taylor (1993) found that 1.2% of 575 horses developed myopathy following nonorthopaedic procedures. Richey et al. (1990) found a significant association between hypotension and anaesthesia duration with respect to post-anaesthetic lameness while Young and Taylor (1993) reported no reduction of incidence
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