A retrospective single-centre study of dogs undergoing general anaesthesia for radiotherapy treatment

This retrospective, single-centre study aimed to establish the types and incidence of complications in dogs undergoing anaesthesia for radiotherapy and identify associated risk factors.
A retrospective analysis of clinical records of dogs undergoing general anaesthesia for radiotherapy treatment at the University of Glasgow between January 2017 and January 2020 was performed. The anaesthetic protocol and incidence of complications were recorded. Complications were defined based on physiological parameters and comments on the clinical record. Factors potentially associated with the incidence of complications were identified using univariable logistic regression (p ≤ 0.1), and used to create a mixed multivariable regression model, with patient identity as a random effect. In the multivariable model p < 0.05 was considered significant.
Overall 129 dogs undergoing 131 courses of radiotherapy, totalling 1289 anaesthetic events, met the inclusion criteria. The final model included 1284 anaesthetic events, owing to missing data. Complications occurred in 1030 anaesthetic events (79.9%), with respiratory complications the most common (n = 467, 36.2%). In the multivariable model, increasing treatment number (Odds Ratio [OR 0.941], 95% confidence interval [CI] 0.907 - 0.976) and increasing age (OR 0.931, 95% CI 0.869 - 0.998) were associated with decreased odds of complications. Factors associated with increased odds of complications included intermittent positive pressure ventilation (OR 1.515, 95% CI 1.103 - 2.081), administration of intravenous fluid therapy (OR 2.909, 95% CI 1.083 - 7.810), and opioid premedication (OR 1.595, 95% CI 1.047 - 2.431). Entire females had reduced odds of complications compared to castrated males (OR 0.448, 95% CI 0.214 - 0.940).
Anaesthetic complications occurred frequently in dogs undergoing radiotherapy. The clinical impact was difficult to determine in this retrospective single-centre study. The incidence decreased over the course of treatments and with increasing patient age. Further investigation of risk factors is warranted, ideally with a prospective multi-centre study.