Recovery of horses from general anaesthesia: A systematic review (2000-2020) of risk factors and influence of interventions during the recovery period

Background In equine anaesthesia, the recovery period is a time of considerable risk and has been the focus of prolific research. Risk factors, including age, type and duration of procedure or temperament may influence recovery quality. Unfortunately, the anaesthetist is unable to control for these factors, therefore various pharmacological interventions and recovery methods have been developed with the objective of improving recovery quality. However, no consensus among anaesthetists has been reached for many of these interventions and their implications for recovery-related mortality and morbidity. Objectives To conduct a systematic review of the published evidence relating to risk factors and interventions in the recovery period which may influence recovery quality from equine general anaesthesia (GA). Study design A systematic evaluation of the equine veterinary literature using the GRADE framework. Methods A literature search was performed and studies were assessed for eligibility by both authors utilising PRISMA guidelines. Studies meeting inclusion criteria were evaluated by both authors, categorically summarised and the quality of evidence for each sub-topic was assessed using the GRADE framework. Results Thirty-nine studies were identified which directly assessed the impact of risk factors and recovery interventions on recovery quality after equine GA. There was evidence to support that peri-anaesthetic risk factors such as anaesthesia duration, American Society of Anesthesiologists (ASA) physical status and surgical procedure influenced recovery quality. We also identified sufficient evidence that administration of alpha-2 adrenoreceptor agonists immediately prior to recovery, improves recovery quality. Main limitations The validity of the results of some studies may have been compromised by missing data and small sample sizes. Conclusions Recovery quality is influenced by factors including: anaesthesia duration, ASA physical status and surgical procedure. Recovery quality can be improved by the administration of an alpha-2 adrenoreceptor agonist immediately prior to recovery.