Anaesthesia of the horse is more perilous than for any other common domestic species (Hubbell et al, 2022), making the high risk of mortality associated with general anaesthesia in horses one of the biggest concerns for equine practitioners and veterinary anaesthetists (Gozalo-Marcilla et al, 2021). An overall mortality rate of 1.9% and a mortality rate of 0.9% in healthy horses was reported by the authors of the Confidential Enquiry into Peri-anaesthetic Equine Fatality (CEPEF-2) study 20 years ago (Johnston et al, 2002). More recently, preliminary findings of the CEPEF-4 study, which is currently well underway, reported an improvement in these figures, but nevertheless, an overall mortality rate of 1.0% remains (Gozalo-Marcilla et al, 2021). The preliminary findings of this study detected a mortality rate of 0.6% in healthy horses undergoing procedures other than exploratory laparotomy for colic (Gozalo-Marcilla et al, 2021), which is still several times higher than in the equivalent cohort of dogs and cats (Brodbelt et al, 2008; Bille et al, 2012; Itami et al, 2017). The increased risk involved in anaesthetising horses has long been established, but there is evidence to indicate that the timing of anaesthesia-related complications has altered over the years. Intra-operative cardiac arrest or cardiovascular collapse accounted for 33% of deaths and fractures, and myopathy during recovery accounted for 32% in CEPEF-2. More recently, it has been reported that the vast majority of fatalities (81–100 %) occur in recovery (Dugdale et al, 2016; Laurenza et al, 2020; Nicolaisen et al, 2022). Reasons for this shift may include changes in the drugs used for induction of anaesthesia and the inhalants used (sevoflurane or isoflurane instead of halothane) (Hubbell et al, 2022); improvements in monitoring equipment and abilities; advancements in anaesthetist training and provision of dedicated case anaesthetists. The safe recovery of horses after general anaesthesia remains a challenge and the flighty nature of horses has been identified to have the greatest influence on recovery quality, and may well limit further risk reduction (Dugdale et al, 2016). This may have implications for equine anaesthetic safety as a whole as since it has been established that the recovery period is the most crucial, anaesthetic-related risk factors are more likely to be similar to those related to quality of recovery in the most recent epidemiology studies (Loomes and Louro, 2021). While some of the mortality risk factors are outside of the control of the anaesthetist, it is also apparent that improvements in recovery safety are required. Understanding the factors that influence recovery quality and overall anaesthetic-related mortality may help the anaesthetist to assess individual risk and tailor anaesthetic management accordingly to maximise patient safety.
The American Society of Anaesthesiologists (ASA) physical status classification system, developed in 1941 by Meyer Saklad, is universally used to assign a ‘grade’ of anaesthetic risk. This system was developed for human patients and has undergone a little adaptation for use in animals. Despite the fact that the ASA system is widely used, it has never been formally validated in either human or veterinary anaesthesia and its reliability has been questioned for some time (McMillan and Brearley, 2013). In human anaesthesia, an association between ASA score and postoperative morbidity has been reported in some studies (Ferrier et al, 2005; Rogers et al, 2005; Thomas et al, 2010), but not in others (Penel et al, 2005; Clayman et al, 1998; Shaari and Urken, 1999). In another study, while there was no difference in postoperative complications between ASA risk groups, there was a statistically significant difference observed regarding intraoperative complications (Karakaş et al, 2016).
In veterinary medicine, a systematic review of 15 studies involving dogs, cats, rabbits, and pigs reported an increased mortality risk within 24 hours of anesthesia in animals with an ASA grade ≥III (Portier and Ida, 2018). In avian patients assigned the ASA grade III–IV, there was an increased odds of death associated with anesthesia compared with patients assigned the ASA grade I–II (Hollwarth et al, 2022). These findings indicate that the ASA system may be valuable for its ability to predict anaesthetic risk in small animals. However, inter-observer agreement was only fair when the ASA system was used to categorise health status in compromised small animal patients (McMillan and Brearley, 2013). The subjective nature of the system, despite its numerical format, may partly explain why assignments of ASA grades can differ between assessors (McMillan and Brearley, 2013; Portier and Ida, 2018). Furthermore, the outcome of anaesthesia may also be influenced by factors other than ASA physical status (Portier and Ida, 2018). To date, a systematic review of the evidence relating to the predictive value of ASA score for perioperative complications in horses is lacking, but several equine studies have identified a positive association between increased ASA score and mortality risk (Johnston et al, 2002; Dugdale et al, 2016; Laurenza et al, 2020). When the increased risk was quantified, for every one unit increase in ASA grade, the odds of death increased by approximately 2.1–2.85 times (Dugdale et al, 2016; Laurenza et al, 2020). The ASA physical classification system has several benefits; it is simple and rapid to perform, requires no further diagnostic testing and can be applied to any patient presenting for general anaesthesia in any situation (McMillan and Brearley, 2013). However, given the unique physical and physiological challenges that horses face in the peri-operative period, it is possible that the ASA physical status classification system alone is unable to account for species-specific risk factors. Hubbell et al (2022) developed a simple rubric to assess equine anaesthetic risk that augments the ASA system with the goal of identifying increased risk in healthy horses, so that measures to reduce risk and ultimately reduce morbidity and mortality can be implemented. In this study, experienced equine anaesthetists were surveyed to identify the relative risk they would assign to a list of factors (Hubbell et al, 2022). Respondents indicated that factors including age (<3 months or >15 years), increased body weight (>700kg), temperament (less manageable or resistant temperament), mobility (mild ataxia or lameness affecting one or more legs), procedure (myelography, airway surgery, abdominal exploratory, ophthalmologic surgery), recovery method (free recovery), anaesthetic duration (90 mins–3 hours), recumbency position (dorsal recumbency) and body shape (round bellied) put horses at double the risk compared to baseline (Hubbell et al, 2022). Fracture repair surgery or an anticipated anaesthetic duration longer than 3 hours was deemed to incur an even higher risk by respondents (Hubbell et al, 2022). The results of surveys may reflect some aspects of personal experience, which may capture additional factors and also support the factors already identified via clinical research.
Factors which may influence anaesthetic risk
Temperament
In healthy horses undergoing magnetic resonance imaging, temperament score before drug administration was weakly but significantly correlated with recovery score (Leece et al, 2008). Horses were scored using a subjective system, with points allocated according to temperament type; (1) calm, well-handled, (2) restless, anxious, (3) aggressive, (4) unhandled, requiring sedation (Leece et al, 2008). The weak negative correlation indicated that horses with less tractable temperaments had poorer recoveries. Similarly, in horses undergoing elective surgery, where recovery quality was scored using a visual analogue scale, a slightly nervous versus calm temperament before anaesthesia was a predictor of poor recovery quality (Hector et al, 2020). In contrast, a prospective clinical study failed to identify an association between temperament score (scored using the results from a unique ‘temperament test’) and recovery score, but it is possible that the use of manual restraint, administration of sedation and rope-assistance in recovery may have obscured any effect (Bryant et al, 2021). Similarly, an earlier study found no effect of temperament on recovery in horses where sedation, manual restraint of horses and a head rope were also employed during recovery (Donaldson et al, 2000). A recently proposed system designed to augment the ASA system, the Combined Horse Anaesthetic Risk Identification and Optimisation Tool (CHARIOT), assigned a higher risk score to horses which are difficult to handle compared to those easily handled (Hubbell et al, 2022).
Age
In a large multicentre study (CEPEF-2), multivariable analysis detected that horses aged between 12 months and 5 years were at a lower risk of anesthetic-related mortality, relative to horses aged between 5–14 years (Johnston et al, 2002). A single centre study reported that increased age was significantly associated with increased mortality, with horses 12–14 years of age attracting twice the mortality risk compared to younger horses, and the risk was tripled for horses aged 15–30 years (Dugdale et al, 2016). In horses undergoing colic surgery, being 10 years of age or older was a significant risk factor for peri-anaesthetic death (Adami et al, 2020). This supports an earlier study where post-operative mortality rates increased with increasing age in horses undergoing colic surgery (Proudman et al, 2006).
The results of a prospective clinical study indicated that age may also influence recovery quality (Hector et al, 2020). In this study of healthy horses undergoing elective surgery, increasing age was associated with poorer recovery quality (Hector et al, 2020). However, in another study involving horses undergoing colic surgery recovery score was negatively correlated to age, indicating that younger horses had poorer recoveries (Adami et al, 2020).
In a single centre case-matched retrospective study, increasing age was identified as a risk factor for fracture or luxation in the immediate recovery period (Bennell et al, 2022). The authors of this study discussed that ageing may be associated with the presence of co-morbidities and body system ageing, together with altered pharmacodynamics of commonly used anesthetic drugs (Bennell et al, 2022).
Weight
Absolute body weight as an independent risk factor may be difficult to separate from body condition score or breed effects. However, in horses undergoing colic surgery, body weight greater than or equal to 500kg was a significant risk factor for peri-anaesthetic death (Adami et al, 2020). The results of a survey of experienced equine anaesthetists indicated that horses >700kg attracted twice the anaesthetic risk compared to lighter horses (Hubbell et al, 2022). An earlier study also reported that heavier breeds carried a higher risk of postoperative fatalities and the authors hypothesised that the size may be a more likely risk factor than any specific breed susceptibility (Proudman et al, 2006). It has been suggested that intra-operatively, larger horse breeds may suffer worse compression atelectasis and ventilation or perfusion mismatching compared to smaller horses, resulting in greater degrees of intra-operative hypoxaemia (Stegmann and Littlejohn, 1987; Nyman et al, 1990). Abdominal shape may also play a role in ventilation–perfusion relationships (Moens et al, 1995; Figure 2) and the recently proposed CHARIOT system assigned greater anaesthetic risk to round-bellied versus flat-bellied horses (Hubbell et al, 2022).
Mobility factors
Lameness and/or ataxia has been regarded to increase anaesthetic risk (Hubbell et al, 2022) and may be linked to the presence of preoperative pain.
Presence of pain
Pain has been proposed to negatively influence recovery (Young and Taylor, 1993). This finding may be because horses are less calm and may attempt to rise sooner, leading to recoveries with higher ataxia, incoordination and muscular weakness (Young and Taylor, 1993; Niimura Del Barrio et al, 2018). The presence of uncontrollable pre-operative pain was deemed to attract twice the peri-anaesthetic risk compared to the presence of controllable pain or freedom from pain when experienced equine anaesthetists were surveyed (Hubbell et al, 2022). In a study by Santiago-Llorente et al (2021), when compared to horses showing satisfactory recoveries, horses with unsatisfactory recovery quality presented with pre-operative pain behaviour. The authors of this study discussed that despite pre- and intra-operative administration of analgesic drugs (flunixin, xylazine, romifidine and opioids), it is possible that a high level of pain may remain during the recovery period in horses that were painful before surgery (Santiago-Llorente et al, 2021). Interestingly, in a study of horses undergoing colic surgery, an increased likelihood of intra-operative mortality was found in horses that showed less severe signs of abdominal pain on admission (Proudman et al, 2006). The authors discussed that this may reflect the extent of devitalisation of bowel, since pain reduces as ischaemia becomes more advanced. Alternatively, the finding may reflect the possibility that horses showing moderate or severe pain generally undergo immediate surgery, and that surgery may be delayed in horses showing less obvious signs of pain (Proudman et al, 2006). In horses undergoing colic surgery, poor premedication effects were also reported to be a risk factor for unsatisfactory recoveries. This may reflect the altered distribution and effect of sedation in systemically compromised horses, or may indicate that horses experiencing increased pain or elevated adrenaline levels may not succumb to the effects of sedation (Santiago-Llorente et al, 2021).
Procedure performed
Myelography, airway surgery, abdominal exploratory and ophthalmologic surgery were assigned scores indicating twice the baseline risk of a superficial laceration repair in surveyed equine anaesthetists (Hubbell et al, 2022).
Myelography
Contrast myelography is increasingly employed to further investigate cervical vertebral pathology in horses (Lindgren et al, 2020). Horses undergoing cervical myelography may experience adverse reactions associated with general anesthesia or myelographic technique, including removal of cerebrospinal fluid (CSF), administration of iodinated contrast material, manipulation of the head and neck, or alterations in craniospinal volume or pressure (Widmer et al, 1998; Deutsch and Taylor, 2022). A multi-centre retrospective study reported that an adverse reaction was observed in 34% of horses undergoing contrast myelography and was associated with longer general anesthesia time and higher contrast-medium volume (Mullen et al, 2015). In that study, most adverse reactions were mild and self-limiting, nonetheless, 2% of horses undergoing myelography were euthanased as a result of the adverse event (Mullen et al, 2015). Intra-procedural adverse events included seizures (focal and generalised), altered mentation, peripheral neuropathy, hyperaesthesia, blindness, increased ataxia, hypertension or hypotension as well as mild abrasions from recovery, hypothermia, intermittent extensor rigidity and pulmonary oedema, carpal bone fractures, myopathy, corneal ulceration, and intermittent second degree atrioventricular block (Mullen et al, 2015).
Earlier studies have indicated that horses with higher neurologic grades can be more ataxic during induction and recovery, and are therefore at a higher risk of falling and inducing spinal cord trauma (Hubbell et al, 1988). Two case reports described tracheal injury and secondary pneumonia after myelography in horses and the authors of both studies indicated that repeated cervical manipulation and endotracheal tube movement causing tracheal erosion was the most likely cause of the complications encountered (Rainger et al, 2006; Díaz et al, 2022). Procedures which involve collection of CSF or injection of contrast agent into the subarachnoid space may cause alterations in intracranial pressure (ICP), and have the potential to precipitate a cardiovascular response. Heart rate and arterial blood pressure remained consistent during iohexol contrast myelography in horses under total intravenous anaesthesia, suggesting that this may be a suitable choice for anaesthetic maintenance (Loomes, 2021a). However, the cardiovascular sequalae resulting from increases or decreases in ICP can range from mild to life-threatening (Bennell and Bardell 2021). A Cushing's-type reflex was reported in a 3-month-old foal immediately after collection of CSF, which manifested as bradycardia and progressed to asystole (Bennell and Bardell, 2021).
Colic surgery
Horses undergoing colic surgery are likely to have pre-existing cardiovascular derangements associated with varying degrees of systemic compromise (Figure 2). The risk of anaesthetic mortality increases up to 11.7% when horses undergoing colic surgery are included (Johnston et al, 2002; Adami et al, 2020; Laurenza et al, 2020).
Another recent study reported that emergency abdominal surgery negatively affected the risk of fatal complications (Nicolaisen et al, 2022).
Ophthalmological surgery
The incidence of unsatisfactory recovery from anaesthesia involving multiple attempts to stand was found to be significantly greater after ocular surgery than after splint-bone excision (Parviainen and Trim, 2000).
Fracture repair
Horses recovering from fracture repair were identified to have a 5.5 times higher risk of fatality in a large multicentre study (CEPEF-2) (Johnston et al, 2002). The reasons for such an elevated risk may include the long anaesthetic durations associated with complex surgeries, pre-existing pain and the potential for horses to be stressed, excited, exhausted and dehydrated, all of which may contribute to less than ideal conditions to withstand the further insult of anaesthesia and surgery (Johnston et al, 2002). Recently, the CHARIOT system proposed for assessing equine anaesthetic risk reported that fracture repair attracts three times the risk compared to superficial laceration repair or arthroscopy (Hubbell et al, 2022).
Anticipated anaesthetic duration
The negative influence on recovery quality and the increased risk of death of increased anaesthetic duration has been well established (Young and Taylor, 1993; Johnston et al, 1995). When the duration was quantified, the likelihood of death increased as the duration of anaesthesia increased beyond 61 minutes, with the greatest risk of death being associated with operations lasting longer than 241 minutes (Johnston et al, 1995). When surveyed, experienced equine anaesthetists assigned a sliding scale of increased risk as anaesthetic duration exceeded a baseline of 30 minutes (Hubbell et al, 2022). Anaesthetic durations of 90 minutes–3 hours was anticipated to incur double the baseline risk, while durations exceeding 3 hours attracted triple the baseline risk (Hubbell et al, 2022). A single centre prospective study identified that recovery quality was negatively correlated with anaesthetic duration (Bryant et al, 2021). Recovery scores were significantly better quality in horses where general anaesthesia time was ≤90 minutes compared with >91 minutes of isoflurane anaesthesia (Bryant et al, 2021). Duration of anaesthesia was also a significant risk factor for peri-anaesthetic death in horses undergoing colic surgery (Adami et al, 2020), where an increasing general anaesthesia duration was associated with a poorer quality of recovery (Louro et al, 2021b). In another retrospective study, the duration of surgery had a significant negative effect on the risk of fatal complications (Nicolaisen et al, 2022).
Timing of surgery
Surgery performed outside of normal working hours (9am–5pm) had an increased mortality risk, which was at its worst between 6pm and 8pm, incurring a relative risk of 9.9 compared to surgeries carried out between 6am and 1pm (Johnston et al, 1995) Reasons for this high risk period, which coincides with the end of the ‘normal’ working day, may include operator team fatigue and reduced staffing levels (Johnston et al, 1995). Surgery performed overnight was also associated with worse recovery scores in another study (Dugdale et al, 2016).
Recumbency position
A single centre retrospective study identified that either left or right lateral position was approximately four times less likely than dorsal position to be associated with mortality (Dugdale et al, 2016). While, in this study, dorsal recumbency was a co-variate of colic surgery, a number of physiological compromises occur in dorsal compared to lateral recumbency. Earlier studies supported this finding and a large multicentre study identified that horses not placed in dorsal recumbency were at reduced risk of death compared to those in dorsal recumbency (Johnston et al, 1995). The results of survey of equine anaesthetists corroborated these findings and horses positioned in dorsal recumbency were assigned anaesthetic risk scores twice that of horses positioned in lateral recumbency (Hubbell et al, 2022).
Intra-operative medications administered
Ketamine
A retrospective analysis identified a four-fold increase in risk of fracture or luxation in the immediate recovery period when additional boluses of ketamine were administered intra-operatively (Bennell et al, 2022). Similarly, in horses recovering after emergency exploratory laparotomy, higher intra-operative dosages of ketamine and/or thiopental were associated with poor recovery quality (Louro et al, 2021b). Intra-anaesthetic ketamine administration may be performed to provide an increased anaesthetic depth, provide additional analgesia where it is considered that the patient is reacting to nociceptive stimuli, or to pre-empt anticipated nociceptive stimuli (Bennell et al, 2022). Avoiding administering additional intraoperative ketamine boluses, where possible, in the last 20 minutes of anesthesia may minimise any negative impact on recovery quality (Bennell et al, 2022).
Aerosolised salbutamol
Administration of aerosolised salbutamol was associated with a five times increased risk of fracture or luxation in the immediate recovery period in one retrospective study, using case matched controls (Bennell et al, 2022). However, in this study, the administration of salbutamol only had a moderate correlation with hypoxaemia, (Bennell et al, 2022), so the precise reason for salbutamol administration may not be consistent. Intra-operative salbutamol administration has been associated with hypokalaemia in horses undergoing colic surgery (Adami et al, 2020) and with a greater reduction in intra-operative serum potassium concentration in healthy horses (Loomes, 2021b). However, the reason for the relationship between salbutamol administration and poor recovery quality remains unclear and is likely to be multifactorial.
Physiological parameters
Intra-operative mortality was significantly and positively associated with heart rate and packed cell volume at admission in horses undergoing colic surgery (Proudman et al, 2006). Similarly, in a another study, intra-operative tachycardia (>55 beats per minute; Figure 3) was a significant risk factor for peri-anaesthetic death in horses undergoing colic surgery (Adami et al, 2020). Tachycardia may reflect a certain degree of cardiovascular instability and may be consistent with absolute or relative hypovolaemia and volume depletion. Intra-operatively, tachycardia may also result from inadequate analgesia or dobutamine overdose (Adami et al, 2020). When recovery quality was analysed in horses after colic surgery, horses with unsatisfactory recovery quality presented with a higher packed cell volume and higher blood lactate compared to horses showing satisfactory recovery quality (Santiago-Llorente et al, 2021).
Intra-operative hypoxaemia (defined as arterial oxygen partial pressure <60 mmHg) was a risk factor for non-safe recoveries in one retrospective study (Rüegg et al, 2016). It has also been established that prolonged periods of hypotension (mean arterial pressure <60mmHg) have a profound effect on recovery quality (Grandy et al, 1987), but there is also evidence to indicate that even very short periods of decreased muscular blood flow under anaesthesia may have an adverse effect on recovery quality (Hector et al, 2020). When hypotension was defined as mean arterial pressure <70 mmHg, poor recovery quality was associated with duration of hypotension in one clinical study (Hector et al, 2020). Furthermore, in horses recovering after colic surgery, administration of a dobutamine dose ≥1.5 mcg/kg/ minute was strongly associated with unsatisfactory recovery quality (Santiago-Llorente et al, 2021). This finding may be explained by the fact that unhealthy horses that are unstable haemodynamically require higher doses of dobutamine compared to healthy animals, and also experience lower mean arterial pressure values (Santiago-Llorente et al, 2021). In addition, dobutamine infusions are not routinely continued during the recovery phase. This withdrawal of blood pressure support in sick horses may leave them haemodynamically unstable for recovery, making them more susceptible to complications and morbidity or mortality during the recovery phase.
Recovery assistance available.
An association between overall anaesthetic-related mortality and poor quality of recovery has been identified (Young and Taylor 1990; Laurenza et al, 2020), indicating that endeavours to optimise recovery safety may significantly improve peri-anaesthetic safety. Various techniques are employed to recover horses from anaesthesia, and none is without complication (Deutsch and Taylor, 2022). Surveyed equine anaesthetists assigned double the risk to free recoveries compared to assisted recoveries (Hubbell et al, 2022). Recovery assistance is most commonly performed using head and tail ropes. The results of surveyed American and European College of Veterinary Anaesthesia and Analgesia diplomats reported that 50% of anaesthetists routinely assisted recoveries (Kästner, 2010). This figure increased to 67–71.5% according to the results of two international surveys (Wohlfender et al, 2015; de Miguel Garcia et al, 2021). However, a lower incidence of recovery assistance was reported in a multi-centre study, where 41% of recoveries were assisted with ropes; 8% were manually assisted (mostly foals) and 51% were free (Gozalo-Marcilla et al, 2021). The variation in these figures may reflect the different demographics of the anaesthetists surveyed, but also illustrates the controversy surrounding the optimal recovery method.
Head and tail rope assisted recovery
The findings from a systematic review of rope-assisted recovery reported that rope assistance may improve recovery time and quality in some horses, but there is insufficient evidence to permit a full recommendation regarding rope assistance during recovery from general anaesthesia in horses (Lloyd and Murison, 2021). However, since it is known that fractures are responsible for the largest proportion of recovery-associated deaths, improvements to the recovery process that can reduce fracture occurrence are warranted (Dugdale et al, 2016).
A small number of equine studies have been performed to investigate rope assisted recovery. Two retrospective studies found no difference in complications between unassisted and rope-assisted recoveries in horses undergoing abdominal surgery (Auer and Huber 2012; Rüegg et al. 2016). In contrast, a prospective randomised study involving healthy horses undergoing elective surgery found that horses assisted with ropes had a better quality of recovery, shorter recovery time, took fewer attempts to stand and sustained fewer injuries in recovery compared to unassisted horses (Arndt et al. 2020). In this study, recoveries were evaluated by the person involved in operating the rope system, which may have introduced evaluator bias, although the objective measures of recovery, such as attempts to stand and number of injuries, are less vulnerable to such influences. In two other studies, head and tail rope assisted recovery significantly reduced the risk of fatal complications (Nicolaisen et al, 2022) and was associated with better recovery quality (Louro et al, 2021b) after emergency abdominal surgery. Recovery safety may be particularly important for horses recovering from colic surgery since they may be systemically compromised and experiencing exhaustion and musculoskeletal weakness. Preliminary results from a multi-centre study reported that for horses undergoing colic surgery, when each phase of anaesthesia was compared (premedication, induction, maintenance and recovery), 50% of anaesthesia-related fatalities occurred in recovery (Gozalo-Marcilla et al, 2021).
The use of ropes may incur technical difficulties related to the ropes themselves. Two studies reported incidences of between 2 – 5.9% of technical problems with the ropes including headcollar and rope failure (Arndt et al, 2020; Nicolaisen et al, 2022). Material fail, twisting of ropes, halters falling off and loss of ropes were observed in another retrospective study (Rüegg et al, 2016). While it is not possible to draw conclusions from such a sparse evidence base, it seems that while rope assistance may improve recovery quality in some horses, total elimination of fatal complications is not yet possible.
Risk reduction
Patient safety should be at the forefront of everything anaesthetists and anaesthesiologists do (McMillan, 2014). An awareness of factors that influence anaesthetic risk is crucial, as is continued research into peri-anaesthetic safety. Epidemiological studies into adverse outcomes in equine anaesthesia will continue to play an important role in identifying (modifiable) risk factors for the foreseeable future (Senior, 2015). Similarly, the performance of regular systematic reviews of the most recent evidence is a useful tool in the armoury for clinical decision making. The results from two recent systematic reviews of the evidence relating to factors influencing recovery quality after general anaesthesia indicated that provision of adequate analgesia for painful procedures is crucial. Furthermore, the use of certain agents as part of a partial intravenous anaesthetic protocol, the cessation of intravenous lidocaine 30 minutes before the end of anaesthesia, and the provision of an α-2 adrenoceptor agonist before recovery, may all have a positive impact on recovery quality (Loomes and Louro, 2021, 2022).
Critical incident reporting and implementation of the surgical safety checklist
While some degree of risk is inevitable, it is important to minimise the contribution of avoidable error. The practice of patient safety incident reporting has the advantage of identifying potential risks to the patient without it necessarily resulting in morbidity or mortality (McMillan, 2014). Documentation and whole-practice awareness together with constructive discussion relating to ‘near-misses’ may help avoid escalation of incidents to fatalities.
Implementation of the surgical safety checklist has been associated with improved postoperative outcomes in clinical settings (Bergström et al, 2016; Cray et al, 2018; Launcelott et al, 2019). Checklists have been shown to reduce mortality and complication rates (Haynes et al, 2009), improve communication and perception of safety in human hospital anaesthesia teams (Tscholl et al. 2015), and reduce the incidence and severity of complications in veterinary settings (Bergström et al, 2016). However, barriers to the effective implementation of checklists have been identified and the perceived impact of checklists could remain varied in veterinary medicine until appropriate veterinary implementation programs are widespread (Hawker et al, 2021). Implementing a peri-anaesthetic checklist can be a challenging process (Menoud et al, 2018), requiring commitment from the whole team. Furthermore, regular reviews could be carried out in equine anaesthetic practice to evaluate whether improvements to safety can be made at the practice level (Senior 2015).
Preparedness
In the event of a complication occurring, emergency preparedness and appropriate equipment accessibility may improve outcomes. Trained individuals supported by well-designed environments, equipment and processes can adapt to unknown situations (Marshall and Touzell, 2020). In-situ simulation training of crisis management by the whole team in the actual clinical setting is perhaps the most effective way of building effective teamwork (Goldhaber-Fiebert and Howard 2013).
Human error
In contrast to human medicine, veterinary studies have rarely taken human error into account (Senior, 2015). One rare study found that errors in case management played a role in 75% of deaths in healthy dogs and cats, with airway complications causing the majority of deaths (Clarke and Hall, 1990). Reducing the opportunity for avoidable errors to occur is achievable, but the safety of patients in the operating theatre relies on a cordial and efficient working relationship between all members of the theatre team (Marshall and Touzell, 2020).
Conclusions
The assessment of an individual patient's anaesthetic risk involves consideration of several factors. The current system based on the classification of physical status has been shown to identify patients with increased risk of complications, and this system may be complemented by the consideration of additional risk factors identified from research findings. Accurate assessment of risk relies on ongoing research reflecting current clinical practice, which allows modification of the assessment system or systems in practical use. A considered assessment of risk allows the anaesthetist to be prepared for complications which may arise in individual patients, and may enhance the effectiveness of the treatment response.
KEY POINTS
- Assessment of equine anaesthetic risk relies on the consideration of individual patient risk factors.
- Ongoing research is required to continue to identify risk factors which are relevant to current clinical practice.
- Acknowledgement of individual patient risk factors and preparedness for complication management may facilitate effective treatment.
- A combination of both technical and non-technical skills is required to optimise patient safety.
- A whole team approach is essential to maximise perioperative patient safety.