Pre-Anaesthetic Assessment in Small Animal Patients: A Practical, Evidence-Based Approach

Pre-anaesthetic assessment is one of the most important steps in ensuring safe and effective anaesthesia in small animal patients. Rather than being a routine checklist, it is a structured and evidence-based process that allows the veterinary team to evaluate risks, optimise patient conditions, and tailor anaesthetic protocols for each individual patient. Despite continued advances in veterinary medicine, anaesthesia-related mortality remains a concern, with UK data showing approximately 1 in 601 dogs and 1 in 419 cats across all health categories dying from an anaesthesia-related event. These numbers show how important it is to plan ahead and make smart clinical decisions before any procedure.

A thorough patient history is often the most valuable starting point. Asking specific, targeted questions about previous anaesthetic events, current medications, recent illnesses, or subtle behavioural changes can reveal important risk factors that may not be immediately apparent. General questions are rarely sufficient; instead, a more detailed and focused approach helps to uncover information that may significantly influence anaesthetic planning. Evidence suggests that history-taking, alongside physical examination, is often more influential in guiding anaesthetic protocols than diagnostic testing alone.

The physical examination remains central to pre-anaesthetic assessment and should never be rushed. Careful evaluation of cardiovascular and respiratory function, hydration status, body condition, and neurological status provides essential insight into how a patient is likely to respond to anaesthesia. In many cases, experienced clinicians are able to anticipate laboratory abnormalities based on examination findings alone, reinforcing the importance of clinical skills in risk assessment. Even mild abnormalities can indicate increased risk and should be considered when developing an anaesthetic plan.

To support risk stratification, the ASA (American Society of Anesthesiologists) classification system is widely used in both human and veterinary medicine. This system provides a structured way to categorise patients based on their overall health, with higher grades being associated with increased morbidity and mortality. For example, mortality in dogs increases from around 0.05% in ASA I–II patients to over 1% in ASA III and above, with similar trends observed in cats. While ASA classification is a useful communication and planning tool, it is not without limitations. It is inherently subjective, can vary among the veterinary team, and does not account for all factors, such as procedural complexity or the severity of individual disease processes. As such, it should always be used alongside clinical judgement rather than as a standalone decision-making tool.

The role of diagnostic testing in pre-anaesthetic assessment continues to be debated. While testing can provide valuable information, particularly in older or higher-risk patients, it should be applied selectively rather than routinely. A minimum database, including parameters such as packed cell volume, total solids, blood glucose, and urea, may be appropriate in some cases, while more advanced diagnostics should be guided by clinical findings. Evidence suggests that in many patients with unremarkable history and examination, laboratory testing may not yield additional clinically significant information. In fact, studies have shown that abnormalities are identified in a minority of cases and only rarely result in changes to anaesthetic protocols or ASA classification. However, testing remains valuable in detecting subclinical disease, particularly in older animals, where up to 30% may have previously unrecognised conditions.

Anaesthetic risk is influenced by a range of patient-specific and procedural factors. Age is a significant consideration, with older patients showing increased risk largely due to the presence of comorbidities rather than age alone. Obesity is another important factor, affecting drug pharmacokinetics, respiratory function, and recovery, and requiring careful dose adjustments based on lean body weight. At the other end of the spectrum, very small or paediatric patients present their own challenges, including increased susceptibility to hypoglycaemia, hypothermia, and difficulties with drug dosing and airway management. Procedure urgency also plays a critical role, as emergency cases often carry a higher risk due to limited time for stabilisation, with mortality increasing significantly compared to elective procedures.

In addition to clinical considerations, pre-anaesthetic assessment carries important legal and ethical responsibilities. Obtaining appropriate consent is essential, particularly for procedures involving risk. Clients must be informed of potential complications, alternative options, and expected outcomes and should be given time to consider this information before proceeding. Failure to obtain informed consent can have significant legal implications, including liability for compensation and reputational damage to the practice.

It is also important to recognise that anaesthesia risks do not end when the procedure is complete. A significant proportion of complications occur during the recovery period, highlighting the need for continued monitoring and appropriate post-operative care. Effective pre-anaesthetic assessment contributes not only to safer induction and maintenance of anaesthesia but also to improved recovery outcomes by allowing the veterinary team to anticipate and mitigate potential complications.

Ultimately, pre-anaesthetic assessment is not about identifying a “low-risk” patient but about understanding and managing the risks of the individual in front of us. By combining thorough history-taking, careful physical examination, and targeted use of diagnostics, veterinary professionals can make informed decisions, tailor anaesthetic plans, and improve patient safety. While tools such as ASA classification and laboratory testing provide valuable support, it is clinical judgement, grounded in a detailed understanding of the patient, that remains the cornerstone of safe anaesthetic practice.