Preanesthetic evaluation

The preanesthetic patient evaluation identifies individual risk factors and underlying physiologic challenges that contribute information for development of the anesthetic plan. Factors to be evaluated include the following:
  • History: Identify risk factors, including responses to previous anesthetic events, known medical conditions, and previous adverse drug responses. Identify all prescribed and over-the-counter medications (including aspirin) and supplements to avoid adverse drug interactions.1
  • Physical examination: A thorough physical examination may reveal risk factors, such as heart murmur and/or arrhythmia or abnormal lung sounds.
  • Age: Advanced age can increase anesthetic risk because of changes in cardiovascular and respiratory function. Disease processes occur more commonly in aged patients. Very young patients can be at increased risk from hypoglycemia, hypothermia, and decreased drug metabolism.
  • Breed: Few breed-specific anesthesia issues are documented. Brachycephalic dogs and cats are more prone to upper airway obstruction. Greyhounds have longer sleep times after receiving some anesthetics such as propofol and thiopentald. Some breeds of dogs (e.g., Cavalier King Charles spaniel) and cats (e.g., Maine coon) may be predisposed to cardiac disease as they age.2
  • Temperament: An aggressive or fractious temperament may pose a danger to staff and can limit the preanesthetic evaluation or make examination impossible. The selection of an alternative preanesthetic drug or drug combination may be required for the aggressive or overly fearful animal due to the need for higher-than-usual drug doses. Conversely, a quiet or depressed animal may benefit from lower doses for sedation or anesthesia.
  • Type of procedure: Evaluate the procedure’s level of invasiveness, anticipated pain, risk of hemorrhage, and/or predisposition to hypothermia. Some procedures may limit physical access to the patient for monitoring.
  • Using heavy sedation versus general anesthesia: This choice depends on the procedure, patient temperament, and the need for monitoring and support. In general, sedation may be appropriate for shorter (<30 min) and less invasive procedures (e.g., diagnostic procedures, joint injections, suture removal, and wound management). Sedated patients, like those under general anesthesia, require appropriate monitoring and supportive care. They may require airway management and/or O2 supplementation. Be prepared to intubate if necessary.
  • Experience and qualifications of personnel: Previous training in local and regional anesthesia techniques will facilitate their perioperative use. Also, a more experienced surgeon may be faster and cause less tissue trauma to a patient than a less experienced one.

Risk factors and individual patients’ needs provide a framework for developing individualized patient plans and may indicate the need for additional diagnostic testing or stabilization before anesthesia.

Individual practice procedures may include a minimum database of laboratory analysis, electro-cardiogram, and diagnostic imaging for different patient groups. There is no evidence to indicate the minimum time frame before anesthesia within which laboratory analysis should be performed. However, the timing should be reasonable to detect changes that impact anesthetic risk. The type and timing of such testing are determined by the veterinarian based on the previously mentioned factors, as well as any change in patient status or the presence of concurrent disease.

Categorization of patients using the American Society of Anesthesiologists (ASA) Physical Status Classification System provides a framework for evaluation (Table 1). Patients with a higher ASA status are at greater risk for anesthetic complications and require additional precautions to better ensure a positive outcome.3

Client communication is important at all times, but especially before anesthetic procedures. Obtain written informed consente after discussing the patient assessment and risks, the proposed anesthetic plan, and any available medical or surgical alternatives with the client. Include such information in informed consent documents as guided by local and state regulatory agencies.4


ASA Physical Status Classification System

  1. Normal healthy patient
  2. Patient with mild systemic disease
  3. Patient with severe systemic disease
  4. Patient with severe systemic disease that is a constant threat to life
  5. Moribund patient who is not expected to survive without the operation

Based on the Physical Status Classification System of the American Society of Anesthesiologists, 520 N Northwest Highway, Park Ridge IL 60068-2573; ASA, American Society of Anesthesiologists.