Veterinary Anesthesia Evaluation

Patient Evaluation and Preparation

• Learning Objectives:
  • Describe who, what, where, when, and why a thorough patient evaluation is needed before anesthesia.
  • Describe anesthetic preparation for veterinary patients.
  • Describe general anesthetic concerns for a patient prior to anesthesia.

Who Should Perform the Pre-Anesthetic Evaluation?

• Ultimately, the veterinarian in charge of the patient is responsible.
• Registered technicians may perform aspects of the evaluation.
• During clinical rotations, different personnel may be involved.
• If both a surgeon and an anesthesiologist are involved, the responsibility of evaluation should be clarified.

What is Part of the Pre-Anesthetic Evaluation?

• Signalment: Species, breed, age, sex, and reproductive status.
• History: Including previous anesthesia events, current illnesses, symptoms, duration, severity, recent/current medications, and vaccination status.
• Physical Exam (PE): Including body weight (BW), body condition score (BCS), temperament/mentation, pain level, and stress level.
• Blood & Urine Sampling: Routine blood work, including complete blood count (CBC) and chemistry profile. Urine analysis (UA).
• Advanced Diagnostics (if indicated): Electrocardiography (ECG), blood pressure (BP), radiographs, abdominal ultrasound (abd U/S), echography, endocrine testing, etc.

Routine ECG Screening

• Patients with cardiovascular (CV) disease.
• Geriatric patients.
• Underlying diseases that may lead to arrhythmias.
• Hyperkalemia.
• Gastric dilatation-volvulus (GDV).
• Splenomegaly.
• Traumatic myocarditis.

Physical Exam Findings

• Temperature: Normal values for specific species.
• Pulse: Rate, rhythm, and quality; auscultate for murmurs, palpate pulse simultaneously.
• Respiration: Describe sounds, assess the trachea (why palpate?).
• Mucous membranes: Hydration status and hemodynamic status.
• Body Weight: Convert pounds to kilograms (lbs. vs. kg).

Physical Findings in Dehydration

• Clinical signs associated with different percentages of dehydration (ranging from subtle loss of skin elasticity to definite signs of shock and impending death).

Remainder of Physical Exam

• Integument.
• Lymph nodes (LN).
• Gastrointestinal (GI) tract (abdominal palpation, gut sounds).
• Genitourinary tract.
• Central nervous system (CNS).

The "SOAP" & Anesthesia Request Form

• A structured form for recording patient information (subjective, objective, assessment, plan). Includes patient data, history, physical exam findings, current medications, ASA status, procedures, and estimated anesthetic parameters.

What Lab Work Should Be Done?

• Young (< 5 years old) and healthy patients: PCV, total solids (TS), glucose, blood urea nitrogen (BUN), and other parameters.
• Older patients or those with a history/current illnesses: Complete blood count (CBC), chemistry profile, urinalysis, and other tests as indicated.
• Research studies: CBC, chemistry profiles, urinalysis are used as a minimal database. Additional tests may include blood gas analysis, coagulation profile, liver function tests, etc.

Where is the Pre-Anesthetic Evaluation Performed?

• Typically in the clinic or during farm calls.
• Find a quiet area to auscultate heart and lungs.
• Adapt the evaluation based on animal's temperament (fractious, zoo/wild). Sedation/tranquilization may be needed.

When Should the Pre-Anesthetic Evaluation Be Performed?

• Usually the day before or up to one week before a planned procedure (additional exam on day of surgery).
• Emergencies: immediately prior to the procedure.
• Postponed surgeries: re-evaluate closer to surgery.

Why a Pre-Anesthetic Evaluation?

• Provides a safer anesthetic episode.
• Formulates an assessment of patient organ function and perioperative risk.
• Provides valuable information to the client.
• Enables documentation of conversations and opinions regarding risks, prior to sedation/anesthesia.

ASA Physical Status Scale

• Categorizes patients based on their physical status (I-V) determined by overall health, presence/absence/severity of disease, pain level, stress level, and overall efficiency/function of organ systems.

What is the Physical Status?

• Presence/absence of disease.
• Determined by history, physical exam, lab tests, and other diagnostics.
• Severity of pain.
• Level of stress.
• Overall organ system efficiency/function.

When Should the ASA Physical Status be Assigned?

• After the complete physical exam & lab work/diagnostic interpretation.
• Distinguish between elective, scheduled, and urgent cases.

Case Examples

• Detailed case descriptions and data (e.g., age, species, presenting complaint, clinical signs, physical exam, lab test results) to illustrate procedures. Includes ASA physical status classifications.

Why is ASA Physical Status Important?

• Used (along with the anesthetist's skill and chosen drugs) to assess anesthetic risk.
• Important for patient selection in research studies.
• Can be used legally to document procedures.

Other Considerations for Dosing Drugs

• Wide species variation(cats vs. dogs).
• Patient size (smaller animals may require higher doses per weight unit).
• Body conformation and fat distribution affect drug absorption and distribution.
• Poor overall condition/starvation and age influence metabolic rate.

Effect of Age When Selecting Anesthetic Drug Dosages

• Neonates/pediatric: decrease dose.
• Juvenile/early adulthood: increase dose.
• Geriatrics: decrease dose.

What Concurrent Medications Could Cause Problems?

• A list of medications potentially interfering with anesthesia (e.g., aminoglycosides, ACE inhibitors, digoxin, beta-blockers, diuretics, NSAIDS, tramadol with MOA inhibitors, TCAs, or PPAs, opioids, etc, and nutraceuticals like St. John's Wort).

Patient Preparation

• Fasting: Guidelines for food and water deprivation by species.
• Hygiene: Encourage bowel/bladder evacuation prior to surgery; clean animals.
• Dehydration and Electrolyte Imbalance: Address anemia
• Preoperative Antibiotics: Recommended protocols. This includes IV cefazolin.
• Specific prep: Enemas and bowel preparations for specific procedures.

Fasting and Water Deprivation Times

• Guidelines for fasting times for various species.

Why is Patient Fasting Necessary for General Anesthesia?

• Decreases the risk of aspiration.
• Prevents stomach distension, affecting ventilation.
• Full stomachs may rupture during induction in some species/conditions.

Why Patient Fasting Not Necessary in All cases

• Neonates, some small birds and mammals are prone to hypoglycemia within a few hours of starvation.
• High metabolic rate, particularly in birds and small mammals.

Depriving Water in Patients with Increased Fluid Needs

• Issues with patients with renal insufficiency, fever, diabetes, and hot environments.

Interesting Relevant Research on Fasting Times

• Research suggests that providing a small amount of canned food 3 hours prior to anesthesia can help reduce gastroesophageal reflux in dogs.

General Anesthetic Concerns

• The four Hs: Hypotension, hypoventilation, hypothermia, and hypoxemia.
• Other considerations: Hemorrhage, pain, delayed recovery, regurgitation, laryngeal spasm, difficult intubation, dysphoria, arrhythmias, myopathy, or neuropathy. Consider other species and disease factors specifically influencing cases.

Important Reminders

• Signed consent: Get verbal consent over the phone, with a secondary confirmation if possible.
• Suggested Reading: Handbook of Veterinary Anesthesia, 5th ed., Ch.2 (pp. 12-21) and relevant AAHA monitoring guidelines.