Veterinary Anaesthesia Module 3010

Introduction to Veterinary Anaesthesia

• Hanna Machin, lecturer in Veterinary Anaesthesia, delivered the online learning module (3010, 2024) at the University of Surrey.
• This module covers premedication, injectable and inhalational anesthetic agents, monitoring in veterinary anaesthesia, common complications and accidents, fluid therapy, and pain management.

Practical Sessions

• Practical 2: Includes anaesthetic machine checks, breathing system safety, endotracheal intubation (dog and cat), and monitoring and patient instrumentation.
• Practical 4: Covers intravenous cannulation.

Online Learning

• The online learning component includes topics like: introduction to anaesthesia, anaesthetic equipment, ECG interpretation, capnography waveforms interpretation, fluid therapy, and CRI calculations.

Learning Objectives

• Define general anesthesia, local anesthesia, and analgesia
• Describe the components and stages of general anesthesia
• Explain the process of anesthesia, including patient preparation and immediate post-anesthetic care.

Definitions

• Anaesthesia: Lack of feeling/sensation (from Greek).
• General Anaesthesia: State of unconsciousness produced by drug administration; characterized by controlled, reversible depression of the central nervous system (CNS) and perception.
• Analgesia: Absence of pain in response to stimulation that would normally be painful.
• Nociception: Process of encoding noxious stimuli (transduction, transmission, modulation of nociceptive stimuli) under general anaesthesia.
• Local Anesthesia (Analgesia): Loss of pain sensation in a circumscribed body area
• Regional Anaesthesia (Analgesia): Insensibility to pain in a larger (but limited) body area. Usually defined by the innervation pattern of affected nerves.

The Triad of General Anaesthesia

• Unconsciousness
• Hypnosis
• Amnesia
• Muscle Relaxation
• Analgesia

The Ideal Anaesthetic Agent

• Rapid onset
• Rapid recovery
• High lipid solubility
• Does not accumulate with prolonged infusion
• Analgesic at sub-anaesthetic concentrations
• No (or minimal) cardiovascular depression
• No (or minimal) respiratory depression
• No emetic effects
• No pain on injection
• No excitation
• No emergence phenomena
• Does not interact with other agents
• Safe following extravascular injection.
• No toxic effects
• No histamine release
• Water-soluble formulation
• Long shelf-life at room temperature

The Anesthesia Timeline

• Pre-anesthetic evaluation and anesthetic plan
• Patient preparation (stabilization, fasting, chronic medications)
• Equipment preparation
• Induction
• Premedication
• Maintenance of anesthesia & monitoring
• Recovery
• Discharge

Pre-anesthetic Evaluation

• Obtain client history
• Perform physical examination
• Discuss risks and procedure
• Evaluate the patient's resuscitation status
• Collect samples (e.g., blood work)
• Confirm signed consent
• Assess for comorbidities (e.g., diabetes, hyperthyroidism)
• Stabilize pre-existing conditions

Stabilize Pre-existing Conditions

• Medical management (diabetes, hyperthyroidism).
• Fluid therapy (hypovolemia, dehydration).
• Analgesia.
• Anxiolysis.
• Oxygen supplementation.

Chronic Medications & Anti-Anxiety

• Continue scheduled medications (e.g., thyroid medication, behavior/analgesia).
• Consider anti-anxiety/sedative medication(s) (e.g., trazadone, gabapentin) 2 hours pre-transport.
• May require discontinuation 2 weeks prior.

Fasting Guidelines

• General Fasting guidelines for healthy patients (different for patients with pre-existing conditions, high risk considerations).

ASA Physical Status Classification System

• Classifies patients based on health status to assess anesthetic risk. Higher ASA status = higher risk.

Equipment Preparation

• Check O2 supply, scavenging system, anesthetic machine(s), breathing system, endotracheal tubes, intubation tools, monitoring equipment, rewarming devices, and emergency drugs.
• Ensure equipment is functional, and necessary drugs are available.

Premedication

• Administered intravenously (IV), intramuscularly (IM), or subcutaneously (SC).
• Requires careful monitoring throughout
• Needs adequate time for drugs to take effect
• Ensure a calm and quiet environment.
• Increase dosage/add drugs if sedation level insufficient.

IV Cannula Placement

• Used for administration of fluids and medications.
• Essential for blood sample collection.
• Important for patient welfare in emergencies.
• Requires aseptic technique.

Pre-oxygenation

• Administering high fraction of inspired oxygen (FiO2) prior to induction.
• Beneficial for patients with expected difficulty during ventilation or intubation. Delay onset of Hb desaturation during apnoea → Hypoxemia.
• Can cause stress, so must be tolerated

Before Starting: Anaesthetic Safety Checklist

• Confirm patient information, owner consent, and procedure.
• Check IV cannula, airway equipment, and anesthetic machine.
• Complete pre-procedure time-out, communicating any risks. Assess and confirm the plan for recovery.
• Assign person to monitor the patient throughout.

Induction of Anaesthesia

• Use endotracheal tubes of various sizes
• Inflate ET tube cuff properly
• Select the correct induction agent
• Use laryngoscope, helper/mouth-gag, and swab to ensure correct placement
• Apply local anesthetic and lube

How to Choose the Correct ETT Size

• Select at least 3 tube sizes: one above, and one below expected size.
• Reference formulas/tables for patients, but ensure careful consideration of overweight patients.

Endotracheal Intubation

• Insert laryngoscope blade under epiglottis, press to visualize trachea.
• Using the tube, carefully insert until the lungs expand properly. Maintain constant monitoring (e.g., capnography, etc).
• Attach breathing system with oxygen and monitor proper parameters (e.g., ETCO2 ).

Securing the Airways

• Proper inflation of ET tube cuff is critical.
• Avoid over-inflation—risk of tracheal ischemia.
• Ideal pressure range for cuff: 20–30 cmH2O
• Use minimum occlusive volume technique and specific devices (syringe devices).

After Induction

• Monitor airway, breathing, circulation, drugs/depth of anesthesia, equipment, and forms.

Monitoring

• Ongoing monitoring is essential. Use various devices to track vital signs.

Stages of Anaesthesia

• Classifies patients based on different stages of anesthesia, using different criteria (e.g., muscle movement/reflexes, pupil responses).

Maintenance of Anaesthesia

• Administration of inhalational agents, injectable agents, and/or supplemental oxygen.

Recovery Checklist

• Communicate safety concerns regarding airway, breathing, circulation, temperature, pain.
• Check if assessment and interventions plan & analgesic plan is confirmed and appropriate.
• Ensure a person is assigned to monitor the patient.

Extubation

• Keep patient in sternal position (if possible).
• Deflate and remove the ET tube.
• Monitor the animal for signs of discomfort (swallowing or movement).

Recovery

• Starts after maintenance agents are discontinued. Monitor consciousness and respond promptly to any complications.
• Ensure use of safe environment, patient warming, fluid therapy, eye lubrication, and proper padding. Use pain scoring and analgesia (or sedation).

Recovery Delay

• Causes of delayed recovery include excessive anesthetic depth, drugs with extended duration of action, prolonged surgery, comorbidities, hypothermia, hypoglycemia, poor circulation, and hypoxemia.

Emergence Delirium

• Characterized by stress, unease, anxiety, vocalization, panting, restlessness, and uncoordinated thrashing.
• May be caused by hypoxemia, pain, and recent opioid administration.
• In some cases, sedation can aid in recovery

Post-Operative Care Plan

• Comprehensive form tracking anesthesia and post-operative care. This may vary from facility to facility.

References

• Various publications from 2020, BSAVA, and AAHA provided.

This quiz explores the key concepts of veterinary anaesthesia as taught in the online learning module at the University of Surrey. It covers essential topics such as anaesthetic agents, monitoring techniques, and practical skills necessary for administering anaesthesia in dogs and cats. Prepare to test your knowledge on this critical area of veterinary practice.