Veterinary Anaesthesia: Injectable Agents

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which injectable anaesthetic agent is typically used for both induction and maintenance of anaesthesia?

Nitrous oxide

Sevoflurane

Isoflurane

Propofol (correct)

What is a common method of delivering injectable anaesthetic agents in veterinary practice?

Intravenous injection (correct)

Intramuscular injection

Subcutaneous infusion

Oral administration

What is the primary purpose of performing a constant rate infusion (CRI) when using injectable anaesthetic agents?

To enhance muscle relaxation

To avoid drug accumulation (correct)

To reduce recovery time

To permit oral administration

Which technique involves the co-administration of injectable and inhalational anaesthetics?

Partial Intravenous Anaesthesia (PIVA) Signup and view all the answers

What impact do factors like patient movement and specific medical conditions have on anaesthesia?

They can indicate the use of Total Intravenous Anaesthesia. Signup and view all the answers

What is the role of using muscle relaxants during general anaesthesia?

To ease intubation and surgical access Signup and view all the answers

Which injectable anaesthetic agent is considered when dealing with severe cardiovascular pathologies?

Etomidate Signup and view all the answers

What type of administration is primarily required for effective use of injectable anaesthetic agents?

Venous access with intravenous injection Signup and view all the answers

What is a significant effect of using Etomidate-Lipuro compared to Hypnomidate?

It has less tissue irritation. Signup and view all the answers

At low doses, what is the primary mechanism of action of Etomidate?

It enhances GABAA activity. Signup and view all the answers

What is a key benefit of co-induction during anesthesia?

It helps in achieving dose sparing and minimizing side effects. Signup and view all the answers

Which of the following statements about central muscle relaxants is true?

They depress internuncial transmission at spinal cord and brainstem. Signup and view all the answers

Which drugs are used commonly for co-induction with propofol or alfaxalone?

Ketamine and Midazolam. Signup and view all the answers

What is a disadvantage of using Hypnomidate?

It can cause damage to red blood cells. Signup and view all the answers

What is a mechanism by which peripheral muscle relaxants operate?

By acting on acetylcholine receptors at the neuromuscular junction. Signup and view all the answers

What happens to the metabolites of Etomidate after it is metabolized?

They are excreted in urine, bile, and feces. Signup and view all the answers

What is the primary mechanism of action for Alfaxalone?

Enhancement of GABA's inhibitory effects on GABAA receptors Signup and view all the answers

Which administration route is NOT suitable for Alfaxalone?

Oral Signup and view all the answers

What is a significant clinical concern associated with repeated daily administration of propofol in cats?

Oxidative injury to feline hemoglobin Signup and view all the answers

What is the primary receptor action of ketamine?

Non-competitive NMDA receptor antagonist Signup and view all the answers

Which of the following statements regarding ketamine's effects is correct?

It alters patient memory and processing. Signup and view all the answers

What can prolong recovery when using Alfaxalone?

Long infusions Signup and view all the answers

Which statement about propofol's pharmacodynamic effects is true?

It may cause minimal hematological changes. Signup and view all the answers

What is the expected onset time for sedation with ketamine?

60-90 seconds Signup and view all the answers

Which anesthetic agent is notably insoluble in water?

Alfaxalone Signup and view all the answers

What is the primary metabolite of ketamine that is active?

Norketamine Signup and view all the answers

What is the primary benefit of using balanced anaesthesia?

To reduce side effects and provide analgesia Signup and view all the answers

Which factors influence the rate of induction in anaesthesia?

Lipid solubility and cardiac output Signup and view all the answers

What is the concentration of propofol typically used in clinical settings?

1% (10mg/ml) Signup and view all the answers

What is the mechanism of action of propofol as an induction agent?

It enhances GABA receptors and inhibits NMDA receptors Signup and view all the answers

What is the effect of high lipid solubility on propofol?

It results in rapid onset of action Signup and view all the answers

What is a common side effect associated with propofol administration?

Mild pain at injection site Signup and view all the answers

When is preservative-free propofol preferred over preservative-containing formulations?

To avoid toxicity in long-term use Signup and view all the answers

Which of the following indicates the correct way to calculate propofol dosing?

Calculate dose before induction, administer to effect Signup and view all the answers

What can decrease the propofol requirement in premedicated animals?

Opioids and alpha2 agonists Signup and view all the answers

What should be avoided during propofol induction to prevent complications?

Rapid injection of the drug Signup and view all the answers

Study Notes

Injectable Anaesthetic Agents

Injectable anaesthetic agents are used in veterinary anaesthesia in various ways.
Pharmacokinetics of these agents are important to understand.
Factors affecting the speed of anaesthesia induction are discussed.
Intravenous drug delivery techniques in domestic species are described.
Contemporary veterinary anaesthesia uses intravenous anaesthetic agents, whose pharmacology is examined.
Methods of providing muscle relaxation during general anaesthesia are outlined.

Ideal Anaesthetic Agent Characteristics

There's no perfect anaesthetic agent.
Desired properties include:
- Fast onset of action
- Short duration of action
- Reversability
- Good bioavailability by various routes
- Long shelf life
- Rapid metabolism
- Minimal side effects
- Non-irritating to tissues
- Inexpensive
- Muscle relaxation
- Analgesic properties
- Minimal environmental pollution
- Stable in storage and solution
- Non-cumulative

Injectable Agents

Propofol:
- Hypnotic alkyl phenol
- Lipid water macroemulsion (propofol in soybean oil, glycerol, egg lecithin, sodium hydroxide)
- Licensed in dogs and cats
- Concentration: 1% (10mg/ml)
- Indications: Induction and maintenance of anaesthesia, status epilepticus, fish and reptile anaesthesia
- Available in preservative-free and preservative-containing formulations (PropoFlo Plus)
Alfaxalone:
- Synthetic neuroactive steroid
- Insoluble in water (Cyclodextrin)
- Preservatives (last 28 days)
- Licensed in dogs, cats and rabbits for IV administration
- Concentration: 10mg/ml
- Indications: Induction and maintenance of anaesthesia, sedation (not licensed), suitable for immersion anaesthesia in amphibians, reptiles & fish
Ketamine:
- Phencyclidine derivative
- Licensed for dogs, cats, horses, cattle, sheep, goats, pigs, rabbits, and exotics.
- IV, IM, SC, and transmucosal absorption
- Aqueous solution: acidic pH: pain on IM injection
- 10% solution (most commonly used)
- Indications: induction (+ other agent(s) to provide myorelaxation), analgesia, sedation (aggressive/painful patients)
- No reversal
Etomidate:
- Imidazole derivative
- Not licensed for animals in the UK
- Different formulations available
- Hypnomidate (propylene glycol)
  - Pain on injection
  - Damage to RBCs, tissue irritation/necrosis
- Etomidate-Lipuro (lipid emulsion)
  - No pain on injection
  - No tissue irritation
- Indications: Induction (with premedication +/- co-induction), 1-3 mg/kg IV

Total Intravenous Anaesthesia (TIVA)

Use of injectable agents to both induce and maintain anaesthesia.
Intermittent boluses or constant rate infusion (CRI)
- Adjust infusion rate over time to avoid accumulation and prolonged recoveries
Indications include patient movement, field anaesthesia, disbudding, severe cardiovascular pathologies, raised ICP, bronchoscopy/thoracostomies.

Partial Intravenous Anaesthesia (PIVA)

Co-administration of injectable and inhalational anaesthetics.
Ketamine, alpha-2 adrenoceptor agonists, opioids (e.g., fentanyl, remifentanil), and lidocaine
Decreases inhalational anaesthetic requirements, reducing side effects.
Provides analgesia and muscle relaxation

Rate of Induction

Factors affecting induction rate include:
- Dose
- Concentration
- Speed of injection
- Cardiac output
- Lipid solubility
- Degree of protein binding
- Rate of metabolism and excretion

Induction Agents Pharmacokinetics

IV administration of a single bolus leads to a high concentration in the blood.
Rapid redistribution to highly perfused organs (heart, brain, kidneys).
Redistribution to less perfused tissues (muscles, fat).
Slow release from fat.
Hepatic metabolism (+/- extra-hepatic).
Renal excretion

Propofol Formulations

Preservative-free formulations encourage bacterial growth, and require discarding at the end of the day.
Preservative-containing (PropoFlo Plus) formulations last for 28 days, but no CRI should be used.

Propofol in Cats

Slower hepatic metabolism (glucuronidation enzyme deficiency).
Felines are prone to oxidative injury from repeated dosages and daily administering.

Alfaxalone Mechanism of Action

Enhances the inhibitory effect of GABA on the GABAA receptor.
At high doses, it acts as a GABAA agonist, opening chloride channels.

Alfaxalone Pharmacokinetics

IV, IM, SC administration (occasional pain).
Rapid induction (30-60 minutes, IV).
Dose premedicated animals (1-2 mg/kg to effect).
IM sedation/anaesthesia (7-10 minutes).
Alpha 2 agonist, opioids, ACP, midazolam: reduce induction dose
Induction usually smooth without excitement
Recovery quality similar to propofol
Prolonged recoveries if long infusions
Excitable recovery (paddling, rigidity, vocalization possible, especially if used alone)
Rapid metabolism (hepatic)

Ketamine Mechanism of Action

Interacts with multiple receptors.
Acts as a non-competitive NMDA receptor antagonist, preventing glutamate from binding.
Affects pain, memory, learning, and neural activity.
Affects the function of NMDA, non-NMDA glutamate receptors, muscarinic and nicotinic receptors, and monoaminergic and opioid receptors
Inhibits voltage-dependent, sodium- and calcium-channels

Ketamine Pharmacokinetics

Can be administered as a bolus or CRI
Sedation dose: 0.5-3 mg/kg IM
Induction dose: ~2.5-5 mg/Kg (higher dose for exotics)
Rapid onset IV (60-90 minutes)
Pain (CRI 10-20 mcg/kg/min intra-op, 2-5 mcg/kg/min post-op)
Hepatic metabolism → active metabolite: Norketamine
Ketamine & Norketamine excreted unchanged (urine) in ; careful if renal dx
Dog, horse: Norketamine further metabolised (inactive compounds), urinary + biliary excretion

Etomidate

Imidazole derivative
Not licensed for animals in the UK
Different formulations available (Hypnomidate, Etomidate-Lipuro (lipid emulsion))

Etomidate Pharmacokinetics

Rapid induction and recovery (often poor quality).
Metabolism (hepatic and plasma esterases).
Inactive metabolites excreted in urine, bile, and feces
Mechanisms of action differ at low and higher doses

Co-induction

Administration of two or more drugs together for induction
Synergistic effects, potentially decreasing side effects and improving stability.
Drugs to be used for co-induction, include:
- Midazolam
- Ketamine
- Lidocaine
- Fentanyl

Muscle Relaxation

Obtaining additional myorelaxation involves:
- Central muscle relaxation: Depressing inter-nuncial transmission in the spinal cord and brainstem (e.g., benzodiazepines, Guaifenesin).
- Peripheral muscle relaxation: Acting at the neuromuscular junction, often via acetylcholine receptors or neuromuscular blocking agents (NMDA). (e.g., depolarizing and non-depolarizing)

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers injectable anaesthetic agents used in veterinary anaesthesia, focusing on their pharmacokinetics, induction factors, and intravenous delivery techniques. It explores the characteristics of ideal anaesthetic agents and their properties essential for effective use in veterinary medicine.