Lecture 10 Analgesia and Anaesthesia

Question 1

Definition Anaesthesia

Answer 1

loss of consciousness and loss of sensation

Question 2

Definition Analgesia

Answer 2

loss of sensitivity to pain

Question 3

General components anaesthesia

Answer 3

1. Unconsciousness
2. Immobility/muscle relaxation –> righting reflex is used as indicator of consciousness in anaesthetised animals
3. Analgesia: absence of pain in response to a noxious/painful stimulus
4. Amnesia: inability to recall events or an experience

Question 4

Types of anaesthesia

Answer 4

1. General: inhalational/injectable
2. Regional: block part of the nervous system. Can be done on different levels (CNS, peripheral).
3. Local: specific area. Blocks conduction of nerve impulses of pain stimuli.
4. Sedation: central depression where the animal is drowsy and relaxed. Animal is unaware of its surroundings but, can be stimulated with noxious stimuli.
5. Tranquilisation: animal is relaxed and non anxious, but is aware of its surroundings

Question 5

Inhalational systems

Answer 5

1. surgical masks: if it does not fit right, large dead space
2. Intranasal intubation: tube in one nostril, so dilutes gas.
3. Endotracheal intubation: most efficient way. Uses a T-piece that goes into trachea (semi-closed system), offers low-resistance breathing and has small dead space

Question 6

MAC

Answer 6

Minimal Alveolar Concentration (MAC)
= Minimum concentration of anaesthetic at 1 atm of pressure that prevents skeletal muscle movement in response to a surgical incision in 50% of patients.

Question 7

Injectable combinations + disadvantages

Answer 7

o Ketamine: dissociative anaesthetic. Preserve/increase heart rate + BP. Potent analgesic at low dosages. Short half-life (mice, 13 min after IP injection). - Could lead to a decreased respiration

o Xylazine: alpha-2 adrenergic agonist, that produces both sedation and analgesia. - Can result in bradycardia (slow heart rate)

o Acepromazine: tranquilizer, no analgesic activity and long half-life. - hypotension.

Disadvantage of combination of all three: hypoxia, hypotension, bradycardia

Question 8

Atipamezole

Answer 8

most commonly used to reverse xylazine effects (alpa 2 adrenergic agonists).
By not reverting, requires almost 24 hours to return to normal values, so longer recovery for the animal.

Question 9

Pre-emptive analgesia + advantages

Answer 9

Done when animal is prepared for surgery, should be provided whenever possible.

Advantages:
- Reduces intensity of painful stimulation
- Improves animal’s comfort after surgery
- Decrease amount of anaesthesia required
- Results in smoother recovery

Question 10

Compounds of analegsia + negative side effects

Answer 10

• non-steroidal anti-inflammatory drugs (NSAIDs): can result in GI ulcers and perforation
• Opioids
  o Full µ agonist: activate µ receptors (morphine, fentanyl). Dose-dependent effect, respiration depression
  o Partial µ agonist: increase with dose, but reaches a plateau (buprenorphine)
  o K agonist: butorphanol, nalbuphine

Can combine NSAIDs and opioids

Question 11

Administration of analgesics

Answer 11

• patches (does not work on rodents)
• injectable: accurate dosing but more stressful
• food + drinking water