Maintenance of Anaesthesia

Question 1

When can you intubate?

Answer 1

Sufficient depth of anaesthesia 
Pull tongue out, laryngoscope on tongue - Don’t touch epiglottis or larynx 
Visualise laryngeal opening 
(Local anaesthesia) 
(Lubrication)

Question 2

cat intubation

Answer 2

Spray larynx with local anaesthetic to desensitise
+ reduce laryngospasm during intubation
“Intubeaze”- lidocaine spray
CAVE: easy to overdose - local anaesthetic toxicity!
Alternative options - V-gel, Laryngeal mask

Question 3

analgesia

Answer 3

Most general anaesthetics provide little analgesia
Analgesia still required even though patient unconscious
Prevent upregulation of pain processing pathways

Question 4

how can we maintain anaesthesia

Answer 4

Inhalational
Intravenous - TIVA (Total Intravenous Anaesthesia), Intermittent boluses, Continuous rate infusion (CRI)
Combination of injectable and inhalational
Occasionally a single intramuscular injection is sufficient

Question 5

Intermittent boluses

Answer 5

simpler
Require less equipment
Swinging plane of anaesthesia

Question 6

Continuous rate infusion

Answer 6

target controlled infusions (TCI)

MRI (minimum infusion rate)

Question 7

injectables for maintenance

Answer 7

Propofol
Alfaxalone
Ketamine - used at low (analgesic) doses with another agent
TIVA + PIVA (partial)

Question 8

drug solubility in blood

Answer 8

More soluble agents: slower to change depth of anaesthesia during maintenance

Question 9

potency

Answer 9

MAC= Minimum Alveolar Concentration required to prevent movement in response to painful stimulus in 50% animals
For clinical anaesthesia aim for ~ 1.25-1.5 x MAC
Depends on other sedative/anaesthetic agents also administered
MAC values vary between species

Question 10

MAC - affected by

Answer 10

Hypothermia decr/ Hyperthermia incr 
Age - very young/old incr young, fit incr 
Severe hypoxia/hypercapnia decr 
Severe hypotension decr 
CNS depressant drugs decr 
Excitation incr 
pregnancy decr

Question 11

MAC - not affected by

Answer 11

Length of anaesthesia
Gender
Blood pH

Question 12

metabolism of sevoflurane

Answer 12

Theoretically free fluoride ions released - Toxic to kidney, No problems reported clinically
Compound A formed during reaction with hot + dry carbon-dioxide absorber - Nephrotoxic, Newer absorbers prevent this reaction
Low flow anaesthesia potentiate these processes

Question 13

nitrous oxide

Answer 13

MAC in animals ~200% - Cannot be used as sole anaesthetic agent
Mild analgesic properties
Very insoluble (Blood:Gas P/C 0.47) - Very fast onset, Can speed onset of another agent: the “second gas effect”
Less important now that insoluble agents are routinely used
Health risk with long term exposure/pregnancy
can cause hypoxia due to decr partial pressure of oxygen in lungs

Question 14

recovery

Answer 14

Most anaesthetic mortality now occurs during recovery period
Extubation - When swallowing reflex returns, Cats maybe slightly earlier to prevent laryngospasm
Later if concerned about airway protection
Continue monitoring: TPR
± Oxygen administration
± Fluid therapy
Temperature – active/passive warming - Many small animals hypothermic
Post-operative analgesia
Nursing care and TLC

Question 15

problems with ET tubes

Answer 15

Occlusion of end of ET tube - Prevented by Murphy’s eye
Endobronchial intubation
Compression of inside of tube
Stretching of tracheal wall
Mucus in tube - risk of occlusion and infection