Inhalational Anaesthesics Flashcards
General characteristics of inhalational anaesthesia
- Any disease of lungs will affect uptake
- Rate of exchange of gas is inversely proportional to its solubility in fluids
- At least 33% of inspired gas should be oxygen (increasing with volatility of the substance)
Examples of inhalational anaesthesia
Nitrous acid
Halothane
Isoflurane
Disadvantage of halothane?
Causes liver toxicity
Types of anaesthesia breathing circuits?
- Without rebreathing system
2. With rebreathing system
Describe a “without rebreathing system” circuit
Open - simple, increasing consumption and polluting air
Semiopen - inspiration from bag of evaporated anaesthesia. Expiration into air.
Explain a “with rebreathing system” circuit
Semiclosed - partial reinspiration of expired gas. Reabsorbant may be used
Closed - patient hermetically attached to system
- To and fro - mixture of inspired and expired gases pass through soda lime absorber
- circle - inspired and expired gas pass through separately
Advantages of inhalational anaesthesia?
Good management possibilities during surgery
Easily prolonged
Low risk of complication
Rapid recovery without excitation
Disadvantages of inhalational anaesthesia?
Complicated technical management
Need training
Need specialised equipment - expensive
Inhalational anaesthesia technique in a horse and ruminants
- Endotracheal tube inserted into pre-anaesthetised horse
- Care taken to ensure horse is not injured when it falls (during induction)
- Care must be taken to avoid myopathy during prolonged surgery
- Circle system normally used, under low flow system (2-4lt/min)
Injectable premed for a horse?
Atropine (SC/IM) Xylazine (IV) Detomidine (IM) Guaifensin (IV) Thiopental (IV)
Inhalational anaesthesia technique in pigs?
Endotracheal tube is inserted with the aid of myorelaxants
System designed for dogs used for small pigs, and horses used for large pigs
Injectable premed for ruminants?
Acepromazine
Xylazine
Diazepam
Detomidine
Inhalational anaesthesia technique in dogs?
Endotracheal tube inserted while anaesthetised and laterally recumbent
Substances added slowly as to not startle animal (unless already premedicated)
Premedication used in dogs
Atropine Chloropromazine Thiopental Atropine Xylazine Ketamine
Premed used in cats
Atropine
Acepromazine
What inhalational anaesthetics should be used in dogs and cats?
Isoflurane (2.5-4.5% induction, 1-3% maintenance)
Sevoflurane
Desflurane
Halothane (2-4% induction, 1% maintenance)
Nitrous oxide
Define minimal alveolar concentration, and its importance?
Concentration of vapour in the lungs that is needed to prevent movement in 50% of subjects in response to pain.
Used to compare strength/potency of anaesthesia vapours
What is the blood:gas coefficient?
Rate of the agent being taken up by the body. Represents the solubility in the blood and tissue and alveolar blood flow
How does ventilation affect inhalational anaesthesia?
Determines the speed of anaesthesic induction by controlling the supply of inhalant agent to the alveoli and replacing agent removed by uptake in the body.
Desoflurane?
Has the lowest B:G and relative potency. This makes it advantageous for induction and recovery speed, and ability to alter depth during surgery
Describe recovery?
When the concentration in the CNS has low enough for the animal to regain consciousness.
Parts to the inhalational device?
- Oxygen source
- Anaesthetic source
- Breathing circuit
- Other (face masks and endotracheal tubes)
Parts to the the oxygen source?
- Oxygen cylinder
- Pressure gauge
- Pressure regulator
- Flowmeter (reads rate of air flow)
- Pipeline system
- Oxygen failure warning device
Parts to the anaesthetic source?
- Vaporiser
