Principles of Anaesthesia

Question 1

What is meant by anaesthesia?

Answer 1

Anaesthesia means ‘loss of sensation’.

Veterinary surgeons use a number of methods to create a loss of sensation, from numbing a small area of skin to bringing about total unconsciousness.

Question 2

General anaesthesia

Answer 2

General anaesthesia is an induced, reversible state of unconsciousness.

Question 3

Triad of anaesthesia

Answer 3

Reversible state of unconsciousness.

Analgesia

Muscle relaxation

Question 4

Dissociative anaesthesia

Answer 4

Where the patient is less aware than normal of what is happening around them.

They are not necessarily unconscious or asleep. They are usually still able to swallow and breathe without intubation.

Question 5

pros and cons for dissociative anaesthesia

Answer 5

pros - causes less respiratory depression or change in blood pressure than general anaesthesia

Cons - heart rate may increase.

Little muscle relaxation or analgesia so other drugs may be given in combination to allow minor surgical procedures.

Question 6

Local anaesthesia

Answer 6

A technique that allows for an isolated part of the body to lose sensation.

Question 7

Topical anaesthesia

Answer 7

Desensitisation of the skin or mucous membranes by application of a local anaesthetic.

The anaesthetic is usually in the form of a cream or gel such as EMLA cream

Question 8

Tidal volume

Answer 8

the volume of air breathed in and out in a normal breath

Question 9

Minute volume

Answer 9

the volume of air breathed in and out in one minute

Question 10

Anatomical/Physiological dead space

Answer 10

the volume of air that is inhaled but which never reaches the alveoli so is therefore not involved in gaseous exchange; it is the air in the trachea, bronchi and larger bronchioles

Question 11

Mechanical dead space

Answer 11

the part of the anaesthetic breathing system where expired waste gases cannot be removed and may be rebreathed;

Question 12

Anaesthetic sparing effect

Answer 12

giving other agents, such as nitrous oxide, analgesic or local anaesthetic drugs to reduce the amount of volatile anaesthetic agent needed to maintain anaesthesia

Question 13

Second gas effect

Answer 13

giving nitrous oxide to speed the uptake of the volatile anaesthetic agent

Question 14

Premedication

Answer 14

drugs or combinations of drugs given before induction of anaesthesia

Question 15

Neuroleptanalgesia

Answer 15

the combination of a sedative and an opioid analgesic drug to produce a calm, pain-reduced state

Question 16

Premedication

Answer 16

Given before general anaesthesia is induced.

Premedications can be made up of different combinations of drugs according to the effect that is required. Often an anlagesic will be combined with a sedative to calm the animal before induction.

Question 17

Tranquillisers

Answer 17

Produce a calming effect characterised by relief from anxiety.

Question 18

Sedatives

Answer 18

produce a calming effect that is accompanied by drowsiness

Question 19

Narcosis

Answer 19

is the term used to describe the particular type of sedation/sleepiness produced by opioids and other agents.

Question 20

The aims of premedication

Answer 20

Calm the patient and make handling easier

Reduce the dose of other anaesthetic agents needed

Provide analgesia

Aid a smooth recovery

Question 21

Carrier gases

Answer 21

The gas that fills the pipes of the anaesthetic machine and breathing system and that carry the vaporised or volatile anaesthetic agent to the patient.

Question 22

Volatile agents

Answer 22

Volatile agents are liquids that are converted into a gas using an anaesthetic vaporiser.

Question 23

Injectable agents

Answer 23

Propofol, alfaxalone and ketamine can all be used to maintain anaesthesia.

The drugs are administered intravenously, either by top-up intermittent bolus injections, or by a constant rate infusion (CRI).