How do we maintain general anaesthesia?

Question 1

1. Who can induce anaesthesia?
2. Who is responsible for maintaining anaesthesia?
3. Who is responsible for the monitoring of the patient? – Who is the most suitable?

Answer 1

1. Vet surgeon, listed / registered vet nurse, student vet nurse when administering a specific amount of medicine.
   Vet surgeon only when administering a medicine to effect.
2. Vet surgeon. But suitably trained person may assist by acting as the vet surgeon’s hands e.g. for moving dials etc.
3. Vet surgeon but can be carried out on the vet surgeon’s behalf by a suitably trained person. – most suitable = listed/registered veterinary nurse or student vet nurse under supervision.

Question 2

1. Equipment needed for gaseous anaesthesia maintenance?

Answer 2

1. GA machine w/ adequate scavenging and a vaporiser.
   A breathing system to deliver gaseous agent to the patient.
   ET tube or face mask

Question 3

Pros of using gaseous agents for anaesthesia maintenance.

Answer 3

Very versatile.
Easy to use.
Can titrate to effect.
Rapidly exhaled so quick recoveries.
Generally safe in most situations.
Accessible in all practices (UK).

Question 4

Cons of using gaseous anaesthesia maintenance.

Answer 4

Some risk to personnel.
Can be unpleasant vapours.
Scavenging required.
Must be in a practice i.e. w/ machine / equipment.
Volatile agents cause patient vasodilation (dose dependent) so potential reduction in BP.
Not good for the planet.

Question 5

Safe use of volatile agents.

Answer 5

Avoid personnel exposure.
Avoid gaseous induction.
Place ET tube and inflate cuff BEFORE turning on vaporiser.
Fill up vaporiser at end of day where most staff have gone and use key to fill.
Leave patient connected to breathing system for as long as possible.
Ensure scavenging system adequate.
Ensure machines are all turned off after use.
Recover patients in a well-ventilated area.
Train staff so they know what to do if spillage.
Think environment!

Question 6

1. MAC of sevoflurane.
2. Blood solubility of sevoflurane – impact on patient.
3. Sevoflurane irritant?
4. MAC of isoflurane.
5. Isoflurane irritant?
6. Isoflurane effect on BP?
7. Isoflurane and sevoflurane analgesic?
8. Isoflurane blood solubility – impact on patient?

Answer 6

1. 2.1-2.6.
2. Low at 0.62 – very quick changes in depth/recovery and induction.
3. Non-irritant to MMs.
4. 1.4-1.6.
5. Yes, irritant to MMs so poorly tolerated for induction.
6. Causes peripheral vasodilation so hypotension.
7. No analgesia w/ iso or sevo.
8. 1.4 – fairly rapid induction and recovery.

Question 7

What route of administration can be used for injectable anaesthesia maintenance?

Answer 7

Intramuscular – by giving a set dose of a combo of drugs to give anaesthesia for a set time.
Intravenous – by giving top ups of an agent when needed.

Question 8

1. Downfalls of IM injection for maintaining anaesthesia.
2. Upsides of IM injection for maintaining anaesthesia.

Answer 8

1. Repeated injections may be needed.
   Difficult to control depth due to slow onset and unpredictable.
   Still advisable to have IV catheter in place.
   Limited range of drugs that can be used.
2. Can provide good anaesthesia.
   Allows pre-set doses i.e. nurse can administer.

Question 9

1. What 4 drugs would be included in quadruple anaesthetic for a cat?
2. And for a triple?

Answer 9

1. Sedator (medetomidine 1mg/ml).
   Anesketin (ketamine 100mg/ml).
   Buprenodale (buprenorphine 300 micrograms/ml).
   Hypnovel (midazolam 10mg/2ml).
2. Sedator (medetomidine 1mg/ml).
   Anesketin (ketamine 100mg/ml).
   Buprenodale (buprenorphine 300 micrograms/ml).

Question 10

1. Downfalls of IV injections for anaesthetic maintenance?
2. Upsides of IV injections for anaesthesia maintenance?

Answer 10

1. Requires secure IV access.
   Can result in an unstable plane of anaesthesia when using bolus techniques.
   Can get cumulative effects of some drugs – spp. differences.
2. Non painful (catheter already in place).
   Can give repeat injections.

Question 11

1. What is TIVA?
2. Downsides of TIVA?
3. Upsides of TIVA?

Answer 11

1. Total Intravenous Anaesthesia.
   The use of a continuous rate of drug to maintain anaesthesia i.e. Propofol.
2. IV access essential.
   Need enough time to prepare.
   Possible long recovery after prolonged infusion.
   May not have syringe driver or pump.
   Technical skill required due to tricky calculations.
3. Useful for situations where volatiles would be unwise i.e. some lung/trachea surgeries.
   Potentially better for the environment than gaseous.

Question 12

1. Pros of inhalational anaesthesia maintenance.
2. Cons of inhalational anaesthesia maintenance.

Answer 12

1. • Easy to administer.
     - Suitable for most patients.
     - Easy to adjust depth.
2. • Requires specialist equipment / intubation / machine / scavenging.
     - Has impact on BP through vasodilation.
     - Personnel risks.

Question 13

1. Pros of injectable anaesthesia maintenance.
2. Cons of injectable anaesthesia maintenance.

Answer 13

1. • Available in all settings.
     - Can be administered by a nurse (once prescribed).
     - Provide good levels of sedation.
2. • Careful dosing needed!
     - Limited choice of drugs.
     - Not so easy to change depth quickly / if at all.

Question 14

Factors affecting selection of maintenance technique.

Answer 14

• Species.
• Behaviour? Can we handle patient?
• Procedure.
• Facilities and access to options.
• Expertise?
• Budget.
• Familiarity.

Question 15

Why is airway maintenance important?

Answer 15

• Patient may regurgitate / aspirate.
• Patient may become apnoeic / suffer cardiac arrest.
• Patient may require support w/ ventilation.

Question 16

1. What airway maintenance related problems may be encountered?
2. How can we identify and avoid these problems?

Answer 16

1. • ET tube / breathing system may twist when moving patient.
     - Accidental disconnection / extubation.
     - Incorrect size tube.
     - Faulty equipment e.g. leaky cuff.
2. • Check equipment.
     - Watch patient, look at thorax.
     - Look at capnography.
     - Look for changes in parameters.
     - Take care when moving patient, move tubes carefully.
     - Use the correct tube size.

Question 17

Why does patient positioning matter?

Answer 17

• Patient often has to be in the same position for a prolonged period of time during op.
• Patient may present w/ pre-existing conditions e.g. osteoarthritis/ muscle wastage etc.
• Patient may be underweight (not as much covering over bony extremities) or overweight (extra pressure of some joints).

Question 18

What does good positioning of a patient achieve?

Answer 18

• Prevention of muscle / nerve damage.
• Prevention of post op pain.
• Optimises ventilation e.g. esp. in brachycephalic/overweight.
• Avoids nasal congestions e.g. in horses.
• Protection of limbs and patient by avoiding leaving limbs hanging off the table.
• Eye protection by applying eye lubricant, avoiding equipment touching eye, avoiding heating devices too close to face.
• Avoiding damage to limbs and joints by not lifting animals by limbs.
• The prevention of injury w/ non-slip flooring and avoidance of high steps up to kennels.
• Prevention of pain by the use of soft/padded bedding, supporting joints w/ rolled up towels / foam wedges during procedures.

Question 19

How do we reduce risk of hypothermia in patients?

Answer 19

• Keep anaesthetic time minimal.
• Minimise wetting of fur/patient i.e. surgical scrub/ultrasound gel.
• Maintain high ambient temperature.
• Use heat and moisture exchangers for breathing systems.
• Use appropriate breathing systems and appropriate flow rates..
• Use warm fluids for IVFT and lavage.
• Keep patient warm from point of pre-med.
• Use insulating materials e.g. vet bed / blankets / foil.

Question 20

Sources of patient warming.

Answer 20

• Blankets / towels / bedding.
• Incubators.
• Electric heat mats.
• Microwave warming bags.
• Hot water bottles.
• Hot hands.
• Forced air warming systems e.g. Bair Hugger.
• Heat lamps.
• Warm water enema / bladder lavage.

Question 21

1. Ideal temperature of patient in recovery?
2. How can we ensure patient warm enough?
3. Why is it best to keep patient warm in recovery?

Answer 21

1. 37 degrees C + above.
2. Provide warm environment.
3. Shivering increases O2 demand and is unpleasant.