How do we monitor anaesthesia? -- General considerations

Question 1

1. Minimum time interval for recording?
2. What info included on GA chart?
3. What time frame is the GA chart used within?
4. What happens to the chart once completed?

Answer 1

1. Every 5 mins.
2. HR, RR, temp, BP, pulse ox, drug doses incl. O2 / VA, date, start and finish times, critical events.
3. Time of pre-med to time of recovery.
4. Filed away / stored on the animal’s file.

Question 2

Stage 1 of anaesthesia.

Answer 2

Begins at time of induction and lasts until unconsciousness is present.
HR and RR often elevated, breath holding can occur, pupils may dilate.

Question 3

Stage 2 of anaesthesia.

Answer 3

Lasts from the onset of unconsciousness until rhythmic breathing is present. All cranial nerve reflexes are present and may hyperactive.
Eye may appear wide and open and pupil dilated.
Eyes will soon rotate to ventromedial position.

Question 4

Stage 3 plane 1 of anaesthesia.

Answer 4

Respiration becomes regular and deep. Spontaneous limb movement absent, but pinch reflex may be brisk.
Nystagmus, if present, will start to slow and disappear.
Eyeball now ventromedial, opening eye will show the sclera.
Plane may be suitable for minor procedures i.e. abscess lancing, skin suturing.

Question 5

Stage 3 plane 2 of anaesthesia.

Answer 5

Eye position ventromedial, eyelids may be partially separated.
Palpebral is sluggish/absent, but ay still have some corneal reflexes may persist.
Muscles appear relaxed, pedal reflex begins to go.
Tidal volume may decrease as RR settles / the HR and BP may be slightly reduced.
Adequate for most surgical procedures

Question 6

Stage 3 plane 3 of anaesthesia.

Answer 6

Eyeball becomes central and eyelids begin to open.
Pupillary diameter increases.
Pedal reflex lost and abdominal muscles are relaxed.
HR and BP may be low.
Plane adequate for all procedures.

Question 7

Stage 4 of anaesthesia.

Answer 7

Overdose.
Characterised by progressive respiratory failure.
Pulse may be rapid or v slow and become impalpable.
Eye may become central w/ no palpebral reflex.
CRT becomes prolonged.
Sometimes accessory respiratory muscles active e.g. twitching of the throat.
May mimic inadequate anaesthesia so tricky.

Question 8

What can we monitor during anaesthesia?

Answer 8

Depth of anaesthesia.
CVS.
Resp. system.
Inhalant / drug admin.
Body temp.
Urine output.
Blood (BG
Neuromuscular function.

Question 9

Why do we monitor anaesthesia?

Answer 9

Things can change very quickly.
Fatality risk.
To make changes to the anaesthesia depth to reduce risk of overdose but also ensure patient unaware.
A legal requirement.
To make interventions where needed.
To be aware of how the patient is coping so we can influence our recovery plan.

Question 10

How can we monitor anaesthesia without equipment?

Answer 10

Pulse palpation (peripheral) for rate and quality.
Respiratory rate for quality and rate.
Eye position.
Jaw tone.
Reflexes.
Temperature.
MMs and CRT for CVS assessment.
Oesophageal stethoscope.

Question 11

1. How can we tell depth of anaesthesia adequate by eyes?
2. How can we tell depth of anaesthesia light by eyes?
3. How can we tell depth of anaesthesia deep by eyes?

Answer 11

1. Eye position down and medially rotating with absent palpebral reflex.
2. Eye position central with palpebral reflex.
3. Eye position central with no palpebral reflex.

Question 12

How can heat be lost from the patient?

Answer 12

• Convection = loss of heat to cool air surrounding the body. May be worsened by low ambient temp. or drafts.
• Conduction = loss of body heat to surfaces that are in contact e.g. cold table / kennel floor..
• Radiation = loss of body heat to structures not in contact w/ the patient.
• Evaporation = loss of body heat from moisture evaporation e.g. scrub/alcohol, open body cavity/respiratory secretions.

Question 13

How does anaesthesia affect hypothermia?

Answer 13

• Increasing blood flow from the core to periphery, increasing heat loss and reducing core temperature.
• Interfering w/ body’s thermoregulatory mechanisms and reducing metabolic rate and heat generated, so loss exceeds production.

Question 14

What can the result of hypothermia be?

Answer 14

CNS depression.
Hypotension.
Bradycardia.
Hypoventilation.
Decreased basal metabolic rate.
Decreased urine output.

Question 15

What are the factors that increase the risk of heat loss?

Answer 15

High SA : vol ratio.
Little body fat.
Thin hair.
Large area of coat loss.
Large amounts of internal tissue exposed.
Insufflation of cold air i.e. during endoscopy / anaesthetic gases.
Extremes of age.
Ectothermic animals e.g. reptiles.

Question 16

How can we reduce the risk of hypothermia during GA?

Answer 16

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

Question 17

Sources for patient warming.

Answer 17

• Blankets/towels/bedding.
• Incubators.
• Electric heat mats.
• Hot water bottles.
• Hot hands.
• Forced air warming systems.
• Heat lamps.
• Warm water enema / bladder lavage (last resort).