Maintenance of Anaesthesia

Question 1

How does the solubility of a drug impact its effects?

Answer 1

High solubility = slow changes
- easily dissolves in blood
- so stays in circulation longer

Low solubility = fast changes
- doesn’t dissolve as easily
- readily enters the brain

Question 2

How would you explain equilibrium in regards to solubility coefficiency?

Answer 2

the concentration of the anaesthetic agent is equal to the concentration in the patient’s alveoli

Question 3

Put in order of highest-lowest solubility

Sevoflurane
Isoflurane
Desflurane
Halothane

Answer 3

Halothane, Isoflurane, Sevoflurane, Desflurane

therefore slowest acting - fastest acting

Question 4

What does MAC mean?

Answer 4

Minimum Alveolar Concentration

the concentration of inhalant that will prevent movement in response to painful stimuli in 50% of patients

it is a measure of anaesthetic potency (effect)
- higher MAC = less potency

Question 5

What factors effect MAC?

Answer 5

Temperature
- hypothermia = decreased MAC

Age
- old age = decreased MAC

Hypotension
- impacted by different drugs

PaO2 < 40mmHg

PaCO2 > 90mmHg

Question 6

What is the MAC for Iso and Sevo?

Answer 6

Isoflurane
- dogs = 1.3%
- cats = 1.6%
- onset of action = moderate

Sevoflurane
- dogs = 2.3%
- cats = 2.6%
- onset of action = fast

Question 7

What are the stages of anaesthesia?

Answer 7

Stage 1
- Induction to unconsciousness
- fear, apprehension then disorientation is seen

Stage 2
- unconsciousness to rhythmical breathing
- all cranial nerve reflexes are present and may be hyperactive

Stage 3
- surgical/stable plane
- consists of 4 planes (deepens with each one)

Stage 4
- coma due to anaesthetic overdose
- respiratory paralysis and agonal gasping can mimic ‘light’ sedation

Question 8

What are the planes of anaesthesia?

what are the signs of each one?

Answer 8

Light
- eye position = central
- palpebral reflex = brisk
- respiratory pattern = rapid
- pulse rate = rapid
- blood pressure = high
- swallowing = present
- pedal withdrawal = present
- anal tone = present

Surgical
- eye position = ventromedial
- palpebral reflex = absent
- respiratory pattern = slow and regular
- pulse rate = normal
- blood pressure = normal
- swallowing = absent
- pedal withdrawal = absent
- anal tone = present

Excessive
- eye position = central
- palpebral reflex = absent
- respiratory pattern = abnormal
- pulse rate = rapid
- blood pressure = low
- swallowing = absent
- pedal withdrawal = absent
- anal tone = absent

Question 9

What are the signs for each plane of anaesthesia when using Ketamine?

Answer 9

Light
- eye position = central
- palpebral reflex = present
- jaw tone = present
- movement = possible
- heart rate = usually increased
- respiratory rate = usually increased
- CV/respiratory variations following stimulation = present

Surgical
- eye position = central
- palpebral reflex = present
- jaw tone = present
- movement = present
- heart rate = normal
- respiratory rate = normal
- CV/respiratory variations following stimulation = usually absent

Excessive
- eye position = central
- palpebral reflex = possible/absent
- jaw tone = possible/absent
- movement = possible/absent
- heart rate = usually decreased
- respiratory rate = usually decreased
- CV/respiratory variations following stimulation = absent

Question 10

What are the signs of an anaesthetic overdose?

Answer 10

respiratory failure
rapid pulse OR very slow and difficult to palpate
eye central and eyelids open
pupils dilated and corneal surface dry
cyanosis (blue/grey mms)
increased CRT