Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

FCP > Anaesthesia: maintenance > Flashcards

Anaesthesia: maintenance Flashcards

1
Q

What are the methods for maintenance of anaesthesia?

A
  1. Inhalational anaesthesia
  2. Total intravenous anaesthesia
  3. Combination of the above: partial intravenous anaesthesia
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is going on here?

A
  • The vaporiser is turned off (see dial on 0)
  • Only fresh gas is going to the patient (oxygen)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is going on here?

A
  • Control dial is turned up
  • Fresh gas flow is divided by the splitting valve so that some of the fresh gas continues along the bypass pathway and the rest enters the chamber containing anaesthetic agent
  • Once in the chamber, the gas becomes saturated by the agent
  • Then the gas and vapour moves out of the outlet and are delivered to the patient
  • Delivery of the agent is affected by the amount of oxygen passing through (FGF rate)
  • Modern vaporisers have a more complicated setup than this
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What happens once the patient inhales the gas

A
  • Anaesthetic agent crosses the alveoli to enter the blood. Agent is soluble in the blood and therefore plasma conc. increases
  • Rate of plasma increase depends on conc. of agent, patient ventilation, cardiac output, how soluble the anaesthetic is in the blood
    • Increased ventilation → faster rise in plasma conc. of agent
    • Increased concentration of agent → faster rise in plasma conc. of agent
    • Increased CO → slower rise in plasma conc.
  • Increased solubility of agent results in slower rise in levels in the brain
    • If agent is poorly soluble in the blood, will diffuse quickly into other tissues. VV if highly soluble.
  • We still don’t really know what the agent does in the brain.
  • Agent then diffuses back into blood, then alveoli → is expired. Only a very tiny proportion of the agent is metabolised.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Types of anaesthetic scavenge systems

A
  1. Charcoal canister to absorb gas - need to weighed often and discarded when exhausted
  2. Passive scavenge system - tube carrying waste gases out of the window
  3. Active scavenge system - uses negative pressure to withdraw gases from the system and then carry them outside
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

MAC

A

Minimum alveolar concentration: the concentration of a vapour in the alveoli of the lungs that is needed to prevent movement in 50% of subjects in response to surgical stimulus.

This is for an unmedicated patient at sea level (1 atmosphere)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

True/false: MAC values are different for different agents and species.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Factors affecting MAC

A
  • Individual variation
  • Drugs given in premed/intra-op - usually decrease MAC
  • Other drugs the patient was given - could increase MAC
  • Body temperature
  • Age

And others

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do the numbers on the dial of the vaporiser correspond to?

A

percentage of gas that is leaving the common gas outlet

Doesn’t exactly correlate to delivery to the patient because it doesn’t account for other factors external to the vaporiser or for imperfect compensation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the difference between isoflurane and sevoflurane? Why does this matter?

A
  • Sevo has a higher MAC and slightly lower blood gas solubility
  • This means sevo diffuses quicker into tissues and brain → quicker change in anaesthetic
  • If you are used to giving iso, and use sevo, you may be more in danger of overdosing your patient.
  • Sevo is more expensive, and the higher MAC means you will end up using more at an equivalent flow rate.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Which might be more suitable for mask induction: sevo or iso?

A

Sevo - doesn’t smell or taste quite as pungent as iso, and is quicker to take effect.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the major disadvantage of inhalational anaesthesia?

A

❌Profound dose-dependent cardiovascular and respiratory depression.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How does inhalational anaesthesia cause CV depression?

A
  • CV depression is mediated by myocardial depression (negative inotrope)
  • There is more vasodilation, and a decrease in vascular activity overall (decreased ability of vasculature to respond to changes)
  • There is also CNS depression and overall reduction in autonomic tone
  • = reduction in BP, CO
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does inhalational anaesthesia cause respiratory depression?

A
  • High concentrations of CO2 usually stimulate respiration → this doesn’t happen in patients anaesthetised with volatile agents
  • There is also depressed hypoxic pulmonary vasoconstriction
    • Pulmonary arteries normally constrict in parts of the lung where there is hypoxia, in order to direct blood into better ventilated areas
    • This doesn’t happen in these anaesthetised patients
  • There is near-complete depression of the ventilatory response to hypoxia and it causes bronchodilator which increases dead space
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Characteristics of nitrous oxide

A
  • Anaesthetic and analgesic vapour at RTP
  • Thought of as a gas rather than a vapour, as it is not delivered by a vaporiser
  • Has a very high MAC so is not useful as a sole anaesthetic agent
  • Reduces the amount of iso or sevo needed, can be used in balanced anaesthesia
  • Provides good analgesic via NMDA receptor antagonism and by stimulating the production of endogenous opioids
  • Poorly soluble in the blood → diffusion hypoxia can be life-threatening
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is use of nitrous oxide decreasing?

A
  • Health and safety concerns about use: long-term exposure can cause bone marrow suppression and teratogenesis
  • Environmental concerns: nitrous oxide exists in the atmosphere for 100+ years and depletes the ozone layer
  • We now have modern opioids and use more local anaesthetic blocks
17
Q

Given that nitrous oxide is poorly soluble in the blood, what precautions should you take regarding the patient?

A
  • Any patient given nitrous oxide should be given 100% for 5-10 mins (nitrous oxide’s poor solubility means it will accumulate in the lungs)
  • Nitrous oxide diffuses quickly into gas-filled spaces, so do not use it in:
    • A dog with a GDV
    • A rabbit
    • A horse
    • A patient with pneumothorax
    • Ocular procedures where bubbles can form in the eyes
    • Endoscopy where the stomach/intestines will be filled with gas
18
Q

Onset of action: nitrous oxide

A
  • Nitrous oxide’s poor solubility in blood mess you get a rapid effect
  • It could be used in conjunction with another anaesthetic agent to increase the speed of induction
  • You would get a rapid response if you increased the flow of nitrous oxide intra-op
19
Q

True/false: nitrous oxide has good CV stability

A

True

20
Q

When might TIVA be the best option?

A
  • In a patient undergoing thoracic surgery
  • In certain neurological deficiencies
  • Where there is a lack of facilities e.g. horse in a field
21
Q

A drug suitable for TIVA should have:

A
  • Rapid onset of action
  • Short duration of clinical effects
  • High clearance rates
  • Rapid metabolism
  • Rapid excretion
22
Q

Which drugs are licensed for TIVA?

A

Propofol (SA)

Alfaxalone (SA)

Ketamine (SA+E)

23
Q

What problems could arise if you use propofol for a long time/repeatedly in cats?

A
  • Potential for oxidative damaged and Heinz body formation
24
Q

Practically, how is TIVA achieved?

A

Can be through top-ups (need to maintain IV access) or through CRI (using a syringe driver ideally, or a drip pump which is less accurate)

25
Q

What is the name given to the combination of drugs used for TIVA in horses undergoing field anaesthesia?

A

Triple drip

26
Q

What are the components of Triple Drip?

A
  • Guaifenesin - muscle relaxant
  • Ketamine - dissociative anaesthetic
  • Detomidine (or xylazine) - alpha-2 agonist
27
Q

How is Triple Drip delivered and how long can it be used for?

A
  • Given CRI to effect; if you notice the horse is too light, you can turn it up
  • Can be used to maintain anaesthetic for up to 1 hr 30 mins → the drugs accumulate in the body
28
Q

How do injectable agents reduce MAC of inhalational agents?

A
  • Injectable agents can significantly reduce the amount of inhalational agents needed
  • However they have a ceiling effect, after which there is no further reduction in MAC (so can’t keep giving more and more)
29
Q

Which drugs could improve CV stability under inhalational anaesthesia?

A
  • Ketamine
  • Lidocaine
30
Q

True/false: opioids are MAC-sparing, so reduce the amount of iso/sevo required.

A

True

31
Q

Why is is beneficial to use a combination of injectables at small doses?

A
  • Most drugs accumulate in the body over time
  • Using a combination at lower doses means less side effects
32
Q

Which technique (CRI or top ups) is optimal to avoid peaks and troughs in the anaesthetic plane?

A
  • CRI is optimal to avoid peaks and troughs
  • If unavailable, boluses can be used
33
Q

True/false: you cannot intubate patients under TIVA.

A

False

If a patient in anaesthetised using TIVA you can still intubate, provide oxygen and give IPPV if needed

34
Q

Why would some drugs be more suitable for CRI than others? Give an example to support this.

A
  • Some drugs have better infusion characteristics (hence more suitable for CRI)
  • This is why morphine is sometimes used instead of methadone
    • Although it is not licensed, morphine accumulates less in the body
35
Q

What is PIVA?

A

Partial Intravenous Anaesthesia

Combination of IV and inhalational techniques are used to maintain anaesthesia

FCP (34 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions