8.2 Anaesthetics Flashcards Preview

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Flashcards in 8.2 Anaesthetics Deck (30):
1

What are the types of anaesthetics?

General
Local
Regional
Dissociative

2

What are the types of general anaethetics?

Volatile
IV

3

Examples of volatiles?

NO
Xenon
Fluranes

4

How do volatiles work?

A gas is passed over a filament where the volatile is turned into its gaseous form and breathed in via a ventilator

5

Advantages to Volatiles?

Easily turned on/off
Add a MAC sparing gas to reduce side effects

6

How do you measure the potency of volatiles?

MAC
Minimum Alveolar Concentration required for 50% of patients to be anaesthatised at that concentration (no response to surgical stimuli)

At equilibrium, it is equal to the spinal cord concentration, therefore CNS

Predicted by lipid solubility --> how well they can cross a membrane

7

What are the stages of anaesthetising a patient?

1) Give them a relaxing agent - premedicate
2) Induce
3) Maintain state - muscle relaxant, analgesia (opioid)
4) Recovery - undo state, give analgesia

8

Stages of Falling Under Anaesthesia... (4)

1) Analgesia
2) Excitation
3) Surgical Anaethesia
4) Respiratory Paralysis

9

How do anaesthetics act on the CNS?
Where does it act?

Analgesia - dorsal horn
Muscle Relaxant - SC
Depress Reflexes - SC
Hypnosis - thalamus and the RAS
Resp/CVS Depression - Brainstem
(Amnesia - Hippocampus)

10

What increases MAC?

Hyperthermia
Young People
Pregnancy
Alcoholics
CNS Stimulants

11

What decreases MAC?

Opioids
Elderly
Hypothermic

12

What affects Volatiles' Pharmacokinetics?

A: MAC and Blood:Gas Coefficient
D: Organ perfusion, Tissue Uptake Capacity
E: Blood:Gas Coefficient, Oil:Gas Coefficient

13

What are some IV general anaesthetics?

Ketamine
Rapid Acting:
Propofol
Barbituates

14

When do you use IV general anaesthetics?

For induction or can do for whole operation (TIVA)
Bypasses the excitation stage of falling under

15

Pharmacokinetics ADME of IV General Anaesthetics?

A: Rapidly to CNS

D: Rapidly redistributed to tissues with higher capacity for Lipophilic drugs,

D/M: Protein Bound

E: Hepatic and Renal Conjugation

16

How do you measure potency of IV?

The plasma concentration to get to a certain endpoint, e.g. no eyelash reflex
Normally you switch to volatiles at this point

17

How do anaethetics work? Targets...

Inhibit excitatory neurones: Glutamate
Excite Inhibitory neurones: GABA and Glycine

18

How does it affect GABA and Glycine Receptors?
What do they normally do?
What effect do they have of pharmacodynamics?

Positive Allosteric Regulation

Bind externally to Cl- pore
Increases sensitivity to GABA, so increases Cl intracellularly to hyperpolarise, sends fewer signals

They increase efficacy and potency

19

Which anaesthetics act on GABA?

All of them except Ketamine, N2O, Xenon

20

Which excitatory neurones are effected?
How?
By which anaesthetics?

NMDA and nACh receptors
Non competitive allosteric antagonist (decrease efficacy but not potency/affinity)

NMDA- Inhibit them to glutamate, decrease the Ca2+ current
nACh - decrease Na+ currents
nACh- contributes to analgesia/amnesia but not sedation

Ketamine and N20

21

When do we use local anaesthetics?

Dentistry
Child Birth
Post-Operative
Chronic Pain Management

22

What is the difference between local and regional anaesthetics?

Local - used against specific peripheral nerves to give a specific loss of sensation
Regional - "block" used to prevent pain signals to a specific organ/limb, uses a local anaethetic and an opioid

23

What are some local anaesthetics?

Lidocaine
Procaine

24

How do local anasthetics work?

Reduce Na+ channels to prevent nerve transmission
so prefers small myelinated nerves
Use-dependent, block the active pain signalling molecules

25

Properties of Local anaesthetics?

Lipid Soluble
Ring and amine structure
Bound by amide or ester bond (ester shorter t1/2)
Short half-life

26

What can you use to prolong local anaethesia?

Adrenaline

27

General ADRs of Anaesthetics?

Depression of Resp/CVS
Arrythmias
Hypotension
Post-Op Cognitive dysfunction
CHeck infections
Nausea (Opioids)

Allergies!

28

An ADR of N20?

Can expand the airways and cavities which causes diffusion hypoxia

29

ADRs of Local Anaesthetics?

Due to systemic spread

30

How do we monitor people pre and peri-op?

Pre - assess general health, the airway, age, take history

Peri - monitor O2, CO2 and N2O sats, ECG, BP, Temp and EEG