Anaesthesia Flashcards
What are the 4 stages of Guedel’s signs?
Stage 1: analgesia and consciousness
Stage 2: unconscious, breathing is erratic but delirium could occur leading to excitement phase
Stage 3: surgical anaesthesia (4 levels)
Stage 4: respiratory paralysis and death
For volatile compounds what do we use to describe potency? Explain what this term means?
Minimum Alveolar Concentration (MAC) Alveolar concentration at which 50% of subjects fail to move to surgical stimulus
At equilibrium, alveolar concentration = _______ concentration
spinal cord
What factors affect induction and recovery from anaesthesia?
Partitian coefficients -Blood: Gas -Oil: Gas
How does the amount of adipose tissue in a patient effect their induction and recovery from anaesthetic compounds?
Compounds have a greater ability to partition into fat which means it will accumulate in the adipose tissue Can take a long time for obese patients to wake up
What factors affect MAC and how do they affect it?
Age (high in infants, lower in elderly) Hyperthermia (increased) Hypothermia (decreased) Pregnancy (increased) Alcoholism (increased) Central stimulants (increased) Other anaesthetics and sedatives (decreased) Opioids (decreased)
Why is nitrous oxide often added to other volatile agents
Induce amnesia and hypnosis - “volatile sparing agent” Allows use of reduced doses of antetheic Therefore reduces the side effect profile
What does the Meyer-Overton correlation show?
Anaesthetic potency in relation to lipid solubility
The greater is the lipid solubility of the compound in olive oil the greater is its anaesthetic potency
Anaesthetic potency correlates to which two factors?
Lipid solubility
GABAA receptor interaction
Which receptor is a critical target for anaesthetics?
Which type of channel is this?
GABAA
Ligand gated ion channel for Cl- conductance
All anaesthetics potentiate GABAA medicated Cl- conductance to depress CNS activity besdies which 3 drugs?
Xe
N2O
Ketamine
How does anaethetic interaction with GABAA receptors cause CNS depression?
Binding to the receptor causes increased permeability to chloride
This casues chloride to enter the cell
The cell becomes hyperpolarised
Becomes difficult to get an action potential
Anaethetics modulate the balance between excitation by _____ and inhibiton by _____
glutamate
GABA
Which areas of brain circuitry are affected by anaethetics?
How do each of these relate to their use in surgery/intubation?
Reticular formation depression - loss of connectivity + sensory information
Hippocampus depression - loss of memory
Brainstem depression - respiratory and some CVS depression
Spinal cord depression at dorsal horn - analgesia
Depression of motor neurone activity - MAC
What are the main IV anaethetics?
Which receptors to they bind to elict their effects?
Propofol - GABAA
Barbituates- GABAA
Ketamine - NMDA
The main IV anaethetics are given IV for what purposes?
Induction
Total IV Anaethesia (TIVA)
How do we describe IV anaesthetic potency?
Plasma concentration to achieve a specific end point (e.g. loss of eyelas reflex, Bispectral Index (BIS))
Induction: Bolus to end point (sleep)
TIVA: defined PK based algorithm to infuse at a rate to maintain set point
Name some examples of local anaethetics
Lidocaine
Bupivacaine
Ropivacaine
Procaine
How does the dissociation constant (pKa) relate to the time of onset of local anaethetics?
The lower the pKa, the faster the onset
How does bupivacaine (a local anaethetic) work in wound analgesia?
Blockage of voltage-gated sodium channels
Cannot produce an AP
Blocks small myelinated nerves (afferents) in perferance= nociceptive and sympathetic block
Compared to Procaine, is Bupivacaine more or less potent and how does its duration of action compare?
More potent + longer duration of action
Which drugs can be used to generate a regional “block”?
Local anaethetics (e.g. lidocaine)
Opioids
What are the main side effects from general anaethesia?
Post-operative nausea and vomitting (PONV)
Hypotension
Post-operative cognitive dysfunction (POCD)
Chest infection
