Anaesthetics Flashcards
What are the types of anaesthesia and how can they be given?
General - inhalation always/ volatile (mask) OR intravenous
Local - regional (block part of the body)
Can use both for extra protection
Conscious sedation - small amounts of anaesthetic or benzodiazepines to produce a ‘sleepy-like’ state (maintain verbal contact)
Stages of anaesthesia
Premedication (hypnotic- benzodiazepine) -> relaxed
Induction (IV/ inhalation) -> asleep
Intra operative analgesia (usually opioid) -> analgesic
Muscle paralysis- facilitate intubation/ ventilation/ stillness -> breathing
Maintenance (IV/ inhalation) -> keep asleep
~~surgery~~
Reversal of muscle paralysis & recovery e.g. postoperative analgesia (opioid/ NSAID/ paracetamol)
Provision for PONV (post- op nausea & vomiting treatment)
How do we normally class anaesthetics?
Vast range of structures
2 main categories: volatile (N20/ contain flurane)
or IV (propofol/ barbiturates/ etomidate/ ketamine)
What are the 4 stages of receiving general anaesthetic for muscle tone, breathing and eye movement?
1 - analgesia - normal - normal breathing - slight eye movement
2 - excitement - normal/ marked increased - irregular faster - moderate
3 - surgical anaesthesia - slight relaxed -> moderately relaxed -> markedly relaxed X2 - breathing shallower - slight eye movement to none
4 - respiratory paralysis - flaccid - no breathing - none
Lose memory then consciousness then movement then CVS response
What are the 4 stages of Guedel’s signs in anaesthesia?
Stage 1 - analgesia and consciousness
Stage 2 - unconscious, breathing erratic but delirium could occur -> excitement phase
Stage 3 - surgical anaesthesia, 4 levels increasing depth until breathing weak
Stage 4 - respiratory paralysis and death
What is anaesthesia a combination of?
Analgesia Hypnosis (loss consciousness) Depression spinal reflexes Muscle relaxation (Insensibility and immobility)
How can we describe the potency of volatile anaesthetics?
MAC - minimum alveolar concentration
[alveolar] at 1atm 50% of subjects fail to move to surgical stimulus (unpremeditated breathing O2/ air)
At equilibrium [alveolar] = [spinal cord]
- anatomical substrate
What affects MAC?
Age (high infants, lower elderly)
Hyperthermia (increased), hypothermia ⬇️
Pregnancy ⬆️
Alcoholism ⬆️
Central stimulants ⬆️
Other anaesthetics and sedatives ⬇️
Opioids ⬇️
Why is nitrous oxide (N2O) sometimes added to anaesthetics?
For reduced dosing - MAC sparing so can use less and less side effects
What type of receptors do most anaesthetics use? Which ones don’t and how do they act?
GABA(A) R - major inhibitory transmitters - LGIC (CL- conductance)
Potentiate GABA activity: Anxiolysis Sedation Anaesthesia Depress CNS activity
Xe, N2O, ketamine don’t - block NMDA receptors (excitatory CNS)
How does reduction in connectivity in brain circuits cause different effects of anaesthetics?
All of the following depressed:
Reticular formation (hindbrain/ midbrain/ thalamus) - normally keeps awake/ activating system
Hippocampus - memory
Brainstem - respiratory/ some CVS
Spinal cord - dorsal horn depressed = analgesia, motor neuronal activity (MAC)
List the main intravenous anaesthetics - what’s the term for when used as sole anaesthetic?
Propofol (rapid), barbiturates (rapid), ketamine (slower)
Given IV for induction
Can be used as sole anaesthetic in TIVA - total Intravenous anaesthetic e.g. face/ airways op
Which receptors do intravenous anaesthetics potentiate?
GABA (A)
Bar ketamine - inhibits NMDA
How do we measure intravenous anaesthetic potency?
Plasma conc to achieve a specific end point e.g. loss eyelash reflex/ BIs value
Induction in mixed anaesthesia - bolus to end point then switch to volatile
TIVA (just IV) - define Pk based algorithm to infuse at a rate to maintain set point, pre-ceded by a bolus
Difference between local regional and general anaesthetic
Local - numbs small area tissue - minor ops
Regional - numbs a larger but limited part of body (spinal, epidural)
General - whole body - unconscious (IV, volatile)
