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)
When are local and regional anaesthetics used instead of general?
Dentistry Obstetrics Regional surgery (CV unstable, need to awake) Post-op (wound pain) Chronic pain management (PHN)
List the main local anaesthetics, what are their characteristics?
Lidocaine, bupivacaine, ropivacaine and procaine
Lipid solubility - higher = higher potency
Dissociation constant (pKa) - lower = faster onset
Chemical link
Protein binding (higher = longer duration)
What differentiates a short acting and long acting local anaesthetic?
All have aromatic ring joined by LINK to amine
Ester link = short duration
Aside link = long duration
How do local anaesthetics work?
I fuse into wound (typically) -> bind to inside of VGNa channel -> block NA influx so prevent depolarisation
USE dependent block - more channels firing more they will be blocked
Block small myelinated (afferent) nerves in preference hence nociceptive and symp block
Adrenaline increased duration
Where are regional anaesthetics often used? How are they given?
Uses local anaesthetic and/ or opioid
Upper extremity e.g. interscalene, supraclavicular, infraclavicular, axillary
Lower extremity e.g. femoral, sciatic, popliteal, saphenous
Extradural/ intrathecal/ combined (labour)
Main anaesthetic side effects
(Many agent specific effects)
General:
- PONV (opioids) post op nausea and vomiting
- CVS - hypotension
- POCD - post op cognitive dysfunction (increased with age)
- chest infection (not coughing)
Local and regional:
- depends on agent and usually from systemic spread
- locals Na+ blockers so CVS toxicity = asytole
Allergic reactions
Anaphylaxis
List the main volatile anaesthetics
N2O Diethyl-ether Chloroform Isoflurane Xe
