Surgery L4 - Anaesthetics Flashcards
(14 cards)
3 Sites of action of Anaesthetics
Loss of consciousness - Thalamus & Reticular activating system
Amnesia – Prefrontal cortex, hippocampus & amygdala
Immobility & analgesia – Spinal cord
4 Stages of Anaesthesia
Stage 1 Analgesia: loss of pain sensation, drowsiness, amnesia & reduced awareness of pain.
Stage 2 Excitement: delirium, rise & irregular BP & respiration, risk of laryngospasm, to shorten this period rapid acting anaesthetics like propofol are administered IV before inhaled aesthetic.
Stage 3 Surgical anaesthesia: loss of muscle tone & reflexes, ideal stage for surgery. Requires careful monitoring.
Stage 4 Medullary paralysis: severe depression of respiration & vasomotor centres, death can occur unless respiration & circulation are maintained.
Inhalation Anaesthetics - 2
- Desflurane: fast on & off, day surgery
- Nitrous oxide: rapid, low potency, in combination, obstetrics, analgesic
IV Anaesthetics – 3
- Propofol: rapid metabolism, induction & maintenance, day surgery
- Benzodiazepines: e.g. midazolam, pre-op
- Opioids: e.g. fentanyl analgesia & supplementsedation. Can cause respiratory depression
MoA of General Anaesthetics - 4
- Multiple actions which inhibit action
- Block excitatory ligand-gated ion channels
- Increase activity of inhibitory ion channels
- Anaesthetic agent can block Ach receptor or ion channel resulting in inhibition of action
MoA of General Anaesthetics – GABA receptor agonists - 3
Some agents better at causing unconsciousness e.g. Barbiturates, Propofol
1. Inhibitory neurotransmitter binds to GABA receptors
2. Ion channels stay open & more K enters cells, causing hyperpolarisation
3. Means cannot be activated
MoA of General Anaesthetics - NMDA Receptors Antagonists - 3
- Some agents better at causing analgesia e.g Ketamine, Nitrous oxide
- When activated NMDA receptors signal pain receptor.
- Drugs block NMDA receptors
(Local anaesthetics) Topical anaesthetics – 2
- Benzocaine (or Lidocaine, tetracain) is the major drug used
- S/E: skin irritation & hypersensitivity reactions
(Local anaesthetics) Infiltration anaesthetics – 2
- Injectionof anaesthetic solution into area of terminal nerve endings
- Used for minor surgical & dental procedures.
E.g. Procaine, chloroprocaine, lidocaine, bupivacaine
(Local anaesthetics) Spinal - 4
- Single injection putting local anaesthetic close to the nerves, numbing lower part of the body
- Rapid onset, only lasts a few hours
- S/Es: low BP, headache, back pain
- Provide pain relief post-surgery
e.g. Lidocaine, tetracaine, & bupivacaine
(Local anaesthetics) Epidural - 3
- Tube threaded through a needle & tube left in epidural space in back. Local anaesthetic is injected down the tube into sac (epidural space).
- Slow onset, long duration
- S/Es: heart rhythm problems or seizures, hematomain the epidural space, headache.
e.g. lidocaine, bupivacaine & articaine
Classification of Local Anaesthetics: Esters 3 & Amides 2
Amides are preferred in clinic as esters are more likely to cause allergic reactions.
Esters
1. Long action (tetracaine)
2. Short action (procaine)
3. Surface action (cocaine)
Amides
1. Long action (ropivicaine)
2. Medium action (lidocaine)
MoA of local anaesthetics - 4
- Block voltage-gated Na channel
- No entry of Na ions into cell, so no depolarization
- Ergo no generation of AP, so no impulse to CNS
- Local anaesthesia
Combined Approaches in Surgical Anaesthesia - 5
- Pre-op (sedation, anxiolysis, amnesia) – e.g. benzodiazepines
- Rapid unconsciousness – IV of rapid short acting agent e.g. thiopental
- Maintain unconsciousness - inhalation agents e.g.nitrous oxide, halothane
- Supplement analgesia - IV agents e.g.fentanyl
- Paralysis - neuromuscular block e.g.suxamethonium
