Perioperative anaesthesia Flashcards
What is general anaesthesia?
A reversible state of unconsciousness
Name the 3 stages of general anaesthesia
Induction
Maintenance
Emergence
What is local anaesthesia?
A nerve block causing revisable absence of pain sensation
Name the 4 techniques used in local anaesthesia
Local anaesthetic field block
Peripheral nerve block
Nerve plexus block
Central neuraxial block - e.g. spinal or epidural
State the characteristics of a subarachnoid (spinal) central neuraxial block
Injection through dura into CSF
Low volume (up to 3ml)
High concentration local anaesthetic - 0.5% bupivicaine
Rapid onset dense sensorimotor block
Profound vasodilation ➔ haemodynamic instability
State the characteristics of an epidural central neuraxial block
Catheterisation of potential space outside dura
High volume (>10ml)
Variable concentration local anaesthetic - analgesia 0.1% bupivicaine, anaesthesia up to 2% lignocaine
Gradual titration of block density, may have motor sparing
Gradual titration ➔ less haemodynamic instability
State one benefit of epidural central neuraxial block over subarachnoid (spinal) central neuraxial block
Epidural block causes less haemodynamic instability
What is the triad of anaesthesia?
Hypnotic agent
Analgesic
Muscle relaxant
Define the induction stage of general anaesthesia
Transition from an awake state to an anaesthetised state
Name 3 IV induction agents used for general anaesthesia
Propofol (rapid) Barbiturates (rapid) Ketamine (slower) Benzodiazepines Dexmedetomidine (no risk of resp depression)
What is the benefit of using opioids during induction of general anaesthesia?
Reduces the dose of induction agent needed
Smooths the induction process
Name 3 factors cause delays in inducing anaesthesia
Slow arm-brain circulation time: e.g. elderly, cardiovascular disease
Patient anxiety
Recreational drug use
Extravastion (leakage of IV fluid into extravascular tissue)
Name the 2 types of induction agents used in general anaesthesia
IV induction*
Inhalational induction
Name 2 inhalation induction agents used for general anaesthesia?
Sevoflurane* Desflurane Isoflurane Halothane Sevoflurane Nitrous oxide
What are the indications for inhalational induction?
Paediatric practice
Cases of difficult airway
Difficult venous access
Inhaled foreign body
What is rapid sequence induction/intubation?
An airway management technique that induces immediate unresponsiveness and muscle relaxation.
Fastest and most effective means of controlling the emergency airway.
Minimises the risk of regurgitation and aspiration.
Which scenarios in particular benefit from rapid sequence induction/intubation?
Intact gag reflex
Unfasted stomach
Life-threatening injury or illness requiring immediate airway control
Outline the mechanism of action of general anaesthetic agents such as Propofol
Majority act via GABA-A receptors -> Cl- ion movement depresses the CNS
Outline the mechanism of action of Xe, Nitrous oxide, and Ketamine as anaesthetic agents
Inhibit NMDA (excitatory glutamate) receptors
What are the effects of CNS depression?
Sedation and reduced anxiety Lack of awareness and amnesia Skeletal muscle relaxation Suppression of undesired reflexes Analgesia
What is the indication for muscle relaxants whilst inducing anaesthesia?
Requirement for intubation
What muscle relaxants can be used during intubation?
Depolarising: Suxamethonium
Non-depolarising: Atracurium
Define the maintenance stage of general anaethesia
Keeping a patient unconscious
Name the 2 types of maintenance agents used in general anaesthesia
Inhaled volatile agents*
Continuous IV infusion
How is the potency of inhalation anaesthesia assessed?
Minimum alveolar concentration (MAC)
Define minimum alveolar concentration (MAC)
Alveolar concentration of a volatile agent needed to eliminate movement in 50% of population in response to a standard incision.
What is the benefit of Nitrous oxide when used in addition to inhaled volatile agents?
Reduces the required dose of other inhalations needed to achieve MAC.
Define the recovery/emergence stage of general anaesthesia
Transition from an anaesthetised state to an awake state
What determines full recovery from general anaesthesia?
Return of consciousness and protective reflexes
What medication should be given prior to emergence from general anaesthesia?
Adequate analgesia
Anti-emesis
Outline the important considerations of perioperative care
Warming - susceptible to hypothermia due to mass vasodilation
Fluid balance
Positioning - prevent nerve and pressure injuries
Patient awareness
Drug interactions
Analgesia
Safety - WHO surgical checklist
What are the 4 stages of Guedal’s classification?
1: Analgesia and consciousness
2: Excitement, unconscious, breathing erratic
3: Surgical anaesthesia
4: Respiratory paralysis and death
