21 General anaesthetics Flashcards
21.01 INHALATIONAL AGENTS
Volatile agents: isoflurane, desflurane, sevoflurane, halothane - actions
CNS depressant
causes unconsciousness
only weakly analgesic
21.01 INHALATIONAL AGENTS
Volatile agents: isoflurane, desflurane, sevoflurane, halothane - MOA
potentiates GABA action on GABAA receptors and opens K+ channels (TREK type) to reduce neuronal activity, especially in cerebral cortex, thalamus and hippocampus
lipid solubility important for action
21.01 INHALATIONAL AGENTS
Volatile agents: isoflurane, desflurane, sevoflurane, halothane - abs/distrib/elim
given by inhalation with oxygen
rate of equilibration with body and onset of anaesthesia depends on the ‘blood/gas solubility’
isoflurane and halothane have a medium onset of action
desflurane and sevoflurane (with lower blood/gas solubilities) have fast onset and recovery
mostly eliminated unchanged via lungs
21.01 INHALATIONAL AGENTS
Volatile agents: isoflurane, desflurane, sevoflurane, halothane - clinical use
maintenance, and less frequently induction, of general anaesthesia
21.01 INHALATIONAL AGENTS
Volatile agents: isoflurane, desflurane, sevoflurane, halothane - adverse effects
cardiac and respiratory depression, hypotension
cardiac dysrhythmias
post-operative nausea and vomiting
rarely malignant hyperthermia and liver damage
21.02 INHALATIONAL AGENTS
Nitrous oxide - actions
antagonist of NMDA
CNS depression, unconsciousness (in combination with other anaesthetics)
analgesia
euphoria
21.02 INHALATIONAL AGENTS
Nitrous oxide - MOA
reduces opening of NMDA receptor channels
release of pro-enkephalins in brain
increases opening of TREK-1 potassium channels
has synergistic action with other inhalational agents (GABA modulators) to induce amnesia and hypnosis
21.02 INHALATIONAL AGENTS
Nitrous oxide - abs/distrib/elim
given by inhalation
low blood/gas partition coefficient results in rapid onset and offset of action
eliminated unchanged via lungs
no metabolism
21.02 INHALATIONAL AGENTS
Nitrous oxide - clinical use
general anaesthesia with good analgesic properties
because of low potency will not produce full surgical anaesthesia by itself - must be combined with more potent agents
in subanaesthetic doses used as analgesic for childbirth and emergency pain relief (e.g. by paramedics)
21.02 INHALATIONAL AGENTS
Nitrous oxide - adverse effects
few side effects, but can cause bone marrow depression
oxygen may be required during recovery due to possibility of ‘diffusion hypoxia’
21.03 INTRAVENOUS ANAESTHESIA
Propofol, etomidate, thiopental, ketamine - actions
ultra short-acting anaesthetics
all have only weak analgesic action, except for ketamine which is a powerful analgesic and also produces ‘dissociative anaesthesia’ in which the patient may remain conscious but have good pain relief and short-term amnesia
21.03 INTRAVENOUS ANAESTHESIA
Propofol, etomidate, thiopental, ketamine - MOA
ketamine blocks NMDA-type glutamate receptor ion channels, whereas other agents bind to a particular site (different to benzodiazepine binding site) on GABAA receptor to enhance opening of intrinsic Cl− channel by GABA
higher concentrations directly activate receptor
21.03 INTRAVENOUS ANAESTHESIA
Propofol, etomidate, thiopental, ketamine - abs/distrib/elim
given by IV injection
propofol and etomidate have fast onset and rapid recovery, whereas thiopental may accumulate and lead to ‘hangover’
ketamine has slower onset and more adverse effects during recovery
21.03 INTRAVENOUS ANAESTHESIA
Propofol, etomidate, thiopental, ketamine - clinical use
anaesthesia for short surgical or diagnostic procedures and to induce anaesthesia for subsequent maintenance with volatile agents
21.03 INTRAVENOUS ANAESTHESIA
Propofol, etomidate, thiopental, ketamine - adverse effects
cardiorespiratory depression: less with etomidate
post-operative vomiting and adrenocortical suppression with etomidate
delirium, hallucinations and dysphoria with ketamine
