Flashcards in Session 7 - Anaesthesia Deck (18)
Give examples of volatile general anaesthetics.
Give examples of intravenous general anaesthetics.
Describe the 4 stages of Guedel’s signs.
Stage 1: analgesia but still conscious, normal muscle tone
Stage 2: unconsciousness, breathing erratic, delirium could occur leading to an excitement phase, normal or increased muscle tone
Stage 3: surgical anaesthesia, with four levels describing increasing depth until breathing is weak, slightly to markedly relaxed muscle tone
Stage 4: respiratory paralysis and death, flaccid muscle tone
Volatile anaesthetic potency is described using what measurement?
MAC (Minimum Alveolar Concentration) - the alveolar concentration of a volatile at which 50% of subjects fail to move in response to a surgical stimulus.
What factors affect MAC?
Age (MAC higher in infants, lower in elderly)
Hyperthermia (increased), hypothermia (decreased)
Central stimulants (increased)
Other anaesthetics and sedatives (decreased)
What factors affect induction and recovery from anaesthetics?
Partition coefficients (solubility)
- blood:gas partition (in blood)
- oil:gas partition (in fat)
Why is nitrous oxide often added to other volatile agents?
Nitrous oxide reduces the MAC required for many volatile anaesthetics to work. Therefore adding nitrous oxide reduces dosing of the other volatile agent.
What is the main target receptor for anaesthetic agents?
What effect do anaesthetics have on GABA receptors and what does this result in?
With the exception of Xe, N2O and ketamine, all anaesthetics potentiate GABA mediated Cl- conductance. This depresses CNS activity leading to:
What systems in the brain are targeted by anaesthetics?
Reticular formation (hindbrain, midbrain and thalamus) depressed.
Hippocampus depressed (memory).
Brainstem depressed (respiratory and some CVS).
Spinal cord - dorsal horn depressed (analgesia) and motor neuronal activity depressed (MAC)
Of the main intravenous anaesthetics which are rapid acting and which are slower acting?
Propofol - rapid
Barbiturates - rapid
Ketamine - slower
What is the main target receptor for ketamine?
Inhibits NMDA receptors
What is TIVA?
Total Intravenous Anaesthesia (TIVA). When a intravenous anaesthetic is used as the sole anaesthetic rather than for induction.
When are local and regional anaesthetics most commonly used?
Regional surgery (patient awake)
Post-op (wound pain)
Chronic pain management (e.g postherpetic neuralgia)
Give examples of local anaesthetics.
What is regional anaesthesia?
Anaesthetising part of the body, often described as a nerve ‘block’. Patient remains awake. Uses local anaesthetic or an opioid.
What are the main possible side effects of general anaesthesia?
Post-operative nausea and vomiting (PONV)
CVS - hypotension
Post-operative cognitive dysfunction (POCD) (increases with age)