15. Anaesthetics Flashcards
What are the two broad categories of anaesthesia?
General and local.
Outline the process of anaesthesia throughout surgery.
Premedication (feel calm), induction (knocked out), intraoperative analgesia (pain relief), muscle paralysis (intubation), maintenance (keep asleep), reverse muscle paralysis (restore respiratory function), provision for post operative nausea and vomiting.
What are some IV gas volatile general anaesthetics?
Propogol, barbiturates, etomidate, ketamine.
What are the four stages of Guedel’s signs?
1 - analgesia + consciousness; 2 - unconscious, erratic breathing; 3 - surgical anaesthesia with increasing depth until weak breathing; 4 - respiratory paralysis and death.
What is anaesthesia a combination of?
Analgesia, hypnosis, depression of spinal reflexes, muscle relaxation.
What is potency?
Dose/concentration for a drug to have an effect.
What does MAC stand for?
Minimum alveolar concentration - volatile anaesthetic potency.
What is the value of MAC?
[Alveolar] at 1atm at which 50% of subjects fail to move to surgical stimulus.
What is the anatomical substrate for MAC and why?
Spinal cord as concentration is the same as in alveolar at equilibrium.
What is the neural substrate for loss of consciousness?
Brain.
What factors affect induction and recovery in anaesthetics?
Partition coefficients (solubility). Blood:gas partition in blood, oil:gas partition in fat.
What does a low blood:gas partition mean for induction and recovery in anaesthetics?
Low value means fast induction and recovery.
What affects MAC?
Age (high in infants, low in elderly), hyperthermia (increases), hypothermia (decreases), pregnancy (increased), alcoholism (increased), other anaesthetics (decreased), opioids (decreased.
Why is nitrous oxide often added to other volatile agents in anaesthetics?
It reduces the dosing required.
What is a key receptor target in anaesthetics?
GABAa receptors.
What is the effect of anaesthetics in GABA activity?
Potentiates it - anxiolysis, sedation, anaesthesia. Increase Cl- conductance and depresses CNS activity.
What is the molecular-cellular target in anaesthetics?
Brain consciousness (balance between glutamate excitation and GABA inhibition).
What are the effects of anaesthetics on the brain circuitry?
Reticular formation depressed, hippocampus depressed, brainstem depressed, spinal cord dorsal horn and motor neuronal activity depressed.
What are the main IV anaesthetics?
Propofol, barbiturates, ketamine.
What is TIVA?
Total intravenous anaesthesia - only IV anaesthetics used.
What are the mechanisms of action of IV anaesthetics?
Most potentiate GABAa, ketamine works on NMDA.
What is IV anaesthetic potency?
Plasma concentration needed to achieve a specific end point.
When are local and regional anaesthetics used?
In dentistry, obstretrics, regional surgery, post-op, chronic pain management.
What are some main local anaesthetics?
Lidocaine, bupivacaine, ropivacaine, procaine.
What is the mechanism of action of bupivacaine infiltration for wound analgesia?
Blocks Na+ channel so no action potential.
What is the role of regional anaesthetics?
Selective anaesthetising of a part of the body, a ‘nerve block’.
What are the main general anaesthetic ADRs?
PONV (post-op nausea + vomiting), CVS hypotension, POCD (post-op cognitive dysfunction,worse with age), chest infection.
What is the main regional anaesthetics ADR concern?
Na+ channel blocker so risk of cardiovascular toxicity.
