what are the two types of GA
inhalation and IV
what are the 3 components of a balanced anaesthesia
pain relief, unconsciousness, reflex inhibition
most commonly used components of balanced anaesthesia
- short acting barbiturates → induction of anaesthesia
- neuromuscular blocking agents → for muscle relaxation
- opioids/NO → for analgesia
how does blood solubility affect onset of inhalant GA
higher the blood solubility, slower onset → GA needs to reach brain from lungs
examples of inhalant GA
volatile liquids - halothane, _____flurane
gases - NO
what is the index used for inhalation anaesthetic potency
MAC - minimum alveolar concentration
what does the MAC value indicate
lower MAC → higher potency
(less of it is required to induce effects of GA)
what factors increases the rate of absorption of GA
- concentration of anaesthetic in inspired air
- solubility of GA
- blood flow through lungs
what affects the distribution of GA
regional blood flow → organs that are highly perfused also receives the most GA (but also gets rid of GA the fastest due to the high perfusion rate)
eg of such organs: brain, liver, lungs and heart
how are GA eliminated
expired breath
what are the 2 advantages of having inhaled + IV anaesthetics
- permits dosage of inhalation agent to be reduced
- produce effects that cannot be achieved with an inhaled GA alone
characteristics of halothane
→ provides little to no analgesia
→ decreases BP due to depression of CO
→ bradycardia and arrhythmia may also occur
→ may also lead to halothane associated hepatitis
characteristics of isoflurane
potent (MAC 1.4%)
decreases BP due to decreased in systemic vascular resistance
characteristics of sevoflurane
→ more rapid rate of onset and recovery
→ metabolised in liver (nephrotoxic)
characteristics of NO
non flammable
alone → gives analgesia and amnesia but not complete unconsciousness (used as an analgesic agent)
used to supplement analgesic effects of primary anaesthetic
which is the only inhalant anaesthetics not compatible with epinephrine
halothane
examples of barbiturate
thiopentone
characteristics of thiopentone
→ rapid onset of action in brain
→ slow elimination as it goes to peripheral organs quickly
MOA of thiopentone
causes CNS depression
characteristics of propofol
→ rapid onset & recovery
→ needs continuous, low dose infusion for extended effects
→ significant cardiovascular effects during induction → hypotension!
on whom must propofol be used with caution
patients who are:
elderly
with compromised cardiac function
hypovolemic
which analgesic produces a state known as dissociative anaesthesia
ketamine
characteristics of ketamine
→ rapid clearance (suitable for continuous infusion)
→ risk of psychologic adverse reactions (can be reduced with diazepam beforehand)
→ only IV anaesthetic with analgesic properties!
examples of anaesthetics adjuncts
benzodiazepines (midazolam)
adrenergic agonists (dexmedetomidine)
analgesics (NSAIDS)
neuromuscular blocking agents (succinylcholine, vecuronium)
