General anaesthetics Flashcards
What is the literal meaning of anaesthesia?
an - a lack of, aisthesis - feeling, perception, sensation.
What is required from anaesthetic?
Abolition of sensation, abolition of pain, “triad of general anesthesia”- unconsciousness, analgesia, muscle relaxation.
What are the characteristics of a general anaesthetic?
Stable, potent, non-toxic, controllable, they have to be rapid on and off, adjustable, minimal cardio-depressant, minimal respitatory depressant, non-irritant.
What are the stages of anaesthesia?
Analgesia, excitement, anaesthesia and medullary paralysis.
What is involved in the first stage of analgesia?
Analgesia - Conscious, drowsy, antinociception and amnesia.
What is involved in the second stage of anaesthesia?
Excitement - Loss of consciousness but delirium, irregular cardio-respiration, apnea, spasticity, gagging, vomiting.
What is involved in the third stage of anaesthesia?
Anaesthesia - Regular respiration, loss of reflex and muscle tone.
What is involved in the fourth stage of anaesthesia?
Medullary paralysis - Depression of cardio-respiration and death.
What are the two main classifications of general anaesthetics?
Inhalation and intravenous.
What are the two types of inhaled anaesthetics?
Gas and liquid.
What are the 4 types of intravenous anaesthetics?
Inducing agent, dissociative, analgesia and sedative relaxant.
What are the features of inhaled anaesthetics?
Inhaled anaesthetics are controllable and have rapid blood-gas exchange. They are usually halogenated ethers or hydrocarbons and are stable and potent.
What are the features of intravenous anaesthetics?
They are injected, they are rapid and short acting and cause induction or anaesthesia.
What are some of the combined approaches used in surgical anaesthesia?
Rapid unconsciousness with IV, maintaining unconsciousness using inhalation agents such as N2O, supplement analgesia such as fentanyl and paralysis such as a neuromuscular block such as succinylcholine.
What are some commonly used inhaled anaesthetics?
Ether, N2O, halothane, enflurane, isoflurane, desflurane and sevoflurane.
What are some commonly used intravenous anaesthetics?
Thiopental, etomidate, propofol, ketamine and midazolam and other benzodiaepines.
What is the lipid theory of anaesthetic action?
Potency is proportional to lipid solubility and narcosis commences when any chemically indifferent substance has attained a certain molar concentration in the lipids of the cell.
How would the lipid theory work?
The idea that an anaesthetic molecule would enter an Na channel and cause it to close. There is increased membrane fluidity and expansion.
Who made the protein theory of anaesthetic action?
Franks and Lieb - 1987.
Who made the lipid theory of anaesthesia?
Overton and Meyer - 1901.
What did the protein theory say?
That luciferase inhibition correlates with anaesthetic potency. It said that anaesthetics interact with membrane proteins.
What proteins do anaesthetics target?
Transmitter receptors (ionotropic and GPCR), ion channels (Na+,K+), transporters and vesicular (release) proteins.
What do general anaesthetics do to inhibitory GABAa receptors?
They potentiate them.
What do general anaesthetics do to excitatory glutamate receptors?
They reduce them.
What do general anaesthetics do to ion channels?
They alter stabilising and destabilising ion channels.
What are some of the gas general anaesthetics?
Nitrous oxide, cyclopropane, xenon.
What are some of the inducing agent anaesthetics?
Thiopentone, propofol, etomidate.
What is a dissociative anaesthetic?
Ketamine.
What is an analgesia anaesthetic?
Fentanyl.
What is a sedative relaxant anaesthetic?
Benzodiazepines, droperidol.
What are the features of N2O and when is it used?
It has rapid onset and low potency, it is used in combination with other anaesthetics.
What are the features of halothane and when is it used?
It is used in vets and developing countries, it is hepatotoxic (damages liver cells) and has a hangover.
What are the features of enflurane?
It fast on and off, it has lower toxicity and is epileptogenic (capable of causing an epileptic attack).
What are the features of isoflurane?
It is non-epileptogenic but has cardio and respiratory effects.
What are the features of desflurane and what is it used for?
It has fast on and off effects and is used in day surgery.
What are the features of sevoflurane?
It is fast, potent but maybe hepatotoxic.
What are the features of thiopental?
It is a barbiturate, it is very fast (20s) on and off (10-15 minutes). It is highly soluble, non-analgesic and causes respiratory depression.
What are the features of etomidate?
It has a rapid metabolism, low cardio-respiratory effects and causes involuntary muscle jerks.
What are the features of propofol?
It has a very rapid metabolism, it can be used for introduction and maintenance and is used in day surgery.
What are the features of ketamine?
It has a slow onset, it is dissociative, analgesic, hallucinogenic, hypertensive and bradycardic.
When are midazolam and other benzodiazepines used?
They are used pre-operation.
What changes in neuronal pathways occur in anaesthesia?
There is more GABA inhibiton - the RAS is not activated, the hypothalamus is not activated so there is no excitation to the cerebral cortex.
