Anaesthesia Flashcards
Give an example of a lipid soluble and an uncharged local anaesthetic. How do they work?
Uncharged: benzocaine
Lipid soluble: tetracaine
Dissolve in membrane and block channel from within.
How do local anaesthetics work?
Na+ channel blockade - prevent propagation of APs
What is anaesthesia?
Insensitivity to pain following the suppression of - afferent sensory reflex (local/regional) and/or central neural processing (general anaesthesia).
Give an example of a local, regional and General method of anaesthesia.
Gel/local injection, inject into CSF, inhalation/I.V.
How can some anaesthetics duration be enhanced?
By using vasoconstrictors.
Where are regional anaesthetics inserted?
L4
Why must you make sure the patient is hydrated before a regional anaesthetic?
May lead to hypotension.
How long does a RA last?
2-3 hours
What are the two ways of giving a GA? Give examples of both.
Inhalation - inorganic gases such as NOS or a volatile liquid such as halothane. I.V - barbiturates eg: thiopental GABAa receptor. Non-barbiturates, ketamine acting on the NDMA receptor.
What are the modes of action of a GA?
Includes altered synaptic transmission in thalamic/cortical structures.
What are the uses of a GA? (4)
Anaesthetic - loss of consciousness, amnesia, inhibition of sensory reflex, skeletal muscle relaxation and analgesia.
Hypnotic - induces sleep, can be roused by external stimuli.
Tranquilliser - quieten without impairing consciousness, ease anxiety without causing sleep.
Medically induced coma
What can an induced coma be induced by?
Dose of barbiturate or propofol.
When is induced coma used?
Protect brain during/following major neurosurgery, reduces energy requirements of the brain and therefore time for healing and swelling.
What happens in stage 1 of anaesthesia?
Induction - transition from alert to unconscious. Autonomic reflexes progressively depressed in dose dependant manner - airway and resp reflexes, ventilation rate, circulatory reflexes.
There is a decrease in higher cortical function, consciousness is not lost but thoughts blurred. Reflexes present, smell and pain lost at end of stage.
How is stage 2 avoided?
Rapid acting anaesthetic.
What happens in stage 2?
Cortical inhibitory centres depressed, muscle tone increases, vomiting, temperature control lost and alpha rhythm of EEG desynchronised - dangerous state.
Describe stage 3
Slow synchronised EEG, regular slow breathing, medically centres depressed, reflexes lost and pupils dilated.
What happens in stage 4?
Loss of respiration, EEG waves are lost and you die.
What are the characteristics of a an ideal inhaling anaesthetic?
Analgesic, full muscle relaxation, no increase in capillary bleeding. Rapid induction and recovery, wide safety margin, free of unwanted side effects, non irritant and nice taste, non-explosive with air.
What is the MAC?
Potency of inhalation anaesthetic agent defined by MAC required to produce surgical anaesthesia.
What is the MAC altered by?
N20, increase in age, pregnancy, some therapeutic drugs.
Why is chloroform bad?
Metabolised by liver and its products are toxic.
How are inhalation agents metabolised?
They are inert and are not metabolised, eliminated via the lungs.
Are bogus injection short or long acting? What does this mean in turns of maintenance?
Short acting, poorly maintained without continuous infusion due to redistribution.
What are Nokia injections ideal for?
Induction, then maintain with inhalation GA
What are the two types of I.V infusion? Give examples of both and their pros and cons.
Thiopental is a barbiturate - is high lipid solubility. They are indicted very quickly but no analgesia, respiratory depression, low therapeutic index, irritant.
Non-barbiturates are ketamine and propofol. Ket is a rapid glutamate receptor blocker, analgesic and amnesic, high B.P and H.R, nausea and confusion during recovery.
Propofol - not analgesic, low incidence of nausea and vomiting, no bronchospasm.
Where are the sites of action for a GA?
Reticular activating system and hippocampus.
What are problems with GA?
Drug interactions, respiratory depression, CV effects, renal failure, hepatotoxicity, malignant, hyperpyrexia.
Give an example of a weak-base local anaesthetic.
Lidocaine
