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Anaesthetic Agents (Propofol (Metabolised in the liver by the process of…
Anaesthetic Agents
Propofol
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When an IV bolus is injected, it can either be eliminated by the liver or re-distributed to other tissues. So a graph would show the distribution phase with a major decrease followed by the elimination phase with a gradual decrease.
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Contraindications- Airway obstruction, Haemodynamic compromise
Side effects: Hypotension is elderly so their dose is reduced, Respiratory depression, pain on injection
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Total Intravenous Anaesthesia (TIVA)- The exact dose is calculated based on factors such as the age and weight of the patient. Continuous infusion to maintain the min desired blood concentration
Recovery = 5mins, Elimination time = 3-4.8 hrs
Thiopentone
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Recovery = 5-7 mins, Elimination time = 11 hours
Used for brain injuries because Thiopentone helps reduce the ICP. The brain's oxygen consumption rate is reduced due to the enuroprotective effect of the barbiturates
Elimination is by first-order kinetics but can become zero-order kinetics. Recovery can be delayed due to large doses
Contraindication- Airway obstruction, Haemodynamic compromise, Skin necrosis when injected into the tissues and can cause PORPHYRIA (Rare disorder of heme molecules metabolism- autonomic, GIT and psychiatric symptoms)
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Volatile Agents
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Can be used to induced anaesthesia Not used for that purpose because it is too slow and has a high incidence of coughing
Upon gas delivery, it is delivered to the lungs and the heart. It then goes to the target organ, brain via the blood. PP of gas builds up in the blood stream and more insoluble agents build up pressure more quickly
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Definition
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Suspension of consciousness employing reversible neurotoxins and it involves suppression of EEG without REM, subsequent rebound REM.
Opiates
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Tachycardia, Hypertension, Vasoconstriction and sweating
Fentanyl, Remifentanil, Morphine
Local Anaesthetics
Blocks Na+ channels and causes reversible depression of nerve conduction when applied to the nerve fibres. The small nerve fibres are blocked first so the C fibres first and the A-alpha first last
The ones with an amide linkage are metabolised by the liver first and the ones with an ester linkage are metabolised in plasma by pseudocholinesterase
Amide linkage-Lignocaine, Mepivacaine and Bupivacaine
Ester linkage- Procaine, Chlorprocaine, Tetracaine
Mortality
The mortality rates due to anaesthetics have decreased due increased knowledge, training, drugs, monitoring and equipment.
IV properties
Consider the physical properties, side effects, metabolism and indications for use. For example, a non polar drug will be able to pass the BBB more easily.