Anesthetic which is least metabolized in the body is:
Ref: Miller Textbook of Anaesthesia. 6th edition.Explanation: "Xenon and Nitrous oxide (N20} doer not undergo any metabolism in human body"All inhalational agents (except Xenon X N20) undergo oxidation in liver by cytochrome P 450 enzymes in Phase l reaction and by conjugation in Phase 2 reactions.XenonOnly gas to be anaesthetic under normobaric conditions.Physical propertiesColourless, odourless, tasteless.Gas undr normal temperature and pressureAnaesthetic agentVery close to the 'ideal agent'Xenon inhibits the plasma membrane Ca 2+ pump, altering excitability.It inhibits the nociceptive responsiveness of spinal dorsal horn neurons.MAC = 71%.Minimal haemodynamic effects.Lowest blood/gas partition coefficient = 0*115 of currently available inhalational agents.Low oil/water partition co-efficient of 20.Rapid induction regardless of duration of administration4 stages of anaesthesia noted with 70% Xenon/ 30% oxygen.Whole body paraesthesia & hvpo-algesia.Euphoria Si increased psvchomotor activity.Analgesia with partial amnesia (after 3- 4min).Surgical anaesthesia with a degree of muscle relaxation.No occupational/ environmental disadvantages.Specific effects on the bodyRespiratoryCentra] depression causes a decrease in respiratory rate with a compensatory increase in tidal volume and can progress to apnoeaCardiovascularNo inhihitory effects on cardiac ion channels i.e. calcium, sodium and inward potassium channels.No significant change in contractility, blood pressure and systemic resistance.Central nervous systemXenon increases cerebral blood flow* increases intracranial pressure and decreases cerebral perfusion pressure in acute head injury patients. This is not associated with cerebral oligaemia or ischaemia.This increase in cerebral blood flow is reveresed by mild hyperventilationAt present it is not recommended for neurosurgery.Endoerine/neurohumoralAttenuates surgical stress due to analgesia.Does not have any short or long term cortisol suppression effects.* ToxicityPlatelet aggregation potentiatedNo reported haematological toxicity.Metabolism and eliminationUnlikely to be involved in any biochemical events in the body.Eliminated via the lungs.
Xenon
Ether
Halothane
Methoxyflurane
Miscellaneous General Anesthesia