<prompt> Anesthetic which is least metabolized in the body is:XenonEtherHalothaneMethoxyflurane  <response>: Ref: Miller Textbook of Anaesthesia. 6th edition.Explanation: Xenon and Nitrous oxide N20 doer not undergo any metabolism in human bodyAll 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 agentXenon 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 bloodgas partition coefficient 0115 of currently available inhalational agents.Low oilwater 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.EndoerineneurohumoralAttenuates 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. 