<prompt> Anesthectic agent with least minimum alveolar concentration MAC:Nitrous oxideIsofluraneDesfluraneXenon  <response>: Ans: b IsofluraneRef: Stoeltings Pharmacology and Physiology in Anesthetic Practice, 4th editionMAC MINIMUM ALVEOLAR CONCENTRATIONMAC is the concentration of inhalational agent in alveoli at 1 atm that prevents skeletal muscle movement in response to a supra-maximal painful stimulus surgical skin incision in 50 of patients.It is used to measure potency of inhalational agentsMAC?1PotencyPotency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity.Lesser amounts of drug required to produce maximum effect is called as more potent drug.For inhalational anaesthetic agents potency are measured by MAC valueLesser the MAC more is the potency MAC ?1 PotencyInhalational agents order from maximum potent to minimum potentMeth oxyfluraneTrileneHalothaneChloroformIsofluraneEnfluraneSevofluraneEtherSevofluraneXenonN2OMAC of Common Inhalational Agents:Inhalational agentsMACMethoxyflurane0.16Trilene0.2Halothane0.75Chloroform0.8Isoflurane1.17Enflurane1.63Sevoflurane1.8Ether1.9Desflurane6.6Xenon71N20104Factor Affecting MAC:Increase of MACDecrease of MACNo Change of MAC. Hyperthermia. Hypernatremia Na. Sympathomimetic drugs. Cyclosporine. Excessive pheomelanin production red hair. Hypothermia. Increasing age 6 per decade. Alpha 2 agonist agents. Acute alcohol ingestion. Pregnancy and postpartum upto 72 hours. Lithium. Lidocaine. Hyponatremia. Ketanserine. Adrenergic antagonist agents. BP40 mm Hg. PaO38 mm Hg. Chronic alcohol abuse. Gender. Duration of anaesthesia. PaCO 15 - 95 mm Hg. PaO38 mm Hg. BP40 mm Hg. Hyper or Hypokalemia. Thyroid dysfunction. Anaesthetic metabolism 