Which gas accumulates in cavities post general anaesthesia?

Ans: A. Nitrous oxideRef: Ajay Yadov, Short Textbook of Anesthesia, 1st edition, pg59.Explanation:NITROUS OXIDE ( LAUGHING GAS)Stored as liquid in blue color cylinder1.5 times more heavier than air35 times more soluble than nitrogenAnesthetic propertiesIt is not a complete anesthetic.It is used as a carrier gas to other anestheticsMAC is 104% (It is not possible to deliver, so not a complete anesthetic)Maximum concentration which can be given is 66%A minimum of 33% of Oxygen has to be given (Otherwise can cause severe hypoxia)It is usually given as N2O 66% and O2 33%' mixtureBlood gas coefficient is 0.47 making it agent with faster induction and recoveryGood analgesicNot a muscle relaxantWhen given with other inhalational agent, it increases the concentration of that agent (Second gas effect) and also its own concentration (Concentration effect)Sudden stoppage can lead to Diffusion Hypoxia)Shou 1 d always be tapered slowly by giving 100% oxygen)MetabolismIt is not metabolized in human body.It is excreted unchanged in lungsSmall amount is excreted v ia skin (Percutaneous excretion)Impurities in N20 cylinder can cause severe laryngospasm. methhemoglobinemia & Pulmonary edemaSystemic ActionsCVS: It does not depress the myocardium in vivo, so it can be safely used in patients with cardiac disease and shockCNS: It increases cerebral metabolic rate and raises intra cranial tensionRS: It causes tachypnea and decrease tidal volume, maintaining minute volumeVentilatory response to hypoxia is bluntedNo significant effect on Liver and KidneysSide EffectsHematological: li inactivates vitamin B12 (If used for >6 hours) - defective folate metabolism - Bone marrow depression - Aplastic anemia and Megaloblastic anemiaCNS: Vitamin B 12 deficiency can cause Demy el i nation of spinal cord (Subacute degeneration of spinal cord) especially involving posterior columns and lateral spinothalamic tractsClosed Gas Spaces: Compliant spaces like gut, penumoperironeum, pneumothorax and non- compliant spaces like middle ear cavity, pneumoencephalum can develop very high pressure following nitrous oxide inhalation.This happens because for I mole of nitrogen removed, 35 moles of nitrous oxide enter (35 times more soluble than nitrogen.Therefore, Nitrous oxide is contraindicated inPneumothoraxPneumoperitoneumPneumoencephalumMiddle ear surgeryPosterior fossa surgeryLaproscopie surgeryAcute intestinal obstruction and volvulus of gutEye surgeriesUses in AnesthesiaAs a supplement to anesthesia (not a complete anesthetic)As a carrier gas for inhalational agentsAs analgesic in obstetrics, dental pain, burn dressing and acute trauma