AIIMS Nov 2006 Clinical Sciences MCQ 189

• First used in 1951 by Cullen on an 81yr old man having an orchidectomy..
• Very close to the ‘ideal agent’
• The very large electron shell of xenon ca be distorted and polarised by nearby molecules, creating a dipole.
• Xenon inhibits the plasma membrane Ca ²⁺ pump, altering excitability. It inhibits the nociceptive responsiveness of spinal dorsal horn neurons.
• MAC = 71%. (With more widespread usage the Russians have noticed the MAC to be closer to 60%)
• 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 and recovery regardless of duration of administration
• 4 stages of anaesthesia noted with 70% Xenon/ 30% oxygen.

1. Whole body paraesthesia & hypo-algesia.
2. Euphoria & increased psychomotor activity.
3. Analgesia with partial amnesia (after 3-4min).
4. Surgical anaesthesia with a degree of muscle relaxation.

• Equivalent analgesia when compared with equipotent doses of N ₂ O The analgesia produced by both gases is not reversible by naloxone.
• No occupational/ environmental disadvantages.
• Respiratory:
  
  
  1. Central depression causes a decrease in respiratory rate with a compensatory increase in tidal volume and can progress to apnoea
  2. Diffusion hypoxia is very mild as the blood/gas partition of Nitrogen (0.014) is only 10 times less than that of Xenon (0.14) as opposed to the almost 40 times less than Nitrous Oxide (0.47)

• Cardiovascular:
  
  1. No significant change in contractility, blood pressure and systemic resistance.
  2. Some reports of decrease in heart rate with variability in rhythm.
  3. No sensitisation of the myocardium to adrenaline
  4. May attenuate the myocardial depressant effects of isoflurane.

• Colourless and odourless gas with no irritation to the respiratory tract. Well tolerated with gas induction
• Low blood/gas and oil/water partition co-efficients allowing rapid induction and eduction
• Produces unconsciousness with analgesia and a degree of muscle relaxation
• MAC of 60-70% allows a reasonable inspired oxygen concentration
• It does cause respiratory depression, to the point of apnoea.
• It is cardiac stable.
• Not metabolised in the body and is eliminated rapidly and completely via the lungs.
• It is non toxic and is not associated with allergic reactions
• Stable in storage, no interaction with anaesthesia circuits or soda lime. Should not be used with rubber anaesthesia circuits as there is a high loss through the rubber
• Non flammable

Category: AIIMS Nov 2006 MCQs