Repeated Medical PG Question- 21

#ANAESTHESIA( NEET-PG)

Q- Most potent analgesic agent among following?

          A. Nitrous oxide

          B. Nitric oxide

          C. CO2

          D. Oxygen

Answer is A. Nitrous oxide

▪️From above options, most potent analgesic agent is Nitrous oxide

▪️Nitrous oxide- 50:50 nitrous oxide and oxygen has revolutionized it as analgesic agent; it has been used as an analgesic agent in obstetric surgeries; dental procedures; in acute trauma; burn dressings and cardiac pain as well.

▪️Nitrous oxide produce analgesia that is in part because of release of proenkephalin derived family of endogenous opioids

Physical properties of N2O:

▪️It is colourless, non-irritating and sweet smelling

▪️Boiling point is -89°C.

▪️Critical temperature is 36.5°C° which is a.bove room temperature, therefore it can be kept in liquefied state.

▪️Stored as liquid in blue color cylindersQ

35 times more soluble than nitrogen

Points to Remember:

▪️Anesthesia without analgesia:Halothane

▪️Only analgesia: N2O

▪️Profound analgesia: Ketamine

▪️Best/maximum analgesia :Trilene

Q- At the end of anaesthesia after discontinuation of nitrous oxide and removal of endotracheal tube, 100% oxygen is administered to the patient to prevent:

           A. Diffusion Hypoxia

           B. Second gas effect

           C. Hyperoxia

           D. Bronchospasm

Answer is A. Diffusion Hypoxia

Diffusion Hypoxia (Fink Effect)

▪️Towards the end of surgery when nitrous oxide delivery is stopped, the gradient reverses and the nitrous oxide from blood gushes in alveoli replacing the oxygen from there causing hypoxia.This is called diffusion hypoxia. 

▪️To avoid this diffusion hypoxia 100% oxygen should be given  for 5-10 minutes after discontinuing nitrous oxide