Nitrous Oxide



  • Colorless, odorless, heavier than air, nonirritating & inflammable gas.
  • Also referred as “Laughing gas”. 

Color coding: 

  • Supplied under pressure in blue colored steel cylinders with blue shoulder in UK & ISO. 
  • PIN index: 3-5


  • Least potent anesthetic agent. (MAC=105%).
  • Pure N2O at 1 atmospheric pressure cannot produce adequate anesthesia.
  • Very low blood solubility → Quick induction with smooth & rapid recover.


  • Good analgesic.
  • Poor muscle relaxant activity.
  • As a carrier & adjuvant to other anesthetics.
    • Mixture of 66% N2O + 33% O2+ 0.2 – 2% another potent anesthetic is employed for most of surgical procedures.


  • Mixture of 50% N2O & 50% O2.
  • Little effect on respiration, heart & BP – Safest anesthetic.


  • Pneumothorax
  • Pneumoperitoneum
  • Emphysema.
  • Volvulus.
  • Acute intestinal obstruction → Increase in pressure & expansion can occur.
  • Pneumocephalus → Increases ICT.
  • On developed pneumocephalus N2O not used for 1 week.


  • Microlaryngeal surgeries→ Increased cuff pressure & aggravated laryngeal edema.
  • Middle ear surgery, tympanoplasties → Increased pressure & graft displacement.
  • Posterior fossa surgery & laparoscopic surgery → Air embolism may occur.
  • Vitreoretinal surgery Diffuses N2O causing bubble expansion.
  • Ear surgery (Tympanic membrane grafting, Cochlear implant).

Adverse effects:

  • Second gas effect.
  • Diffusion hypoxia.
  • Prevented by administering 1000/0 oxygen after N2O discontinuation & endotracheal tube removal.

Bone marrow depression.

  • Bone marrow changes prevented by pretreating patients with large doses of folinic acid.

Vit B12 deficiency:

  • Manifestations – Megaloblastic anemia, subacute combined cord degeneration.
  • Methemoglobinemia & laryngospasm may occur.

Long term administration:

  • Produce hematologic toxicity & neurotoxicity.
  • Due to interaction of N20 with Vit B12.
  • Increases pressure significantly in closed air spaces.

Exam Important

  • Use of nitrous oxide is contraindicated in  Tympanic membrane grafting, Pneumoencephalography, Vitreoretinal surgery, Cochlear implant, Microlaryngeal surgery & Vitreoretinal surgery
  • Nitrous oxide should be avoided in middle ear surgery when tympanic grafts are used
  • Gas stored in liquid form is Nitrous oxide
  • Nitrous oxide causes bone marrow suppression
  • Blue cylinder with blue shoulder is the color coding for Nitrous oxide gas cylinder for UK and ISO. 
  • Nitrous oxide is a low potency anesthetic agent as Nitrous oxide has a low lipid solubility and its MAC value of 105%.
  • PIN index for nitrous oxide is 3-5
  • At the end of anaesthesia after discontinuation of nitrous oxide and removal of endotracheal tube, 1000/0 oxygen is administered to the patient to prevent Diffusion Hypoxia
  • Nitrous oxide shows Blunts ventilatory response to hypoxia
  • Laughing gas is Nitrous oxide
  • Nitrous oxide causes megaloblastic anemia
Don’t Forget to Solve all the previous Year Question asked on NITROUS OXIDE

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