Nitrous Oxide

Nitrous oxide

Nitrous oxide

Nitrous oxide

Nitrous oxide may cause bone marrow supression by interfering with the production of factors necessary for DNA synthesis. 

Nitrous oxide has few adverse effects, it is a mild cardiac depressant

and pulmonary vasoconstrictor and is relatively contraindicated in patients with pulmonary hypertension.

It cause diffusional hypoxia.

It inhibits folate metabolism and is contraindicated in pregnancy.

It promote expansion of internal gas-filled structures, and is avoided in patients with pneumothorax, pneumocephalus, and vascular air embolism.

Blue cylinder with blue shoulder is the colour coding for Nitrous oxide gas cylinder for UK and ISO. 

Colour coding of Gas cylinders

Colour coding of Gas cylinders (for UK and ISO) :

Nitrous oxide is a non irritating low potency anaesthetic agent,

unconsciousness cannot be produced in all individuals without concomitant hypoxia.

It has a MAC value of 105%.

MAC value is a measure of potency of the drug,

it is the lowest concentration of anaesthetic in pulmonary alveoli needed to produce immobility in response to a painful stimulus in 50% individuals

 Higher the MAC lower the potency and lipid solubility and vice versa.

Pin Index safety system:

• To discourage incorrect cylinder attachments, a pin index safety system has been adopted by cylinder manufacturers.

• The relative positioning of the pins and holes is unique for each gas.

Pin Index safety system for medical gas cylinders:

Ref: Morgan, Jr. G.E., Mikhail M.S., Murray M.J. (2006). Chapter 2. The Operating Room: Medical Gas Systems, Environmental Factors, & Electrical Safety. In G.E. Morgan, Jr., M.S. Mikhail, M.J. Murray (Eds), Clinical Anesthesiology, 4e.

Conditions in which nitrous oxide might be hazardous include,

• Air embolism
• Pneumothorax
• Acute intestinal obstruction
• Intracranial air (tension pneumocephalus following dural closure or pneumoencephalography)
• Pulmonary air cysts
• Intraocular air bubbles
• Tympanic membrane grafting

Ref: Morgan, Jr. G.E., Mikhail M.S., Murray M.J. (2006). Chapter 7. Inhalation Anesthetics. In G.E. Morgan, Jr., M.S. Mikhail, M.J. Murray (Eds), Clinical Anesthesiology, 4e.

A i.e. Diffusion Hypoxia

Ans. D i.e. 3, 5

Ans. B i.e. Blunts ventilator response to hypoxia

• Discovered by: Priestly
• Cylinder colour: Blue
• PIN index (code): 3,5
• Also known as: Laughing gas,
• Adverse effects:

– Megaloblastic anemia,

– Bone marrow suppression,

• Second gas effect/ diffusion hypoxia
• C/I in:

– Pneumothorax,

– Air embolism etc.

Ans. C: Nitrous oxide

Nitrous oxide is known as “laughing gas” due to the euphoric effects of inhaling it, a property that has led to its recreational use as a dissociative hallucinogen

Ans. D: Nitrous oxide is widely used

It is done as an OPD procedure without analgesia

CO2 (-60 degree C), Freon (-60 degree C) and nitrous oxide (-80 degree C) are the freezing agents

Ans. a. Nitrous oxide

• 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.”- Wiley and Churchill-Davidson A Practice of Anesthesia 7/e p536
• Miller says “Nitrous oxide produce analgesia that is in part because of release of proenkephalin derived family of endogenous opioids

Physical properties of N20

• 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

Remember: Anesthesia with

Ans. is  ‘d’  i.e., Good muscle relaxant

Nitrous oxide N,O

• It is colourless, odourless, heavier than air, nonirritating and noninflammable gas.
• It is also called laughing gas.
• MAC is 105% (least potent) – even pure N,O at I atmospheric pressure can not produce adequate anaesthesia. 
• It has good analgesic but poor muscle relaxant activity.
• It is supplied under pressure in blue coloured steel cyclinders.
• It has very low blood solubility → induction is quick and smooth with rapid recovery.
• Second gas effect and diffusion hypoxia occur with N₂0 only.
• N,0 is generally used as a carrier and adjuvant to other anaesthetics →  A mixture of 70% N20 + 25 – 30% 0, + 0.2 – 2% another potent anaesthetic is employed for most of the surgical procedures.
• Entonox is a mixture of 50% N₂0 and 50% 02.
• It has little effect on respiration, heart and BP.
• It can cause bone marrow depression and vit Budeficiency.
• N₂0 is the only anaesthetic reported to produce hematologic toxicity and neurotoxicity with long term administration.
• Both toxicities are the result of the interaction of N₂0 with vit B12.
• Complete bone marrow failure can be expected after several days of continuous exposure.
• Bone marrow changes are preventable by pretreating patients with large doses offolinic acid.
• Other manifestations of vit B 12 deficiency eg. megaloblastic anemia, subacute combined degeneration of cord may also occur.
• Methemoglobinemia and laryngospasm may occur.
• It is contraindicated in patients with air cavities like pneumothorax, pneumoperitoneum and volvulus →  expansion and increase in pressure occur.