Chemical and Physical Properties
a. Chemically it is dinitrogen monoxide (N2O)
d. Heavier than air
g. Like oxygen it supports combustion
h. causes euphoria when inhaled in small amounts, so named as laughing gas. In past it was abused for recreational purposes.
a. MAC – has a large value of more than 100
b. It is least potent anesthetic agent
c. Has low Blood: Gas partition coefficient – 0.47, as is less soluble in blood.
d. Induction & recovery –rapid
e. Elimination –after action 99.9% nitrous oxide is exhaled unchanged without any metabolism, mostly by lungs, little through skin. Minute quantity is degraded by intestinal bacteria.
Has cardiovascular depressant effects but countered by sympathetic stimulation. Itself does not have much significant effect. Effect shown is that of agent given along with nitrous oxide. When given with halothane, increased cardiac output occurs. When opioids are given heart rate and blood pressure are decreased.
2. Respiratory system
Not significant. Causes increase in respiratory rate and decrease in tidal volume.
Increased cerebral blood flow leading to increased intracranial pressure.
4. GIT / Muscles
Has no significant effect on GIT and skeletal muscles.
As it is least potent anesthetic, it is commonly used for analgesic property in concentration of 20%.
For sedation concentration range is between 30-80%. Not more than 80% as leads to hypoxia.
Most common ratio of 70% nitrous oxide and 30% oxygen is used.
– adjunct; used along with others as an adjunct most commonly, so called second gas effect.
– for short surgical procedures
Like dental extraction, post operation pain, in painful dressings, fracture manipulations, during child birth.
1. Diffusional hypoxia / anoxia
When nitrous oxide administration is stopped immediately after body, nitrous oxide from body tissues and blood rapidly diffuses into alveoli. These alveoli are filled with nitrous oxide and the patient suffers from hypoxia (even death might occur). R emedy is to stop administration of nitrous oxide, but not of oxygen.
2. Vitamin B12 deficiency
As inhibits methionine synthetase, it is required for vitamin B12 synthesis. By inhibitory action causes B12 deficiency, leading to megaloblastic anemia and peripheral neuropathy.
On prolonged exposure, decrease in methionine synthase occurs, which interferes with vitamin B12 metabolism, leading to megaloblastic anemia.
5. Effect on air-containing cavities
In body where air containing cavity (esp. obstructed middle ear, air embolus, pneumothorax, head injury, leading to formation of air containing lesion, majority of gas being nitrogen. Nitrous oxide replaces this nitrogen in cavity. It is more than 30 times soluble than nitrogen. Nitrous oxide enters rapidly while nitrogen exits slowly, so cavity may enlarge. When patient is suspected, nitrous oxide is not used.
6. Effect of N2O & O2 in same cylinder
Two gases are present in the same cylinder. When temperature is lowered, to fill the cylinder, nitrous oxide liquefies earlier than oxygen. When patient is given anesthesia through these cylinders, first he gets pure oxygen and insufficient anesthesia. Later on he starts having pure nitrous oxide, leading to hypoxia.
To avoid this, it is advised to keep cylinders at a bit higher temperature, keeping them horizontally. During use they are shaken well before administration.
Recovery rarely exceeds 1-4 min
Special equipment for administration
Penetrates into cavities
Nausea/ vomiting uncommon
Co2 accumulation and hypoxia on prolonged administration
Little effects on circulation, respiration, liver, kidney
Megaloblastic anemia on prolonged administration
- It was previously used and was a potent general anesthetic.
Not used now.
Many a times patients complained of severe cardiovascular collapse known as cyclopropane shock. To avoid it, patient is administered small amounts of carbon dioxide.