Nitrous Oxide
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Nitrous oxide is used in combination with other inhalation agents. It has a low potency meaning it is not suitable for use as the sole anaesthetic agent. It is used as part of a balanced anaesthetic technique as it has been shown to reduced the required concentration of volatile agent, but also shows some analgesic properties. Care must be taken when using nitrous oxide as it reduces the inspired oxygen availability, so should be closely monitored.
Pharmacokinetics
Nitrous oxide is both nonirritant and nonflammable. The blood:gas partition coefficient is very low. This means that speed of induction can be increased when nitrous oxide is used in combination with a volatile agent. It also exhibits the second gas effect. This occurs as the volume of nitrous oxide present in the alveoli is high, meaning it has a concentrating effect on the second agent present, increasing the uptake of the second agent. However, patients are at risk of diffusional hypoxia when nitrous oxide is used. This is due to the diffusion of nitrous oxide into the alveoli from the blood is faster then that of nitrogen from the alveoli to blood, making the alveolar oxygen concentration is lower. To help prevent this, the nitrous oxide should be turned off a short while before the oxygen. The MAC of nitrous oxide is extremely high meaning it has a low potency and so cannot be used as the single anaesthetic agent, and must be used in combination.