During induction of

general anesthesia General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...

, when a large volume of a gas (e.g.

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...

) is taken up from

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * ...

into pulmonary capillary blood, the concentration of gases remaining in the alveoli is increased. This results in effects known as the "

concentration effect In the study of inhaled anesthetics, the concentration effect is the increase in the rate that the Fa (alveolar concentration)/Fi (inspired concentration) ratio rises as the alveolar concentration of that gas is increased. In simple terms, the high ...

" and the second gas effect. These effects occur because of the contraction of alveolar volume associated with the uptake of the nitrous oxide. Previous explanations by Edmond I. Eger and Robert K. Stoelting have appealed to an extra-inspired tidal volume due to a potential negative intrapulmonary pressure associated with the uptake of the nitrous oxide. There are two extreme breathing patterns and the extra-inspired

tidal volume Tidal volume (symbol VT or TV) is the volume of air moved into or out of the lungs during a normal breath. In a healthy, young human adult, tidal volume is approximately 500 ml per inspiration or 7 ml/kg of body mass. Mechanical vent ...

is an artificial construct associated with one of these patterns. * * Errata British Journal of Anaesthesia 1997;79:268 Thus it is the volume change that actually causes the effects.

An applicable example from Stedman's medical dictionary

When a constant concentration of an anesthetic such as

halothane Halothane, sold under the brand name Fluothane among others, is a general anaesthetic. It can be used to induce or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva, which can be particularly useful i ...

is inspired, the increase in alveolar concentration is accelerated by concomitant administration of nitrous oxide, because alveolar uptake of the latter creates a potential subatmospheric intrapulmonary pressure that leads to increased tracheal inflow.

References

{{DEFAULTSORT:Second Gas Effect Anesthesia

An applicable example from Stedman's medical dictionary

See also

References