Second gas effect

The second gas effect applies to the situation in anaesthetics where a gas such as nitrous oxide is given in a high enough concentration so that its subsequent uptake from the alveolus causes an increase in the concentration of the other gases. For example if breathing 20% oxygen and 80% N2O (nitrous oxide) in the alveoli say half the N20 was taken up into the bloodstream then of the original 100% of the mixture 20% oxygen will remain with 40% N20. the new concentration of oxygen will thus be increased with now 33.3% of the gas mixture comprising of oxygen.

Additional recommended knowledge

Weighing the right way

How to quickly check pipettes?

How to ensure accurate weighing results every day?

This can also be applied to increase the alveolar concentration of a volatile anaesthetic. Imagine in the above example that there was 19% oxygen and 1% anaesthetic gas then after N20 uptake there would be 1.7% anaesthetic gas and 31.7% oxygen.