Second gas effect is

The increase in the paial pressures of the other gases in the alveolar mixture resulting from the rapid uptake of high concentrations of nitrous oxide during inhalational anesthesia induction is known as the second gas effect. The second gas effect is also evident in this example: the rapid uptake of N2O and reduced alveolar gas volume sustains Piso near its original inspired value and increases alveolar PO2, thereby augmenting uptake of these gases. Note also that the rapid uptake of N2O into blood results in an effective increase in minute ventilation, because more circuit gas is passively drawn into alveoli as alveolar gas is absorbed rapidly. These effects have been demonstrated in humans and animals, and theoretically, are sho-lived and peain only to the period of initial rapid transfer of N2O from alveoli to blood. The second gas effect may persist beyond the initial rapid phase of N2O uptake. Ref: Miller's anesthesia 8th edition Ref: Morgan & Mikhail's clinical anesthesiology 6e