Effect of Uneven Pulmonary Distribution of Blood and Gas on Induction with Inhalation Anesthetics

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Abstract
Un-even ventilation-perfusion or shunting of blood from the right to left side of the heart causes a reduced proportion of the cardiac output to be exposed to alveolar anesthetic gas. This poses a barrier to the passage of anesthetic from alveoli to arterial blood and as such reduces the rate at which induction takes place. The delay of induction for various degrees of shunting may be quantitatively described through the use of electrical analogues. For very soluble agents (ether, methoxyflurane) the delay is minimal but for relatively insoluble agents (N2O, cyclopropane) the delay may be considerable. The delay is greater at higher lung volumes, as in the emphysematous patient, and in airway obstruction with gas trapped distal to the obstruction.

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