Anesthetic uptake: Right-to-left shunt
In general a right-to-left intracardiac shunt or transpulmonary shunt will slow the rate of inhalational induction of anesthesia. This occurs because of a dilutional effect of shunted blood, which contains no volatile anesthetic, on the arterial anesthetic partial pressure coming from ventilated alveoli. The impact of a right-to-left shunt on the rate of increase in pulmonary arterial anesthetic partial pressure and, ultimately, the rate of induction of anesthesia is greatest for poorly soluble volatile anesthetics. This occurs because uptake of poorly soluble volatile anesthetics into pulmonary venous blood is minimal; thus, the dilutional effect of the shunt on pulmonary venous anesthetic partial pressure is essentially unopposed. In contrast, the uptake of highly soluble volatile anesthetics is sufficient to partially offset the dilutional effect. Very soluble agents arterial concentration is normal, insoluble agents the uptake is slowed.
Effect of Intracardiac Shunts on Anesthetic Induction
- Right to Left (IV): rapid induction (easy to remember – blood bypasses lungs, straight to brain)
- Right to Left (volatile): slower induction
- Left to Right (IV): little effect on induction
- Left to Right (volatile): little effect on induction