- Shunt: During single lung ventilation, perfusion to the unventilated lung is still present. This leads to an intrapulmonary shunt and can precipitate hypoxemia. Protective mechanisms like hypoxic pulmonary vasoconstriction can help counteract the shunt, but only to a certain extent. Hypoxic pulmonary vasoconstriction can also exacerbate pulmonary hypertension. [More…]