Hypoxic pulmonary vasoconstriction occurs when the microvasculature perfusing hypoxic alveoli vasoconstricts, diverting blood to oxygenated alveoli to match ventilation with perfusion.  Hypoxic pulmonary vasoconstriction can occur within seconds and reach a maximum intensity within minutes of hypoxia developing. It appears to be triggered by a mitochondrial redox signal secondary to changes in molecular oxygen that activates voltage-gated potassium and calcium channels which results in vasoconstriction.  One-lung ventilation can acutely cause global alveolar hypoxia and hypoxic pulmonary vasoconstriction in the nonventilated lung. It is estimated that blood flow to a nonventilated lung can be reduced by as much as 50% if the lung is without atelectasis. 


The pulmonary angiograms were performed in a patient with a history of hemoptysis in whom a computed tomography angiogram demonstrated a pulmonary pseudoaneurysm with a presumed bronchial fistula in the right lung. The patient was scheduled for embolization with interventional radiology under general anesthesia. Because of concern for potential bleeding, lung isolation with a left-sided double lumen tube was positioned with the right lung open to ambient pressure. Isoflurane 1.1% was used for maintenance anesthesia. After approximately 15 min of one-lung ventilation, a pulmonary angiogram was performed that dramatically revealed selective peripheral microvascular perfusion to the left lung, but almost no microvascular perfusion to the right lung (fig. panel A; Supplemental Digital Content 1, http://links.lww.com/ALN/C912). This limited visualization of the right pseudoaneurysm. Repeat angiogram after 5 min of two-lung ventilation restored symmetric microvascular perfusion (fig. panel B; Supplemental Digital Content 2, http://links.lww.com/ALN/C913). The patient subsequently underwent selective catheterization and coil embolization of the pulmonary artery pseudoaneurysm.