Poor oxygenation of blood that occurs when a horse is anesthetized and placed on its back is a critical risk factor for anesthetic complications, and the risk of complications from low oxygen continues into anesthetic recovery. When nitric oxide (NO) is delivered as a pulse in the beginning of the horse’s inspiration (PiNO), the oxygenation improves immediately. Using scintigraphy, we showed that pulmonary blood flow is redistributed from the compressed dependent lung to well ventilated lung regions (‘matching’ ventilation and perfusion). The limitation for clinical use is that PiNO is proven effective with spontaneous breathing only. The purpose of the proposed project is to adapt PiNO to positive pressure ventilation, which is commonly used in anesthetized horses. We will develop a novel technique, volume perfusion CT, to study ventilation-perfusion matching during ventilation. We will also investigate the effects of improved oxygenation during anesthesia on anesthetic recovery.