ISOFLURANE INHIBITS HYPOXIC PULMONARY VASOCONSTRICTION - AN IN-VIVO FLUORESCENCE MICROSCOPIC STUDY IN RABBITS

Background: Contradictory results have been reported in previous studi es investigating the effect of Isoflurane on hypoxic pulmonary vasocon striction by indirect approaches. The current study measured the effec ts of one-lung ventilation (1LV) and isoflurane 1.5% by direct visual observation of the pulmonary microcirculation. Methods: Ten New Zealan d White rabbits were anesthetized with intravenous thiopental, alpha-c hloralose, and piritramid. Arterial, central venous, pulmonary arteria l, left atrial, and airway Pressures and cardiac output were recorded continuously. 1LV was facilitated by a bronchial blocker in the right main bronchus. A transparent window was implanted into the right thora cic wall for videofluorescence microscopy of the subpleural pulmonary microcirculation. After intravenous injection of fluorescein isothiocy anate-labeled red blood cells, vessel diameters, red blood cell flux, red blood cell velocity, and dynamic microhematocrit were measured in pulmonary arterioles and venules during two-lung ventilation and 1LV d uring baseline anesthesia and with supplementary isoflurane 1.5%. Resu lts: During intravenous anesthesia, 1LV caused significant reduction o f vessel diameters and red cell nux and velocity and an increase in mi crovascular hematocrit in pulmonary arterioles and venules. The decrea ses in arteriolar diameters and red blood cell flux and velocity induc ed by 1LV were significantly attenuated by isoflurane as compared with those measured during baseline anesthesia (P = 0.010, P = 0.029 and P = 0.047). Accordingly, 1LV-induced reduction of venular red cell flux (P = 0.023) and velocity (P = 0.036) were less pronounced during isof lurane. Isoflurane caused a significant decrease in arterial pressure. Venous admixture increased and arterial oxygen tension decreased sign ificantly during 1LV; the changes were more pronounced during 1LV with isoflurane 1.5% than during 1LV with baseline anesthesia. Conclusions : 1LV leads to a marked reduction of microvascular diameters and blood flow in the hypoxic lung. Isoflurane 1.5% inhibits hypoxic pulmonary vasoconstriction in pulmonary arterioles and increases regional blood flow In the hypoxic lung.