Background: The use of anesthetic drugs with minimal inhibitory effects on the hypoxic pulmonary vasoconstriction (HPV) could have a decisive role in preventing the hypoxemia during one-lung ventilation (OLV). 
Objective: The aim of this study was to compare the effects of propofol and isoflurane on the changes in gas exchange parameters following OLV in thoracic surgery.
Methods: This double-blinded randomized controlled clinical trial was conducted on patients who were candidates for elective right thoracotomy referred to the central operating room of Ghaem Hospital in Mashhad, Iran, during February 2016-2017. Patients with age range of 18 to 75 years, class I and II American Society of Anesthesiologists (ASA) and thoracotomy with OLV for pulmonary resection or cyst drainage were included. The patients were randomly allocated (1:1 ratio) into two groups of propofol (P, 50-100μg/kg/min) and isoflurane (I, 1 minimum alveolar concentration (MAC) 1.1%). Partial pressure of carbon dioxide (PaCO2), partial pressure of oxygen (PaO2), end-tidal carbon dioxide (ETCO2) and arterial oxygen saturation (SPO2) were recorded before and 15 minutes after OLV and compared between the two groups. The comparison of the mean gas exchange parameters before and 15 minutes after OLV was performed using Mann-Whitney test in SPSS version 19 software. P<0.05 was considered statistically significant. 
Results: In this study, 122 patients with mean age of 59.4±14.1 years (two groups of 61) were studied. Both groups were matched for age or gender. The two groups had no significant difference in the gas exchange parameters before the OLV. Only PaCO2 (p=0.001) and ETCO2 (p=0.001) were significantly higher in the propofol group after 15 minutes OLV than in the isoflurane group. However, PaO2 (p=0.67), O2Sat (p=0.333) and PaCO2-ETCO2 gradient (p=0.809) showed no significant difference between the two groups at this minute.
Conclusion: Based on the results of this study, the propofol or isoflurane selection seems to have no significant effect on the arterial oxygenation. On the other hand, isoflurane and propofol could be an appropriate anesthetic for thoracic surgery by normalizing the carbon dioxide gradient range during the OLV.
Clinical Trial Registration: The study was also registered at the Iranian Registry of Clinical Trials (IRCT2015123013159N8).
Funding: The study was financially supported by the Deputy of Research of Mashhad University of Medical Sciences (grant number: 940119).


Keywords: Hypoxemia, One-Lung Ventilation, Propofol, Isoflurane, Oxygenation


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