The Association Between the Initial End-Tidal Carbon Dioxide Difference and the Lowest Arterial Oxygen Tension Value Obtained During One-Lung Anesthesia With Propofol or Sevoflurane

ObjectiveThe purpose of this study was to examine the correlation between the lowest PaO2 value recorded during the first 45 minutes of one-lung ventilation (OLV) and the end-tidal CO2 (ETCO2) difference between two-lung ventilation (TLV) and the early phase of OLV.DesignA prospective, randomized study.SettingA university hospital.ParticipantsThirty-six patients scheduled for elective thoracic surgery.InterventionsThoracic surgery patients were randomly assigned to 1 of 2 groups (group P [n = 18], maintained with propofol; group S [n = 18], maintained with sevoflurane). After setting up, the authors measured arterial blood gases at FIO2 = 1.0 as follows: during TLV and at 5 minutes, 15 minutes, 30 minutes, and 45 minutes after the start of OLV. ETCO2 was recorded just before and at 3 minutes after the start of OLV. The authors examined the relationship between the initial ETCO2 difference and the lowest PaO2 value recorded during the first 45 minutes of OLV.Measurements and Main ResultsThere was a significant negative correlation between the lowest PaO2 (x) value and the initial ETCO2 difference (y) during OLV in each group (group P: y = −0.0203x + 7.2571, r2 = 0.5351; group S: y = −0.0257x + 7.3158, r2 = 0.6129). This correlation was not significantly different between the groups.ConclusionThe present study indicates that the ETCO2 difference between TLV and early OLV has an association with impaired oxygenation later during OLV. This would be a simple and clinically convenient predictor of the lowest PaO2 value likely to be reached during one-lung anesthesia with either propofol or sevoflurane.