• A Herrera, A Pajeulo, M J Morano, M P Ureta, A Ruiz, and M de las Mulas.
• Servicio de Anestesiología y Reanimación, Hospital Universitario Virgen del Rocío, Sevilla.
• Rev Esp Anestesiol Reanim. 1993 Sep 1; 40 (5): 258-67.

ObjectivesThe lateral decubitus position, the thoracotomy and selective single-lung ventilation all cause serious changes in oxygenation. The aim of this study is to examine the usefulness of continuous monitoring of mixed venous saturation (SvO2) under these conditions.Material And MethodsTwenty-three patients scheduled for pulmonary resection by thoracotomy in lateral decubitus position with single-lung ventilation were monitored continuously for SvO2 by reflection oximetry and a fiber-optic catheter in the pulmonary artery (Abbot Oximetrix 3). Cardiorespiratory profiles were obtained 15 minutes after induction (M1), after 15 minutes in lateral decubitus position (M2), 5 min after start of pleurotomy (M3), 5 min (M4) and 20 min (M5) after lung collapse, 5 min after closure of the thoracic wall (M6), and after 5 min in supine decubitus position (M7).ResultsThe decrease in SvO2 was not statistically significant. It reached its lowest level at M5 and rose significantly in M6 (p < 0.05). For all SvO2 measurements there was a significant correlation between Oximetrix 3 and Co-oximeter readings. C(a-v)O2 and O2 uptake correlated significantly at all measurements, as did those of PvO2 and Qva/Qt except at M6. VO2I correlated inversely from M1 to M5, and CI an DO2I only at M6 and M7. PaO2 and SaO2 were significantly correlated during single-lung ventilation (M4 and M5) and later (M6). The combined changes in SaO2(a-v) and CI explain the changes in SvO2 only during and after selective ventilation, and the changes are more likely to be reflected by SaO2 than by CI.ConclusionsUnder the conditions studied, continuous monitoring of SvO2 is a reliable method, indicating primarily oxygenation, and cardiac output secondarily, particularly during single-lung ventilation, and also reflecting the balance of oxygen supply and demand in tissues. Given the lack of specificity, however, hemodynamic and gas measurements must be taken to diagnose the cause of any change in the supply/demand balance whenever there is a sudden drop in SvO2.

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