Background. The technique of one lung ventilation (OLV) is used with the purpose of achieving isolation of the diseased lung being operated upon, using a double-lumen endobronchial tube. Thoracic surgical procedures which are performed in the lateral decubitus position, nowadays could not be imagined without OLV. In spite of advantages regarding surgical exposure, OLV is associated with serious respiratory impairment. Hypoxemia is considered to be the most important challenge during OLV. The goal of this study was to establish the magnitude of intrapulmonary shunt, as well as the immensity of hypoxia during general anesthesia with OLV.
Materials and Methods. In this prospective interventional clinical study thirty patients were enrolled who underwent elective thoracic surgery with a prolonged period of OLV. The patients received balanced general anesthesia with fentanyl/propofol/rocuronium. A double-lumen endobronchial tube was inserted in all patients, and mechanical ventilation with 50% oxygen in air was used during the entire study. Arterial blood gases were recorded in a lateral decubitus position with two-lung ventilation, at the beginning of OLV (OLV 0) and at 10 and 30 min. (OLV 10, OLV 30, respectively) after initiating OLV in all patients. Standard monitoring procedures were used. Arterial oxygenation (PaO2), arterial oxygen saturation (SaO2) and venous admixture percentage – intrapulmonary shunt (Qs/Qt %) were measured, as well as mean arterial pressure and heart rate during the same time intervals. For the purpose of this study, the quantitative value of Qs/Qt% was mathematically calculated using the blood gas analyser AVL Compact 3. A p value <0.05 was taken to be statistically significant.
Results. When OLV was instituted, arterial oxygenation decreased, whereas Qs/Qt% increased, about 10 min. after commencement, with improvement of oxygenation approximately half an hour afterwards. A statistically relevant difference (p<0.05) occurred in PaO2, SaO2 and Qs/Qt at the different time points.
Conclusion. Hypoxia during OLV, with an increase in Qs/Qt, usually occurs after 10 min. of its initiation. After 30 min, the values of the Qs/Qt ratio regularly return to normal levels.
Key words: one-lung ventilation, thoracic surgery, venous admixture, intrapulmonary shunt