Background: The most favorable anesthetic technique for patients undergoing thoracotomy with one lung ventilation (OLV) has not been yet certainly established. The effect of intraoperative thoracic epidural anesthesia (TEA) with local anesthetics on hypoxic pulmonary vasoconstriction (HPV) and oxygenation during thoracic surgery and OLV still remains unclear. The aim of this study was to assess the venous admixture (shunt) during general anesthesia (GA) and OLV, in combination of TEA and GA with OLV, as well as to compare the values of the shunt obtained for the duration of both anesthetic techniques.

Keywords: one-lung ventilation, epidural anesthesia, venous admixture

Materials/methods: In this prospective randomized clinical study sixty patients who had prolonged period of OLV for elective thoracic surgery were randomly allocated into two groups (n=30 each). In 30 patients (GA group), fentanyl/propofol/rocuronium anesthesia was used. Another 30 patients (TEA group) were anesthetized with fentanyl/propofol/rocuronium plus epidural thoracic bupivacaine 0.25%, 6-8 ml/h. A double-lumen endobronchial tube was inserted, 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 10 and 30 min (OLV 10, OLV 30, respectively) after initiating OLV in all patients. The monitoring was standard. Arterial oxygenation (PaO2), arterial oxygen saturation (SaO2) and venous admixture percentage (Qs/Qt %) were measured. For the purpose of this study, the quantitative value of Qs/Qt% was mathematically calculated by the blood gas analyzator AVL Compact 3. A p value

Results: When OLV was instituted arterial oxygenation decreased, whereas Qs/Qt% increased, about 10 min of the commencement, with improving of the oxygenation approximately half an hour afterwards. Statistical difference (p<0,05) occurred inside the groups regarding PaO2, SaO2 and Qs/Qt in the different  measurings. There were no statistical differences (p>0,05) between the two groups for PaO2 at OLV 10 (GA=13,78+/-5,84 kPa, TEA=11,87+/-4,95 kPa) and OLV 30 (GA= 15,66+/-6,62kPa, TEA=14,88+/-4,45kPa); for SaO2 at OLV 10 (GA=93,52+/-6,03%, TEA=92,92+/-5,2% ) and OLV 30 (GA=95,31+/-4,62%, TEA=95,89+/-3,78 %) and with values of Qs/Qt% at OLV 10 (GA=8,03+/-10,59%, TEA=10,93+/-10,80%) and OLV 30 (GA=3,94+/-6,21%,TEA=4,8+/-7,58%).

Conclusions:  Hypoxia during OLV with increase of Qs/Qt usually occurs after 10 min of its initiation, for the period of general anesthesia, as well as combined general and thoracic epidural anesthesia.  Following 30 min of the beginning of OLV, the values of the Qs/Qt regularly decrease back to the normal quantities. Both techniques, general anesthesia and general anesthesia combined with TEA are suitable for thoracic surgery when OLV is used, considering arterial oxygenation. There was no significant difference in PaO2 and Qs/Qt during each administration.

Gordana Taleska
University Medical Centre Ljubljana, Slovenia

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