Comparison of the effects of isoflurane and propofol in conjunction with thoracic epidural block on oxygenation and shunt fraction during one-lung anesthesia / 中华麻醉学杂志

ABSTRACT

Objective To compare the effects of isoflurane and propofol on arterial oxygenation and intrapulmonary shunt during one-lung ventilation (OLV) when combined with continuous thoracic epidural block. Methods Twenty-four ASA Ⅰ -Ⅱ patients with normal ventilatory function undergoing elective thoracic surgery were enrolled in this study. Patients with abnormal cardiac, liver or kidney function were excluded. The patients were premedicated with scopolamine 0. 3mg I. M. .Epidural block was performed at T7-8 or T8-9 . An epidural catheter was placed and its position confirmed by epidural 1% lidocaine 5 ml. General anesthesia was induced with propofol l.5mg?kg-1, fentanyl 3?g?kg-1 and vecuronium 0.lmg?kg-1 . Double-lumen catheter was inserted and its correct position was confirmed by a combination of unilateral lung ventilation and auscultation in both supine and lateral position. The patients were mechanically ventilated. Tidal volume was set at 8-10 ml?kg-1, FiO2 = 1, IE=11.5, RR=10-12bpm and PETCO2 was maintained between 35-45 mm Hg. The parameters remained unchanged during one-lung ventilation. The patients were assigned to one of two groups propofol group and isoflurane group. Anesthesia was maintained with propofol infusion in propofol group and isoflurane inhalation in isoflurane group and BIS was maintained at 45-55. A bolus of 0.5 % ropivacaine 7-9ml was given epidurally followed by 0.5% ropivacaine infusion at a rate of 3-5ml?h-1 in both groups during maintenance of anesthesia. Besides ECG, BP and BIS, continuous cardiac output(CCO Baxter) was monitored during operation. Blood samples were taken from radial artery and pulmonary artery simultaneously before anesthesia when patients were lying supine and breathing spontaneously (T0 ), in lateral position when both lungs were ventilated (T1 ), at 5,15, 30, 60 min of one-lung ventilation(T2-5 ) and when both lungs were ventilated again for 30min(T6) for blood gas analysis. Qs/Qt was calculated.Results (1) The two groups were comparable with respect to demographic data. Propofol infusion was maintained at 4-6 mg?kg-1?h-1 in propofol group and end-tidal isoflurane was maintained between 0.3%-0.5% in isoflurane group. (2) Venous admixture increased significantly at T1 and further increased after T2 and reached its peak at T3(31.1% ?4.2%) in propofol group and at T4 (33.5% ? 7.8% ) in isoflurane group. Shunt fraction was significantly lower in propofol at T4-5 than that in isoflurane group. (3) PaO2 decreased significantly during OLV in both groups, but there was no significant difference in PaO2 between the two groups. Conclusions When combined with thoracic epidural block, intravenous propofol infusion exerts less effect on intrapulmonary shunt than isoflurane inhalation during OLV but there was no significant difference in arterial oxygenation between the two groups.