Effect Of Dexmedetomidine On Intrapulmonary Shunt During One-lung Ventilation In High Altitude Areas

Objective This study was aimed to explore how dexmedetomidine（Dex）effected intrapulmonary shunt ratio and pulmonary vascular system during VATS with single lung ventilation among natives in Qinghai who were exposed to high altitude environment since born,and to investigate correlation between time and intrapulmonary shunt ratio changes when only one side of the lung is ventilated in permanent high-altitude residents.Methods 60 inpatients for selective thoracoscopic lobectomy were taken into this prospective cohort study.There were two different groups（30 patients each）that a patient may participate in without the patient knowing which group he was in.Before induction,dexmedetomidine 1μg/kg was given over a period of 10 min to group A,then the dosage was tune down to 0.5μg/kg/h for further infusion throughout the operation until 30 min before suturing the surgical incision.Group B was given a solution of saline instead of Dex in the same manner.Drug preparation and infusion rate calculation were performed by the same person.Radial artery cannulation and central venous catheterization（right side preferred）was performed for collecting blood sample and getting a constant invasive arterial pressure reading.ABG samples were obtained at four intervals:T₀（during two-lung ventilation and right before the initiation of one-lung ventilation）,T₁（OLV 10 min）,T₂（OLV 30 min）,and T₃（OLV 1 h）.For further evaluation of pulmonary shunting,the Shunt equation:Qs/Qt=（Cc’O2-CaO2）/（Cc’O2-CvO2）×100%was applied to see the fluctuations of the fraction.Measurement of PaO2,SpO2,PaCO2,P_peak,HR and MAP were taken at the same time intervals to estimate if oxygenation and hemodynamic management were acceptable.Operation time,blood loss,hospital stay,and transferring to ICU unexpected postoperatively were also taken into account to evaluate whether dexmedetomidine was safe to use perioperatively and to optimize the outcomes of inpatients underwent thoracic surgery.Results There was no statistical difference in gender（P=0.602）,age（P=0.491）,BMI（P=0.607）,ASA classification（P=0.766）,and surgical site（left or right）（P=0.795）;the intrapulmonary shunt fraction under general anesthesia and bilateral lung ventilation at T₀ shows no difference.At T₁,T₂ and T₃,the shunting in group A was less severe than group B（P<0.05）.In addition,Qs/Qt increased rapidly 10 minutes after the initiation of OVL and then ascend further from T1 to T₂ but with a slightly flattened curve.Interestingly,from T₂ to T₃,the shunt fraction had no significant increase in group B.There was no difference in PaO₂、SpO₂、PaCO₂、MAP、Ppeak（P>0.05）,in the meantime it should be noted that at T₀ the HR was lower from patients who were given Dex before anesthesia induction.There was no patient in the two groups who was transferred to the ICU after surgery,nor did Dex have an impact on operation time,blood loss,and hospital stay.Conclusion Dexmedetomidine can reduce Qs/Qt during OLV in patients who had been living in high-altitude areas since born by enhancing hypoxic pulmonary vasoconstriction,thereby improving the oxygenation of patients undergoing thoracoscopic surgery.