Effect Of Dexmedetomidine On Arterial Oxygenation And Intrapulmonary Shunt During One-lung Ventilation Under Total Intravenous Anaesthesia

Introduction and objectiveOne-lung ventilation(OLV) as a special ventilation mode is widely used in operative procedures in the thoracic cavity.Perfusion of the nonventilated lung leads to a right-left transpulmonary shunt,to arterial oxygen tension(PaO2) decreased significantly during OLV. During this process, hypoxaemia is reported to occur with an incidence of approximately4-10%. Many factors can affect the PaO2during OLV, including hypoxic pulmonary vasoconstriction (HPV), surgical position, double-lumen tube position and ventilation strategies. HPV allows for shunting of blood away from the nonventilated lung to the ventilated lung and thus allows for the maintenance of adequate oxygenation.Many factors, such as cardiac output, vasodilator,can affect HPV. Narcotic drugs also affect HPV. Inhalation anesthetics are considered to be dose-dependently attenuated HPV, while intravenous anesthetic drugs such as fentanyl or ketamine has little effect on HPV.Dexmedetomidine, a selective agonist of the α2-drenergic receptors, has8times greater affinity for the α2-adrenergic receptors than clonidine. Dexmedetomidine has been shown to have sedative, hypnotic and analgesic effects without affecting breathing, so now widely used in the intensive care unit and perioperative period. The effects of dexmedetomidine on HPV and its effects on oxygenation during OLV are unclear. In this study, by observing PaO2and pulmonary shunt fraction (Qs/Qt) of the patients under total intravenous anesthesia undergoing lobectomy, we prospectively evaluated the effects of dexmedetomidine on arterial oxygenation and intrapulmonary shunt during OLV.Methods1.40patients scheduled for a lobectomy were randomly assigned to Group dexmedetomidine(Group D) and Group control(Group C),20cases each. Patients with conventional fasting, do not use premedication, into the operating room monitoring electrocardiogram (ECG), blood pressure (BP), oxygen saturation (SpO2), bispectral index (BIS),20gauge cannula needle for radial artery catheterization, monitoring arterial blood pressure (ABP).The right internal jugular vein was selected for catheterization. Before induction of anesthesia, Group D given intravenous dexmedetomidine loading dose (lμg·kg-1), infusion time control in10-15min.After completion of the loading dose, a continuous infusion of dexmedetomidine was started at0.3μg·kg-1·h-1. Group C, in the same syringe infusion same volume of saline. Anaesthetic induction included midazolam (2mg) followed by etomidate (0.2mg·kg-1),fentanyl (4μg·kg-1),rocuronium (0.6mg·kg-1) to facilitate endotracheal intubation. Double-lumen endobronchial tube (DLT) inserted through the mouth, selected37Fr for male,35Fr for female. Auscultation confirmed correct endotracheal tube position. After positioning the patient in lateral decubitus, the correct position of the double-lumen tube was checked using a fibreoptic bronchoscope. Then contact the DLT to Detex-Ohmeda Aespire anesthesia machine to control ventilation. Ventilatory settings were identical during two-lung ventilation (TLV) and OLV:Tml·kg-1tidal volume,12/min ventilatory rate, volume control mode, inspiratory to expiratory ratio1:2, and FiO21. If the peak airway pressure than30cmH2O during OLV, tidal volume and ventilatory rate appropriately adjust to maintain peak airway pressure below30cmH2O.Meanwhile, PetCO2maintained at around35mmHg. Maintenance anaesthesia consisted of propofol target-controlled infusion and fentanyl intravenous bolus injection. TCI of propofol was administered with the Marsh pharmacokinetic model. The initial target plasma concentration of propofol was3μg·ml-l, target plasma concentrations of propofol were titrated to maintain BIS values between40and60throughout the intraoperative period.After the tracheal intubation, patients were given an infusion of cis-atracurium2μg·kg-1·min-1. The mean arterial pressure (MAP) and heart rate (HR) were maintained within20%of the preoperative baseline values. Vasoactive agents were administered when necessary. Intraoperative fluid was administered at a rate of6ml·kg-1·h-1, was adjusted according to the preoperative requirements and blood loss during surgery. OLV was started just before the pleura were opened. Monitoring indicators:①Record preoperative pulmonary function and arterial blood gas:a second volume (FEV1),forced vital capacity (FCV),a second ratio (FEV1/FCV),arterial partial pressure of oxygen (PaO2).②Record before induction of anesthesia (T0),15minutes after TLV (T1),15minutes after OLV (T2) and15minutes after TLV resumed (T3)—this four time points,MAP and HR; record T1, T2, T3these three time points Graseby3500propofol effect-site concentration (Ce) and BIS values.③In T1, T2, T3these three time points collected radial artery and central venous blood to do blood gas analysis:Record Hb, PaO2, PaCO2, arterial oxygen saturation (SaO2),central venous oxygen tension (PcvO2), central venous oxygen saturation degree (ScvO2), calculated intrapulmonary shunt fraction (Qs/Qt).④Record OLV time, operation time, recovery time, extubation time.⑤Record the dosage of fentanyl, atropine, ephedrine.2. Statistical analysis:Statistical tests were performed using SPSS version13.0. Data are expressed as mean±standard deviation. Measurement data were compared using Student’s t-test for independent samples (intergroup comparison), count data were compared using chi-square test. In all tests, the level of significance was set at5%.Results1. Four patients were excluded from the analyses. Three patients because of hypoxemia during OLV (two patients in D group, one patient in C group),1patient in C group excluded because of intraoperative blood transfusion.2. Preoperative general condition,pulmonary function, PaO2were no significant difference between the two groups (P>0.05).3. Hemodynamic parameters:MAP at each time point were no statistical difference between the two groups (P>0.05); HR at T1was significantly slower in group D than in C group (P<0.05), HR in another three time points were no statistical difference between the two groups (P>0.05).4. PaO2and intrapulmonary shunt fraction (Qs/Qt):PaO2at T1, T2, T3time points were no statistical difference between the two groups (P>0.05); pulmonary shunt fraction (Qs/Qt) in T1,T2, T3time point were no statistical difference between the two groups (P>0.05).5. Propofol effect-site concentration (Ce), BIS values and fentanyl dosage:Propofol effect-site concentration (Ce) in T1, T2, T3time points were significantly lower in D group than in C group (P<0.05); BIS values at T1, T2, T3time points were no statistical difference between the two groups (P>0.05); fentanyl dosage were no statistical difference between the two groups (P>0.05).6. Both operative time and OLV time were no statistical difference between the two groups (P>0.05);both awake time and extubation time was significantly longer in D group than in C group (P<0.05).7. Intraoperative number of patients using atropine and ephedrine were no statistical difference between the two groups (P>0.05).Conclusion1. Dexmedetomidine does not adversely affect arterial oxygenation and intrapulmonary shunt fraction (Qs/Qt) during OLV under total intravenous anesthesia.2. Dexmedetomidine can significantly reduce the requirement of propofol in the same range of BIS.3. Dexmedetomidine can significantly extend both awake time and extubation time.