To collect data on the effects of Dexmedetomidine(DEX)(0.3mcg/kg loading dose followed by an infusion of 0.3mcg/kg/hr)on Hypoxic pulmonary vasoconstriction when administered to patients during surgery with one lung ventilated thoracic procedures. Dexmedetomidine has both vasoconstricting and vasodilatatory effect on peripheral vasculature but its effect on pulmonary vessels is not known. If it is predominantly a vasodilator on pulmonary vessels it can inhibit hypoxic pulmonary vasoconstriction and will increase shunting of venous blood to arterial circulation without oxygenation. If our study proves it to be a vasodilator for pulmonary vessels then it will not be wise to use it in thoracic procedure with one lung ventilation. If our study proves that it is a vasoconstrictor for pulmonary vessels, then it will be an excellent adjunct to other anesthetic agents during one lung ventilation.