Comapring the values derived from tools which reads strength of peripheral blood flow,derivative of blood flow and blood pressure changes with respiratory cycle , to predict significant reduction of blood pressure after giving anaesthesia medicines to a patient during surgery:a observational study

Primary outcome(s): To detect whether perfusion index(PI), pleth variability index(PVI) and pulse pressure variation(PPV) values can predict hypotension after general anaesthesia induction during major surgeryTimepoint: To detect whether perfusion index(PI), pleth variability index(PVI) and pulse pressure variation(PPV) can predict hypostension by 5 minutes after anaesthesia induction.