- age < 50 yr, ASA grade IV, severe cardiac or pulmonary insufficiency (FEV1 < 1 litre) , malignant hypertension, psychiatric illness (intake of psychiatric medication other than selective serotonin re-uptake inhibitors), diastolic blood pressure more than 110 mmHg. emergency surgery, coagulopathy, significant renal and hepatic dysfunction (creatinine > 50% or liver enzymes > 50% upper limit of normal values)