Inclusion Criteria:  Age ≥18 Elective high-risk head and neck or maxillo-facial surgery  Exclusion Criteria:  Patient refusal Reduced ejection fraction below 40% and heart failure History of atrial Fibrillation, pulmonary embolism, recent cardioversion, recent cardiac ischemic episode, chronic hypotension, chronic kidney insufficiency (serum creatinine > 1.5) Septic state Baseline heart-rate < 50 or > 90 bpm History of psychiatric disease or medication