A Cohort Prospective Study of Predictors Influencing the Quality of Visualization of the Operating Field During Orthognathic Surgery

100 patients undergoing bimaxillary osteotomy under general anesthesia will be included into this prospective cohort study. There will be two episodes of controlled hypotension for upper and lower jaw respectively. Hypotension will be induced and sustained according to the same procedure as described here. Controlled hypotension will be induced (intravenous administration of nitroglycerin 2-10 µg/kg/min) 15 minutes prior to the start of mucosal detachment, and will be sustained for the osteotomy stage. The surgeon will evaluate the surgical field quality (in terms of bleeding) according to Modena Bleeding Score (MBS), with scores 1-2 being satisfactory to proceed with the osteotomy. The following arterial pressure correction (proceeding with controlled hypotension or returning to normotension) will depend on the bleeding in the surgical field and the monitoring of cerebral oxygen saturation carried out using near-infrared spectroscopy (NIRS) . The lowest targeted arterial pressure in order to have a clear surgical field will be 55 mmHg. However when the cerebral oxygen saturation decreases by 20% compared with the baseline at any arterial pressure level intervention would be carried out by Norepinephrine (intravenous, individual dosage for each patient - as judged by the anesthesiologist). Arterial blood samples will be taken at 3 time points (at the start of the surgery, during controlled hypotension phase, after extubation) for arterial gas analysis. Two blood samples will be taken to measure (prior to surgery and immediately after surgery) neuron-specific enolase (NSE), cystatin c and troponin I levels. The general condition, operation, anesthesia and hospitalization related data of the patients will be recorded. Cognitive function will be evaluated within 3 days before surgery and 2 days and 1 month after surgery.