<qa>  What is a preferred method for reducing surgical bleeding during septoplasty operations?Controlled hypotension is a preferred method for reducing surgical bleeding during septoplasty operations however, the level of hypotension and bradycardia should not disrupt cerebral oxygenation. On this account, the investigators aim to investigate the effects of different volatile anesthetics combined with a short-acting opioid on cerebral oxygenation during controlled hypotension using near infrared spectroscopy. 