This study will compare the effects of sevoflurane, desflurane and total intravenous anaesthesia on pulmonary function tests in patients undergoing endoscopic endonasal transsphenoidal surgery of pituitary gland. Participants will be divided into three equal groups. The first group will receive sevoflurane, second grup will receive desflurane and third grup will receive total intravenous anaesthesia. Investigators are also going to evaluate blood gas analysis.