Cardiovascular, metabolic and hormonal changes during isoflurane N2O anaesthesia

Isoflurane was used in 10 ASA I or II female patients, undergoing hysterectomy. It was given at a constant inspired concentration of 1.3% in a 50% N2O/50% O2 mixture, after induction of anaesthesia using etomidate (0.3 mg kg-1) and intubation following pancuronium (0.1 mg kg-1). No analgesic supplement was given. The patients were hyperventilated minimally (PaCO2 4.7-5.3 kPa). At standardized times (before induction, after induction, 5', 25', 50' and 75' min after surgical incision, awake and awake +60'), cardiovascular (blood pressure, cardiac output, stroke volume, heart rate), respiratory (blood gases), metabolic (oxygen consumption, blood glucose) and hormonal (noradrenaline, adrenaline, cortisol, prolactin) changes were measured. Blood pressure changes were very moderate (mean values were lower than before induction), but heart rate was increased significantly. Decreases in stroke volume and changes in cardiac output were not significant. Oxygen consumption was decreased below basal values during surgery. Blood glucose levels increased significantly in the course of surgery and remained raised postoperatively. Adrenaline and noradrenaline levels increased significantly. At each examination time, cortisol levels were decreased significantly. Prolactin levels had decreased significantly 75 mins after incision and remained low 60 mins after awakening.