Effects of lorazepam on oxygen saturation before cardiac surgery

We have studied patients presenting for coronary artery bypass surgery on two nights before surgery. Oxygen saturation during a night when the patient received no night sedation was compared with the night before surgery, when lorazepam 3-4 mg was given. There was no difference between the two nights when the total time at oxygen saturations less than 90% were compared, but the minimum oxygen saturation value when the patient received lorazepam was significantly smaller. No patient had significant sleep apnoea.