Oxygen concentrations and responses of the immune system in surgery

Surgery for many procedures involving the leg requires the surgeons to stop the blood flow for a variable period of time. During this period certain changes occur in the leg. When the blood supply is restored, these changes result in a very strong stimulus to the immune system. Some of these changes are beneficial, promoting healing of wounds and repair of damaged tissues. Some of these changes, however, can cause depression of the immune system and make infections more likely. During surgery, the anaesthetist administers anaesthetic drugs, and oxygen. The amount of oxygen that is given varies according to a number of factors. There is some evidence that the amount of oxygen in the body at the time of restoring blood supply to a limb may be of importance. This importance is in terms of the damage that may occur during surgery and the recovery from the surgery. We do not know how much oxygen is good or bad when the blood supply is restored, and we would like to perform a study looking at this question. At all times in this study, patients will receive at least more than the minimum amount of oxygen that is necessary for all of the bodies organs to function entirely normally, and make a complete recovery from anaesthesia and surgery. Study protocol After randomisation to one of the three groups, patients will receive a standardised general anaesthetic based upon the gas “Sevoflurane”. All patients will receive 30% oxygen during the surgery, up until the time of restoring blood supply to the leg. At that point patients in one of three groups will receive either a). 30% oxygen before the blood supply is restored and continued until the end of surgery -(Conventional Care) b). 30% oxygen before the blood supply is restored and then 50 % until the end of surgery c). 30% oxygen before the blood supply is restored and then 80 % until the end of surgery - all of the above are in addition to the usual standard anaesthetic care. A small ( 3 ml. ) sample of blood will be taken at ten separate times up until 2 hours after the blood supply is restored. The study period then ends for each patient at that point. In summary, our hypothesis is that different concentrations of oxygen will produce changes in biochemistry that we wish to measure. These changes will help us to identify which is the best oxygen concentration to give to patients who are having this type of surgery.