In most situations where there is severe blood loss, patients will receive blood product transfusions. If it is a planned procedure this can be autologus blood donation by the patient prior to the procedure or if in the emergency situation by donor blood transfusion. In rare situations, such as when the patient will not receive blood products for religious reasons, HBO can be used as a supportive therapy until there has been sufficient red cell regeneration. In these situations there has been enough blood loss that respiratory requirements cannot be met.
Under normobaric conditions most of the oxygen available for tissue use is bound to haemoglobin molecules and in arterial blood the haemoglobin is approximately 98% saturated. In the hyperbaric environment, as well as the haemoglobin being saturated, there is a high concentration of oxygen dissolved in the plasma. Various animal studies have shown that there is an improved survival in animals with haemorrhagic shock treated with HBO compared to control groups. There was limited human experience until 1987 when it was reported on a case series of 26 patients, these patients had blood loss of over 50% and without receiving any blood products had a survival of 70%.
Hyperbaric oxygen treatments need to be repeated until there is sufficient improvement in the haematocrit and haemoglobin to meet the patient’s oxygen requirements. HBO treatments are given with increasing lengths of air breaks between treatments, treatments are for one hour per exposure, normobaric oxygen is given between treatments but with appropriate air breaks to avoid pulmonary oxygen toxicity.