Effects of hyperbaric oxygenation therapy on cerebral metabolism and intracranial pressure in severely brain injured patients

Object. Hyperbaric oxygenation (HBO) therapy has been shown to reduce morta lity by 50% in a prospective randomized trial of severely brain injured pat ients conducted at the authors' institution. The purpose of the present stu dy was to determine the effects of HBO on cerebral blood flow (CBF), cerebr al metabolism, and intracranial pressure (ICP), and to determine the optima l HBO treatment paradigm. Methods. Oxygen (100% O-2, 1.5 atm absolute) was delivered to 37 patients i n a hyperbaric chamber for 60 minutes every 24 hours (maximum of seven trea tments/patient). Cerebral blood flow, arteriovenous oxygen difference (AVDO (2)), cerebral metabolic rate of oxygen (CMRO2), ventricular cerebrospinal fluid (CSF) lactate, and ICP values were obtained 1 hour before and 1 hour and 6 hours after a session in an HBO chamber. Patients were assigned to on e of three categories according to whether they had reduced, normal, or rai sed CBF before HBO. In patients in whom CBF levels were reduced before HBO sessions, both CBF and CMRO2 levels were raised 1 hour and 6 hours after HB O (p < 0.05). In patients in whom CBF levels were normal before HBO sessions, both CBF an d CMRO2, levels were increased at 1 hour (p < 0.05), but were decreased by 6 hours after HBO. Cerebral blood flow was reduced 1 hour and 6 hours after HBO (p < 0.05), but CMRO2 was unchanged in patients who had exhibited a ra ised CBF before an HBO session. In all patients AVDO(2) remained constant b oth before and after HBO. Levels of CSF lactate were consistently decreased 1 hour and 6 hours after HBO, regardless of the patient's CBF category bef ore undergoing HBO (p < 0.05). Intracranial pressure values higher than 15 mm Hg before HBO were decreased 1 hour and 6 hours after HBO (p < 0.05). Th e effects of each HBO treatment did not last until the next session in the hyper baric chamber. Conclusions. The increased CMRO2 and decreased CSF lactate levels after tre atment indicate that HBO may improve aerobic metabolism in severely brain i njured patients. This is the first study to demonstrate a prolonged effect of HBO treatment on CBF and cerebral metabolism. On the basis of their data the authors assert that shorter, more frequent exposure to HBO may optimiz e treatment.