Background: Prolonged coma is not an uncommon clinical problem following resuscitation from cardiac arrest. Early and precise prediction of outcome is highly desirable for ethical and economical reasons. The aims of this study were to use positron emission tomography (PET) to investigate the regional dynamic changes of cerebral blood flow and metabolism during the early period after cardiopulmonary resuscitation (CPR) in unconscious patients and to evaluate if PET may be a potential prognostic evaluator.
Methods and results: PET and Glasgow Coma Scale examinations were sequentially performed on days 1, 3 and 7 in seven patients remaining comatose post CPR. Each PET included regional determinations of cerebral blood flow (rCBF), oxygen metabolism (rCMRO(2)), oxygen extraction ratio (rOER), and cerebral blood volume (rCBV). One patient was excluded due to complex trauma problems. Three patients remained unconscious until death and three woke up. All patients initially exhibited low CMRO(2) and CBF. Increased OER was only found exceptionally and when present was predominantly in focal areas. The comatose patients showed progressive depression of CMRO(2) and after 1 week had lower CMRO(2) than those patients who woke up. This difference was most pronounced in the putamen and occipital cortex. Two of the seven patients developed large focal infarcts.
Conclusions: An initially low CMRO(2) was common to all patients. Early development of subclinical focal ischemic lesions was also common. The progressive depression of CMRO(2) over the first week in those patients remaining unconscious may be an indication of prolonged but not necessarily permanent coma. Further studies are required to identify pathophysiological features that can predict the long-term clinical outcome in patients who remain unconscious after 1 week.