ObjectivesFirst, to examine factors that may be related to brain swelling, which was identified by the absence or compression of the lateral and third ventricles and perimesencephalic cisterns on brain computed tomography (CT) scans in the early postresuscitation period in patients who suffered an out-of-hospital cardiac arrest. Second, to characterize the neurologic outcome in those patients in whom cardiac arrest was followed by brain swelling. DesignProspective and retrospective analyses. SettingsGeneral ICU, tertiary care hospital. PatientsFifty-three patients (35 male, 18 female) who had an out-of-hospital cardiac arrest and who also had a brain CT examination on the third day after resuscitation. The 53 patients were divided into two groups: group A (25 patients) experienced brain swelling on postresuscitation day 3; group B (28 patients) did not experience noticeable brain swelling. InterventionsNone Measurements and Main ResultsThere was a significant difference between the two groups in the etiology of the cardiac arrest. Twenty-three of 25 patients in group A had cardiac arrest due to respiratory distress, whereas this finding was true in only five patients in group B. In laboratory data, arterial pH was significantly lower in group A than in group B (6.93 vs. 7.09), as was base deficit (-21.0 mmol/L in group A vs. −13.7 mmol/L in group B). Neurologic outcome was evaluated 1 wk after resuscitation. There were significantly more patients in group A who were not awake and who were diagnosed as braing dead. ConclusionsThe cause of brain swelling may be related to the development of the metabolis acidosis (possibly lactic acidosis) due to hypoxie before the resuscitation period. Brain swelling may be one of the indicators that predicts a poes neurologic outcome in the patients who suffes an out-of-hospital cardiac arrest. (Crit Care Med 1993; 21:104–110)