Harbingers of Poor Outcome the Day after Severe Brain Injury: Hypothermia, Hypoxia, and Hypoperfusion

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Abstract
Traumatic brain injury (TBI) can be compounded by physiologic derangements that produce secondary brain injury. The purpose of this study is to elucidate the frequency with which physiologic factors that are associated with secondary brain injury occur in patients with severe closed head injuries and to determine the impact of these factors on outcome. The records of 81 adult blunt trauma patients with Glasgow Coma Scale scores < or = 8 and transport times < 2 hours to a Level I trauma center were retrospectively reviewed searching for the following 11 secondary brain injury factors (SBIFs) in the first 24 hours postinjury: hypotension, hypoxia, hypercapnia, hypocapnia, hypothermia, hyperthermia, metabolic acidosis, seizures, coagulopathy, hyperglycemia, and intracranial hypertension. We recorded the worst SBIF during six time periods: hours 1, 2, 3, 4, 5 to 14, and 16 to 24. Occurrence of each SBIF was then correlated with outcome. Hypocapnia, hypotension, and acidosis occurred more frequently than other SBIFs (60-80%). Hypotension, hyperglycemia, and hypothermia were associated with increased mortality rate. Patients with episodes of hypocapnia, acidosis, and hypoxia had significantly longer intensive care unit length of stay (LOS). These three SBIFs and hyperglycemia related to longer hospital LOS as well. Hypotension and acidosis were associated with discharge to a rehabilitation facility rather than home. Finally, multivariate regression analysis revealed that hypotension, hypothermia, and Abbreviated Injury Scale score of the head were independently related to mortality, whereas other SBIFs, age, Injury Severity Score, and Glasgow Coma Scale score were not. Metabolic acidosis and hypoxia were related to longer intensive care unit and hospital LOS. Our early management of head-injured patients stresses avoidance and correction of SBIFs at all costs. Nonetheless, SBIFs occur frequently in the first 24 hours after traumatic brain injury. Six of the 11 factors studied are associated with significantly worse outcomes. Hypotension and hypothermia are independently related to mortality. Because these SBIFs are potentially preventable, protocols could be developed to decrease their frequency.