A novel method of evaluating the impact of secondary brain insults on functional outcomes in traumatic brain-injured patients

Objectives: Prior studies suggest that the emergency department (ED) occurrence of secondary brain insults (SBIs), such as systemic hypotension and hypoxia, worsens outcome in patients with traumatic brain injury. However, previous methods of assessing SBIs have been relatively crude, generally only determining the incidence and duration of events. The authors hypothesized that a new method that accounts for the cumulative depth and duration of SBIs would provide a more informative measure that better correlates with outcome. Methods: The authors developed a computer algorithm to calculate the total "dose" of an SBI (in this case, hypotension and hypoxia) as the area under the curve between a cut-point value and a measured vital sign over time. To test this method, the authors used an existing data set of head trauma patients for whom occurrence in the ED of any hypotension had been shown to be associated with in-hospital mortality. The authors applied the algorithm using the cut-point values from the prior study (systolic blood pressure less than or equal to 90 mm Hg and oxygen saturation less than or equal to 92%). The effects of SBIs on in-hospital mortality and three-month Glasgow Outcome Scale score were evaluated. Results: Of 107 patients overall, 26 had hypotension (dose range 0.2-898 mm Hg . min) and 40 had hypoxia (dose range 0.005-6.7% . min). Moderate and high doses of hypotension were more strongly associated with outcome than the measures from the initial study (any hypotension and number of hypotensive episodes). Hypoxia had no effect. Conclusions: New methods of measuring SBIs that take into account depth and duration of episodes may more accurately reflect the influence of these events on outcome after head trauma.