• Sung Yang, David Stepien, Dennis Hanseman, Bryce Robinson, Michael D Goodman, Timothy A Pritts, Charles C Caldwell, Daniel G Remick, and Alex B Lentsch.
• 1Institute for Military Medicine, Division of Trauma and Critical Care, Department of Surgery, University of Cincinnati College of Medicine, Cincinnati, OH. 2Department of Pathology and Laboratory Medicine, Boston University School of Medicine, Boston, MA.
• Crit. Care Med. 2014 Sep 1; 42 (9): 2092-100.

ObjectivesTraumatic brain injury results in significant morbidity and mortality and is associated with infectious complications, particularly pneumonia. However, whether traumatic brain injury directly impacts the host response to pneumonia is unknown. The objective of this study was to determine the nature of the relationship between traumatic brain injury and the prevalence of pneumonia in trauma patients and investigate the mechanism of this relationship using a murine model of traumatic brain injury with pneumonia.DesignData from the National Trauma Data Bank and a murine model of traumatic brain injury with postinjury pneumonia.SettingAcademic medical centers in Cincinnati, OH, and Boston, MA.Patients/SubjectsTrauma patients in the National Trauma Data Bank with a hospital length of stay greater than 2 days, age of at least 18 years at admission, and a blunt mechanism of injury. Subjects were female ICR mice 8-10 weeks old.InterventionsAdministration of a substance P receptor antagonist in mice.Measurements And Main ResultsPneumonia rates were measured in trauma patients before and after risk adjustment using propensity scoring. In addition, survival and pulmonary inflammation were measured in mice undergoing traumatic brain injury with or without pneumonia. After risk adjustment, we found that traumatic brain injury patients had significantly lower rates of pneumonia compared to blunt trauma patients without traumatic brain injury. A murine model of traumatic brain injury reproduced these clinical findings with mice subjected to traumatic brain injury demonstrating increased bacterial clearance and survival after induction of pneumonia. To determine the mechanisms responsible for this improvement, the substance P receptor was blocked in mice after traumatic brain injury. This treatment abrogated the traumatic brain injury-associated increases in bacterial clearance and survival.ConclusionsThe data demonstrate that patients with traumatic brain injury have lower rates of pneumonia compared to non-head-injured trauma patients and suggest that the mechanism of this effect occurs through traumatic brain injury-induced release of substance P, which improves innate immunity to decrease pneumonia.

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