J Trauma Acute Care Surg. 2021 Mar 4. doi: 10.1097/TA.0000000000003148. Online ahead of print.
BACKGROUND: Flow cytometry (FCM) is a rapid diagnostic tool for monitoring immune cell function. We sought to determine if assessment of cell phenotypes using standardized FCM could be used to identify nosocomial infection after trauma.
METHODS: Prospective study of trauma patients at a Level 1 center from 2014-2018. Clinical and FCM data were collected within 24h of admission. Random forest (RF) models were developed to estimate the risk of severe sepsis (SS), organ space infection (OSI) and ventilator-associated pneumonia (VAP). Variables were selected using backwards elimination and models were validated with leave-one-out.
RESULTS: 138 patients were included (median age 30y (23-44), median ISS 20 (14-29), 76% (105/138) black, 60% (83/138) gunshots). The incidence of SS was 8.7% (12/138), OSI 16.7% (23/138), and VAP 18% (25/138). The final RF SS model resulted in 5 variables [RBCs transfused in first 24h; absolute counts of CD56- CD16+ lymphocytes, CD4+ T cells, and CD56 bright natural killer (NK) cells; percentage of CD16+ CD56+ NK cells] that identified SS with AUC 0.89, sensitivity 0.98, and specificity 0.78. The final RF OSI model resulted in 4 variables (RBC in first 24h, shock index, absolute CD16+ CD56+ NK cell counts, percentage of CD56 bright NK cells) that identified OSI with AUC 0.76, sensitivity 0.68, and specificity 0.82. The RF VAP model resulted in 6 variables (SOFA score; ISS; CD4- CD8- T cell counts; percentages of CD16- CD56- NK cells, CD16- CD56+ NK cells, and CD19+ B lymphocytes) that identified VAP with AUC 0.86, sensitivity 0.86, and specificity 0.83.
CONCLUSION: Combined clinical and FCM data can assist with early identification of posttraumatic infections. The presence of NK cells supports the innate immune response that occurs during acute inflammation. Further research is needed to determine the functional role of these innate cell phenotypes and their value in predictive models immediately after injury.
LEVEL OF EVIDENCE: Level III, prognostic.