The impact of age on the innate immune response and outcomes after severe sepsis/septic shock in trauma and surgical intensive care unit patients.

BACKGROUND: Advancing age is a strong risk factor for adverse outcomes across multiple disease processes. However, septic surgical and trauma patients are unique in that they incur two or more inflammatory insults. The effects of advanced age on sepsis pathophysiology and outcomes remain unclear.
METHODS: We performed a single-center, prospective observational cohort study of surgical intensive care unit patients with severe sepsis/septic shock. Peripheral blood was collected for genomic, cytokine, and biomarker analysis at 0.5 day, 1 day, 4 days, 7 days, 14 days, 21 days, and 28 days after sepsis onset. Based on sensitivity analysis, cohorts were defined as "young" (<55 years) and "aged" (≥55 years). We compared age-defined cohorts to determine differences in patient characteristics, biomarker profiles, and clinical outcomes.
RESULTS: The cohort included 173 patients with severe sepsis (n = 93; 53.8%) or septic shock (n = 80; 46.2%), with a mean age of 60.9 (±14.5) years. Intra-abdominal sepsis was the leading source (n = 81; 46.8%), followed by necrotizing soft tissue infection (n = 33, 19.1%) and pneumonia (n = 30; 17.3%). Aged patients had a higher comorbidity burden, but were otherwise similar to the young cohort. The aged cohort had a higher severity of early physiologic derangement (median APACHE II, 23 vs. 18; p = 0.002), greater incidence of multiple organ failure (64.3% vs. 40.4%, p = 0.006), and hospital mortality (15.9% vs. 2.1%; p = 0.016). Six-month mortality was significantly higher in the aged cohort as compared with young cohort (31% vs. 9%; p = 0.003). Aged septic patients biomarker trajectories suggestive of persistent immunosuppression (absolute lymphocyte count, soluble programed death ligand-1) and catabolism (Urine 3MH-Cr ratio, insulin growth factor, IGF1BP3, albumin) out to 28 days after sepsis.
CONCLUSION: Aged, critically ill surgical patients have greater organ dysfunction and incidence of adverse clinical outcomes after sepsis. Biomarker profiles suggest an immunophenotype of persistent immunosuppression and catabolism. Advanced age may necessitate novel therapeutic strategies to promote multisystem organ recovery and improve survival after sepsis. LEVEL OF EVIDENCE: Prognostic, level II.