Pain trajectories in the emergency department: Patient characteristics and clinical outcomes.

Background: Little is known about pain trajectories in the emergency department (ED), which could inform the heterogeneous response to pain treatment. We aimed to identify clinically relevant subphenotypes of pain resolution in the ED and their relationships with clinical outcomes.

Methods: This retrospective cohort study used electronic clinical warehouse data from a tertiary medical center. We retrieved data from 733,398 ED visits over a 7-year period. We selected one ED visit per person and retrieved data including patient demographics, triage data, repeated pain scores evaluated on a numeric rating scale, pain characteristics, laboratory markers, and patient disposition. The primary outcome measures were hospitalization and ED revisit.

Results: 28,105 adult ED patients were included with a total of 154,405 pain measurements. Three distinct pain trajectory groups were identified: no pain (57.1%); moderate-to-severe pain, fast resolvers (17.9%); and moderate pain, slow resolvers (24.9%). The fast resolvers responded well to treatment and were independently associated with a lower risk of hospitalization (adjusted odds ratio [aOR], 0.75; 95% confidence interval [CI], 0.70-0.81). By contrast, the slow resolvers had lingering pain in the ED and were independently associated with a higher risk of ED revisit (aOR, 2.65; 95%CI, 1.85-3.69). This group also had higher levels of inflammatory markers, including a higher leukocyte count and a higher level of C-reactive protein.

Conclusions: We identified three novel pain subphenotypes with distinct patterns in clinical characteristics and patient outcomes. A better understanding of the pain trajectories may help with the personalized approach to pain management in the ED.