The Emergency Severity Index (ESI) is a tool for use in emergency department (ED) triage. The ESI triage algorithm yields rapid, reproducible, and clinically relevant stratification of patients into five groups, from level 1 (most urgent) to level 5 (least urgent). The ESI provides a method for categorizing ED patients by both acuity and resource needs. (https://www.ahrq.gov/professionals/systems/hospital/esi/index.html ) Based upon AHRQ 2012 Edition on the Implementation Handbook - version 4.