What is an Emergency Severity Index (ESI) rating in an emergency room?

Emergency Severity Index (ESI) Rating

The Emergency Severity Index (ESI) is a five-level emergency department triage algorithm that stratifies patients based on both acuity and anticipated resource consumption, with ESI-1 representing the highest acuity (requiring immediate lifesaving intervention) and ESI-5 representing the lowest acuity (minimal or no resources needed). 1, 2

ESI Level Definitions

The ESI system operates on a hierarchical decision-making process:

• ESI Level 1: Patients requiring immediate lifesaving intervention, particularly those needing immediate airway management or medications to prevent imminent death or disability 2

• ESI Level 2: High-acuity patients who are stable enough to wait at least 10 minutes but will require multiple ED resources (typically 2 or more) 2, 3

• ESI Level 3: Patients requiring multiple ED resources (average 3.3 resources) but without the urgency of Level 1 or 2 3

• ESI Level 4: Lower-acuity patients requiring only one ED resource (average 1.2 resources) 3

• ESI Level 5: Lowest-acuity patients requiring minimal to no resources (average 0.2 resources) 3

Resource Consumption Prediction

A unique and validated component of ESI is its ability to predict actual ED resource utilization, with mean resource use decreasing monotonically from ESI-1 (5 resources) through ESI-5 (0.2 resources). 3

The algorithm accurately predicts:

• Number of diagnostic tests and procedures required 3
• ED length of stay, with ESI-2 patients averaging 255 minutes, ESI-3 averaging 304 minutes, and ESI-4 averaging 193 minutes 3
• Appropriate resource allocation for ED operational planning 3

Common Pitfalls in ESI Assignment

Undertriage of high-acuity patients represents a critical safety concern, with studies showing that 41% of patients may receive inappropriately low ESI scores, resulting in median waiting times of 58 minutes for patients who should have been triaged as ESI-2. 1

Specific biases affecting ESI assignment include:

• Mode of arrival bias: EMS-transported patients with abdominal pain are 7.19 times more likely to be assigned ESI-2 compared to walk-in patients with identical clinical presentations (OR 7.19,95% CI 2.75-18.8), though this may actually be appropriate given their higher admission rates 4

• Demographic disparities: Among patients with identical ESI-3 assignments, African American patients are significantly less likely to receive prioritized rooming compared to Caucasian patients (aOR 0.636,95% CI 0.545-0.743), and increasing age is associated with rooming prioritization violations 5

• Insufficient recognition of ESI-1 criteria: The strongest predictor of need for immediate intervention is the triage nurse's clinical judgment regarding airway compromise or need for immediate medications, yet many patients requiring immediate lifesaving interventions are initially assigned ESI-2 2

Clinical Application

The ESI algorithm should be applied systematically by assessing:

1. First: Does the patient require immediate lifesaving intervention? (ESI-1) 2
2. Second: Is the patient high-risk or in severe distress requiring rapid evaluation? (ESI-2) 2
3. Third: How many ED resources will this patient require? (ESI-3,4, or 5 based on anticipated resource needs) 3

Triage nurses must avoid the common error of conflating "stable to wait" with "lower acuity," as 20.2% of ESI-2 patients actually require immediate lifesaving interventions and should be reclassified as ESI-1. 2