What are the guidelines for applying the Emergency Severity Index (ESI) version 4 triage system to patients presenting to the emergency department?

Emergency Severity Index (ESI) Version 4 Triage Guidelines

The ESI is a five-level emergency department triage algorithm that stratifies patients based on both acuity and anticipated resource needs, with Level 1 representing the highest acuity (life-threatening, requiring immediate intervention) and Level 5 representing the lowest acuity (minimal resources needed). 1

Core ESI Algorithm Structure

The ESI triage process follows a systematic four-step decision pathway:

Step A: Does the patient require immediate life-saving intervention?

• ESI Level 1 criteria include: patients who are intubated, apneic, pulseless, unresponsive with no gag reflex, severe respiratory distress requiring immediate intervention, or in active seizure 2
• These patients bypass all other assessment steps and receive immediate resuscitation 3

Step B: Should the patient wait, or is this a high-risk situation?

• ESI Level 2 patients have high-risk conditions requiring rapid assessment even with stable vital signs 2
• Examples include: chest pain with cardiac risk factors, severe pain (≥8/10), altered mental status, sexual assault victims, signs of sepsis, or any condition where deterioration is likely 2, 4
• Critical distinction: Sexual assault patients are classified as ESI Level 2 regardless of stable vital signs or absence of visible injuries, due to time-sensitive medical and forensic needs 2

Step C: How many resources will the patient need?

For patients who are stable and not high-risk, resource prediction determines triage level:

• ESI Level 3: Requires 2 or more resources (laboratory tests, imaging, IV fluids, medications beyond simple oral analgesics, consultations) 5
• ESI Level 4: Requires 1 resource only 5
• ESI Level 5: Requires no resources (examination only, simple prescription, or reassurance) 5

Step D: What are the patient's vital signs?

• Abnormal vital signs in otherwise stable patients may elevate triage level 3
• Consider age-appropriate vital sign parameters 6

Key Performance Characteristics

The ESI demonstrates superior accuracy compared to three-level triage systems, with hospitalization rates correlating directly with acuity level: 96.2% for ESI-1,47.0% for ESI-2,30.9% for ESI-3,6.7% for ESI-4, and 6.6% for ESI-5 5. This gradient validates the system's discriminatory power.

Critical Implementation Pitfalls

Undertriage Risk

• Most common error: Assigning lower acuity based solely on normal vital signs while missing high-risk clinical scenarios 7
• Patients retrospectively identified as ESI-2 but initially triaged as ESI-4 experienced inappropriate median wait times of 58 minutes 7
• Avoid being influenced by: absence of visible injuries (particularly in sexual assault or head trauma), patient's calm demeanor, or mode of arrival 2, 4

Mode of Arrival Bias

• EMS arrival creates inappropriate bias toward higher acuity assignment (OR 7.19 for ESI-2 vs ESI-3 in abdominal pain patients) 4
• However, EMS patients have higher admission rates (65% vs 34%), suggesting some appropriateness to this bias 4
• Recommendation: Focus on clinical presentation and resource needs rather than transport mode, but recognize that EMS transport may indicate legitimate concern from prehospital providers 4

Resource Prediction Errors

• Accurately distinguishing between 1 and 2 resources requires experience and knowledge of typical ED workflows 1
• Common mistakes: Underestimating resources for elderly patients (who often require multiple tests), pediatric patients (who may need specialized imaging or consultation), or patients on anticoagulation 6, 8

Special Population Considerations

Pediatric Patients

• Infants and young children require modified assessment parameters 6
• Falls from seemingly minor heights (even 20 inches) can cause significant injury in infants due to proportionally larger heads and thinner skulls 6
• Sleepiness after head trauma in infants requires careful evaluation as potential altered mental status 6
• Pediatric-capable trauma centers should be preferentially selected for injured children 8

Geriatric Patients (>55 years)

• Lower threshold for ESI-2 assignment due to increased risk of rapid deterioration 8
• Systolic blood pressure <110 mmHg may represent shock in patients >65 years 8
• Ground-level falls can result in severe injury requiring trauma center care 8
• Anticoagulation status elevates risk significantly, particularly with head injury 8

Sexual Assault Patients

• Always assign ESI Level 2 regardless of vital signs or visible injuries 2
• Time-sensitive needs include emergency contraception (most effective when given immediately), STI prophylaxis, and forensic evidence collection 2
• Requires immediate access to private examination space 2

Advantages of ESI Implementation

The ESI reduces subjectivity in triage decisions and provides more accurate acuity discrimination than three-level systems 1. Users report high satisfaction (82% adoption rate among trained facilities) due to simplicity and standardization 1. The system's strength lies in combining physiologic acuity with resource utilization, creating operational efficiency 3, 5.

Quality Assurance Considerations

• Continuous monitoring of undertriage and overtriage rates is essential 7
• Target metrics: Correlation between assigned ESI level and actual hospitalization rates, ED length of stay by triage level, and time to physician evaluation 7, 5
• Most facilities have not formally assessed ESI impact on operations, representing a missed opportunity for quality improvement 1