ESI Composition Skill

Overview

Performs Phase 2 of the hybrid ESI classification pipeline: deterministic ESI-v4 assignment from structured facts using pure Python logic and configurable rules.

Unlike LLM-based classifiers, this skill never uses an LLM. It applies the official ESI-v4 decision tree through rule-based code, providing:

• •Audit trail: Exact rules that triggered classification
• •Reproducibility: Same input always produces same output
• •Performance: Fast (<5ms) with no API calls
• •Compliance: Aligns with validated ESI protocol

When to Use

• •Final ESI assignment after fact extraction
• •Part of hybrid pipelines (esi-extraction → esi-composition)
• •When reproducibility and audit trails are required
• •When cost/latency must be minimized

Input/Output

Input:

• •extracted_facts (object): From esi-extraction skill
• •OR manually provided: vital_signs, high_risk_keywords

Output:

• •esi_level (1-5): Final ESI classification
• •decision_path (string): Path through decision tree
• •triggers (array): Rules that fired
• •reasoning (string): Human-readable explanation

ESI-v4 Decision Algorithm

ESI-1: Immediate Life-Threatening

Exact Triggers:

• •Heart rate = 0 OR oxygen saturation < 60% (cardiac arrest/severe hypoxia)
• •Respiratory rate > 40 or < 8 (severe respiratory distress)
• •Systolic BP < 70 (severe shock)
• •High-risk keywords: "unresponsive", "unconscious", "cardiac arrest", "not breathing"

Code Path: rules/esi_rules.json → esi_1_immediate_life_threat

ESI-2: Emergent (High-Risk)

Exact Triggers:

• •Systolic BP < 90 (hypotension/shock signs)
• •Heart rate > 120 (severe tachycardia)
• •Respiratory rate > 30 or < 8 (severe tachypnea/depression)
• •Oxygen saturation < 90% (hypoxia)
• •Pain level ≥ 7 (severe pain)
• •Fever > 38.5°C + altered mental status (sepsis pattern)
• •Trauma with systolic BP < 110
• •High-risk keywords: "chest pain", "SOB", "difficulty breathing", "stabbed", "gunshot"

Code Path: rules/esi_rules.json → esi_2_high_risk

ESI-3: Urgent, Likely ≥2 Resources

Rules:

• •Requires exactly 2 or more resources
• •Valid resources: lab, imaging, specialist, observation, procedure, monitoring, medication, therapy
• •Acute injury (likely needs X-ray, CT)
• •Stable with concerning symptoms

Code Path: rules/esi_rules.json → Resource counting logic

ESI-4: Less Urgent, Likely 1 Resource

Rules:

• •Needs exactly 1 resource
• •Minor injury, minor illness
• •Stable, low-risk presentation

ESI-5: Non-Urgent

Rules:

• •No resources needed
• •Self-limiting condition
• •Advice/education only

Best Practices

Input Quality

• •Always provide complete vital_signs for accurate classification
• •Include high_risk_keywords list for pattern matching
• •Pass facts from esi-extraction skill for consistency

Audit Trail

• •Always review decision_path for clinical oversight
• •Share triggers list with clinicians for verification
• •Document reasoning for medical records

Resource Allowlisting

• •Skill validates resources against rules/resources.json
• •Allowed types: lab, imaging, specialist, observation, procedure, monitoring, medication, therapy
• •Unknown resource types are rejected (fail-safe)
• •Each resource type has examples and high-effort classification
• •Update rules/resources.json allowed_resources list when adding new types

Examples

Example 1: ESI-2 (Hypotension + Tachycardia)

Input:
{
  "vital_signs": {
    "systolic_bp": 85,       // < 90 → hypotension trigger
    "heart_rate": 125,       // > 120 → tachycardia trigger
    "respiratory_rate": 32,  // > 30 → tachypnea trigger
    "oxygen_saturation": 95
  },
  "symptoms": {},
  "risk_factors": {"high_risk_keywords": []}
}

Output:
{
  "esi_level": 2,
  "decision_path": "Rule: High-risk situation or severe symptom → ESI-2",
  "triggers": ["hypotension_systolic_lt90", "tachycardia_hr_gt120", "abnormal_respiratory_rate"],
  "reasoning": "ESI-2 assigned via Rule: High-risk situation or severe symptom → ESI-2"
}

Example 2: ESI-4 (1 Resource, Stable)

Input:
{
  "vital_signs": {
    "systolic_bp": 130,      // Normal
    "heart_rate": 82,        // Normal
    "respiratory_rate": 16   // Normal
  },
  "symptoms": {"pain_level": 3},
  "risk_factors": {"high_risk_keywords": []},
  "resources": {
    "lab": true,             // 1 resource
    "imaging": false,
    "specialist": false,
    "monitoring": false
  }
}

Output:
{
  "esi_level": 4,
  "decision_path": "No ESI-1 or ESI-2 triggers → Resource count = 1 → ESI-4",
  "triggers": [],
  "reasoning": "Stable vital signs, mild pain, needs 1 resource. ESI-4 classification."
}

Troubleshooting

Issue: ESI-5 when expecting ESI-3

• •Cause: Resource count <2 detected
• •Solution: Verify requires_imaging, requires_lab flags are set correctly

Issue: ESI-2 when expecting ESI-3

• •Cause: Vital danger detected (hypotension, extreme tachycardia, etc.)
• •Solution: Review vital_signs for abnormal readings; verify clinical assessment

Issue: "Invalid resource type" error

• •Cause: Unknown resource in resources field
• •Solution: Update rules/resources.json with new resource type, or remove invalid resource

See Also

• •esi-extraction: Upstream fact extraction skill
• •rules/esi_rules.json: ESI-1 and ESI-2 trigger definitions
• •rules/resources.json: Valid resource types and categories
• •compose_esi.py: Implementation logic