ATLS Classification of Hemorrhagic Shock
The Advanced Trauma Life Support (ATLS) system classifies hemorrhagic shock into four classes (I through IV) based on estimated blood loss, vital signs, mental status, and urine output, serving as a framework for initial trauma assessment and resuscitation strategy. 1, 2
The Four Classes of Hemorrhagic Shock
Class I Hemorrhage
- Blood loss: <750 mL (<15% of blood volume) 1, 2
- Heart rate: <100 beats per minute 1, 2
- Blood pressure: Normal 1, 2
- Pulse pressure: Normal 1, 2
- Respiratory rate: 14-20 breaths per minute 1, 2
- Urine output: >30 mL/hour 1, 2
- Mental status: Slightly anxious 1, 2
Class II Hemorrhage
- Blood loss: 750-1,500 mL (15-30% of blood volume) 1, 2
- Heart rate: >100 beats per minute 1, 2
- Blood pressure: Normal 1, 2
- Pulse pressure: Decreased 1, 2
- Respiratory rate: 20-30 breaths per minute 1, 2
- Urine output: 20-30 mL/hour 1, 2
- Mental status: Mildly anxious 1, 2
Class III Hemorrhage
- Blood loss: 1,500-2,000 mL (30-40% of blood volume) 1, 2, 3
- Heart rate: >120 beats per minute 1, 2
- Blood pressure: Decreased 1, 2, 3
- Pulse pressure: Decreased 1, 2
- Respiratory rate: 30-40 breaths per minute 1, 2
- Urine output: 5-15 mL/hour 1, 2, 3
- Mental status: Anxious, confused 1, 2, 3
Class IV Hemorrhage
- Blood loss: >2,000 mL (>40% of blood volume) 1, 2
- Heart rate: >140 beats per minute 1, 2
- Blood pressure: Decreased 1, 2
- Pulse pressure: Decreased 1, 2
- Respiratory rate: >40 breaths per minute 1, 2
- Urine output: Negligible 1, 2
- Mental status: Lethargic 1, 2
Clinical Application and Response to Resuscitation
The ATLS classification should be used in conjunction with the patient's response to initial fluid resuscitation to guide the urgency of surgical intervention. 1, 2
Three Response Patterns to Initial Resuscitation:
- Rapid responders: Vital signs return to normal and remain stable; typically Class I-II hemorrhage 2
- Transient responders: Initial improvement followed by deterioration; require immediate surgical intervention 1, 2, 3
- Minimal or no responders: Ongoing instability despite resuscitation; require immediate surgical intervention 1, 2, 3
Management Implications by Class
- Class I-II: May respond to crystalloid resuscitation alone 2
- Class III: Requires aggressive resuscitation, immediate blood product transfusion, and urgent bleeding control within 60 minutes 3
- Class IV: Requires immediate massive transfusion protocol activation and emergency surgical hemorrhage control 2, 3
Important Limitations and Pitfalls
The ATLS classification has significant limitations in real-world application that clinicians must recognize. 1, 4, 5
- A retrospective analysis showed that increasing blood loss produces increases in heart rate and decreases in blood pressure, but to a lesser degree than suggested by the ATLS classification 1
- There are no significant changes in respiratory rate or consciousness level with bleeding as predicted by ATLS 1
- A large study of 630,635 trauma patients found that almost half (47.7%) did not meet criteria for any ATLS shock class, and uncategorized patients had higher mortality (7.1%) than Class I-II patients 4
- Only 9.3% of trauma patients could be allocated into one of the ATLS shock classes when combining heart rate, systolic blood pressure, and Glasgow Coma Scale 5
- The classification may overestimate the degree of tachycardia associated with hypotension and underestimate mental disability in hypovolemic shock 5
Despite these limitations, the ATLS classification remains a useful conceptual framework when combined with other clinical parameters including mechanism of injury, anatomical injury pattern, base deficit/lactate levels, and shock index. 1, 2