A 32-year-old man is brought to the trauma bay following a motor vehicle collision with active hemorrhage from a femoral artery laceration. Which feature best distinguishes Class III hemorrhagic shock from Class II hemorrhagic shock in this patient?
A. Systolic blood pressure remains >100 mmHg with tachycardia >100 bpm
B. Barely palpable pulse with systolic BP <60 mmHg and profound confusion
C. Anxiety and mild tachycardia with normal blood pressure and urine output >30 mL/hr
D. Altered mental status with systolic BP 90–100 mmHg and urine output <20 mL/hr
Explanation
Classification of Hemorrhagic Shock by Class
Key Point
The ATLS classification divides hemorrhagic shock into four classes based on the degree of blood loss (% of total blood volume) and corresponding physiological response. Class III represents 30–40% blood loss (~1500–2000 mL in a 70 kg adult).
Discriminating Features of Class III vs. Class II
Table
Feature
Class II (15–30% loss)
Class III (30–40% loss)
Class IV (>40% loss)
Systolic BP
Normal (>100 mmHg)
90–100 mmHg (hypotensive)
<90 mmHg (severe)
Heart Rate
100–120 bpm
120–140 bpm
>140 bpm
Mental Status
Anxious, alert
Confused, anxious
Lethargic, unresponsive
Urine Output
20–30 mL/hr
<20 mL/hr (oliguria)
Minimal/absent
Skin Perfusion
Pale, cool
Pale, cold, clammy
Mottled, cyanotic
High-YieldNEET PG
The hallmark of Class III is the onset of hypotension (SBP 90–100 mmHg) combined with altered mental status and oliguria (<20 mL/hr). This is the critical threshold where compensatory mechanisms begin to fail and organ perfusion becomes compromised.
Clinical Pearl
Class III shock is the "tipping point" — patients are no longer maintaining normal blood pressure through sympathetic compensation alone. This is when aggressive fluid resuscitation and definitive hemorrhage control become urgent.
Mnemonic: ATLS Shock Classes (by % loss)
Class I: 0–15% (minimal signs)
Class II: 15–30% (tachycardia, normal BP)
Class III: 30–40% (hypotension, altered mentation, oliguria) ← The discriminator
Class IV: >40% (profound shock, near-death)
Why This Matters
Class III is the threshold where:
1.
Blood pressure begins to fall (SBP 90–100 mmHg) — compensatory mechanisms are overwhelmed
2.
Mental status changes (confusion, anxiety) — cerebral perfusion is compromised
3.
Urine output drops <20 mL/hr — renal perfusion is failing
Class II patients still maintain normal blood pressure and urine output >30 mL/hr despite tachycardia.
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
