Answer: Pulse Pressure (Option B)
In a trauma patient who has lost 25% of their blood volume (Class II hemorrhagic shock), pulse pressure is the parameter most expected to be decreased among the options provided. 1
ATLS Classification Framework
According to the American College of Surgeons Advanced Trauma Life Support (ATLS) classification, a 25% blood volume loss corresponds to Class II hemorrhagic shock (15-30% blood loss). 1
Expected Physiological Changes in Class II Hemorrhage:
Pulse pressure: Decreased 1
Urine output: 20-30 mL/hour (still maintained, though reduced from normal >30 mL/hour) 1
Respiratory rate: 20-30 breaths/minute (increased, not decreased) 1
Mental status: Mildly anxious (Glasgow Coma Scale typically preserved) 1
Why Pulse Pressure Decreases First
Pulse pressure narrows in Class II hemorrhage due to compensatory mechanisms: 1
- Sympathetic activation causes peripheral vasoconstriction, elevating diastolic blood pressure 1
- Systolic blood pressure remains normal or slightly reduced in Class II shock 1
- The narrowing gap between systolic and diastolic pressures (pulse pressure) serves as an early indicator of hypovolemia before frank hypotension develops 1
Analysis of Other Options
Urine output (Option A): While reduced to 20-30 mL/hour in Class II hemorrhage, it does not become severely decreased until Class III (5-15 mL/hour) or negligible until Class IV. 1 At 25% blood loss, urine output is maintained through compensatory mechanisms. 1
Respiratory rate (Option C): This parameter increases (20-30 breaths/minute) rather than decreases in Class II hemorrhage as a compensatory response to maintain tissue oxygenation. 1 Hyperventilation is common in trauma patients during resuscitation. 1
Glasgow Coma Scale (Option D): Mental status in Class II hemorrhage is characterized as "mildly anxious" with preserved consciousness. 1 Significant GCS deterioration occurs in Class III (anxious, confused) and Class IV (confused, lethargic) hemorrhage. 1
Clinical Pitfalls to Avoid
Do not rely solely on blood pressure for assessment: Blood pressure remains normal in Class II hemorrhage despite significant blood loss due to compensatory mechanisms. 1, 2 Pulse pressure narrowing is a more sensitive early indicator. 1
Recognize the progression pattern: As hemorrhage advances from Class II to Class III (30-40% loss), urine output drops dramatically to 5-15 mL/hour, respiratory rate increases further to 30-40 breaths/minute, and mental status deteriorates. 1