In a trauma patient with a 25% blood volume loss, what is most expected to decrease: urine output, pulse pressure, respiratory rate, or Glasgow Coma Scale (GCS)?

Pulse Pressure is Most Expected to Decrease

In a trauma patient with 25% blood volume loss (Class II hemorrhagic shock), pulse pressure is the most expected parameter to decrease among the options provided. 1, 2

Physiological Basis for Pulse Pressure Narrowing

• Pulse pressure narrows in Class II hemorrhage due to compensatory sympathetic activation causing peripheral vasoconstriction, which elevates diastolic blood pressure while systolic pressure remains relatively normal. 2

• According to the American College of Surgeons ATLS classification, a 25% blood volume loss corresponds to Class II hemorrhagic shock (15-30% blood loss), which is specifically characterized by decreased pulse pressure while systolic blood pressure remains normal. 1, 2

• The narrowing gap between systolic and diastolic pressures serves as an early and sensitive indicator of hypovolemia, making it more reliable than blood pressure alone for detecting Class II shock. 2

Why Other Options Are Less Expected to Decrease

Urine Output (Option A)

• In Class II hemorrhage, urine output is reduced to 20-30 mL/hour but remains measurable and does not become severely decreased until Class III shock (5-15 mL/hour). 1, 2
• Urine output does not decrease significantly until approximately 20°C in hypothermic patients, and renal blood flow initially increases with compensatory mechanisms before declining. 1

Respiratory Rate (Option C)

• Respiratory rate actually increases (not decreases) to 20-30 breaths/minute in Class II hemorrhage as a compensatory response to maintain tissue oxygenation. 1, 2
• This represents a physiological compensation mechanism rather than a decrease. 1

Glasgow Coma Scale (Option D)

• Mental status in Class II hemorrhage is characterized as "mildly anxious" with preserved consciousness according to the American College of Surgeons. 1, 2
• The GCS remains essentially normal in Class II shock, with significant deterioration (anxious/confused) not occurring until Class III shock. 1

Clinical Significance

• The American College of Surgeons specifically recommends not relying solely on blood pressure for assessment in Class II hemorrhage, as it remains normal despite significant blood loss. 2
• Pulse pressure narrowing is a more sensitive early indicator than absolute blood pressure values, making it the most reliable hemodynamic parameter to detect 25% blood volume loss. 2

Answer: B. Pulse pressure