Trauma — Haemodynamic Signs of Class IV Haemorrhagic Shock
A 32-year-old man is brought in after a motorcycle collision. He is unconscious with a Glasgow Coma Scale score of 6 and has a deep thigh laceration that has bled heavily at the scene. His blood pressure is unrecordable, extremities are cold and pale, and haemoglobin is 60 g/L. He takes no regular medications. Which pulse finding is most likely on examination?
- A.Slow, full pulse below 50 beats/min
- B.Bounding pulse with warm peripheries
- C.Rapid, thready pulse above 140 beats/minCorrect
- D.Normal-rate pulse of 70 to 90 beats/min
Explanation
An unrecordable blood pressure, cold pale extremities, coma and a haemoglobin of 60 g/L after major external bleeding indicate class IV haemorrhagic shock, with an estimated loss of more than 40% of circulating volume. At this stage the sympathetic response produces marked tachycardia, classically above 140 beats/min, with a weak, thready pulse from a very narrow pulse pressure. The main competing idea is that his coma reflects a head injury and that intracranial hypertension produces a Cushing response with bradycardia. A Cushing response, however, combines bradycardia with hypertension, which is incompatible with an unrecordable pressure. Advanced Trauma Life Support teaches that hypotension in a trauma patient should be attributed to blood loss until proven otherwise, and an isolated brain injury rarely causes shock. Here, reduced consciousness is explained by cerebral hypoperfusion. Bounding pulses and warm peripheries belong to distributive states such as early sepsis, and a normal rate would be unexpected with this volume loss. Heart rate can be misleadingly slow in older patients, athletes, people on beta-blockers or with pacemakers, and in pre-terminal haemorrhage, when bradycardia signals imminent cardiac arrest.
Why each option
- A.
- Bradycardia with a full pulse suggests a Cushing response, which requires hypertension and does not fit an unrecordable blood pressure.
- B.
- Bounding pulses and warm peripheries indicate distributive shock, not the vasoconstriction of severe haemorrhage with cold, pale extremities.
- C.
- Correct. Class IV haemorrhage with more than 40% volume loss produces marked tachycardia and a weak, thready pulse from a narrow pulse pressure.
- D.
- A normal heart rate is unexpected after this degree of blood loss unless beta-blockers, a pacemaker or pre-terminal decompensation are present.
Reference: American College of Surgeons — Advanced Trauma Life Support (ATLS) Student Course Manual, 10th edition 2018, Chapter 3 Shock; UpToDate — Initial management of moderate to severe hemorrhage in the adult trauma patient
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