General MedicineTier 1Disease (DEADMAN)

Hypotension or shock - hypovolaemic

Description

Shock from reduced circulating volume - haemorrhagic (trauma, GI bleed, ruptured aneurysm, obstetric) or non-haemorrhagic (vomiting, diarrhoea, burns, third-spacing, heat illness, DKA/HHS osmotic diuresis)

Leading cause of preventable trauma death when haemorrhage is not recognised/controlled early
Non-haemorrhagic causes common in elderly (dehydration from reduced intake, diuretic use, GI losses)

Reduced preload -> reduced stroke volume -> reduced cardiac output -> compensatory tachycardia and vasoconstriction (maintains BP until ~30% volume loss, then decompensation is rapid)
Ongoing hypoperfusion -> anaerobic metabolism -> lactic acidosis -> multi-organ dysfunction if uncorrected
Haemorrhagic shock additionally triggers trauma-induced coagulopathy (acidosis, hypothermia, dilution - "lethal triad")

Clinical - tachycardia, narrow pulse pressure, delayed capillary refill, cool peripheries, reduced urine output, hypotension is a late sign
Classify haemorrhagic shock by class I-IV (blood volume loss %, physiological response) - guides resuscitation intensity
Identify and localise the source of loss (bleeding site, GI losses, burns extent)

1. Control the source

Haemorrhage control first - direct pressure, tourniquet, surgical/endoscopic/interventional radiology as indicated - resuscitation without source control fails

2. Resuscitation

Balanced crystalloid for non-haemorrhagic losses; blood products (early, balanced ratio of RBC:FFP:platelets) for major haemorrhage rather than crystalloid-predominant resuscitation
Permissive hypotension (target SBP ~80-90 in penetrating trauma without head injury) until haemorrhage controlled - avoid over-resuscitation diluting clotting factors
Tranexamic acid early in trauma haemorrhage (within 3 hours of injury)
Correct the lethal triad - warm fluids/blood, correct acidosis, replace calcium (citrate toxicity with massive transfusion)

3. Non-haemorrhagic

Replace the specific fluid/electrolyte deficit (crystalloid for dehydration, correct the underlying cause - antiemetics, treat diarrhoea cause, burns fluid formula)

Trauma-induced coagulopathy, acute kidney injury, multi-organ dysfunction if resuscitation delayed
Abdominal compartment syndrome with over-resuscitation

Early haemorrhage control and balanced resuscitation substantially improve survival in trauma
Compensated shock can decompensate rapidly and without warning once physiological reserve is exhausted - vigilance needed even with "normal" vital signs early on
Non-haemorrhagic hypovolaemic shock generally has a better prognosis once the underlying cause is treated and volume replaced

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