Hypovolaemic Shock — Recognition and Field Management

Hypovolaemic shock is a life-threatening condition that occurs when a significant reduction in circulating blood volume — from haemorrhage (bleeding) or fluid loss — causes the heart to be unable to pump sufficient blood to meet the body's oxygen demands. Without intervention, it is fatal.

In emergency situations — accidents, trauma, severe internal or external bleeding, major burns, or severe dehydration — recognising and managing hypovolaemic shock before emergency services arrive significantly affects survival. The time between injury and hospital care is when field first aid has its greatest impact.

Understanding Shock — What Is Happening Physiologically

Shock is not a disease itself — it is the body's response to critically insufficient oxygen delivery:

1. Blood is lost — through external wound, internal haemorrhage, or fluid loss.
2. Blood pressure drops — reduced volume means reduced pressure.
3. The body compensates — heart rate increases; blood vessels constrict to maintain pressure to vital organs; blood is redirected from skin and extremities to the brain and heart.
4. Compensation fails — as blood loss continues, the compensatory mechanisms cannot maintain adequate circulation.
5. Organ failure — without sufficient oxygen, organs fail; brain damage and cardiac arrest follow.

The first aid priority is to: (1) stop or slow blood loss, and (2) maintain circulation and preserve the remaining blood volume.

Stages of Hypovolaemic Shock

Understanding the stages helps recognise how severe the shock is:

Stage	Blood Loss	Signs	Consciousness
Class I (Compensated)	< 15% (< 750ml)	Slight anxiety; heart rate normal or slightly elevated	Normal
Class II (Early)	15–30% (750–1500ml)	Increased heart rate (>100); rapid breathing; pale skin; anxious	Normal but agitated
Class III (Progressive)	30–40% (1500–2000ml)	Heart rate >120; very pale; confusion; reduced urine; skin cold and clammy	Confused
Class IV (Severe)	> 40% (> 2000ml)	Heart rate > 140 or falling; barely detectable pulse; unconscious or near	Unconscious or obtunded

A person can compensate well at early stages and appear reasonably alert. Deterioration from Class II to Class III can be rapid, particularly if bleeding is not controlled.

Signs of Shock

The signs of developing shock can be remembered with these indicators:

Sign	Detail
Pale, cold, clammy skin	Blood diverted away from skin; sweating from sympathetic response
Rapid, weak pulse	Heart trying to compensate for reduced volume
Rapid, shallow breathing	Body trying to get more oxygen
Thirst	Fluid loss signal; the person will report extreme thirst
Anxiety and agitation	Early — from sympathetic activation and hypoxia
Confusion and drowsiness	Later stage — cerebral hypoperfusion
Yawning	Attempt to increase oxygen intake
Nausea and vomiting	Common in shock
Loss of consciousness	Late stage — critical

⚠️ Do not rely on blood pressure to assess shock — in healthy adults, blood pressure is maintained by compensatory mechanisms until blood loss exceeds 30–40%. By the time blood pressure drops significantly, the person is already in Class III shock. Heart rate and skin signs are earlier and more sensitive indicators.

First Aid — Priority Actions

1. Control Bleeding

This is the highest priority — nothing else matters until bleeding is controlled:

• Direct pressure: Apply firm, continuous pressure to the wound with the cleanest available material. Do not remove it to check — add more material on top if it soaks through.
• Pressure dressing: Once initial pressure is applied, bandage firmly to maintain pressure without tourniquets.
• Tourniquets for limb bleeding: For severe limb haemorrhage where direct pressure is inadequate, a tourniquet applied 5–7cm above the wound is life-saving. Note the time of application.
• Wound packing for junctional wounds: Deep wounds in the groin, armpit, or neck that cannot be tourniqueted should be packed tightly with gauze and firm pressure applied.

2. Position

Situation	Position
Conscious, no spinal injury suspected	Legs elevated (if no lower limb fractures) — helps blood return to core
Unconscious, breathing	Recovery position
Suspected spinal injury	Minimal movement; call for assistance
Breathing difficulty	Do not force flat; semi-recumbent

The traditional "legs elevated" position (modified Trendelenburg) has limited evidence for long-term benefit but no evidence of harm and may transiently improve cerebral perfusion.

3. Prevent Heat Loss

Shock and haemorrhage cause hypothermia, which worsens coagulopathy (clotting ability):

• Cover with a blanket, coat, or any available insulating material
• Cover the head
• Minimise bare ground contact
• This is particularly important outdoors and in cold environments

4. Do Not Give Oral Fluids

Despite extreme thirst, do not give oral fluids to a shocked person:

• Cannot be managed at surgically necessary rates
• Risk of aspiration if consciousness deteriorates
• May cause vomiting
• Delays surgical fluid replacement
• Emergency services will establish IV access

5. Call 999 and Keep the Call Open

Call 999 immediately. Provide:

• Exact location
• Mechanism of injury
• Current conscious state
• Estimated blood loss (this is always an underestimate; describe visible blood)
• Any interventions already performed

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Quick Reference

Priority	Action
1 — Stop bleeding	Direct pressure; tourniquet for limb haemorrhage
2 — Position	Legs elevated if conscious and no limb fractures
3 — Warmth	Cover; insulate from ground
4 — Monitor	Pulse, breathing, consciousness every 1–2 minutes
5 — Call 999	Immediately; keep line open
Do not	Give oral fluids; remove pressure dressing; delay calling
Early shock signs	Pale, clammy, rapid pulse, anxiety
Late shock signs	Confusion, loss of consciousness