General Surgery
Shock
MBBS surgery notes on shock: hypovolaemic, cardiogenic, obstructive and distributive types, haemorrhage grading and damage control resuscitation, mapped to NMC codes SU2.1 to SU2.3.
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Shock
MBBS surgery notes on shock: hypovolaemic, cardiogenic, obstructive and distributive types, haemorrhage grading and damage control resuscitation, mapped to NMC codes SU2.1 to SU2.3.
This chapter defines shock as a failure of tissue perfusion and works through its classification, recognition and resuscitation. It emphasises the early compensated signs, the grading of haemorrhage and the modern principles of damage control resuscitation in trauma.
High-yield: Shock
- Shock is inadequate tissue perfusion and oxygen delivery relative to demand, leading to cellular hypoxia and anaerobic metabolism.
- The surgical types are hypovolaemic, cardiogenic, obstructive and distributive, the last including septic, anaphylactic and neurogenic shock.
- Hypovolaemic shock from haemorrhage is the commonest type in trauma and is graded I to IV by the estimated blood loss.
- Class I loss is up to 15% of blood volume with normal signs; class IV is more than 40% with marked tachycardia, hypotension and confusion.
- Tachycardia and a narrowed pulse pressure appear early, while a fall in systolic blood pressure is a late and ominous sign in young patients.
- The healthy young compensate well and can lose up to 30% of blood volume before the systolic pressure drops, which masks the severity.
- A raised serum lactate and a base deficit reflect the depth of hypoperfusion and are better guides than blood pressure alone.
- Septic shock is distributive: warm peripheries, vasodilatation, a low systemic vascular resistance and a high cardiac output early on.
- Neurogenic shock from spinal cord injury gives hypotension with bradycardia, unlike the tachycardia of hypovolaemia.
- Initial management follows the airway, breathing, circulation approach with two wide-bore cannulae and balanced crystalloid or blood.
- In haemorrhagic shock, permissive hypotension and early balanced blood product transfusion are preferred to large crystalloid volumes.
- The lethal triad of trauma is hypothermia, acidosis and coagulopathy, each worsening the others and driving mortality.
- Anaphylactic shock is treated first with intramuscular adrenaline, then oxygen, fluids, antihistamine and corticosteroid.
- Damage control resuscitation aims to stop bleeding, restore perfusion and correct coagulopathy before definitive surgery.
- Persistent hypotension despite fluids should prompt a search for ongoing haemorrhage, tension pneumothorax or cardiac tamponade.
Classes of haemorrhagic shock
- **Class I:** Up to 15% blood loss. Normal pulse, pressure and mentation; minimal anxiety.
- **Class II:** 15 to 30% loss. Tachycardia, narrowed pulse pressure, mild anxiety and reduced urine output.
- **Class III:** 30 to 40% loss. Marked tachycardia, hypotension, confusion and oliguria; blood usually needed.
- **Class IV:** Over 40% loss. Severe tachycardia, low pressure, negligible urine and depressed consciousness; immediate resuscitation.
NMC competencies in this chapter
- **SU2.1:** Definition, types and pathophysiology of shock
- **SU2.2:** Clinical features and monitoring of shock
- **SU2.3:** Principles of resuscitation and management of shock
Frequently Asked Questions
What are the main types of shock?
Hypovolaemic, cardiogenic, obstructive and distributive shock. Distributive shock includes septic, anaphylactic and neurogenic causes, each with a different pattern of perfusion failure.
Why can blood pressure stay normal in early haemorrhage?
Young patients compensate with vasoconstriction and tachycardia and can lose up to 30% of blood volume before the systolic pressure falls, so a normal pressure does not exclude serious bleeding.
How does neurogenic shock differ from hypovolaemic shock?
Neurogenic shock from spinal cord injury causes hypotension with bradycardia and warm peripheries, whereas hypovolaemia produces tachycardia and cool, clammy skin.
What is the lethal triad of trauma?
Hypothermia, acidosis and coagulopathy. Each worsens the others, so damage control resuscitation focuses on warming, controlling bleeding and correcting clotting early.
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