Shock Classification and Management
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Direct answer
Shock is inadequate tissue perfusion for metabolic need, classified as hypovolaemic, cardiogenic, obstructive or distributive, and recognised early by tachycardia with a narrowed pulse pressure before blood pressure falls. Haemorrhagic shock is graded into four classes by blood loss, hypotension appearing only in class III and above. Management treats the cause: transfusion and haemostasis for bleeding, decompression for tension pneumothorax and tamponade, adrenaline for anaphylaxis, and antibiotics with fluids and noradrenaline for septic shock.
What you must remember
- The four classes of haemorrhagic shock: class I, under about 750 mL, minimal findings; class II, 750 to 1500 mL, tachycardia with narrowed pulse pressure and a normal blood pressure; class III, 1500 to 2000 mL, hypotension with confusion — the first class needing blood; class IV, over 2000 mL, lethal.
- Septic shock follows the hour-one bundle: lactate, blood cultures, broad-spectrum antibiotics within an hour, 30 mL per kg crystalloid for hypotension or lactate of 4 mmol/L or more, and noradrenaline as first-line vasopressor to hold mean arterial pressure at 65 mmHg or above.
- Obstructive shock: tension pneumothorax — tracheal shift, absent unilateral breath sounds, distended neck veins — is needle-decompressed at the fifth intercostal space in the anterior axillary line, then given a chest tube; cardiac tamponade with Beck triad goes to pericardiocentesis or thoracotomy.
- Anaphylactic shock: intramuscular adrenaline 0.5 mg (0.5 mL of 1 in 1000) into the mid-outer thigh, repeated as needed, with airway support, oxygen, crystalloid and adjuncts.
- Neurogenic shock after high spinal injury: hypotension with bradycardia and warm dry extremities from lost sympathetic tone — fluids plus vasopressors, with atropine for symptomatic bradycardia.
- Haemorrhage management: early blood products over excessive crystalloid, tranexamic acid within three hours in trauma, permissive hypotension until control in selected patients, and calcium with warming to break the lethal triad.
- End points of resuscitation: urine output of 0.5 mL per kg per hour, mean pressure 65 mmHg or more, and improving lactate clearance.
Common confusion
The exam exploits compensation: a narrow pulse pressure with tachycardia and a normal pressure means class II haemorrhage, not wellness. Candidates also mix the vasopressor situations — noradrenaline for septic, adrenaline for anaphylactic, vasopressors plus fluids for neurogenic. Cardiogenic shock resists fluids and needs inotropes, the opposite of the distributive pattern.
Exam-focused takeaway
FMGE shock questions are classification-plus-intervention questions. Expect blood loss percentages mapped to pulse, pressure and mental status, where hypotension first appears in class III and blood becomes the answer. Then the emergency pairs: sepsis gets antibiotics within the hour, 30 mL per kg crystalloid and noradrenaline to a mean pressure of 65; anaphylaxis gets intramuscular adrenaline 0.5 mg; tension pneumothorax gets a needle before a tube; tamponade gets Beck triad and theatre; neurogenic shock gets vasopressors, bradycardia its signature. End haemorrhage answers with tranexamic acid timing and the lethal triad.
Frequently asked questions
What are the four physiological categories of shock?
Hypovolaemic, cardiogenic, obstructive and distributive — the last including septic, anaphylactic and neurogenic shock.
In which class of haemorrhagic shock does hypotension appear?
Class III, roughly 30 to 40 per cent loss; classes I and II maintain blood pressure with tachycardia and narrowed pulse pressure.
What is the first-line vasopressor in septic shock?
Noradrenaline, targeted to a mean arterial pressure of 65 mmHg or above after initial fluid and antibiotics.
How is anaphylactic shock treated first?
Intramuscular adrenaline, 0.5 mg of 1 in 1000 into the mid-outer thigh, repeated as required, with airway and fluid support.
Why does neurogenic shock cause bradycardia?
Loss of sympathetic outflow below a high spinal lesion leaves unopposed vagal tone, producing hypotension with bradycardia and warm dry limbs.
What is the lethal triad of trauma?
Hypothermia, acidosis and coagulopathy — a self-reinforcing cycle in massive haemorrhage, broken by warming, blood products and calcium.