6. Shock & Circulatory Collapse

📄Definition

Shock is a life-threatening state of circulatory failure resulting in inadequate tissue perfusion and cellular hypoxia, leading to end-organ dysfunction and death if untreated.

Shock is classified into four major haemodynamic types:

  • Cardiogenic
  • Hypovolaemic
  • Distributive
  • Obstructive

🎯 EXAM ANCHOR – CORE CONCEPT (PARA)

  • Shock = circulatory failure → inadequate oxygen delivery → organ dysfunction

  • Hypotension may be absent early

  • Raised lactate = tissue hypoperfusion

📌 PARA commonly asks:

What defines shock physiologically?

Types of Shock (Classification)

🧠Mnemonic: “CHOD”

Causes (Aetiology)

The causes of shock are best categorized by the haemodynamic mechanism of failure.

1. Cardiogenic (Pump Failure)

  • Acute Myocardial Infarction: Most common cause (especially anterior MI).

  • Acute Valvular Dysfunction: e.g., Papillary muscle rupture leading to acute Mitral Regurgitation.

  • Myocarditis: Viral or inflammatory.

  • Arrhythmias: Extreme bradycardia (Heart block) or tachycardia (VT/VF).

2. Hypovolaemic (Fluid Loss)

  • Haemorrhagic: Trauma, Ruptured AAA, Ectopic pregnancy, or massive GI bleed.

  • Non-haemorrhagic: Severe dehydration, vomiting/diarrhoea, or “Third-spacing” in major burns/pancreatitis.

3. Obstructive (Physical Blockage)

  • Massive Pulmonary Embolism: Prevents blood reaching the Left Atrium.

  • Tension Pneumothorax: Mediastinal shift kinks the Great Veins, stopping return to the heart.

  • Cardiac Tamponade: Fluid in the pericardium prevents the ventricles from filling.

4. Distributive (Vasodilation)

  • Sepsis: Overwhelming systemic inflammatory response.

  • Anaphylaxis: IgE-mediated massive histamine release.

  • Neurogenic: Loss of sympathetic tone following a high Spinal Cord Injury.

🎯 EXAM ANCHOR – CORE CONCEPT (PARA)

Type

Primary Problem

Key Examples

Cardiogenic

Pump failure

MI, severe HF, arrhythmia

Hypovolaemic

↓ Preload

Haemorrhage, dehydration

Distributive

↓ SVR

Sepsis, anaphylaxis

Obstructive

Outflow obstruction

PE, tamponade, tension pneumothorax

📌 PARA commonly asks:

Which type of shock is caused by pulmonary embolism?

🛡️ Causes (Aetiology)

Cardiogenic

  • Acute MI

  • Severe heart failure

  • Malignant arrhythmias

  • Acute valvular failure (e.g. papillary muscle rupture)

Hypovolaemic

  • Haemorrhage (GI bleed, trauma, ruptured AAA)

  • Severe dehydration (vomiting, diarrhoea, burns)

Distributive

  • Sepsis

  • Anaphylaxis

  • Neurogenic shock

Obstructive

  • Pulmonary embolism

  • Cardiac tamponade

  • Tension pneumothorax

Risk Factors

🧠 Mnemonic: “HARD PUMP”

  • Haemorrhage / dehydration

  • Acute MI

  • Ruptured aneurysm

  • Drugs (vasodilators, beta-blockers)

  • PE

  • Uncontrolled infection (sepsis)

  • Malignant arrhythmia

  • Pre-existing heart failure

📋 Clinical Features

🧠Mnemonic: “SHOCKED”

  • Systolic BP ↓ or narrow pulse pressure

  • Hypoxia

  • Oliguria (<0.5 mL/kg/hr)

  • Confusion

  • Kool peripheries (except early septic shock)

  • Elevated lactate

  • Diaphoresis / tachycardia

🎯 EXAM ANCHOR – CORE CONCEPT (PARA)

  • Normal blood pressure does NOT exclude shock
  • Early shock = tachycardia + rising lactate

📌 PARA commonly asks:

Which laboratory marker indicates tissue hypoperfusion?

🩺 Examination Findings

  • Tachycardia

  • Hypotension (late sign)

  • Prolonged capillary refill (>2 seconds)

  • Cold clammy skin (except early septic shock)

  • Raised JVP (cardiogenic / obstructive)

  • Reduced urine output

🔍 Investigations

First-Line:

Investigation

Purpose

ABG / VBG

Lactate, metabolic acidosis

Bloods (FBC, U&Es, LFTs, CRP)

Identify cause

ECG

MI, arrhythmia

CXR

PE signs, pulmonary oedema, pneumothorax

Urine output

Marker of perfusion

Second-Line

Investigation

When

Troponin

Suspected cardiogenic shock

Blood cultures

Suspected septic shock

CTPA

Suspected PE

CT Abdomen

Suspected bleeding / ischaemia

Specialist

Investigation

Use

Echocardiography

Cardiogenic vs obstructive shock

CT Mesenteric Angiography

Suspected intestinal ischaemia

🎯 EXAM ANCHOR – CORE CONCEPT (PARA)

  • Raised lactate is the most reliable biochemical marker of shock.

📌 PARA commonly asks:

Which laboratory marker indicates tissue hypoperfusion?

Management

  • Immediate (All Shock)

Mnemonic: “ABCDE + FLUIDS”

  • Airway
  • Breathing (high-flow oxygen)
  • Circulation (2 large-bore IV cannulae)
  • Disability (GCS, glucose)
  • Exposure
  • Fluids (crystalloid bolus unless cardiogenic)

🎯 EXAM ANCHOR – CORE CONCEPT (PARA)

  • Hypovolaemic / septic shock → IV crystalloid

  • Cardiogenic shock → cautious fluids ± inotropes

📋 Definitive Treatment (Cause-Specific)

Shock Type

Key Treatment

Cardiogenic

Treat MI, inotropes, urgent cardiology

Hypovolaemic

IV fluids ± blood products

Septic

IV antibiotics within 1 hour

Anaphylactic

IM adrenaline

Obstructive

PE thrombolysis, pericardiocentesis

📌 PARA commonly asks

What is the first-line treatment for septic shock?

⚠️ Complications

  • Acute kidney injury

  • Multi-organ failure

  • ARDS

  • Disseminated intravascular coagulation (DIC)

  • Death

🚩Red Flags

  • Lactate ≥2 mmol/L

  • Persistent hypotension despite fluids

  • Reduced urine output

  • Altered mental state

  • Evidence of end-organ damage

🧐 Differential Diagnoses

  • Sepsis without shock

  • Acute heart failure

  • Massive PE

  • Severe dehydration

  • Adrenal crisis

Review & Safety Netting

  • Continuous NEWS2 monitoring

  • Escalate early to senior / critical care

  • Reassess response to fluids within 30–60 minutes

📌 Key PARA Exam Traps

  • Shock ≠ hypotension

  • Normal BP does not exclude shock

  • Lactate rises before BP falls

  • Cardiogenic shock → fluids can worsen pulmonary oedema

  • Obstructive shock requires mechanical relief, not fluids alone

🔎 Key PARA Exam Traps

💡 Shock ≠ hypotension

💡 Normal BP does not exclude shock

💡 Lactate rises before BP falls

💡 Cardiogenic shock → fluids can worsen pulmonary oedema

💡 Obstructive shock requires mechanical relief, not fluids alone

🔎 Last updated in line with:

  • NICE NG51 – Sepsis recognition, diagnosis and early management
  • NICE CG94 – Unstable angina and NSTEMI
  • NICE NG158 – Venous thromboembolic diseases
  • NICE NG39 – Major trauma
  • GMC PARA Curriculum – Cardiovascular emergencies

Last reviewed: February 2026

🔒 PASSMAP ensures all content is NICE-aligned and reviewed for Physician Associate Registration Assessment (PARA) success.

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Educational platform. Not medical advice.

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