🧠 SHOCK - Complete 1-Hour Study Guide

⏱️ MINUTE 0-10 | THE BIG PICTURE — What Is Shock?

Core Definition

Shock = Inadequate tissue perfusion → Cellular hypoxia → Cell death (if untreated)

"A state of systemic tissue hypoperfusion resulting from reduced cardiac output and/or reduced effective circulating blood volume."

Why does it happen? Three mechanisms:

1. Pump fails → Cardiogenic shock
2. Tank is empty → Hypovolemic shock
3. Pipes too wide / broken → Distributive shock (Septic, Neurogenic, Anaphylactic)

⏱️ MINUTE 10-25 | TYPES OF SHOCK

Master Mnemonic: "CHANDA"

• Cardiogenic
• Hypovolemic
• Anaphylactic
• Neurogenic
• Distributive (septic)
• Additional: Obstructive (sometimes classified separately)

1. Cardiogenic Shock

• Tamponade (cardiac)
• Arrhythmia
• Pulmonary embolism (outflow obstruction)
• EMI (Myocardial Infarction - intrinsic pump failure)

• ↓ CO, ↓ BP
• ↑ SVR (body tries to compensate)
• ↑ PCWP (back-pressure, pulmonary congestion)
• Skin: Cold, clammy, pale

2. Hypovolemic Shock

• Hemorrhage (trauma, GI bleed, ruptured ectopic)
• Burns (massive plasma loss)
• Diarrhea/vomiting
• Third-spacing (peritonitis, pancreatitis)

• ↓ CO, ↓ BP, ↓ PCWP
• ↑ SVR (compensatory vasoconstriction)
• Skin: Cold, clammy

3. Septic Shock (Most Complex - Learn This Deeply!)

• Sepsis = Life-threatening organ dysfunction from dysregulated host response to infection
• Septic shock = Sepsis + profound circulatory + metabolic abnormalities with greater mortality

1. Gram-positive bacteria (most common - e.g., Staph, Strep)
2. Gram-negative bacteria
3. Fungi

Microbe (Gram+/Gram-/Fungi)
        ↓
Activate Innate Immune Cells (via TLRs, G-protein receptors, C-type lectins)
        ↓
Release of Cytokines: TNF, IL-1, IL-6, IL-12, IFN-γ
        ↓
┌──────────────────────────────────────────┐
│ 1. Endothelial activation → ↑ permeability, edema
│ 2. Vasodilation → Hypotension (↓ SVR)
│ 3. ↑ NO → Systemic vasodilation
│ 4. DIC (procoagulant state: ↑ TF, ↓ thrombomodulin, ↓ protein C)
│ 5. Metabolic: Hyperglycemia, lactic acidosis, insulin resistance
│ 6. Adrenal insufficiency (cortisol failure)
└──────────────────────────────────────────┘
        ↓
Multi-Organ Dysfunction Syndrome (MODS)

• Early ("warm shock"): ↑ CO, ↓ SVR, skin WARM & flushed
• Late ("cold shock"): ↓ CO, ↓ BP, skin cold, clammy

4. Neurogenic Shock

• No compensatory tachycardia (because sympathetics are lost)
• Bradycardia + hypotension = red flag (vs other shocks which cause tachycardia)
• Skin: Warm, dry (not cold/clammy)

5. Anaphylactic Shock

• History of allergen exposure
• Urticaria, bronchospasm, angioedema
• Treatment: Epinephrine (first-line always!)

Quick Comparison Table

⏱️ MINUTE 25-38 | STAGES OF SHOCK

Stage 1 - NON-PROGRESSIVE (Compensated)

• Baroreceptor reflexes detect ↓ BP
• Catecholamines (adrenaline, noradrenaline) released
• ADH (vasopressin) released → fluid retention
• RAAS activated: Renin → Angiotensin II → Aldosterone → Na+ and water retention
• Sympathetic stimulation → Tachycardia + vasoconstriction

• Tachycardia
• Peripheral vasoconstriction (cold, pale skin)
• Blood shunted to VITAL ORGANS (heart + brain are protected)
• Oliguria (kidney conserving fluid)

Stage 2 - PROGRESSIVE (Decompensated)

• Persistent oxygen deficit → Anaerobic glycolysis → Lactic acid accumulates
• Lactic acidosis → Arterioles dilate (pH blunts vasomotor response)
• Blood pools in microcirculation
• Endothelial injury → DIC begins
• Vital organs start to fail

Stage 3 - IRREVERSIBLE

• Lysosomal enzymes leak → Further cell destruction
• Myocardial contractility worsens severely
• Gut ischemia → Bacterial translocation → Bacteremia can be superimposed
• Renal failure (ATN)
• Death inevitable despite treatment

⏱️ MINUTE 38-48 | ATLS CLASSES OF HEMORRHAGIC SHOCK

Memory Trick: "Rule of 15s and 30s"

• Class I ends at 15% loss
• Class II = 15-30%
• Class III = 30-40%
• Class IV = >40%
• HR jumps to >100 at Class II, >120 at III, >140 at IV
• BP only drops at Class III (before that, the body compensates!)

Key Clinical Pearl:

BP is the LAST thing to fall! Pulse pressure narrows first (↑ diastolic from vasoconstriction, then ↓ systolic). Don't wait for hypotension to diagnose shock!

⏱️ MINUTE 48-55 | ORGAN EFFECTS IN SHOCK (Morphology)

• Brain (hypoxic encephalopathy)
• R - Rarely affected in pure hypovolemic shock, but in sepsis...
• Adrenals (lipid depletion; Waterhouse-Friderichsen syndrome in DIC/meningococcemia)
• Intestine (ischemia → bacterial translocation)
• Nephron/Kidney (Acute Tubular Necrosis - most common cause of death in progressive shock)
• Kidney (oliguria → anuria → ATN)
• Adrenals and Gut ischemia

Fibrin Thrombi

• Form in any tissue but most visible in kidney glomeruli
• Sign of DIC complicating shock

⏱️ MINUTE 55-60 | CLINICAL RECOGNITION + MANAGEMENT OVERVIEW

Clinical Features by Type:

• Hypovolemic/Cardiogenic: Hypotension, weak rapid pulse, tachypnea, cool clammy cyanotic skin
• Septic (early): Fever, warm flushed skin, tachycardia, hypotension
• Neurogenic: Bradycardia + hypotension (paradox!), warm dry skin

Management Principles

• Stop the bleeding (source control)
• Large-bore IV access x2
• Crystalloids initially (Lactated Ringer's preferred over NS)
• Blood products for Class III/IV (1:1:1 ratio: pRBC:FFP:Platelets in massive transfusion)
• Avoid sodium bicarbonate for acidosis (treat the cause, not the pH)
• Goal: Base deficit correction + lactate clearance

1. Blood cultures FIRST, then antibiotics within 1 hour
2. IV fluid resuscitation (30 mL/kg crystalloid)
3. Vasopressors if no response: Norepinephrine (first-line)
4. Stress-dose steroids (hydrocortisone 200mg/day) if vasopressor-refractory
5. Monitor lactate (goal: clearance >10% in 2 hours)

• Epinephrine IM 0.3-0.5 mg (thigh) - ALWAYS first-line
• Antihistamines + steroids (adjuncts, not first-line)
• IV fluids + airway management

• Spinal immobilisation
• Vasopressors (phenylephrine or norepinephrine)
• Bradycardia → Atropine

🧠 MASTER MNEMONICS SUMMARY

⚡ RAPID REVISION - HIGH-YIELD FACTS (Read This Last)

1. Shock = tissue hypoperfusion = cellular hypoxia
2. Septic shock has WARM SKIN early (all others = cold, clammy)
3. Neurogenic shock = bradycardia (others = tachycardia) - no sympathetics!
4. BP falls only at Class III haemorrhage - don't wait for it!
5. Lactic acidosis = marker of anaerobic metabolism = progressive shock
6. Kidney (ATN) = most clinically significant organ failure in shock
7. Lungs = "shock lung" = ARDS (only in septic/traumatic shock, NOT pure hypovolemic)
8. DIC seen in up to 50% of septic shock patients
9. Adrenal failure in DIC → Waterhouse-Friderichsen syndrome
10. First-line vasopressor in septic shock = Norepinephrine
11. First-line in anaphylaxis = Epinephrine (IM, not IV)
12. Septic shock mortality remains 20-40% despite treatment
13. In irreversible shock: lysosomal enzyme leak + gut bacterial translocation = death spiral
14. Blood is shunted to heart + brain in compensated shock (skin sacrificed first)
15. Pulse pressure narrows BEFORE systolic BP falls - earliest BP change in hemorrhage

📅 1-HOUR SCHEDULE

• Minutes 0-10: Core definition and the 3 fundamental mechanisms of shock
• Minutes 10-25: All 5 types (Cardiogenic, Hypovolemic, Septic, Neurogenic, Anaphylactic) with hemodynamic profiles, a comparison table, and the mnemonic CHANDA
• Minutes 25-38: The 3 stages of shock (Non-progressive → Progressive → Irreversible) with the exact pathophysiology at each stage
• Minutes 38-48: The full ATLS 4-class hemorrhagic shock table with every parameter - this is the most commonly tested content in surgery exams
• Minutes 48-55: Organ-specific morphological changes (ATN, shock lung/ARDS, DIC, adrenal failure, Waterhouse-Friderichsen)
• Minutes 55-60: Management principles + 15 high-yield rapid-revision facts

SHOCK - Full Explanation (Topic by Topic)

🔴 TOPIC 1: WHAT IS SHOCK?

Shock = Inadequate tissue perfusion → Cells starve of oxygen → Cells die

"A state of systemic tissue hypoperfusion resulting from reduced cardiac output and/or reduced effective circulating blood volume."

Why does shock kill you?

1. They switch from aerobic respiration (efficient, normal) to anaerobic glycolysis (inefficient, produces lactic acid)
2. Lactic acid builds up → Metabolic acidosis
3. Acidosis damages cell membranes, enzymes stop working
4. Lysosomes burst → Release digestive enzymes inside the cell → Cell destroys itself
5. Organ after organ fails → Death

🔴 TOPIC 2: TYPES OF SHOCK

• The pump (heart)
• The tank (blood volume)
• The pipes (blood vessels)

TYPE 1 - CARDIOGENIC SHOCK ("Pump Failure")

• T - Tamponade (fluid around heart squeezes it, can't fill properly)
• A - Arrhythmia (heart beating too fast/irregularly - no time to fill)
• P - Pulmonary Embolism (clot blocks outflow from right heart)
• E - MI / Extensive myocardial damage (muscle is dead, can't contract)

• CO drops → Blood pressure falls
• Body senses danger → Releases catecholamines (adrenaline) → Vasoconstriction
• Skin becomes cold, pale, clammy (blood is being shunted away from skin to vital organs)
• Pulse is weak and fast
• Because the pump is failing, blood backs up → Pulmonary congestion, breathlessness

TYPE 2 - HYPOVOLEMIC SHOCK ("Empty Tank")

• Hemorrhage - trauma, GI bleed, ruptured ectopic pregnancy, aortic aneurysm
• Burns - you lose massive amounts of plasma through burned skin
• Diarrhea/Vomiting - fluid leaves the gut
• Third-spacing - fluid goes to wrong compartments (pancreatitis, peritonitis, bowel obstruction) - it's still in the body but not in circulation

• Less blood → Less filling of heart chambers → Reduced stroke volume → ↓ CO → ↓ BP
• Body compensates with tachycardia + vasoconstriction
• Kidneys activate RAAS → Try to retain salt and water
• ADH is released → Kidneys retain water

• PCWP is LOW (tank is empty, no back-pressure into lungs)
• No pulmonary congestion

TYPE 3 - SEPTIC SHOCK ("Broken Pipes + Poison in the Blood")

Sepsis = Life-threatening organ dysfunction caused by a dysregulated host response to infection

Septic shock = Sepsis + persistent hypotension despite fluid resuscitation + need for vasopressors + lactate >2 mmol/L

THE PATHOGENESIS - Step by Step:

• Gram-positive bacteria (most common) - release exotoxins, have cell wall components
• Gram-negative bacteria - release LPS (lipopolysaccharide / endotoxin) from their outer membrane
• Fungi - release cell wall components (glucans)

• TLRs (Toll-Like Receptors) - like alarm bells that recognise "foreign patterns" (PAMPs = Pathogen-Associated Molecular Patterns)
• G-protein coupled receptors - detect bacterial peptides
• C-type lectin receptors (Dectins) - detect fungal wall components

• Macrophages, neutrophils, dendritic cells activate
• Release: TNF, IL-1, IL-6, IL-12, IFN-γ and many others
• These are the molecules that cause ALL the downstream damage

• Cytokines → Endothelium produces massive amounts of NO (Nitric Oxide)
• NO is a potent vasodilator
• Blood vessels dilate everywhere → Blood pressure drops → Tissue hypoperfusion
• This is why early septic shock = WARM, flushed skin (unlike all other shocks!) - blood is still flowing to skin, just at low pressure

• Cytokines loosen tight junctions between endothelial cells
• Fluid leaks out of vessels into tissues → Massive edema
• Proteins leak out → Oncotic pressure drops → More edema
• Lung edema → ARDS ("Shock Lung")

• Proinflammatory cytokines:
  • ↑ Tissue Factor expression (clotting ON switch)
  • ↓ Thrombomodulin (clotting OFF switch is broken)
  • ↓ Protein C (another anti-clot mechanism lost)
  • ↑ PAI-1 (prevents clot breakdown)
• Result: Tiny clots form in capillaries throughout the body
• Eventually, all clotting factors and platelets are consumed
• Patient ends up BLEEDING paradoxically (coagulation factors exhausted)
• Organ infarcts from microthrombi + bleeding from factor depletion = lethal combination

• Insulin resistance + hyperglycemia (cytokines block GLUT-4)
• ↑ Gluconeogenesis (TNF, IL-1, glucocorticoids, glucagon all drive it)
• ↑ Lactate (anaerobic metabolism) → Lactic acidosis
• Adrenal insufficiency - cortisol production fails OR frank adrenal necrosis from DIC (Waterhouse-Friderichsen syndrome)

TYPE 4 - NEUROGENIC SHOCK ("Cut Nerve Wires to the Pipes")

• All other shocks → Tachycardia (sympathetic compensates)
• Neurogenic shock → Bradycardia (the very system that would cause tachycardia is destroyed)
• Hypotension + Bradycardia = neurogenic shock (called "warm shock" too - but caused by spinal injury)

TYPE 5 - ANAPHYLACTIC SHOCK ("Allergic Pipe Explosion")

1. Prior sensitisation to allergen → IgE antibodies produced and coated on mast cells
2. Re-exposure to allergen → IgE cross-links → Mast cell degranulation
3. Releases: Histamine, leukotrienes, prostaglandins
4. Histamine → Vasodilation + ↑ capillary permeability → Hypotension

• Bronchospasm (wheeze, dyspnoea)
• Urticaria/Angioedema (skin rash, swelling)
• Hypotension (cardiovascular collapse)

• Adrenaline IM 0.3-0.5mg into the outer thigh
• It reverses bronchospasm AND vasoconstriction simultaneously
• Antihistamines and steroids are adjuncts only

🔴 TOPIC 3: STAGES OF SHOCK

STAGE 1: NON-PROGRESSIVE (Compensated) Shock

1. Baroreceptors in aortic arch and carotid sinus detect ↓ BP → Send signal to brain
2. Sympathetic nervous system activates:
   • Heart rate ↑ (tachycardia)
   • Force of contraction ↑
   • Peripheral vasoconstriction (skin, gut, skeletal muscle)
   • Blood shunted to brain and heart (these vessels are NOT sensitive to sympathetic vasoconstriction)
3. Adrenal medulla releases catecholamines (adrenaline, noradrenaline) → Amplifies above
4. ADH (vasopressin) released from posterior pituitary → Kidneys retain water
5. RAAS activated:
   • ↓ Renal perfusion → Juxtaglomerular cells release Renin
   • Renin → converts Angiotensinogen → Angiotensin I
   • ACE converts Angiotensin I → Angiotensin II (powerful vasoconstrictor)
   • Angiotensin II → stimulates Aldosterone from adrenal cortex
   • Aldosterone → Kidney retains Na+ and water → Urine output drops

• Tachycardia ✓
• Cold, pale skin ✓
• Mild anxiety ✓
• Urine output slightly reduced ✓
• Blood pressure may still be NORMAL (body is compensating!)

STAGE 2: PROGRESSIVE (Decompensated) Shock

1. Persistent ↓ O₂ delivery → Cells switch to anaerobic glycolysis → Lactic acid produced
2. Lactic acidosis (pH falls) → Arterioles dilate (pH blunts smooth muscle vasomotor response)
3. Blood pools in capillaries → Venous return drops → CO drops further → Vicious cycle
4. Endothelial cells become ischemic → Tight junctions break down → Edema worsens
5. DIC begins (especially in septic shock) - microthrombi block capillaries
6. Vital organs begin to fail:
   • Kidneys → Oliguria
   • Brain → Confusion
   • Lungs → ↑ work of breathing

↓O₂ → Anaerobic glycolysis → Lactic acid
    → ↓pH → Arteriole dilation
    → Blood pooling → ↓CO → ↓O₂ (back to start, worse each time)

STAGE 3: IRREVERSIBLE Shock

1. Lysosomes rupture inside cells → Release digestive enzymes → Cell auto-digests
2. Myocardium fails severely (not just from poor perfusion - cardiomyocytes are dying)
3. Gut barrier breaks down:
   • Intestinal mucosal cells die
   • Gut bacteria translocate across the wall into the bloodstream
   • Bacterial sepsis is now superimposed on top of whatever caused the shock in the first place
4. Renal failure (ATN - acute tubular necrosis) → Anuria
5. Multi-Organ Dysfunction Syndrome (MODS) → Death

🔴 TOPIC 4: ATLS HEMORRHAGIC SHOCK CLASSES (The 4-Class System)

CLASS I - Minor Hemorrhage

• Blood loss: 0-15% (up to ~750 mL - think donating blood)
• HR: <100 | BP: Normal | RR: 14-20/min
• Urine: >30 mL/hr
• CNS: Slightly anxious (you'd be too if you're bleeding!)
• Treatment: Oral fluids + crystalloids. Body compensates easily.

CLASS II - Moderate Hemorrhage

• Blood loss: 15-30% (750-1500 mL - significant, like a bad trauma)
• HR: >100 | BP: Still normal (body still compensating!) | Pulse pressure: Narrowed
• RR: 20-30/min | Urine: 20-30 mL/hr
• CNS: Mildly anxious
• Key point: Pulse pressure narrows because diastolic rises (vasoconstriction) even as systolic is maintained - earliest BP change!
• Treatment: Crystalloid IV fluids

CLASS III - Severe Hemorrhage

• Blood loss: 30-40% (1500-2000 mL)
• HR: >120 | BP: Now FALLS | RR: 30-40/min
• Urine: 5-15 mL/hr (kidneys shutting down)
• CNS: Anxious or confused
• This is the crossover point - compensation is failing, BP drops here
• Treatment: Crystalloid + Blood transfusion required

CLASS IV - Life-threatening Hemorrhage

• Blood loss: >40% (>2000 mL)
• HR: >140 | BP: Markedly decreased | RR: >35/min
• Urine: Negligible (kidney shut down)
• CNS: Confused/lethargic (brain hypoxia)
• Immediately life-threatening. Minutes matter.
• Treatment: Massive transfusion protocol (1:1:1 - pRBC:FFP:Platelets)

The KEY exam insight:

Blood pressure is the LAST parameter to fall (only drops at Class III+). Tachycardia and narrowed pulse pressure come first. If you wait for hypotension, you've already lost Class II.

🔴 TOPIC 5: ORGAN EFFECTS (What Shock Does to Organs)

🧠 Brain

• Hypoxic encephalopathy - neurons die first (most sensitive to hypoxia)
• Watershed infarcts - areas between two arterial territories (most vulnerable when pressure drops)
• Clinical: Confusion → Lethargy → Coma → Death

❤️ Heart

• Subendocardial ischemia/necrosis (inner lining of heart gets least blood)
• Worsens CO further → Vicious cycle

🫘 Kidneys (Most clinically important organ in shock)

• Acute Tubular Necrosis (ATN) - tubular cells are exquisitely sensitive to ischemia
• Presents as: Oliguria → Anuria
• If patient survives shock, ATN causes a phase of renal failure (managed with dialysis)
• Tubular cells can regenerate - so this is potentially reversible if patient survives!

🫁 Lungs

• In hypovolemic shock alone: Relatively resistant
• In septic shock / trauma: Diffuse Alveolar Damage (DAD) → ARDS = "Shock Lung"
• Mechanism: Inflammatory mediators damage alveolar-capillary membrane → Flooding of alveoli
• Clinical: Progressive hypoxia, bilateral infiltrates, poor O₂ despite high FiO₂

🦠 Adrenal Glands

• Cortical cell lipid depletion - adrenals are using up stored lipids to make cortisol (stress response)
• In severe DIC (especially meningococcaemia): Bilateral adrenal haemorrhage = Waterhouse-Friderichsen Syndrome → Acute adrenal insufficiency

🍽️ GI Tract

• Ischemic colitis and stress ulcers
• Mucosal barrier breaks down → Bacterial translocation (gut bacteria enter bloodstream)
• This can turn hypovolemic shock into septic shock in late stages

🔬 Fibrin Thrombi

• Form in small vessels throughout the body
• Most easily seen in kidney glomeruli on microscopy
• Sign of DIC complicating shock

🔴 TOPIC 6: MANAGEMENT OVERVIEW

UNIVERSAL PRINCIPLES OF SHOCK MANAGEMENT:

1. Secure airway, give oxygen
2. IV access (large bore, ideally 2 x wide-bore cannulas in antecubital fossa)
3. Identify and treat the cause (this is the definitive treatment)
4. Fluids (type and amount depend on shock type)
5. Monitor response: HR, BP, urine output (target >0.5 mL/kg/hr), mental status, lactate clearance

For Hypovolemic (Hemorrhagic):

• Stop the bleeding first (pressure, surgery, endoscopy)
• Warm IV crystalloids (Lactated Ringer's is better than NS - less acidosis)
• Class III/IV → Massive Transfusion Protocol: pRBC + FFP + Platelets in 1:1:1 ratio
• Avoid over-resuscitation (causes abdominal compartment syndrome, dilutional coagulopathy)
• Permissive hypotension in penetrating trauma (target SBP 80-90 until surgical control)

For Septic:

• Hour-1 bundle:
  1. Measure lactate
  2. Blood cultures (before antibiotics)
  3. Broad-spectrum antibiotics within 1 hour of recognition
  4. 30 mL/kg IV crystalloid for hypotension or lactate ≥4
  5. Vasopressors if hypotension persists: Norepinephrine is first-line
• Steroids: Hydrocortisone 200 mg/day if vasopressor-refractory (adrenal insufficiency)
• Target: MAP ≥65 mmHg, lactate clearance

For Anaphylactic:

1. Epinephrine IM 0.3-0.5 mg (anterolateral thigh) - IMMEDIATELY, no delay
2. Remove allergen if possible
3. Airway management (can swell shut rapidly)
4. IV fluids (large volumes)
5. Antihistamines (H1 + H2 blockers) and steroids - secondary measures only

For Neurogenic:

• Immobilise spine
• IV fluids (cautious - heart is fine, just pipes are dilated)
• Vasopressors: Phenylephrine (pure alpha - vasoconstrictor without increasing HR)
• If bradycardia: Atropine or temporary pacing

🧠 FINAL UNDERSTANDING CHECK - CAN YOU ANSWER THESE?

1. A patient with MI comes in cold, clammy, BP 80/60, pulse 120. What type of shock? What will PCWP be?
2. A 25-year-old stabbed in the abdomen, HR 115, BP normal, pulse pressure narrowed, anxious. What class of hemorrhage? What does "normal BP" tell you?
3. A septic patient has warm skin and HR 130 but BP 85/50. Why is the skin warm?
4. A spinal injury patient has BP 70/50 and HR 55. Why is the HR low?
5. In progressive shock, why does acidosis make things worse?
6. A shock patient survives but now has anuria 2 days later. What organ lesion explains this?

1. Cardiogenic shock. PCWP will be HIGH (blood backs up into lungs).
2. Class II hemorrhage. Normal BP means the body is still compensating - but tachycardia and narrow pulse pressure tell you significant blood loss has occurred. Never be reassured by normal BP alone.
3. Early septic shock - massive vasodilation from NO and cytokines means blood is still perfusing the skin at low pressure. It's a distributive shock, not a flow-failure shock.
4. Neurogenic shock - the sympathetic nervous system that would cause tachycardia is destroyed by the spinal injury. Paradoxical bradycardia with hypotension is the hallmark.
5. Acidosis dilates arterioles (pH blunts smooth muscle tone) → Blood pools in capillaries → ↓ venous return → ↓ CO → More hypoxia → More lactic acid → Worse acidosis. It's a vicious cycle.
6. Acute Tubular Necrosis (ATN) from ischemia during shock. The tubular cells need 48-72 hours to die and manifest as renal failure. This is why oliguria/anuria appears AFTER shock is treated.

CARDIOGENIC SHOCK - Complete Deep Dive

🔴 DEFINITION

Cardiogenic shock (CS) = Low cardiac output state resulting in life-threatening end-organ hypoperfusion and hypoxia, despite adequate intravascular volume.

• Systolic BP <90 mmHg for ≥30 minutes (or MAP <65 mmHg requiring vasopressors)
• Cardiac Index <2.2 L/min/m² (severely reduced)
• PCWP >15 mmHg (blood backing up into lungs - this distinguishes it from hypovolemic shock)
• Evidence of tissue hypoperfusion (lactate >2 mmol/L, cold extremities, oliguria, altered consciousness)

🔴 PART 1: CAUSES

PRIMARY CAUSE: Acute MI - accounts for ~80% of all cardiogenic shock

• Anterior MI (larger territory = more muscle dead)
• Older age
• Diabetes mellitus
• Prior MI (already damaged heart)
• Multivessel coronary disease

Full Classification of Causes (Mnemonic: "PUMP CAVE")

Mechanical Complications of MI (Important for exams!)

🔴 PART 2: PATHOPHYSIOLOGY

The Vicious Cycle - Step by Step:

• Coronary artery blocked → Myocardial ischemia → LV systolic and diastolic dysfunction
• Dead muscle cannot contract (systolic failure) AND cannot relax (diastolic failure)

• Stroke volume ↓ → Cardiac output ↓
• Blood pressure falls → Tissue hypoperfusion begins

• ↓ CO → ↓ Blood pressure → ↓ Coronary perfusion pressure
• The coronary arteries fill in diastole - they need adequate aortic pressure
• Lower aortic pressure = less coronary blood flow = more ischemia
• More ischemia = more muscle dies = even less CO = even less coronary perfusion
• This is the vicious spiral → Death if not broken

• LV can't empty → LV end-diastolic pressure (LVEDP) rises
• Pressure backs up into pulmonary veins → Pulmonary capillary pressure rises
• Fluid leaks into lung alveoli → Pulmonary oedema
• Pulmonary oedema → ↓ O₂ exchange → Hypoxia
• Hypoxia → more myocardial ischemia → more pump failure (vicious cycle again!)

• Baroreceptors sense ↓ BP → Activate sympathetic nervous system
• Catecholamines released → Tachycardia + Peripheral vasoconstriction
• Initially: Vasoconstriction maintains BP and shunts blood to heart and brain ✓
• Later: ↑ SVR = ↑ afterload = the failing heart has to work HARDER against more resistance = worsens pump failure ✗
• The body's own compensation becomes the enemy

• Myocardial injury (dead cells) triggers inflammatory response
• Inflammatory cytokines (TNF-α, Interleukins) released → Activate iNOS and eNOS
• iNOS/eNOS → ↑ NO production → ↑ Peroxynitrite (cardiotoxic!)
• This causes paradoxical vasodilation and directly kills more cardiomyocytes
• Catecholamine sensitivity ↓ (drugs work less well)
• Contractility ↓ further

• Anaerobic glycolysis → Lactic acidosis
• Acidosis → Reduces efficacy of catecholamines and inotropes (drugs stop working)
• Hypoxia + Acidosis + ↓ Contractility → Progressive LV dysfunction → Death

Summary Diagram (Text Version):

AMI → LV dysfunction
         ↓
    ↓ CO, ↓ BP
    /            \
Forward         Backward
failure         failure
   ↓               ↓
↓ Coronary    LVEDP↑ → Pulmonary oedema
 perfusion         ↓
   ↓           Hypoxia
More ischemia     ↓
   ↓          More ischemia
↓↓ CO ←←←←←←←←←←←←←←←←←←
   ↓
SIRS → TNF, IL → NO → Vasodilation
              → Peroxynitrite → ↓Contractility
   ↓
Lactic acidosis → Catecholamines ineffective
   ↓
DEATH (unless spiral is broken)

Haemodynamic Profile Summary:

• Cardiogenic: PCWP HIGH (lungs are wet/congested)
• Hypovolemic: PCWP LOW (tank is empty, lungs are dry)

🔴 PART 3: CLINICAL FEATURES

"The 5 Ws of Cardiogenic Shock Presentation"

Symptoms:

• Chest pain (if AMI is the cause - may have already had it for hours)
• Severe breathlessness / dyspnoea (pulmonary oedema - lungs are flooding)
• Extreme fatigue and weakness
• Anxiety and sense of impending doom
• Altered mental state - confusion, drowsiness (cerebral hypoperfusion)

Signs (System by System):

• Pulse: Weak, thready, rapid (low stroke volume; may be slow if complete heart block)
• BP: <90 mmHg systolic (or drop of >30 mmHg from baseline)
• Narrow pulse pressure (low SBP, high DBP from vasoconstriction)
• JVP elevated (blood backing up, especially in RV failure or tamponade)
• S3 gallop on auscultation (sound of blood hitting a stiff, failing ventricle)
• S4 gallop (stiff LV - diastolic dysfunction)
• Murmurs - NEW murmur = mechanical complication! (MR, VSR)

• Tachypnoea (fast breathing, >20/min)
• Bilateral crackles (basal, spreading up as oedema worsens)
• May be in frank pulmonary oedema - pink frothy sputum, orthopnoea, sitting bolt upright, using accessory muscles

• Skin: Cold, pale, clammy, mottled, cyanotic (peripheral vasoconstriction + poor perfusion)
• Prolonged capillary refill time (>2 seconds)
• Cold extremities despite feeling feverish centrally

• Oliguria (<0.5 mL/kg/hr) progressing to anuria (renal hypoperfusion)

• Agitation, confusion, restlessness, stupor (cerebral hypoperfusion)

Classic Clinical Picture to memorise:

"A 70-year-old with known IHD presents 4 hours after onset of crushing chest pain. He is pale, sweating profusely, gasping for air, cannot lie flat. HR 120, BP 80/60, RR 28. There are bilateral crackles up to the mid-zones. JVP is elevated. S3 present. Extremities are ice cold and mottled."

SCAI Classification (Current Standard)

🔴 PART 4: INVESTIGATIONS

ECG:

• ST-elevation (STEMI) or T-wave changes
• New LBBB
• Arrhythmias (VT, AF, Complete Heart Block)

Echocardiogram (MOST IMPORTANT investigation):

• Confirms LV dysfunction (EF severely reduced)
• Identifies mechanical complications (MR, VSR, tamponade, RV failure)
• Essential for diagnosis and guiding treatment
• Do it immediately at the bedside

Blood tests:

• Troponin ↑↑ (myocardial necrosis)
• Lactate ↑ (>2 mmol/L = tissue hypoperfusion, >5 = very poor prognosis)
• ABG: Hypoxia, metabolic acidosis, ↑ CO₂
• Creatinine ↑ (renal hypoperfusion/AKI)
• LFTs ↑ (hepatic hypoperfusion - "shock liver")
• BNP/NT-proBNP ↑↑ (heart failure marker)
• FBC, coagulation (DIC if severe)

Chest X-Ray:

• Cardiomegaly
• Bilateral pulmonary infiltrates (pulmonary oedema - "bat-wing" pattern)
• Kerley B lines (interstitial oedema)
• Upper lobe venous diversion

Invasive Monitoring (Swan-Ganz / Pulmonary Artery Catheter):

• Confirms: ↓ CO, ↑ PCWP, ↑ SVR
• Used in complex cases to guide vasopressor/inotrope titration

🔴 PART 5: MANAGEMENT

1. Stabilise (buy time)
2. Fix the cause (definitive treatment)
3. Support failing organs

STEP 1: Immediate Stabilisation (First 30-60 minutes)

• High-flow O₂ (15L via non-rebreather mask)
• If pulmonary oedema + respiratory distress → Non-invasive ventilation (NIV/CPAP)
  • CPAP reduces work of breathing AND reduces preload (helpful in oedema)
  • Intubation if unable to maintain airway or respiratory failure

• Large-bore IV access x2
• Foley catheter (monitor urine output hourly)
• Continuous ECG monitoring + SpO₂ + arterial line (continuous BP)
• Cautious fluids - unlike hypovolemic shock, you do NOT aggressively push fluids
  • Small bolus (250 mL) only if there are signs of hypovolaemia or RV infarction
  • Too much fluid = worsens pulmonary oedema in LV failure

• Arrhythmia → Cardiovert (if VT/VF) or pace (if complete heart block)
• Cardiac tamponade → Emergency pericardiocentesis
• Tension pneumothorax → Needle decompression

STEP 2: Vasopressors and Inotropes

Vasopressors (Raise BP):

Inotropes (Strengthen the squeeze):

STEP 3: Reperfusion - THE DEFINITIVE TREATMENT for MI-related CS

Restore blood flow to the dead/dying heart muscle. Everything else is just buying time.

• Gold standard for STEMI complicated by cardiogenic shock
• Open the blocked artery with a stent → Restore flow → Stop more muscle dying → Break the vicious cycle
• Target: Door-to-balloon time <90 minutes (or <120 min if transfer required)
• Even in very sick patients, revascularisation improves survival
• Recent data: Revascularise the culprit vessel only first (not all blocked vessels at the same time - immediate multivessel PCI increases mortality)

• If anatomy not suitable for PCI (left main disease, complex multivessel disease)
• Can be done emergently but has higher operative risk in CS

• If PCI not available within 120 minutes and no contraindications
• Less effective than PCI but better than nothing

STEP 4: Mechanical Circulatory Support (MCS)

IABP (Intra-Aortic Balloon Pump):

• A balloon in the descending aorta, inflates in diastole → ↑ coronary perfusion pressure (coronaries fill in diastole!)
• Deflates rapidly in systole → Creates suction effect → ↓ afterload → Heart pumps easier
• Easy to insert percutaneously
• Note: The IABP-SHOCK II trial showed NO mortality benefit vs medical therapy alone - now used mainly as a bridge

Impella (Axial Flow Pump):

• Tiny motor pump placed across the aortic valve into the LV
• Actively pumps blood from LV into aorta → Unloads the LV
• Provides 2.5-5.0 L/min of support
• Better haemodynamic support than IABP
• Current evidence does not show clear mortality benefit over medical therapy in most patients, but remains widely used

VA-ECMO (Venoarterial Extracorporeal Membrane Oxygenation):

• Takes blood from venous system, oxygenates it outside the body, pumps it back into the arterial system
• Provides full cardiopulmonary bypass - takes over both heart and lungs
• Used in Stage E (Extremis) - cardiac arrest, refractory shock
• The ECLS-SHOCK trial (2023): VA-ECMO did NOT show mortality benefit vs medical therapy, AND had significantly more bleeding and limb ischaemia complications
• Still used selectively as a bridge to decision (bridge to transplant, bridge to VAD)

VAD (Ventricular Assist Device):

• Long-term device implanted surgically
• Used as bridge to transplant or destination therapy in refractory CS
• Decision made by multidisciplinary heart team

STEP 5: Management of Specific Causes

STEP 6: Monitoring Response to Treatment

• MAP ≥65 mmHg
• Urine output >0.5 mL/kg/hr
• Lactate clearance >10-20% every 2 hours (falling lactate = organs recovering)
• SpO₂ >94%
• Mental status improving
• Extremities warming up

🔴 PROGNOSIS

1. Age >73 years
2. Prior stroke
3. Blood glucose at admission >10.6 mmol/L (191 mg/dL)
4. Creatinine >132.6 μmol/L (1.5 mg/dL) at admission
5. TIMI flow <3 after PCI
6. Lactate >5 mmol/L at admission

• Score 0-2 = lower risk (~24% mortality)
• Score 4-6 = very high risk (~75%+ mortality)

🧠 THE BIG PICTURE - How Everything Connects

CAUSE (AMI, Arrhythmia, Tamponade, etc.)
         ↓
    LV/RV Dysfunction
         ↓
    ↓ Cardiac Output
    /             \
Forward failure  Backward failure
↓ Coronary flow  ↑ LVEDP → Pulmonary oedema
↓ BP            ↓ O₂ exchange
↑ Ischaemia     ↑ Hypoxia
         \       /
          ↓↓ CO
          ↓
SIRS + NO ↑ → ↓ Contractility further
          ↓
    Lactic acidosis
          ↓
MANAGEMENT INTERRUPTS THE SPIRAL:
→ O₂, Ventilation (fix hypoxia)
→ Vasopressors (fix BP)
→ Inotropes (improve contractility)
→ PCI/CABG (fix the cause - most important!)
→ MCS (mechanical support when drugs fail)

⚡ HIGH-YIELD EXAM FACTS

1. Most common cause = Acute MI (anterior) causing LV failure (~80% of cases)
2. Classic haemodynamics: ↓ CO, ↓ BP, ↑ SVR, ↑ PCWP, ↓ SvO₂
3. PCWP is HIGH - this differentiates it from hypovolemic shock (PCWP low)
4. Skin: Cold, pale, clammy (NOT warm - that's septic shock)
5. JVP elevated + pulmonary oedema + hypotension = cardiogenic shock until proven otherwise
6. New murmur after MI = mechanical complication (MR, VSR, free wall rupture)
7. RV infarction = elevated JVP + clear lungs + hypotension (no pulmonary oedema - lungs are DRY)
8. In RV infarction: NEVER give nitrates or diuretics (reduce preload → catastrophic BP drop)
9. Definitive treatment for MI-CS = Emergency PCI (restore coronary flow)
10. First-line vasopressor = Norepinephrine
11. First-line inotrope = Dobutamine
12. IABP works by: Inflating in diastole (↑ coronary flow) + Deflating in systole (↓ afterload)
13. ECLS-SHOCK trial (2023) = VA-ECMO showed no mortality benefit + more complications
14. SCAI Stage A-E: At risk → Beginning → Classical → Deteriorating → Extremis
15. Mortality = 40-60%. Still one of medicine's most lethal emergencies.