SHOCK – Cardiovascular Failure

Learning Objectives

By the end of this lecture, you should be able to:

• Define shock and understand its types
  
  

• Explain the physiological response to shock
  
  

• Recognise clinical signs and stages
  
  

• Understand the principles of fluid resuscitation
  
  

• Know when and how to use vasopressors and inotropes
  
  

Definition of Shock

Shock is a life-threatening circulatory failure that results in inadequate tissue perfusion, leading to cellular hypoxia and organ dysfunction.

It is not simply low blood pressure — patients may have normal BP but still be in shock if perfusion is inadequate.

Types of Shock

Type

Primary Cause

Examples

Hypovolaemic

↓ Intravascular volume

Hemorrhage, burns, vomiting, diarrhoea

Cardiogenic

Pump failure

MI, arrhythmias, cardiomyopathy

Distributive

Vasodilation → relative hypovolemia

Sepsis, anaphylaxis, neurogenic shock

Obstructive

Physical obstruction to flow

PE, cardiac tamponade, tension pneumothorax

Pathophysiology of Shock

1. Initial insult → ↓ perfusion
   
   

2. Activation of sympathetic nervous system:
   
   

   • ↑ Heart rate
     
     

   • Vasoconstriction
     
     

   • ↑ Contractility
     
     

3. If unresolved → organ failure
   
   

Clinical Stages of Shock

1. Compensated (Early) Shock
   
   

   • Normal BP (due to vasoconstriction)
     
     

   • Tachycardia
     
     

   • Cool peripheries
     
     

   • Delayed capillary refill
     
     

2. Decompensated (Progressive) Shock
   
   

   • Hypotension
     
     

   • Confusion or restlessness
     
     

   • Oliguria
     
     

   • Metabolic acidosis
     
     

3. Irreversible Shock
   
   

   • Multiorgan failure
     
     

   • Anaerobic metabolism
     
     

   • Death if not reversed rapidly
     
     

Clinical Features of Shock

• HR: Tachycardia
  
  

• BP: Normal in early, ↓ in late
  
  

• RR: Tachypnoea
  
  

• Skin: Pale, clammy, cyanotic
  
  

• Urine Output: <0.5 mL/kg/hr (oliguria)
  
  

• Mentation: Confusion, drowsiness
  
  

Investigations

• Full blood count, urea, creatinine
  
  

• Lactate (marker of anaerobic metabolism)
  
  

• ABG: metabolic acidosis
  
  

• ECG, cardiac enzymes (in cardiogenic shock)
  
  

• CXR, echocardiogram
  
  

• FAST scan (to detect intra-abdominal bleeding)
  
  

• Cultures (in septic shock)
  
  

Management Principles of Shock

A. ABC Approach

• Airway: Ensure patency
  
  

• Breathing: Oxygenate, ventilate
  
  

• Circulation: Restore intravascular volume
  
  

B. Fluid Resuscitation

Indication: Hypovolaemic, distributive, obstructive shock

Fluids:

• Crystalloids: Normal saline or Ringer's lactate
  
  

• Bolus: 500–1000 mL over 15–30 min (adults)
  
  

• Children: 20 mL/kg over 10–15 min
  
  

Reassess: HR, BP, capillary refill, urine output

C. Blood Products

• Used if haemorrhage is cause
  
  

• Transfuse based on clinical signs and haemoglobin <7 g/dL (may be higher in trauma or brain injury)
  
  

D. Vasopressors and Inotropes

Used when fluids fail to restore perfusion.

Drug

Class

Dose/Route

Notes

Noradrenaline

Vasopressor

0.05–1 mcg/kg/min IV

First-line in septic shock

Adrenaline

Inotrope/vasopressor

0.05–2 mcg/kg/min IV

Anaphylactic and cardiogenic shock

Dopamine

Inotrope/vasopressor

2–20 mcg/kg/min IV

Dose-dependent effects

Dobutamine

Inotrope

2–20 mcg/kg/min IV

Useful in cardiogenic shock with low output

Phenylephrine

Pure vasopressor

0.1–0.5 mcg/kg/min IV

Used when HR is high, pure α action

Specific Treatment per Shock Type

Type

Key Treatment

Hypovolaemic

Crystalloids + blood if needed

Cardiogenic

Inotropes (dobutamine), diuretics, treat cause

Distributive

Fluids + vasopressors (noradrenaline)

Obstructive

Relieve obstruction (e.g. chest drain, thrombolysis, pericardiocentesis)

Monitoring Response to Treatment

• Urine output: aim > 0.5 mL/kg/hr
  
  

• BP and MAP: target MAP > 65 mmHg
  
  

• Heart rate: trend toward normal
  
  

• Mental status: improved sensorium
  
  

• Lactate: decreasing levels
  
  

• Capillary refill time: <2 seconds