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Flashcards in SPR L11 Pathophysiology of Shock Deck (13):

Pathophysiology of Shock


•Definition of shock

•Main causes of shock

•Direct consequences

•Compensatory mechanisms

•Principles of monitoring and management


Give a definition of shock

•Acute circulatory failure

•Low arterial blood pressure

•Inadequate tissue perfusion

•Cellular hypoxia


What are the causes of shock?

  • Hypovolaemic: loss of circulating blood volume
    • bleeding
    • burns
  • Cardiogenic: acute pump failure due to myocardial damage
  • Obstructive: mechanical interference with flow

    • pulmonary embolus

    • restricted myocardial filling, eg cardiac tamponade, tension pneumothorax

  • Distributive: generalised vasodilatation
    • anaphylactic shock
    • septic shock
    • neurogenic shock


What are the direct consequences of shock?


What are the compensatory reflexes of shock (1)?


What are the compensatory mechanisms of shock (2)?


Signs and Symptoms

Give examples of symptoms seen in all causes of shock

  • Reduced BP (may be maintained initially)
  • Reduced systemic perfusion

    • drowsy/unconscious

    • ooliguria/anuria

  • Increased sympathetic tone

    • tachycardia

    • sweating

  • Respiratory compensation for metabolic acidosis

    • hyperventilation (‘air hunger’)



Give Signs and Symptoms of the following

  1. Hypovolaemic shock
  2. Cardiogenic shock
  3. Obstructive shock
  4. Anaphylactic and septic shock


  1. Reduced CVP, Reduced cutaneous perfusion (COLD/pale peripheries, slow capillary refill, peripheral cyanosis in absence of CENTRAL)

  2. Elevated JVP,  Signs of heart failure (pulmonary oedema, gallop rhythm - tachyC with a 3rd heart sound)

  3. Elevated JVP and Signs of pulmonary embolism/Signs of cardiac tamponade/Signs of tension pneumothorax

  4. Low JVP, Signs of vasodilatation (WARM peripheries, bounding pulse, rapid capillary refill_


Monitoring Shock

What should be monitored?

  • Tissue perfusion
    • skin colour, temperature, capillary refill

    • urinary flow

    • metabolic acidosis

  • Cardiovascular pressure measurements
    • systemic arterial BP

      • cuff

      • intrarterial catheter

    • central venous pressure

      • JVP is a clinical estimate of CVP

      • critically ill patient – catheter in subclavian or internal jugular v. 

      • measure pressure relative to level of Rt atrium

    • pulmonary artery pressure

      • balloon flotation (‘Swan-Ganz’) catheter

    • left atrial pressure

      • pulmonary artery occlusion pressure


(CO in other cards)




Monitoring Shock

How can Cardiac Output be measured?

  • thermodilution method
    • pulmonary artery catheter in R atrium
    • inject known volume cold fluid
    • measure blood temperature at catheter tip
  • oesophageal Doppler

    • Doppler ultrasound measurement of aortic blood flow

    • relies on Doppler shift in frequency of ultrasound; depends on red cell velocity

  • echocardiography

    • Direct assessment of stroke volume and heart rate:

        CO = SV X HR


Management of Shock

   Goal: restore and maintain adequate tissue oxygenation/perfusion

What are the targets for the following...

  1. MAP
  2. CVP
  3. Urinary Output
  4. Venous O2 Saturation (SvO2) 


Outline the main mechanisms targeted (see picture)


  1. > 65 mmHg
  2.  > 12 mmHg
  3.  > 0.5 ml/kg/hr
  4.  >65% (ñO2 extraction)


Management of Shock

How can the following be targeted in the management of shock?

  1. Pre-load
  2. Myocardial contractility
  3. After-load

  1. replace fluid loss rapidly, monitor to avoid overload: elevated Lt atrial pressure and pulmonary oedema

  2. positive inotropesadrenaline, noradrenaline, dopamine

  3. vasoconstrictors to increase after-load (PR) and BP: noradrenaline and vasopressin

    vasodilators to reduce after-load and increase CO - reduces myocardial wall tension and improves coronary flow, may be useful in cardiogenic shock (and cardiac failure): nitrates, eg sodium nitroprusside (NO production)


Management of Shock

How can Obstructive Shock be managed?

Treat the underlying condition

  • drain pericardium in tamponade
  • release pressure in tension pneumothorax

  • surgical removal of clot in life threatening pulmonary embolus (rare)

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