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Flashcards in SPR L11 Pathophysiology of Shock Deck (13):
1

Pathophysiology of Shock

Outcomes

•Definition of shock

•Main causes of shock

•Direct consequences

•Compensatory mechanisms

•Principles of monitoring and management

2

Give a definition of shock

•Acute circulatory failure

•Low arterial blood pressure

•Inadequate tissue perfusion

•Cellular hypoxia

3

What are the causes of shock?

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  • 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

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4

What are the direct consequences of shock?

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5

What are the compensatory reflexes of shock (1)?

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6

What are the compensatory mechanisms of shock (2)?

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7

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’)

 

8

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_

9

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)

 

 

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10

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

11

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)

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

12

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)

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13

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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