Session 11 ILOs - Haemodynamic shock

Question 1

Describe the essential characteristics of haemodynamic shock

Answer 1

Haemodynamic shock is an acute condition of inadequate blood flow throughout the body, where a catastrophic fall in arterial blood pressure leads to circulatory shock

Can be due to either:

• Fall in CO
• Fall in TPR (beyond heart’s ability to compensate)

Question 2

Describe the characteristics of hypovolaemic, cardiogenic, mechanical and distributive shock such as anaphylactic shock

Answer 2

Haemodynamic shock due to 2 causes:

a) Fall in cardiac output:

1. Cardiogenic shock (pump failure)
   - Defining factor is drop in arterial BP
   - Causes include myocardial infarction, serious arrhythmias or acute worsening of heart failure
   - Tissues become poorly perfused
2. Mechanical shock (cannot fill)
   - Cardiac tamponade = high central venous pressure and low arterial BP
   - Pulmonary embolism = high pulmonary artery pressure and low LA and arterial BP
   - Caused by cardiac tamponade or massive pulmonary embolism (pulmonary artery pressure is too high so reduced emptying of right ventricle)
3. Hypovolaemic shock (loss of blood volume)
   - Compensatory sympathetic stimulation e.g. tachycardia
   - Caused most commonly by a haemorrhage or pure blood loss, but severity is related to amount and speed of blood loss
   - Danger of decompensation

b) Fall in TPR:

4. Excessive vasodilation
   - Caused by either toxic shock (i.e. sepsis) or anaphylactic shock
   - Decreased arterial BP, tachycardia and warm extremities initially but then later in sepsis you get vasoconstriction

Question 3

Describe the general features of management of the various types of shock

Answer 3

1. Cardiogenic
   - Help to treat the cause i.e. remove blockage if MI
2. Mechanical
   - Cardiac tamponade = insert needle to relieve the fluid
   - Pulmonary embolism = anticoagulants to remove the clot
3. Hypovolaemic
   - Saline solution to increase the blood volume
4. Excessive vasodilation
   - Toxic shock = treat underlying because
   - Anaphylaxis = give adrenaline to activate vasoconstriction (alpha 1 AR activation)

Question 4

Describe the body’s compensatory responses to hypovolaemia to maintain arterial blood pressure

Answer 4

• Venous pressure falls due to fluid loss which causes CO to fall and consequently arterial BP falls
• Detected by baroreceptors

Compensatory response:

• Increased sympathetic stimulation
• Tachycardia, increased force of contraction and increased vasoconstriction and VENOconstriction
• Also normally at the capillaries, fluid moves out into tissue due to balance of starling’s forces however if the blood volume drops then the hydrostatic force drops and fluid moves into the capillaries

Longer term compensation = RAAS system

Question 5

Explain how prolonged peripheral vasoconstriction in response to hypovolaemia can lead to decompensation

Answer 5

Danger of decompensation:

• Peripheral vasoconstriction can result in tissue damage due to hypoxia
• Tissues release chemical mediators = vasodilators
• This causes the TPR to fall and BP falls dramatically
• Multi-organ failure and death

It’s the prolonged vasoconstriction that can cause a build up of these vasodilators (due to prolonged tissue hypoxia and damage) therefore eventually the vasodilator concentration overcomes the sympathetic NS and you get widespread vasodilation