Shock

Question 1

What is haemodynamic shock?

Answer 1

Acute condition of inadequate blood flow throughout the body

Question 2

What causes a haemodynamic shock?

Answer 2

A catastrophic fall in arterial blood pressure

• Fall in CO
• Fall in TPR beyond capacity

(aBP = CO x TPR)

Question 3

What are the three types of shock caused by a fall in CO?

Answer 3

1) Cardiogenic shock
2) Mechanical shock
3) Hypovolaemic shock

Question 4

What is cardiogenic shock?

Answer 4

Inability of the heart to eject enough blood (pump failure)

Question 5

What are the potential causes of cardiogenic shock?

Answer 5

• Following myocardial infarction
• Serious arrhythmias (e.g. tachycardia=less time to fill so lower SV)
• Acute worsening of heart failure

Question 6

What is mechanical shock?

Answer 6

Less ejection of the blood from restricted filling of the heart (obstructive)

Question 7

What is cardiac tamponade and how does it lead to mechanical shock?

Answer 7

Blood or fluid build up in pericardial space

-pressure constricts the heart preventing it to fill (limits end diastolic volume)

Question 8

How can a massive pulmonary embolism lead to mechanical shock?

Answer 8

• Embolus occludes a large pulmonary artery = high pressure
• Right ventricle can’t empty = CVP is high
• REDUCED RETURN OF BLOOD TO LEFT HEART

Question 9

What is hypovolaemic shock?

Answer 9

Shock from severe reduction of blood volume

-poor venous return

Question 10

Where is hypovolaemic shock most commonly seen in?

Answer 10

Haemorrhage

Question 11

What defines the severity of a hypovolaemic shock?

Answer 11

The amount and speed of blood loss

30-40% decrease

Question 12

Explain how a haemorrhage leads to hypovolaemic shock

Answer 12

1) Venous pressure falls
2) Cardiac output falls (from Starling’s law)
3) Detected by baroreceptors (increased sympathetic stimulation = tachycardia, peripheral vasoconstriction)

Question 13

What are other causes of hypovolaemic shock apart from haemorrhage?

Answer 13

• Severe burns
• Diarrhoea
• Vomiting
• Loss of Na+

Question 14

What is the danger to decompensation of baroreceptors in hypovolaemic shock?

Answer 14

There will still be tissue damage to hypoxia leading to release of chemical mediators

• Vasodilators (overides sympathetic compensation)
• TPR falls = blood pressure falls
• Multi-system failure

Question 15

What shock is caused by a reduction in TPR?

Answer 15

Distributive (normovolaemic) shock

Question 16

What are the two examples of distributive shock?

Answer 16

1) Septic (toxic) shock

2) Anaphylactic shock

Question 17

Describe how sepsis can lead to distributive shock

Answer 17

Bacteria releases endotoxins

• Excessive inflammatory response
• Profound vasodilation
• Dramatic fall in TPR
• Fall in arterial pressure = impaired perfusion

Question 18

What is anaphylactic shock?

Answer 18

Shock from released histamines from mast cells in response to a severe allergic reaction

Question 19

How does an anaphylaxis lead to a distributive shock?

Answer 19

Histamines from mast cells are powerful vasodilators

• Decreased TPR
• Decreased aBP = decreased tissue perfusion

Question 20

How is an anaphylactic shock treated?

Answer 20

Giving adrenaline