Week 12 - Shock

Question 1

How do you treat a cardiac arrest?

Answer 1

• Basic life support (chest compressions and external ventilation)
• Advanced life support (defibrillation which depolarises all the cells, allowing coordinated electrical activity to restart)
• Adrenaline (enhances myocardial function and increases peripheral resistance)

Question 2

What is shock?

Answer 2

An acute condition of inadequate blood flow throughout the body

• A catastrophic fall in arterial blood pressure leads to circulatory shock
• Can be due to a fall in cardiac output or total peripheral resistance

Question 3

What types of shock are due to a fall in cardiac output?

Answer 3

• Cardiogenic
• Mechanical
• Hypovolaemic

Question 4

What is cardiogenic shock and what are its characteristics?

Answer 4

Acute failure of the heart to maintain cardiac output following MI or due to serious arrhythmias

• Central venous pressure may be normal or raised
• Heart fills but fails to pump effectively (ventricles don’t empty properly)
• Dramatic drop in arterial pressure
• Tissues are poorly perfused: coronary arteries (exacerbates problem), kidneys (reduced urine production)

Question 5

What is mechanical shock and what are its characteristics?

Answer 5

The ventricles cannot fill properly

• High central venous pressure
• Low arterial blood pressure
• May be due to a pulmonary embolism or cardiac tamponade

Question 6

How can cardiac tamponade cause mechanical shock?

Answer 6

Fluid in the pericardial space restricts filling of the heart
- Hence there is reduced cardiac output

Question 7

How does a pulmonary embolism cause mechanical shock?

Answer 7

• Massive PE
• Occludes a large pulmonary artery
• Right ventricle can’t empty
• Central venous pressure is high
• Reduced return of blood to the left heart, limiting filling of the left heart
• Left atrial pressure is low
• Arterial blood pressure is low
• Hence causes shock

Question 8

What is hypovolaemic shock and what are its characteristics?

Answer 8

• Reduced blood volume
• ## Most common cause is haemorrhage (also from severe burns or severe diarrhoea/vomiting and loss of Na+)

Question 9

What are the different types of distributive shock?

Answer 9

• Toxic

- Anaphylactic

Question 10

What is toxic shock and what are its characteristics?

Answer 10

• Low resistance shock
• Due to septicaemia
• Endotoxins are released by circulating bacteria which cause vasodilation
• Leads to a dramatic fall in TPR and hence a fall in arterial pressure
• Impaired perfusion of vital organs
• Capillaries become leaky
• Decreased arterial pressure is detected by baroreceptors which increases sympathetic output
• – Vasoconstriction effect is overridden by mediators of vasodilation
• – Heart rate and stroke volume increase
• Patient has tachycardia and warm, red extremities

Question 11

What is anaphylactic shock and what are its characteristics?

Answer 11

• Severe allergic reaction
• Release of histamine from mast cells, which has a powerful vasodilator effect (reduces TPR)
• Dramatic drop in arterial pressure stimulates sympathetic response
• – Increases CO but can’t overcome vasodilation
• Impaired perfusion of vital organs
• Mediators also cause bronchoconstriction and laryngeal oedema
• Patient will have difficulty breathing, collapsed, rapid HR, and red, warm extremities
• It is acutely life-threatening
• Treat with adrenaline

Question 12

What is a cardiac arrest?

Answer 12

Unresponsiveness associated with lack of pulse

• Heart has stopped/ceased to pump effectively
• Asystole (loss of mechanical and electrical activity)
• Ventricular fibrillation is the most common form of cardiac arrest (may occur following MI, due to electrolyte imbalance or due to some arrhythmias)