Week 12 - Shock Flashcards Preview

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Flashcards in Week 12 - Shock Deck (12):

How do you treat a cardiac arrest?

- 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)


What is shock?

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


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

- Cardiogenic
- Mechanical
- Hypovolaemic


What is cardiogenic shock and what are its characteristics?

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)


What is mechanical shock and what are its characteristics?

The ventricles cannot fill properly
- High central venous pressure
- Low arterial blood pressure
- May be due to a pulmonary embolism or cardiac tamponade


How can cardiac tamponade cause mechanical shock?

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


How does a pulmonary embolism cause mechanical shock?

- 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


What is hypovolaemic shock and what are its characteristics?

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


What are the different types of distributive shock?

- Toxic
- Anaphylactic


What is toxic shock and what are its characteristics?

- 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


What is anaphylactic shock and what are its characteristics?

- 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


What is a cardiac arrest?

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)