S5) Circulatory Shock

Question 1

What is haemodynamic shock?

Answer 1

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

Question 2

What are the causes for the catastrophic drop in blood pressure which leads to haemodynamic shock?

Answer 2

Question 3

Identify and define three different types of shock occurring due to a fall in cardiac output

Answer 3

• Cardiogenic shock – ventricle cannot empty properly

- Mechanical shock – ventricle cannot fill properly

- Hypovolaemic shock – reduced blood volume leads to poor venous return

Question 4

What is cardiogenic shock?

Answer 4

Cardiogenic shock is the acute failure of the heart to maintain cardiac output (pump failure)

Question 5

Identify 3 potential causes for cardiogenic shock

Answer 5

• Myocardial infarction (damage to left ventricle)
• Serious arrhythmias
• Acute worsening of heart failure

Question 6

What are the consequences of cardiogenic shock?

Answer 6

• CVP normal/raised
• aBP lowered
• Tissues poorly perfused

I. Coronary arteries (exacerbates problem)

II. Kidneys (reduced urine production)

Question 7

Cardiac tamponade is an example of mechanical shock.

What is this condition?

Answer 7

Cardiac tamponade is when blood/fluid builds up in pericardial space, restricting the filling of both sides of the heart and limiting the end diastolic volume

Question 8

What are the consequences of cardiac tamponade?

Answer 8

• High CVP
• Low aBP
• Continued electrical activity

Question 9

A pulmonary embolism is another example of mechanical shock.

What are the consequences of this?

Answer 9

• High pulmonary artery pressure → right ventricle cannot empty
• High CVP → reduced return of blood to the left heart
• Low LAP
• Low aBP

Question 10

State two characteristic symptoms of mechanical shock due to PE

Answer 10

• Chest pain
• Dyspnoea

Question 11

In four steps, explain how an embolus reaches the lungs

Answer 11

⇒ Deep vein thrombosis

⇒ Portion of thrombus breaks off

⇒ Embolus travels in venous system to right side of the heart

⇒ Pumped out via pulmonary artery to lungs

Question 12

What is hypovolaemic shock?

Answer 12

Hypovolaemic shock is a state of shock due to reduced blood volume, most commonly due to haemorrhage

Question 13

The severity of hypovolaemic shock is related to amount and speed of blood loss.

How does the shock vary with amount of blood loss?

Answer 13

• < 20% blood loss unlikely to cause shock
• 20-30% blood loss show some signs of shock response
• 30-40% bloow loss shows substantial decrease in mean aBP and serious shock response

Question 14

Explain what happens during a haemorrhage

Answer 14

⇒ Venous pressure falls

⇒ Cardiac output falls (Starling’s Law)

⇒ Arterial pressure falls

Question 15

Describe the compensatory response observed in hypovolaemic shock

Answer 15

⇒ Low aBP detected by baroreceptors

⇒ Increased sympathetic stimulation

⇒ Tachycardia, increased contractlity

⇒ Peripheral vasoconstriction and venoconstriction

Question 16

How does a patient in hypovolaemic shock present?

Answer 16

• Tachycardia
• Weak pulse
• Pale skin
• Cold, clammy extremities

Question 17

Besides haemorrhages, when else can hypovolaemic shock occur?

Answer 17

• Severe burns
• Severe diarrhoea / vomiting
• Severe loss of Na⁺

Question 18

In 5 steps, explain how peripheral vasoconstriction (shutdown) impairs tissue perfusion

Answer 18

⇒ Tissue damage due to hypoxia

⇒ Release of chemical mediators

⇒ Vasodilation (TPR & BP falls)

⇒ Vital organs can no longer be perfused

⇒ Multi system failure

Question 19

What is distributive shock?

Answer 19

• Distributive shock is low resistance shock (normovolaemic) due to profound peripheral vasodilation (decrease in TPR)
• Blood volume is constant, but volume of the circulation has increased

Question 20

Identify two different types of shock due to a fall in total peripheral resistance

Answer 20

• Anaphylactic shock
• Septic shock

Question 21

What is anaphylaxis?

Answer 21

Anaphylaxis is a severe allergic reaction

Question 22

In 5 steps, explain how anaphylaxis leads to a state of distributive shock

Answer 22

⇒ Release of histamine from mast cells

⇒ Vasodilation (fall in TPR)

⇒ Dramatic drop in arterial pressure

⇒ Increased sympathetic response can’t overcome vasodilation

⇒ Impaired perfusion of vital organs

Question 23

How do patients present with anaphylactic shock?

Answer 23

• Dyspnoea (bronchoconstriction, laryngeal oedema)
• Collapse
• Tachycardia
• Red, warm extremities

Question 24

Anaphylactic shock is an acutely life threatening.

How can it be managed?

Answer 24

Adrenaline – vasoconstriction via action at α1 adrenoceptors

Question 25

What is sepsis?

Answer 25

Sepsis is a serious life-threatening response to infection, can lead to septic shock

Question 26

What is septic shock?

Answer 26

Septic shock is persisting hypotension requiring treatment to maintain blood pressure despite fluid resuscitation

Question 27

In 5 steps explain how sepsis leads to a state of distributive shock (septic shock)

Answer 27

⇒ Endotoxins released by circulating bacteria

⇒Profound inflammatory response

⇒ Vasodilation (& increased permeability)

⇒ Dramatic fall in TPR & aBP

⇒ Impaired perfusion of vital organs

Question 28

How do patients present with septic shock?

Answer 28

• Tachycardia
• Warm, red extremities initially
• Vasoconstriction (later on)

Question 29

When would one start to consider cardiac arrest?

Answer 29

• Unresponsiveness associated with lack of pulse
• Heart has stopped or has ceased to pump effectively

Question 30

Identify and describe the three forms of cardiac arrest

Answer 30

• Asystole – loss of electrical and mechanical activity
• Pulseless Electrical Activity
• Ventricular fibrillation – uncoordinated electrical activity

Question 31

How does one manage cardiac arrest?

Answer 31

• Basic life support – chest compression and external ventilation
• Advanced life support – defibrillation
• Adrenaline – enhances myocardial function and increases TPR

Question 32

Describe the impact of defibrillation on the heart in advanced life support

Answer 32

⇒ Electric current delivered to the heart

⇒ Depolarises all the cells – puts them into refractory period

⇒ Allows coordinated electrical activity to restart