1- Cardiovascular response to shock

Question 1

what is shock?

Answer 1

an abnormality of circulatory system resulting in inadequate tissue perfusion & oxygenation

Question 2

how does shock lead to cellular failure?

Answer 2

shock→inadequate tissue perfusion →inadequate tissue oxygenation →anaerobic metabolism →accumulation of metabolic waste products →cellular failure

Question 3

what causes inadequate tissue perfusion? (explanation of shock types)

Answer 3

• loss of blood volume
• sudden severe impairment of heart function (like damage to pump)
• physical obstruction to circulation
• excessive vasodilation and abnormal distribution of blood flow

Question 4

what are the types of shock?

Answer 4

1. hypovolemic shock
2. cardiogenic shock
3. obstructive shock
4. distributive shock

Question 5

what is hypovolemic shock?

Answer 5

caused by loss of blood volume
- haemorrhagic
- non haemorrhagic

Question 6

what is cardiogenic shock?

Answer 6

caused by sudden severe impairment of cardiac function 2. - heart suddenly unable to pump sufficient blood to provide adequate tissue perfusion

e.g. severe heart attack (severe acute myocardial infarction)

Question 7

what is obstructive shock?

Answer 7

caused by physical obstructive to circulation either into or out of the heart
e.g. cardiac tamponade, tension pneumothorax, pulmonary embolism, severe aortic stenosis

Question 8

what is distributive shock?

Answer 8

caused by excessive vasodilation and abnormal distribution of blood flow

→neurogenic e.g. spinal cord injury

→vasoactive e.g. septic shock, anaphylactic shock

Question 9

how does hypovolemic shock lead to inadequate tissue perfusion?

Answer 9

loss of blood volume →decreased blood volume →decreased venous return →decreased end diastolic volume →decreased stroke volume →decreased cardiac output and decreased blood pressure→inadequate tissue perfusion

Question 10

how does cardiogenic shock lead to inadequate tissue perfusion?

Answer 10

sustained hypotension caused by decreased cardiac contractility

decreased cardiac contractility →decreased stroke volume →decreased stroke volume →decreased cardiac output & decreased blood pressure →inadequate tissue perfusion

Question 11

how does tension pneumothorax (type of obstructive shock) lead to inadequate tissue perfusion?

Answer 11

increased intrathoracic pressure →decreased venous return (due to affected pressure gradient) →decrease end-diastolic volume →decreased stroke volume →decreased cardiac output and decreased blood pressure →inadequate tissue perfusion

Question 12

how does neurogenic shock lead to inadequate tissue perfusion?

Answer 12

loss of sympathetic tone to blood vessels & heart →massive venous & arterial vasodilation (effects heart rate) →decreased venous return and decreases SVR and decreased heart rate →decrease cardiac output and decreased blood pressure →inadequate tissue perfusion

Question 13

What is the only type of shock that results in decreased heart rate?

Answer 13

neurogenic shock (all the others heart rate increases)

Question 14

how does vasoactive shock lead to inadequate tissue perfusion?

Answer 14

release of vasoactive mediators →massive venous & arterial vasodilation & also increased capillary permeability →decreased venous return & decreased SVR →decrease cardiac output and decreased blood pressure →inadequate tissue perfusion

Question 15

how would you treat shock?

Answer 15

• ABCDE approach
• high flow oxygen
• volume replacement (except for cardiogenic shock)
• call for help early
• inotropes for cardiogenic shock
• immediate chest drain for tension pneumothorax
• adrenaline for anaphylactic shock

Question 16

what are the causes of hypovolaemic shock?

Answer 16

haemorrhage (trauma, surgery, GI haemorrhage) →decreased blood volume →decreased CO →circulatory shock (decreased MAP)

vomiting, diarrhoea, excessive sweating →decreased ECFV (including plasma) →decreased blood volume →decreased CO →circulatory shock (decreased MAP)

Question 17

how long can compensatory mechanisms for hemorrhagic shock last?

Answer 17

compensatory mechanisms can maintain blood pressure until about 30% of blood volume lost

Question 18

what about haemorrhagic shock means small volume pulse?

Answer 18

decreased stroke volume

Question 19

what about haemorrhagic shock that means tachycardia?

Answer 19

increased heart rate via baroreceptor reflex

Question 20

what about haemorrhagic shock means cool peripheries?

Answer 20

cardiac output may be decreased and increased systemic vascular resistance via baroreceptor reflex

Question 21

what level of blood loss means decreased mean arterial blood pressure in hemorrhagic shock?

Answer 21

if >30% blood loss