Cardiovascular Responses to Shock

Question 1

define shock

Answer 1

an abnormality of the circulatory system resulting in inadequate tissue perfusion and oxygenation

Question 2

outline the physiology of shock

Answer 2

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

adequate tissue perfusion depends on adequate blood pressure and adequate cardiac output

Question 3

describe hypovolaemic shock - haemorrhagic

Answer 3

haemorrhagic - trauma, surgery, GI haemorrhage
non-haemorrhagic - vomiting, diarrheoa, excessive sweating

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 4

describe cardiogenic shock

Answer 4

sustained hypotension caused by decreased cardiac contractility
e.g. acute MI

decreased cardiac contractility
decreased stroke volume
decreased cardiac output and decreased blood pressure
inadequate tissue perfusion

frank-starling law shifted to right, much shorter and lower (PP)

Question 5

describe obstructive shock

Answer 5

increased intra-thoracic pressure
decreased venous return
decreased end diastolic volume
decreased stroke volume
decreased cardiac output and decreased blood pressure
inadequate tissue perfusion
e.g. cardiac temponade, tension pneumothorax, PE, severe aortic stenosis

Question 6

describe distributive shock - neurogenic

Answer 6

loss of sympathetic tone to blood vessels and heart
massive venous and arterial vasodilation, effect on heart rate
decreased venous return and decreased systolic venous resistance, decreased heart rate (unlike other types of shock)
decreased cardiac output and decreased blood pressure
inadequate tissue perfusion
e.g. spinal cord injury

Question 7

describe distributive shock - vasocactive

Answer 7

release of vasoactive mediators
massive venous and arterial vasodilation- also increased capillary permeability
decreased venous return and decreased systolic venous resistance
deceased cardiac output and decreased blood pressure
inadequate tissue perfusion
e.g. septic shock, anaphylactic shock

Question 8

outline the management of shock

Answer 8

ABCDE approach
high flow oxygen
volume replacement (except for cariogenic shock)
call for help early

inotropes for cardiogenic shock
immediate chest drain for tension pneumothorax
adrenaline for anaphylactic shock
vasopressors for septic shock

Question 9

describe the cardiovascular responses to hypovolaemic shock

Answer 9

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

decreased MAP >30% blood loss
increased systemic vascular resistance via baroreceptor reflex
cardiac output may be decreased => increased heart rate via baroreceptor reflex (tachycardia) and decreased stroke volume (small volume pulse)