Circulation 3 - circulatory shock

Question 1

What is circulatory shock?

Answer 1

profound circulatory failure causing poor perfusion/ oxygenation of vital organs.

Question 2

How do you diagnose shock?

Answer 2

low blood pressure and its physiological consequences

Question 3

What is systolic pressure?

Answer 3

should be 120
pressure during systole- when the heart pumps blood around the body

Question 4

What is diastolic pressure?

Answer 4

should be 80
so the pressure when heart is at rest in arteries around body

Question 5

What does normal blood pressure rely on?

Answer 5

-enough blood in system (5L in adult)
-smooth muscle in vessels having a certain ‘tone’
-heart pumping blood

Question 6

What will happen if tone is decreased in muscle cells?

Answer 6

vessels will dilate and blood can pool (usually peripherally) which results in a reduction in blood pressure.

Question 7

How does body detect blood pressure and oxygen?

Answer 7

bifurcation- (splitting of artery into internal and external carotid arteries) of the carotid arteries.

At the bifurcation, you’ve got the carotid body and carotid sinus on each side. 2 carotid bodies and 2 carotid sinuses on either side of the neck.

Question 8

What is the function of the carotid bodies?

Answer 8

they are to do with detecting partial pressure of oxygen and carbon dioxide in blood.

Question 9

What is function of the carotid sinuses?

Answer 9

respond to changes in blood pressure

Question 10

Describe how carotid sinuses act to change in blood pressure?

Answer 10

if blood pressure drops- the carotid sinuses respond by nerve signals to the brain stem.

Question 11

How does brain stem react to reduction in blood pressure?

Answer 11

the brain stem, in turn, tells the heart to pump harder and faster, via nerve signals.

Part of sympathetic NS-> part of the overall autonomic nervous system

Question 12

What is the physiological response to low blood pressure?

Answer 12

faster pulse/ heart rate

Question 13

What else does brainstem do to keep the person alive?

Answer 13

sympathetic nervous system stimulation causes->

-increased vascular tone in vessels , limbs and abdomen -> increasing systemic vascular resistance and directing blood to major organs (chest and head) as more pressure in less important

-adrenal glands secrete adrenaline-> heart pumps even harder and faster

Question 14

In practice, circulatory shock is present if:

Answer 14

Low blood pressure (60/40) combined with fast pulse (e.g. >100)

hypotension and tachycardia

Question 15

What are the 3 main causes of circulatory shock?

Answer 15

1. Hypovolaemic/ Haemorrhagic

2.Septic

3. Cardiogenic
4. other (anaphylactic, neurogenic, obstructive)

Question 16

Describe hypovolaemic shock?

Answer 16

-rib penetrates spleen and causes major bleed into abdominal cavity

-systemic (arterial) blood pressure normal for a small period of time

-as blood flows out of damaged spleen less blood is present in other vessels

-vessels collapse as they have no blood in them

• eventually less blood in inferior vena cava which also collapses (no blood can be pumped to the lungs or around body)

-venous pressure falls to 0 and very little blood goes to lungs, brain and rest of body

-systemic blood pressure drops and carotid sinuses recognise that and start sending signals via sympathetic NS up to brain stem and to heart

Question 17

Circulatory shock symptoms?

Answer 17

Patient feeling ill
rapid breathing
fast heartbeat
pale, sweaty skin

Question 18

Dealing with hypovolaemic shock in hospital?

Answer 18

Tender abdomen
Blood pressure 60/40, pulse 120 = Shock
Diagnosis of abdominal trauma with hypovolaemic (or haemorrhagic) shock.
Transfused blood to restore blood volume. Operation to remove spleen

Question 19

What is cardiac output
and what is it dependent on?

Answer 19

amount of blood coming out of heart per minute

-depends on heart rate and stroke volume

Question 20

What is stroke volume and what is it dependent on?

Answer 20

how much blood is being ejected from the heart per beat of the heart

affected by preload (amount of blood in your ventricles during diastolic filling)
, afterload (how much blood is left in ventricles after systole - contracted and pumped as much blood as it can out), contractility (ability of heart to effectively pump blood out of it)

Question 21

What two things determine blood pressure?

Answer 21

peripheral vascular resistance and cardiac output

Question 22

What do you have a major reduction of in hypovolemic shock?

Answer 22

reduction in preload as less blood in circulation.
Reduces the amount of blood being returned to heart by inferior vena cava -which then reduces amount of blood available at end of diastole to be ejected from heart so preload of heart goes down.

AND as preload goes down, stroke volume may go down.

Heart rate will stay constant so will have reduction in cardiac output and this will lower peripheral vascular resistance and hence you become hypotensive in face of a reduced circulatory vol and preload.

Question 23

Describe cardiogenic shock?

Answer 23

not due to blood loss- so venous pressure is normal or even increased

hypotension and tachycardia

no changes to preload
but because heart not pumping effectively we have changes in afterload and contractility
leads to reduction in stroke volume …

Question 24

Describe systemic generalised vasodilatation?

Answer 24

bacteria can have effect on the endothelial cells in the vessels themselves to secrete more nitric oxide.
This causes blood vessels to reduce their tone in smooth muscles and dilate.
The production of lactic acid in septicaemia can reduce tone in vessels causing general vasodilation.
Get increased blood flow and pooling of blood.

Question 25

Describe septic shock?

Answer 25

not enough blood gets back to the heart
-reduction in filling pressure and venous pressure
-now not enough blood can go to brain and rest of body

IN SEVERE SEPTIC SHOCK
Muscle of heart, just like muscle in vessels, also looses it’s tone – may then get slow heart = bradycardia

Question 26

What are complications of shock?

Answer 26

Brain injury (ischaemic infarction of brain tissue)

Decreased perfusion of kidneys -> initially reversible, then more severe (ischaemic necrosis of renal tubules)
-reduced urine output, reduced excretion of toxic substances

Others (many)