Circulation 3- Circulatory shock

Question 1

What is shock?

Answer 1

Profound circulatory failure causing poor perfusion of vital organs.
Shock= low blood pressure and its physiological consequences.

Question 2

Characterisitcs of shock

Answer 2

low blood pressure (60/40) combined with fast pulse (100)

Question 3

What does normal blood pressure rely on?

Answer 3

• Enough blood in the system (about 5 litres in an adult)
• Smooth muscles in vessels having a certain “tone”
• Heart pumping blood

Question 4

What happens when there is a problem with “enough blood in the system”

Answer 4

No blood in the vessel causes it to collapse and blood pressure becomes low and then becomes unrecordable

Question 5

What happens when there is a problem with “Smooth muscles in vessels having a certain “tone” “

Answer 5

If smooth muscle tone is decreased, then the vessel will dilate. If enough blood vessels are affected then blood pressure may fall.

Question 6

What happens when there is a problem with “Heart pumping blood”

Answer 6

If heart does not pump enough blood, then blood pressure will fall

Question 7

How does the body detect blood flow/blood pressure/oxygen?

Answer 7

• The main “detector system” is carotid bodies.
• Runs along both sides of the neck.
• Bifurcation (splitting) of artery into internal and external carotid arteries.

Question 8

What do the 2 carotid bodies consists of?

Answer 8

• Groups of cells which sense the blood flowing past them

Question 9

What do the 2 carotid bodies respond to more specifically?

Answer 9

The partial pressure of oxygen

Question 10

What happens if the blood pressure drops?

Answer 10

Reduces the partial pressure of oxygen

Question 11

How does the carotid body respond?

Answer 11

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

Question 12

What happens if the heart pumps faster?

Answer 12

Pulse is faster.

Question 13

What is the physiological response to low blood pressure?

Answer 13

Faster (heart rate) pulse

Question 14

What else does the brainstem do to keep you alive?

Answer 14

• Sweaty
• Sympathetic nervous system stimulation which causes increased vascular tone in vessels in limbs and abdomen. The blood is pushed up to chest and head.
• Results in circulation of remaining blood around heart, lungs and brain and keeps the vital organs alive.
• Adrenal glands secrete adrenaline and heart pumps even harder and faster

Question 15

What are the 3 main causes of circulatory shock?

Answer 15

• Hypovolaemic- main one.
• Septic (infectious shock)
• Cardiogenic

Question 16

What does hypovolaemic shock mean?

Answer 16

low volume of blood related shock.

Question 17

Example of hypovolaemic shock

Answer 17

man Hit by car. Fractured left rib goes through spleen.

Spleen ruptures with loss of 3 litres (of his 5 litre blood volume) into abdominal cavity. Abdominal pain.

• Rib penetrates spleen and causes major bleed (bleed = haemorrhage)
• Systemic (arterial) blood pressure normal for a small period of time but then…
• As blood flows out of damaged spleen, less blood is present in other vessels so the vessels collapse as they have no blood in them.
• Eventually there is less blood in inferior vena cava which also collapses.
• If inferior vena cava has no blood in it then venous pressure falls to virtually zero.
• Now almost no blood enters the right side of the heart
• Now very little blood goes through the lungs
• Now very little blood goes to brain and the rest of the body
• Systemic blood pressure now drops

Question 18

How does the body respond to this example?

Answer 18

• Carotid bodies sense lower partial pressure of oxygen
• Carotid bodies upregulate the sympathetic nervous system. This is shown by various signs (in addition to low blood pressure) i.e. :
• Patient usually feels very ill
• Rapid breathing
• Fast heartbeat (fast pulse, but may be weak)
• Pale, sweaty skin

Question 19

What does hypovolaemic shock reflect?

Answer 19

• Severe reduction in amount of blood in circulation.
• Nothing wrong with the heart- it can pump really well but not enough blood in the system
• High pulse reflects the physiological response to low blood pressure that is mediated by carotid bodies.

Question 20

2. Sepsis shock example

Answer 20

30 year old woman gets urinary tract infection which then causes kidney infection then bacteria go into blood (= septicaemia, infection in blood). Eventually molecules released cause generalised vasodilatation

• Vasodilation is general and results in pooling of blood in veins (of for instance legs)
• All blood volume in legs but not enough in heart, lungs, brain, and rest of body.
• Venous pressure and filling are low.
• Complicaitons of shock:
  o Decreaed perfusion of brain – initially is reversible but then becomes permanent
  o Decreased perfusion of kidneys- initially reversible but then becomes more severe
  o Brain injury (ischaemic infarction of brain tissue)
  o Renal injury (ischaemic necrosis of renal tubules)

Question 21

3. Cardiogenic shock example

Answer 21

70 year old man with heart disease. Heart starts failing and eventually can no longer pump enough blood to maintain blood pressure

• Blood pressure falls, pulse rate goes up
• Diagnosis= cardiogenic shock (doesn’t occur due to blood loss; venous pressure is normal or even increased)
• Treatment= drugs to increase heart function