Haemorrhage and shock

Question 1

What is haemorrhage?

Answer 1

A loss of blood.

It can be:

1) external - skin cut
2) revealed - blood in faeces (visible but difficult to quantify)
3) concealed - haemorrhagic stroke e.g. leaking aortic aneurysm

Question 2

What are some symptoms and signs of haemorrhage?

Answer 2

Depending on severity of the haemorrhage…

• constricted veins (more difficult to cannulate)
• rapid and weak pulse: tachycardia with low stroke volume - heart pumps many times per sec but only a little blood present at each beat
• reduced urine output (fluid output)
• nauseau

Question 3

Why is arterial blood pressure rescued by haemorrhage?

Answer 3

• blood vol decreases
• venous pressure and return decreases (amount of blood returning from periphery to heart)
• atrial pressure decreases
• ventricular end-diastolic volume decreases
  = can’t fill vents with as much blood
• stroke vol decreases
• cardiac output decreases
• arterial blood pressure decreases

Question 4

What do the reflex responses to haemorrhage try to achieve?

Answer 4

1) survival: sec-min (baroreceptors)

2) return to normal: hr-days
adaptations, restore blood

Question 5

What is the cardiovascular response to haemorrhage?

Answer 5

1) SV decreases
2) = CO decreases (SV x HR)
3) = mean arterial pressure decreases (CO x TPR)

Reflex responses:

1) increase in HR (= increase in CO)
2) increase in TPR (= increase in MAP)

= to help SV, CO and MAP return to normal

Question 6

What is total peripheral resistance?

Answer 6

Resistance that must be overcome to push blood through the circulatory system + create flow

Question 7

What is the arterial baroreceptor reflex and what constitutes it?

Answer 7

• aortic and carotid sinuses (or carotid artery) baroreceptors constitute the arterial baroreceptors
• are the sensors for the arterial baroreceptor reflex

= sensor the arterial blood pressure then increase or decreases sympathetic or parasympathetic stones

Question 8

What is angiotensin?

Answer 8

A powerful vasoconstrictor

Decreases excretion of salt + water by kidneys

Question 9

What is the renin-angiotensin system?

Answer 9

A decrease in BP stimulates the production of renin in kidneys

Renin contributes to the production of angiotensin

Question 10

Why is arterial blood pressure better maintained (for longer at normal levels) than CO?

Answer 10

Sympathetic reflexes have a greater vasoconstrictor effect on arterioles than on veins

Question 11

What causes arterial pressure to plateau around 50%?

Answer 11

The activation of the CNS ischaemic response, which causes profound vasoconstriction

Question 12

What amount of blood loss has no effect on CO and arterial pressure?

Answer 12

10% (similar to blood donation ~500 ml)

Question 13

What is the blood volume for men and women?

Answer 13

Women:
67 ml kg-1

Men:
77 ml kg-1

70kg man = 5,400 ml

Question 14

Why is the rate of blood loss important?

Answer 14

A very rapid loss of 30% can be fatal, but a loss of 50% over 24 hours may be survived

Question 15

What is the loss of blood for 20-50% equivalent to?

Answer 15

20% is unlikely to elicit shock

20-30% can induce shock. Blood pressure may be depressed.

30-50% causes severe shock and a profound fall in arterial pressure and CO - may become irreversible (refractory)

More than 50%: death is generally inevitable

Question 16

Define circulatory shock

Answer 16

The acute failure of the cardiovascular system to perfuse the tissues of the body adequately

Question 17

Define cardiogenic shock

Answer 17

Caused by an acute impairment of cardiac function (myocardial infarction, myocarditis; 85% mortality)

Question 18

Define septic shock

Answer 18

Caused by bacteraemia, especially endotoxin (powerful cardiovascular toxin)

Question 19

Define hypovolaemic shock

Answer 19

Caused by a fall in blood or plasma volume (diarrhoea, vomiting, dehydration, haemorrhage (most common))

Question 20

What are the stages of shock?

Answer 20

Character is of CS change with different degrees of severity.

1) non-progressive shock
2) progressive shock, reversible with therapy
3) irreversible shock, no form of therapy is adequate to save the person’s life

Guyton and Hall (2006):
Time course of arterial blood pressure in dogs after degrees of acute haemorrhage was measured.

The circulatory system can recover as long as the degree of haemorrhage is no greater than a certain critical amount.

Question 21

What is non-progressive shock?

Answer 21

Shock doesn’t progress if the sympathetic reflexes and other factors compensate enough to the loss of blood by preventing further deterioration of the circulation

Question 22

How is compensation in non-progressive shock achieved?

Answer 22

1) baroreceptor reflexes
2) CNS ischaemic response
3) formation of angiotensin in the kidneys
4) release of vasopressin by the pituitary gland
5) absorption of fluids from intestinal tract, and from interstitial spaces of he body into the blood capillaries

Question 23

What is reversible and irreversible shock?

Answer 23

Effect of 45% blood loss: progressive, reversible and irreversible shock

Reversible:

• Some responses within 30 mins can increase CO
• Have a transfusion within first hour = can return to normal relatively rapidly

Irreversible:

• CO increases but effect is transient due to organ failure, etc
• “Golden hour” has passed

Question 24

What can positive feedback lead to?

Answer 24

Progression of shock.

1) arterial pressure excessively low = coronary blood flow decreases below level required for adequate nutrition of myocardium
2) lack of nutrition = weakens heart muscle > decreases CO > decreases coronary blood flow even more
3) shock becomes more and more severe via positive feedback cycle