Haemodynamic shock

Question 1

Equation for (MAP) mean arterial blood pressure?

Answer 1

MAP = CO x TPR

Question 2

Average SV?

Answer 2

70ml

Question 3

What is pulse pressure and why is it important?
What are the units?
Normal range?

Answer 3

• Difference between systolic and diastolic blood pressure.
• Independant indicator of heart function

mmHg (milimeters mercury)

30-50mmHg

Question 4

Patient has a blood pressure of 120/80mmHg.

What is their pulse pressure?

Answer 4

120- 80 = 40mmHg

Question 5

How can you calculate MAP using a blood pressure reading? E.g. 120/80mmHg

Answer 5

MAP= CO x TPR
MAP = diastolic pressure + 1/3 pulse pressure

Question 6

What causes haemodynamic shock?

Answer 6

Catastrophic fall in mean arterial blood pressure which can lead to multi-organ failure due to poor perfusion.
Note; MAP is determined by CO and TPR, so a fall in either of these will cause arterial pressure to fall

Question 7

All types of haemodynamic shock cause MAP to fall. Which types do this by reduction in;

• CO?
• TPR?

Answer 7

Reduced CO;

• Hypovolaemic shock
• Mechanical shock (reduced filling)
• Cardiogenic shock

Reduced TPR;
- Septic shock
- Anaphylactic shock
(Both are excessive peripheral vasodilation under the umbrella term; Distributive shock/ normovolaemic shock)

Question 8

What is distributive shock?

Also known as?

Answer 8

Shock (catastrophic fall in MAP) due to reduced TPR

Normovolaemic shock

Question 9

What happens to blood volume in a normovolaemic shock?

Answer 9

Blood volume is constant, but profound peripheral vasodilation causes the volume of blood in circulation to increase

Question 10

Why does vasodilation occur in sepsis?

Answer 10

Bacteria release endotoxins which stimulates an excessive inflammatory response leading to excessive vasodilation

(Note; vasodilation usually facilitates delivery of blood cells to the site of injury)

Question 11

Excluding vasodilation (fall in TPR) how else does sepsis cause a reduction in MAP?

Answer 11

Leaky capillaries cause loss of blood volume into the tissues. Venous return reduces so SV and CO.
(CO = HR x SV).
MAP = CO x TPR

Question 12

Explain the heart rate and extremities of a person with distributive shock?

Answer 12

• Tachycardia because baroreceptors activate SNS in response to the arterial pressure falling. SNS increases HR and contractility
• Red, warm skin due to fall in TPR caused by profound peripheral vasodilation (increased peripheral perfusion)

Question 13

Where are the baroreceptors located?

Answer 13

Carotid sinus and aortic arch

Question 14

What is the major inflammatory mediator in anaphylaxis?

What do the mediators cause?

Answer 14

Histamine

Bronchoconstriction
Vasodilation

Question 15

When does histamine produce a drop in MAP?

How is it released?

Answer 15

Anaphylactic shock

IgE inappropriately binds the foreign antigen. The complex activates the high affinity IgE receptor on mast cells and basophils causing release of histamine