21. Haemodynamic Shock

Question 1

What is the equation for mean arterial BP?

Answer 1

CO x TPR

OR

Diastolic pressure + 1/3 pulse pressure

Question 2

What is the equation for cardiac output?

Answer 2

SV x HR

Question 3

What is haemodynamic shock?

Answer 3

Acute condition of inadequate blood flow throughout the body

A catastrophic fall in arterial blood pressure leads to circulatory shock

Question 4

What can haemodynamic shock be due to?

Answer 4

Fall in CO
Fall in TPR beyond capacity of the heart to cope

Mean arterial BP = CO x TPR

Question 5

How can a fall in cardiac output occur?

Answer 5

Mechanical - pump cannot fill
Pump failure
Loss of blood volume

Question 6

How can a fall in peripheral resistance occur?

Answer 6

Excessive vasodilation

Leads to redistribution of blood and an increased volume of the circulatory system

Question 7

What are the different shocks due to a fall in cardiac output?

Answer 7

Cardiogenic shock - ventricles cannot empty properly
Mechanical shock - ventricle cannot fill properly
Hypovolaemic shock - reduced blood volume leads to poor venous return

Question 8

What is cardiogenic shock?

Answer 8

Acute failure of the heart to maintain cardiac output

Question 9

What are the potential causes of cardiogenic shock?

Answer 9

Following myocardial infarction - damage to LV
Due to serious arrhythmias
Acute worsening of heart failure

Question 10

Which arrhythmias can lead to cardiogenic shock?

Answer 10

Heart block as causes bradycardia
Tachycardia as not enough time for ventricle filling
Ventricle fibrillation

Question 11

How can cardiogenic shock cause an increased central venous pressure?

Answer 11

Blood not being pumped out of the heart effectively, end systolic volume high, systolic pressure high, harder to fill the heart, therefore increased venous pressure

Question 12

Which tissues may be poorly perfused in cardiogenic shock?

Answer 12

Coronary arteries - exacerbates problem

Kidneys - reduced urine production (oliguria)

Question 13

When may a ventricular fibrillation cardiac arrest occur?

Answer 13

Often following MI or electrolyte imbalance or some arrhythmias (long QT and torsades de pointes)

Question 14

What advanced life support is given in a cardiac arrest?

Answer 14

Defibrillation

• electric current delivered to the heart
• depolarised all the cells and puts them into refractory period
• allows coordinated electrical activity to restart

Question 15

Why is adrenaline given in cardiac arrest?

Answer 15

Enhances myocardial function

Increases peripheral resistance

Question 16

Give 2 examples of mechanical shock?

Answer 16

Cardiac tamponade

Massive pulmonary embolism

Question 17

What is cardiac tamponade?

Answer 17

Blood or fluid build up in pericardial space
Restricts filling of the heart - limits end diastolic volume
Affects left and right sides of the heart

Question 18

How does cardiac tamponade change blood pressure?

Answer 18

High central venous pressure as heart cannot fill properly so systolic pressure increases, harder to fill the heart so venous pressure increases

Low arterial pressure as stroke volume is decreased so cardiac output is deceased, so blood pressure is decreased

Question 19

What effect does a massive pulmonary embolism have on the blood pressure?

Answer 19

Embolus occludes a large pulmonary artery
So pulmonary artery pressure is high 
So right ventricle cannot empty
Leads to high central venous pressure
Leads to reduced return of blood to left heart from lungs
Limits filling of left heart
Left arterial pressure is low
Arterial blood pressure is low
Leads to mechanical shock

Question 20

How might an embolus reach the lungs?

Answer 20

Typically due to deep vein thrombosis
Portion of thrombus breaks off
Travels in venous system to right side of heart
Pumped out via pulmonary artery to lungs
Effect of this will depend on the size of embolus

Question 21

What is hypovalaemic shock?

Answer 21

Reduced blood volume

Most commonly due to haemorrhage

Question 22

How much blood is lost to give hypovalaemic shock?

Answer 22

20-30% some signs of shock response
30-40% substantial decrease in mean aBP and senior shock response

Severity of shock is related to amount and speed of blood loss

Question 23

What happens during haemorrhage?

Answer 23

Venous pressure falls therefore cardiac output falls (starlings law)
Arterial pressure falls
Drop in BP detected by baroreceptors

Question 24

What is the compensatory response to haemorrhage and hypovalaemic shock?

Answer 24

Increased sympathetic stimulation
Tachycardia
Increased force of contraction
Peripheral vasoconstriction
Venoconstriction - increase TPR to increase BP

Question 25

What happens in the capillaries in hypovalaemic shock?

Answer 25

Increased peripheral resistance reduces the capillary hydrostatic pressure Net movement of fluid into capillaries to try to increase the blood pressure

Question 26

What does a patient with hypovalaemic shock present with?

Answer 26

``` Tachycardia Weak pulse Pale skin Cold, clammy extremities Low central venous pressure ```

Question 27

What else can cause hypovalaemic shock?

Answer 27

Severe burns | Severe diarrhoea or vomiting and loss of Na+

Question 28

What is the danger in hypovalaemic shock and how does this happen?

Answer 28

Danger of decompensationn Peripheral vasoconstriction impairs tissue perfusion Tissue damage due to hypoxia Release of chemical mediators - build up of vasodilators which overcome sympathetic NS ability for vasoconstriction Leads to peripheral vasodilation, BP falls, vital organs no longer perfused, multi system failure

Question 29

What are the long term responses to restore blood volume?

Answer 29

Renin-angiotensin-aldosterone system - promote water and Na+ reabsorption in kidneys Anti-diuretic hormone - promote retention of fluid at kidney Takes about 3 days if salt and water intake are adequate

Question 30

What types of cardiac arrest can you get?

Answer 30

Asystole - loss of mechanical and electrical activity Pulseless electrical activity Ventricular fibrillation

Question 31

What is distributive shock?

Answer 31

Low resistance shock (normovolaemic) | Profound peripheral vasodilation - decreased TPR

Question 32

Give 2 examples of distributive shock

Answer 32

Toxic shock | Anaphylactic shock

Question 33

What are the processes in toxic septic shock in relation to the circulatory system?

Answer 33

Endotoxins released by circulating bacteria Profound inflammatory response Causes profound vasodilation Dramatic fall in TPR Fall in arterial pressure Impaired perfusion of vital organs Capillaries become leaky, reduced blood volume Increased coagulation and localised hypo-perfusion

Question 34

What is the body’s response to decreased arterial pressure in septic shock?

Answer 34

Detected by baroreceptors - increased sympathetic output Vasoconstrictor effect overridden by mediators of vasodilation Heart rate and stroke volume increased

Question 35

What can a patient present with if they have septic shock?

Answer 35

Tachycardia | Warm, red extremities initially but later takes of sepsis, vasoconstriction, localised hypo-perfusion

Question 36

What happens in anaphylactic shock?

Answer 36

Severe allergic reaction Release of histamine from mast cells Powerful vasodilator effect - fall in TPR Dramatic drop in arterial pressure - increased sympathetic response, increased cardiac output Impaired perfusion of vital organs Mediators also cause bronchoconstriction and laryngeal oedema

Question 37

What signs will a patient with anayphylactic shock?

Answer 37

Difficulty breathing Collapsed Rapid heart rate Red, warm extremities

Question 38

Why is adrenaline given in anaphylactic shock?

Answer 38

Vasoconstriction via action at alpha 1 adrenoceptors