Haemodynamic Shock

Question 1

What is the equation for mean arterial blood pressure ?

Answer 1

Cardiac output x total peripheral resistance

Question 2

Define haemodynamic shock

Answer 2

An acute condition of inadequate blood flow throughout the body which is caused by a catastrophic fall in arterial blood pressure.

Question 3

What are the two causes of haemodynamic shock ?

Answer 3

1. Fall in cardiac output
2. Fall in peripheral resistance

Mean arterial BP = CO x TPR

Question 4

What are the three types of shock due to a reduction in cardiac output ?

Answer 4

1. Cardio genie shock
2. Mechanical shock
3. Hypovolaemic shock

Question 5

What is carcinogenic shock ? And what are the possible causes of carcinogenic shock

Answer 5

A carcinogenic shock is acute failure of the heart to maintain cardiac output ( pump failure )

This can be caused by :

1. After MI which damages left ventrickle
2. Due to serious arrhythmias eg heart block
3. Acute worsening of heart failure

Question 6

What are the consequences of cardiogenic shock ?

Answer 6

The heart continues to fill normally , but the heart fails to pump the blood out of the heart.

This leads to a reduction in stroke volume , therefore reduction in cardiac output. Which leads to a dramatic drop is arterial BP. This leads to tissues being poorly perfumed incl the coronary arteries. Kidneys may also become poorly perfumed which reduced urine production ( oliguria ).

Central venous pressure may be normal or raised.

Question 7

Why in cardiogenic shock , may the central venous pressure be raised sometimes ?

Answer 7

The heart can not pump the blood then fills the heart. Therefore end systolic pressure increases in the heart. Therefore , this becomes difficult for blood from veins ( Vena cava , pulmonary veins ) to fill the heart with blood.

Question 8

What is mechanical shock ? And what are the two possible causes of mechanical shock

Answer 8

Mechanical shock is where the ventricular cannot fill properly.

Two possible causes for this : Cardiac tamponade and pulmonary embolism

Question 9

What is Cardiac tamponade ? And why does it result in mechanical shock ?

Answer 9

Cardiac tamponade is where there is an accumulation of blood or fluid in the pericardial space ( the space between the parietal serosa and visceral serosa). This increases pressure on the heart and compresses it because heart cannot relax and fill properly.This restricts filling of the heart - thus limits end diastolic volume. Affects BOTH sides of the heart.

This results in low arterial blood pressure because stroke volume has been reduced and so cardiac output has also been reduced.

There is a high central venous pressure because the blood that doesn’t enter the heart will remain in the veins. Bulging jugular veins then.

Also because the heart attempts to beat due to continued electrical activity there is tachycardia

Question 10

What is a pulmonary embolism ? And why does it lead to mechanical shock ?

Answer 10

• occlusion of a pulmonary artery in the lungs typically due to deep vein thrombosis. Where a portion of the thrombus breaks off and travels in venous system to right side of the heart - where it is then pumped out via pulmonary artery to lungs.
• this leads to mechanical shock because the right ventricle cannot empty its blood due to the occlusion of the pulmonary artery. Therefore end systolic pressure is very high in right ventricle. This leads to high central venous pressure because if there is a high systolic pressure in right side of the heart , the veins will find it difficult to empty their blood.
• there would be a reduced return of blood the left heart because if blood isn’t being pumped out of the right side , then less will enter the left side. Therefore stroke volume reduced and cardiac output reduced

Question 11

Compare the atrial pressures in mechanical shock caused by a pulmonary embolism in right and left side of the heart

Answer 11

Left atrial pressure is low because there is reduced return of blood to the heart.

Right atrial pressure is high because the pulmonary artery cannot empty the blood due to an occlusion,

Question 12

What is the pressure in pulmonary artery during mechanical shock caused by pulmonary embolism ?

Answer 12

High

Question 13

What is hypovolaemic shock ?

Answer 13

Reduced blood volume

<20% blood loss unlikely to cause shock
20-30% blood loss some signs of shock
30-40% leads to substantial decrease in mean arterial BP and serious shock response.

Question 14

What is the most likely cause of hypovolaemic shock ? And how does this cause hypovolaemic shock

Answer 14

Haemorrage - this causes a considerable amount of blood loss. This means that venous pressure falls because there’s less blood in the system)

• arterial pressure falls because there will be reduced venous return to the heart and so reduced SV and CO.

Starlings law states as venous pressure increases , stroke volume would also increase.

Question 15

What are other uncommon causes of hypovolaemic shock ?

Answer 15

Severe burns ( dehydration )

Severe diarrhoea + vomiting and loss of Na+

Question 16

How does the body cope with hypovolaemic shock ?

Answer 16

Compensatory response - this results increased sympathetic stimulation. This Is detected by baroreceptors. This results in tachycardia , increased force of contraction ( SV increases ) , peirpheral vasoconstriction and venoconstriction ( increases TPR )

Therefore the patient will present with tachycardia , weak pulse , pale skin and cold clammy extremities ( due to vasoconstriction which limits blood flow to the periphery). Low CVP.

Question 17

Why is. There net movement of fluid into capillaries instead of tissues in hypovolaemic shock

Answer 17

Due to the increased peripheral resistance (due to vasoconstriction) there would be reduced hydrostatic pressure in capillaries.

Question 18

What is a severe danger of hypovolaemia ?

Answer 18

Danger of decompensation ( compensatory responses shut down). Therefore vasoconstriction shuts down.

This impairs tissue perfusion - Leads to tissue damage due to hypoxia. Vital organs can no longer be perfused. There is a massive release of chemical mediators which causes vasodilation which causes blood pressure to fall dramatically.

Leads to multi system organ failure.Q

Question 19

What are long term responses to restore blood volume in hypovolaemia?

Answer 19

RAAS

Question 20

What is distributive shock ? And what are two examples of distributive shock ?

Answer 20

This is where there is profound peripheral vasodilation which causes a massive reduction in total peripheral resistance. ( blood volume is constant but volume of the circulation has increased)

Two examples are :

Toxic shock
Anaphylactic shock

Question 21

What is toxic shock ?

Answer 21

An example of distributive shock.

The cause is sepsis which is a serious life threatening response to infection. This is where endotoxins released by bacteria cause profound inflammatory response causing profound vasodilation. This cases dramatic fall in TPR. This causes a fall in arterial blood pressure. This leads to impaired perfusion of viral organs.

This also increases coagulation.

Capillaries also become leaky which reduced blood volume.

Question 22

How does a patient deal with sepsis shock ? And what will they present with clinically

Answer 22

They will have persistent hypotension requiring treatment to maintain blood pressure.

This decreased arterial pressure is detected by baroreceptors which increases sympathetic output ( vasoconstriction effect overridden however by vasodilation - hence why the patient presents with warm , red extremities initially but later stages of sepsis they will not.

Heart rate and stroke volume also increased in an attempt to maintain arterial blood pressure.

Question 23

What is anaphylactic shock ?

Answer 23

An example of distributive shock.

This is a severe allergic reaction caused by the release of histamine from mast cells. This has a powerful vasodilator effect which causes a fall in total peripheral resistance. This then causes a dramatic fall in arterial pressure.

This results in an increased sympathetic response detected by baroreceptors - this leads to increased cardiac output, however this can not overcome vasodilation hence why patient will present with red , warm extremities. They will also have a a rapid heart rate due to sympathetic response. They will have difficulty breathing due to bronchoconstriction caused by some mediators.

There will also be impaired perfusion of vital organs due to vasodilation this can lead to collapsing.

Question 24

How to treat someone with an anaphylactic shock ?

Answer 24

Adrenaline which would cause vasoconstriction via action of a1 adrenoreceptors.

Often given in a form of EpiPen.

Question 25

What is cardiac arrest and possible. Caused ?

Answer 25

Heart has stopped or ceased to pump effectively.

This can be due to asystole due to loss electrical and mechanical activity. Or it could be due to ventricular fibrillation ( uncoordinated electrical activity) - this is the most common form of cardiac arrest often following MI or electrolyte imbalance or some arrhythmias.

Question 26

How to treat cardiac arrest ?

Answer 26

1. Basic life support : cheats compression and external ventilation
2. Advanced life support : defibrillation which depolarises the whole heart. This is where the electrical current is delivered to the heart and depolarises all cells ( puts them in the refractory period) and allows coordinated electrical activity to restart.
3. Adrenaline : enhances myocardial function and increases peripheral resistance.