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CVS > 21. Haemodynamic Shock > Flashcards

21. Haemodynamic Shock Flashcards

1
Q

What is the equation for mean arterial BP?

A

CO x TPR

OR

Diastolic pressure + 1/3 pulse pressure

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2
Q

What is the equation for cardiac output?

A

SV x HR

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3
Q

What is haemodynamic shock?

A

Acute condition of inadequate blood flow throughout the body

A catastrophic fall in arterial blood pressure leads to circulatory shock

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4
Q

What can haemodynamic shock be due to?

A

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

Mean arterial BP = CO x TPR

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5
Q

How can a fall in cardiac output occur?

A

Mechanical - pump cannot fill
Pump failure
Loss of blood volume

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6
Q

How can a fall in peripheral resistance occur?

A

Excessive vasodilation

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

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7
Q

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

A

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

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8
Q

What is cardiogenic shock?

A

Acute failure of the heart to maintain cardiac output

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9
Q

What are the potential causes of cardiogenic shock?

A

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

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10
Q

Which arrhythmias can lead to cardiogenic shock?

A

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

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11
Q

How can cardiogenic shock cause an increased central venous pressure?

A

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

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12
Q

Which tissues may be poorly perfused in cardiogenic shock?

A

Coronary arteries - exacerbates problem

Kidneys - reduced urine production (oliguria)

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13
Q

When may a ventricular fibrillation cardiac arrest occur?

A

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

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14
Q

What advanced life support is given in a cardiac arrest?

A

Defibrillation

  • electric current delivered to the heart
  • depolarised all the cells and puts them into refractory period
  • allows coordinated electrical activity to restart
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15
Q

Why is adrenaline given in cardiac arrest?

A

Enhances myocardial function

Increases peripheral resistance

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16
Q

Give 2 examples of mechanical shock?

A

Cardiac tamponade

Massive pulmonary embolism

17
Q

What is cardiac tamponade?

A

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

18
Q

How does cardiac tamponade change blood pressure?

A

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

19
Q

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

A 
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
20
Q

How might an embolus reach the lungs?

A

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

21
Q

What is hypovalaemic shock?

A

Reduced blood volume

Most commonly due to haemorrhage

22
Q

How much blood is lost to give hypovalaemic shock?

A

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

23
Q

What happens during haemorrhage?

A

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

24
Q

What is the compensatory response to haemorrhage and hypovalaemic shock?

A 
Increased sympathetic stimulation
Tachycardia
Increased force of contraction
Peripheral vasoconstriction
Venoconstriction - increase TPR to increase BP
25
Q

What happens in the capillaries in hypovalaemic shock?

A

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

26
Q

What does a patient with hypovalaemic shock present with?

A 
Tachycardia
Weak pulse
Pale skin
Cold, clammy extremities
Low central venous pressure
27
Q

What else can cause hypovalaemic shock?

A

Severe burns

Severe diarrhoea or vomiting and loss of Na+

28
Q

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

A

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

29
Q

What are the long term responses to restore blood volume?

A

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

30
Q

What types of cardiac arrest can you get?

A

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

31
Q

What is distributive shock?

A

Low resistance shock (normovolaemic)

Profound peripheral vasodilation - decreased TPR

32
Q

Give 2 examples of distributive shock

A

Toxic shock

Anaphylactic shock

33
Q

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

A

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

34
Q

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

A

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

35
Q

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

A

Tachycardia

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

36
Q

What happens in anaphylactic shock?

A

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

37
Q

What signs will a patient with anayphylactic shock?

A

Difficulty breathing
Collapsed
Rapid heart rate
Red, warm extremities

38
Q

Why is adrenaline given in anaphylactic shock?

A

Vasoconstriction via action at alpha 1 adrenoceptors

CVS (21 decks)

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