S5) Circulatory Shock Flashcards
What is haemodynamic shock?
Haemodynamic shock is an acute condition of inadequate blood flow throughout the body due to a catastrophic fall in arterial blood pressure
What are the causes for the catastrophic drop in blood pressure which leads to haemodynamic shock?
loss of blood volume = not enough blood returning to the heart
Identify and define three different types of shock occurring due to a fall in cardiac output
- Cardiogenic shock (pump failure) – ventricle cannot empty properly
- Mechanical shock (obstructive) – ventricle cannot fill properly
- Hypovolaemic shock – reduced blood volume leads to poor venous return
What is cardiogenic shock?
Cardiogenic shock is the acute failure of the heart to maintain cardiac output (pump failure)
Identify 3 potential causes for cardiogenic shock
- Myocardial infarction (damage to left ventricle)
- Serious arrhythmias
- Acute worsening of heart failure
What are the consequences of cardiogenic shock?
- CVP (central venous pressure) normal/raised
- aBP (arterial blood pressure) lowered
- Tissues poorly perfused
I. Coronary arteries (exacerbates problem)
II. Kidneys (reduced urine production = dark coloured urine)
Cardiac tamponade is an example of mechanical shock.
What is this condition?
Cardiac tamponade is when blood/fluid builds up in pericardial space, restricting the filling of both sides of the heart and limiting the end diastolic volume
What are the consequences of cardiac tamponade?
- High CVP = blood is trying to get inot the heart but it cant so builds up
- Low aBP = reduction in stroke vol (heart can still contract but there is just a lower volume of blood)
- Continued electrical activity
treat by pericardio centisis (stick needle under ribs to remove fluid)
A pulmonary embolism is another example of mechanical shock.
What are the consequences of this?
- pulmonary artery is occulded
- High pulmonary artery pressure → right ventricle cannot empty
- High CVP → reduced return of blood to the left heart
- Low LAP (left atrial pressure)
- Low aBP (arterial blood pressure)
State two characteristic symptoms of mechanical shock due to PE
- Chest pain
- Dyspnoea (shortness of breath)
In four steps, explain how an embolus reaches the lungs
⇒ Deep vein thrombosis
⇒ Portion of thrombus breaks off
⇒ Embolus travels in venous system to right side of the heart
⇒ Pumped out via pulmonary artery to lungs
effect of this depends on the size
What is hypovolaemic shock?
Hypovolaemic shock is a state of shock due to reduced blood volume, most commonly due to haemorrhage
The severity of hypovolaemic shock is related to amount and speed of blood loss.
How does the shock vary with amount of blood loss?
- < 20% blood loss unlikely to cause shock
- 20-30% blood loss show some signs of shock response
- 30-40% bloow loss shows substantial decrease in mean aBP and serious shock response
Explain what happens during a haemorrhage
⇒ Venous pressure falls
⇒ Cardiac output falls (Starling’s Law)
⇒ Arterial pressure falls
detected by baroreceptors in carotid sinus and aortic arch
Describe the compensatory response observed in hypovolaemic shock
⇒ Low aBP detected by baroreceptors
⇒ Increased sympathetic stimulation
⇒ Tachycardia, increased contractlity
⇒ Peripheral vasoconstriction and venoconstriction
- long term: RAAS system and ADH
- interstitual fluid moves into the capillaries to increase blood volume, reduced hydrostatic pressure out capillary due to reduced blood pressure
How does a patient in hypovolaemic shock present?
- Tachycardia
- Weak pulse
- Pale skin
- Cold, clammy extremities
Besides haemorrhages, when else can hypovolaemic shock occur?
- Severe burns
- Severe diarrhoea / vomiting
- Severe loss of Na+
In 5 steps, explain how peripheral vasoconstriction (shutdown) impairs tissue perfusion
⇒ Tissue damage due to hypoxia
⇒ Release of chemical mediators
⇒ Vasodilation (TPR & BP falls)
⇒ Vital organs can no longer be perfused
⇒ Multi system failure
What is distributive shock?
- Distributive shock is low resistance shock (normovolaemic - no change in blood volume but vasodialation) due to profound peripheral vasodilation (decrease in TPR)
- Blood volume is constant, but volume of the circulation has increased
Identify two different types of shock due to a fall in total peripheral resistance
- Anaphylactic shock
- Septic shock
What is anaphylaxis?
Anaphylaxis is a severe allergic reaction
- release of histamine from mast cells (for defence)
- vessels dialate = drop in TPR = heart cant cope
- impared perfusion of vital organs
- hard to breath (bronchoconstriction)
In 5 steps, explain how anaphylaxis leads to a state of distributive shock
⇒ Release of histamine from mast cells
⇒ Vasodilation (fall in TPR)
⇒ Dramatic drop in arterial pressure
⇒ Increased sympathetic response can’t overcome vasodilation
⇒ Impaired perfusion of vital organs
How do patients present with anaphylactic shock?
- Dyspnoea (bronchoconstriction, laryngeal oedema)
- Collapse
- Tachycardia
- Red, warm extremities (vasodialation)
Anaphylactic shock is an acutely life threatening.
How can it be managed?
Adrenaline – vasoconstriction via action at α1 adrenoceptors
