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?
Identify and define three different types of shock occurring due to a fall in cardiac output
- Cardiogenic shock – ventricle cannot empty properly
- Mechanical shock – 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 normal/raised
- aBP lowered
- Tissues poorly perfused
I. Coronary arteries (exacerbates problem)
II. Kidneys (reduced urine production)
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
- Low aBP
- Continued electrical activity
A pulmonary embolism is another example of mechanical shock.
What are the consequences of this?
- High pulmonary artery pressure → right ventricle cannot empty
- High CVP → reduced return of blood to the left heart
- Low LAP
- Low aBP
State two characteristic symptoms of mechanical shock due to PE
- Chest pain
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
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
Describe the compensatory response observed in hypovolaemic shock
⇒ Low aBP detected by baroreceptors
⇒ Increased sympathetic stimulation
⇒ Tachycardia, increased contractlity
⇒ Peripheral vasoconstriction and venoconstriction
How does a patient in hypovolaemic shock present?
- 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) 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
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)
- Red, warm extremities
Anaphylactic shock is an acutely life threatening.
How can it be managed?
Adrenaline – vasoconstriction via action at α1 adrenoceptors
What is sepsis?
Sepsis is a serious life-threatening response to infection, can lead to septic shock
What is septic shock?
Septic shock is persisting hypotension requiring treatment to maintain blood pressure despite fluid resuscitation
In 5 steps explain how sepsis leads to a state of distributive shock (septic shock)
⇒ Endotoxins released by circulating bacteria
⇒Profound inflammatory response
⇒ Vasodilation (& increased permeability)
⇒ Dramatic fall in TPR & aBP
⇒ Impaired perfusion of vital organs
How do patients present with septic shock?
- Warm, red extremities initially
- Vasoconstriction (later on)
When would one start to consider cardiac arrest?
- Unresponsiveness associated with lack of pulse
- Heart has stopped or has ceased to pump effectively
Identify and describe the three forms of cardiac arrest
- Asystole – loss of electrical and mechanical activity
- Pulseless Electrical Activity
- Ventricular fibrillation – uncoordinated electrical activity
How does one manage cardiac arrest?
- Basic life support – chest compression and external ventilation
- Advanced life support – defibrillation
- Adrenaline – enhances myocardial function and increases TPR
Describe the impact of defibrillation on the heart in advanced life support
⇒ Electric current delivered to the heart
⇒ Depolarises all the cells – puts them into refractory period
⇒ Allows coordinated electrical activity to restart