Haemodynanic Shock Flashcards
What is Haemodynamic shock?
• Acute condition of inadequate blood flow throughout the body
• A catastrophic fall in arterial blood pressure leads to
circulatory shock
- Mean arterial BP = CO x TPR
- Shock can be due to fall in CO
- Or fall in TPR beyond capacity of the heart to cope
Shock can be divided into a fall in cardiac output and a fall in peripheral resistance. What is the result of this?
Fall in CO:
- Causes mechanical problems where the pump cannot fill
- Pump failure
- Loss of blood volume
Fall in peripheral resistance:
- Excessive vasodilation
What are the different types of shock that are 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?
Acute failure of the heart to maintain cardiac output - pump failure
Potential causes:
• following myocardial infarction
– damage to left ventricle
- due to serious arrhythmias - Tachycardia and bradycardia
- acute worsening of heart failure
What happens in cardiogenic shock?
- Heart fills, but fails to pump effectively
- Central venous pressure (CVP) may be normal or raised
- Dramatic drop in arterial BP
• Tissues poorly perfused
- Brain needs contestant perfusion, neurones die quickly in absence of oxygen
– coronary arteries may be poorly perfused, this exacerbates problem
– Kidneys may be poorly perfused
• reduced urine production - oliguria
What is cardiac arrest?
When heart stops
Not related to Haemodynamic shock
Defined as: Unresponsiveness associated with lack of pulse
- Heart has stopped or has ceased to pump effectively
- Asystole (loss of electrical and mechanical activity)
- Pulseless Electrical Activity (PEA)
• Ventricular fibrillation (uncoordinated electrical activity)
– most common form of cardiac arrest
– often following MI because depolarisation sets off electrical activity in an uncontrolled way
– or electrolyte imbalance
– or some arrhythmias (eg long QT and Torsades de Pointes)
What is Asystole?
When you lose electrical activity of the heart so you cannot get any mechanical activity of the heart
How would you treat or manage cardÏact arrest?
• Basic life support
– chest compression and external ventilation
• Advanced life support
– defibrillation
– electric current delivered to the heart
– depolarises all the cells – puts them into refractory period
– allows coordinated electrical activity to restart
• Adrenaline
– enhances myocardial function
– increases peripheral resistance and increases blood pressure and maintains increased BP
What is an example of mechanical shock?
Mechanical shock – cardiac tamponade
• Cardiac tamponade – blood or fluid build up in pericardial space (this is a fibrous and rigid space) – restricts filling of the heart – limits end diastolic volume – affects left and right sides of heart
• High central venous pressure
- blood is returning to the heart but the heart can’t be filled
• Low arterial blood pressure
- heart isn’t filling in diastole so can’t get good CO in systole
• Heart attempts to beat
– continued electrical activity
- this increase in heart rate but can’t increase the CO because stroke volum is too low
What is another thing that can cause a mechanical shock?
• Massive pulmonary embolism (PE)
• Embolus occludes a large pulmonary artery
– Pulmonary artery pressure is high
– Right ventricle cannot empty
– Central venous pressure high
– Reduced return of blood to left heart – Limits filling of left heart
– Left atrial pressure is low
– Arterial blood pressure low
– Shock
- blocking the filling of right side of heart
– Also chest pain, dyspnoea
How might an embolus reach the lungs?
- Typically due to deep vein thrombosis
- Portion of thrombus breaks off
- Travels in venous system to right side of the heart
- Pumped out via pulmonary artery to lungs
- The effect of this will depend on the size of the embolus and size of artery that is blocked
How does hypovolaemic shock reduce CO?
- Reduced blood volume
- Most commonly due to haemorrhage
- < 20% blood loss unlikely to cause shock
- 20-30% some signs of shock response
- 30-40% substantial decrease in mean aBP and serious shock response
- Severity of shock is related to amount and speed of blood loss
How does your body respond to hypovolaemic shock?
• Haemorrhage
– venous pressure falls (filling pressure)
– Therefore stroke volume reduces and then cardiac output falls and then so does blood pressure(Starling’s Law)
– arterial pressure falls
– detected by baroreceptors
• Compensatory response
– increased sympathetic stimulation
–-> tachycardia
–-> increased force of contraction
– peripheral vasoconstriction because you get sympathetic outflow to arterioles which releases noradrenaline to alpha 1 receptors leading to increase in peripheral resistance
– venoconstriction
—> can help maintain venous pressure and so maintain filling of the heart
This system doesn’t cope well in high volume of blood loss
How do the capillaries cope with hypovolaemic shock?
• Normally at the capillaries you get a small movement of fluid out to the tissues
- the hydrostatic pressure of the blood in the capillaries pushes fluid out of the capillaries
- pressure of the proteins inside forces fluid into capillaries
• This then returns to the venous system via the lymphatic drainage
• In hypovolaemic shock this reverses
- get some ‘internal transfusion’
• Increased peripheral resistance reduces the capillary hydrostatic
pressure
• Net movement of fluid into capillaries because we have reduced capillary hydrostatic pressure
What are the symptoms of hypovolaemic shock?
• Patient has: – Tachycardia – Weak pulse – Pale skin – Cold, clammy extremities
