Haemodynamic Shock Flashcards
Define shock
When the arterial pressure is too low, thus not enough blood flow
Use the pressure equation to explain what can cause shock
Shock can be due to fall in CO - mechanical pump cannot fill, pump failure, loss of blood volume
Shock can also be due to TPR fall beyond capacity of the heart to cope - excessive vasodilation
What is hypovolaemic shock
More than 20% reduced blood volume leads to poor venous return
What is the most common cause of hypovolaemic shock
Haemorrhage
Venous pressure falls
Cardiac output falls as reduction in stroke volume (Starling’s Law)
Arterial pressure falls - detected by baroreceptors
How does the body cope with hypovolaemic shock
Compensatory response - increase sympathetic stimulation
Tachycardia
Increased force of contraction
Peripheral vasoconstriction
Venoconstriction to maintain venous pressure
Internal transfusion - movement of fluid from tissues to capillary
Increased peripheral resistance reduces capillary hydrostatic pressure
Reduction in hydrostatic pressure so fluid moves in to maintain blood pressure
What are symptoms of hypovolaemia
Pale skin - peripheral venoconstriction
Tachycardia
Weak pulse
Cold/clammy extremities
What is the severe effect of hypovolaemia
Build up of hypoxia and tissue damage due to peripheral vasoconstriction
Need to get fluid into patient to maintain plasma volume
What is cardiogenic shock
Acute failure of the heart to maintain cardiac output - pump failure
What are potential causes of cardiogenic shock
Following myocardial infarction - damage to left ventricle
Due to serious arrhythmia - heart beating too slow or severe tachycardia so not enough time to fill
Acute worsening of heart failure
What are the major effects of cardiogenic shock
Tissues poorly profused
Poor perfusion of coronary arteries
Poor perfusion of kidneys - reduced urine production
Brain needs to maintain perfusion
Could progress into cardiac arrest - unresponsiveness due to lack of pulse
Could be asystole - loss of electrical and mechanical activity
Pulseless electrical activity - electrical but no mechanical activity
Ventricular fibrillation - uncoordinated electrical activity
Chest compression and defibrillation to resuscitate
Adrenaline given to enhance myocardial function and increase TPR
What is mechanical shock
Restriction on the filling of the heart
What are the major causes of mechanical shock
Cardiac tamponade - blood or fluid build up in pericardial space
Restricts filling of the heart - limits end diastolic volume
Affects left and right sides of heart
High central venous pressure - blood returns but can’t fill heart
Low arterial blood pressure - not able to fill in diastole
Pulmonary embolism - 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, chest pain, dyspnoea (difficult breathing)
What is anaphylactic shock
Severe allergic reaction (anaphylaxis)
Explain the mechanism of anaphylactic shock
Release of histamine from mast cells
Vasodilation effect leads to fall in TPR and arterial pressure
Reduction in peripheral resistance leads to increase in volume of circulation
Increase in the number of tubes available in circulation
What are the complications of anaphylactic shock
Increased sympathetic response increases cardiac output, but cannot overcome vasodilation
Mediators also cause bronchoconstriction and oedema - difficulty breathing
Patient will have difficulty breathing, collapses, rapid heart rate, red warm extremities
Give adrenaline - vasoconstriction via action at α1 adrenoceptors
