Haemodynamic shock Flashcards
How is mean arterial blood pressure calculated?
maBP = CO x TPR
maBP = diastolic pressure + 1/3 pulse pressure
What is another term for haemodynamic shock?
Circulatory shock
What is haemodynamic shock?
Acute condition
gives large drop in arterial blood pressure
inadequate blood flow throughout the body
What can cause haemodynamic shock?
Decrease in CO
Decrease in TPR
What are the causes of decreased CO?
Loss of blood volume
Heart cannot fill
Heart cannot pump
What is the cause of decreased TPR?
Excessive vasodilation
What are the types of shock caused by decreased CO?
Hypovolaemic shock
Mechanical shock
Cardiogenic shock
What is cardiogenic shock?
Ventricle fills normally
but cannot pump adequately
What are some of the possible causes of cardiogenic shock?
Myocardial infarction - damage to LV
Serious arrythmias
Acute worsening of heart failure
What is the CVP in cardiogenic shock? Why?
Normal or raised
due to backup of blood behind heart
What is the arterial blood pressure in cardiogenic shock? Why?
Dramatic decrease
due to ventricle not pumping adequately
What happens to the perfusion of tissues in cardiogenic shock?
Decreased perfusion of tissues
What are the effects of reduced perfusion of coronary arteries?
Exacerbates the situation
What are the effects of reduced perfusion of kidneys?
Oliguria - reduced urine production
What is cardiac arrest?
Heart has stopped pumping effectively
How does cardiac arrest present?
Unresponsiveness with lack of pulse
What are the different causes of cardiac arrest?
Asystole
Pulseless electrical activity
Ventricular fibrillation
What is asystole?
Lack of electrical activity in heart
gives loss of mechanical activity too
What is pulseless electrical activity?
Electrical activity present
but has been uncoupled from mechanical activity
no mechanical activity
What is ventricular fibrillation?
Uncoordinated electrical activity in ventricles
no synchronised contraction of ventricular myocytes
What can cause ventricular fibrillation?
After myocardial infarction
Electrolyte imbalance
Some arrythmias e.g. long QT syndrome
What is the most common form of cardiac arrest?
Ventricular fibrillation
How is cardiac arrest treated?
Basic life support
Advanced life support
Arenaline
What does basic life support involve?
Chest compressions
External ventilation
What does advanced life support involve?
Defibrillation
How does defibrillation work?
Delivers electric current to all cardiomyocytes
all depolarised
all in refractory period
co-ordinated electrical activity can resume
How does adrenaline work?
Increases myocardial function - heart rate, force of contraction
Increases peripheral resistance - vasoconstriction
What is mechanical shock?
Heart cannot fill properly
low EDV
What are some of the causes of mechanical shock?
Cardiac tamponade
Pulmonary embolism
What is cardiac tamponade?
Build up of fluid in pericardial space
Fibrous pericardium is non-extensible
Heart becomes compressed
Which side of the heart does cardiac tamponade affect?
Both sides
What is the CVP with mechanical shock? Why?
High
due to backup of blood before heart
What is the arterial blood pressure with mechanical shock? Why?
Low
because low EDV, SV, CO
How does a pulmonary embolism lead to mechanical shock?
Pulmonary embolism occludes pulmonary artery
Pulmonary artery pressure increases
RV pressure increases
CVP increases
Reduced blood flow to LA
Reduced filling of LV
What is the LA pressure with a pulmonary embolism?
Low
Where does a pulmonary embolism usually arise from?
Thrombus in deep vein of leg - DVT
How does the pulmonary embolism reach the lungs?
Portion of thrombus breaks off Carried in veins Passes through RA, RV Enters pulmonary artery to lungs Becomes trapped
What do the effects of a pulmonary embolism depend on?
The size of the embolus
What are the additional symptoms of a pulmonary embolism?
Chest pain
Dyspnea - breathlessness
due to pulmonary oedema
What is hypovolaemic shock?
Significantly reduced blood volume
What is the most common cause of hypovolaemic shock?
Haemorrhage
How much blood volume has to be lost in order for hypovolaemic shock?
20-30% loss - some signs of shock
30-40% loss - serious shock
The severity of hypovolaemic shock depends on…?
Amount of blood lost
How fast the blood was lost
What is the CVP with hypovolaemic shock? Why?
Low
Due to loss of blood
What is the arterial blood pressure with hypovolaemic shock? Why?
Low
Due to reduced filling of LV
reduced EDV, SV, CO
What is the compensatory response with hypvolaemic shock?
Decrease in arterial blood pressure detected by baroreceptors
Increase in sympathetic output to heart and blood vessels
What are the results of the compensatory response with hypovolaemic shock?
Tachycardia
Increased force of contraction
Peripheral vasoconstriction
Venoconstriction
How is the increased force of contraction brought about?
By increasing contractility of muscle fibres
What effect does the compensatory response have at the capillaries?
Increase in peripheral resistance
reduces capillary hydrostatic pressure
net movement of fluid into capillaries
How does hypovolaemic shock present?
Tachycardia
Weak pulse
Pale skin
Cold, clammy extremities
Why is the skin pale?
Peripheral vasoconstriction
reduced blood flow to skin surfaces
Why are the extremities cold and clammy?
Peripheral vasoconstriction
reduced blood flow to extremities
Sympathetic activation of sweat glands
What are some other causes of hypovolaemic shock?
Severe burns
Severe vomiting and diarrhoea, loss of Na+
What is the danger of decompensation with hypovolaemic shock?
Peripheral vasoconstriction impaires tissue perfusion Tissues become ischaemic, hypoxic Tissues become damaged Tissues release chemical mediators Cause vasodilation, TPR drops
What are the consequences of decompensation?
Impaired organ perfusion
Multiple organ failure
Mutli system failure
How is hypovolaemia treated?
Fluid, electrolytes
Blood transfusions
How is hypovolaemia normally managed by the body?
Longer term response
RAAS
ADH
How long does it take the body to restore 20% of blood volume?
Approx. 3 days
with adequate salt and water intake
What type of shock is caued by decreased TPR?
Distributive shock
What are some other terms for distributive shock? Why?
Low resistance shock - drop in TPR
Normovolaemic shock - normal blood volume
What increases in distributive shock?
Excessive vasodilation
gives increase in volume of circulation
What is meant by volume of circulation?
The amount of space in blood vessels
What are the types of distributive shock?
Toxic shock - septic shock
Anaphylactic shock
What causes septic shock?
Endotoxins released by bacteria
cause massive inflammatory response
get excessive vasodilation
get increased permeability of capillaries
reduced blood volume
What else can cause inadequate perfusion of tissues in septic shock?
Increased coagulation
blood clots form within vessels
What is the definition of septic shock?
Persisting hypotension despite fluid resuscitation
requires treatment to maintain blood pressure
What is the phsyiological response to septic shock?
Baroreceptors detect decrease in blood pressure
Increased sympathetic output
Gives increase in heart rate
force of contraction
vasoconstriction
Is the vasoconstriction effect maintained?
No
Overridden by chemical mediators causing vasodilation
How does septic shock present?
Tachycardia
Warm, red extremities initially - not later!
Why does the patient have warm, red extremities?
Due to excessive vasodilation
increased blood flow to peripheries
What causes anaphylactic shock?
Severe allergic reaction
What happens in a severe allergic reaction?
Release of histamine and other chemical mediators
Causes excessive vasodilation
What is the physiological response to anaphylactic shock?
Decrease in blood pressure detected by baroreceptors
increased sympathetic output
Increase in heart rate
Increase in force of contraction
Vasoconstriction
Is the sympathetic response to anaphylactic shock effective?
No
can’t overcome the excessive vasodilation
What are the symptoms of anaphylactic shock?
Tachycardia
Warm, red extremities
Difficulty breathing
Why does the patient have difficulty breathing?
Allergic reaction also causes
bronchoconstriction
laryngeal oedema
How is anaphylactic shock treated? Why?
Adrenaline
Causes vasoconstriction
binds to A1 receptors in blood vessels
What is the arterial blood pressure with distributive shock? Why?
Low
Drop in TPR
What happens to the perfusion of organs in distributive shock? What does this lead to?
Impaired perfusion
Gives organ damage, dysfunction, failure
