18 - Haemodynamic Shock Flashcards
What are the equations mean arterial blood pressure?
- CO X TPR
- Diastolic pressure + 1/3 pulse pressure
What is haemodynamic shock and what causes it?
Acute condition of inadequate blood flow through the body, due to the fact that there is a massive fall in arterial blood pressure
Causes:
- Fall in TPR
- Fall in CO
What are the different types of shock due to a fall in cardiac output?
What is cardiogenic shock and some of the causes of this?
- Inability of the heart to eject enough blood due to a pump failure. Heart can fill but not empty properly.
- Fall in CO
Causes:
- Following MI
- Serious arrhythmia e.g heart block or tachycardia
- Acute worsening of heart failure
What are some symptoms of cardiogenic shock?
- Kidneys poorly perfused –> oliguria
- Coronary arteries poorly perfused –> exacerbates problem
- Increase in central venous pressure
How is a cardiac arrest dealt with?
What do all of the types of haemodynamic shock have in common?
Dramatic decrease in arterial blood pressure
How can you have cardiogenic shock if the heart rate has increased?
CO = SV X HR
Heart rate may be increasing but SV may be falling
What is mechanical shock and some of the causes of this?
Restriction of the filling of the heart OR obstruction to blood flow through the lungs. Can still contract but not relax and fill properly
Causes:
- Cardiac tamponade
- PE
How does cardiac tamponade cause shock?
- Blood or fluid in pericardial space
- Restriction of filling of the heart limiting end diastolic volume
- Affects both sides of heart with an increase in CVP, drop in arterial BP
What are some of the signs of mechanical shock?
Increase CVP as there is a drop in SV in the ventricle so back up
How does a PE cause shock?
- Embolus blocks large pulmonary artery
- CVP high as right ventricle cannot empty as increased after load
- Reduced return to left sie of the heart so limited filling of left side. Low atrial pressure in left and decreased arterial blood pressure
How does and embolus reach the lungs?
- DVT
- Returned to right side of heart via venou system
- Pumped out of pulmonary artery to lungs
- Effects depend on size of embolus
What is cardiac arrest defined as and what are some of the causes?
Unresponsiveness associated with a lack of pulse as the heart has stopped or ceased to pump effectively
- Asystole: loss of electrical and mechanical activity
- PEA: loss of mechanical but still electrical
- VF: uncoordinated electrical activity
What are some causes of ventricular fibrillation?
- Following MI
- Electrolyte imbalance
- Arrythmeas (long QT and Torsades de Pointes)
What is hypovolaemic shock?
Reduced blood volume
- 20-30% blood loss some signs of shock
- 30-40% blood loss causes large decrease in b.p and serious shock
What does the severity of hypovolemic shock depend on?
The amount and speed of blood loss
How does a loss of blood volume cause hypovolaemic shock?
- Haemorrhage
- Venous pressure falls
- CO falls (Starling’s)
- Arterial pressure falls
- Detected by baroreceptors
What are some initial compensatory responses to hypovolaemic shock?
- Increased sympathetic stimulation due to baroreceptor stimulation: tachycardia, increased contractility, peripheral vasoconstriction and venoconstriction to increase TPR and CO
- Internal transfusion: constriction of arterioles and decreased blood volume decrease capillary hydrostatic pressure so net movement of fluid back into capillaries
What are the signs of hypovolaemic shock?
- Tachycardia
- Weak pulse
- Pale skin (vasoconstriction)
- Cold, clammy extremities
- Low CVP
What can hypovolaemic shock be caused by?
- Severe burns
- Severe diarrhoea or vomiting
- Haemorraghe
Why may a patient in hypovolaemic shock appear to have stabilised their blood pressure but then crash and have a cardiac arrest?
DECOMPENSATION
- Peripheral vasoconstriction in compensatory response induces tissue hypoxia
- Tissues produce chemical mediators (vasodilators) to overcome hypoxia
- TPR falls due to dilation
- BP drops
- Vital organs can no longer be perfused so multi system failure
What is a longer term response to a loss of blood volume?
- RAAS
- ADH
Can restore body fluids within 3 days when less than 20% has been lost. Not good for acute situations and dependent on adequate salt and water intake
What kind of haemodynamic shock is caused by a drop in TPR?
- Distributive (normovolaemic)
- No change in blood volume but high peripheral vasodilation
e. g toxic (septic) and anaphylatic shock
How is toxic shock a form of normovolaemic shock?
- Bacteria in blood release endotoxins
- Systemic inflammatory response
- Vasodilation so fall in TPR and arterial BP
- Capillaries leaky so loss of blood volume eventually
- Impaired perfusion of vital organs
- Increased coagulation and localised hypoperfusion in extremities
What are the symptoms of a patient in toxic shock and why?
- Tachycardia
- Warm red extremities initially but later stages cold as vasoconstriction and localised hypoperfusion
- Symptoms due to increased sympathetic innervation as baroreceptors detect fall in b.p. However vasoconstrictive effect is overcome by vasodilator mediators
How is anaphylactic shock a form of distributive shock?
- Severe allergic reaction causing release of histamine from mast cells
- Vasodilator effect so drop in TPR and arterial BP
- Impaired perfusion of organs
- Chemical mediators from mast cells can lead to bronchoconstriction and laryngeal oedema so difficulty breathing
What are the symptoms of anaphylatic shock?
- Difficulty breathing
- Collapsed
- Rapid heart rate
- Warm red extremities
How do you treat anaphylactic shock?
- High dose of adrenaline to cause vasoconstriction using a1 receptors on blood vessel smooth muscle
- Pharmacological level causes activation of a1 not b2 like physiological
In mechanical shock due to cardiac tamponade, what happens to the left atrial pressure?
Increases as there is a restriction of the size of the atria from the pericardium
Where should you insert the needle when carrying out a pericardiocentesis?
Just below xiphoid process and upwards
Why would you infuse a patient with colloid when they are in haemodynamic shock due to a loss of blood volume?
- Hypovolaemic shock
- Has high molecular weight so increase the oncotic pressure in the capillaries so there is more tissue fluid reabsorbed
What will the pulse of a patient in anaphylactic shock feel like?
Weak but fast
