CVS 11 Haemodynamic Shock Flashcards
What is haemodynamic shock?
Acute condition of inadequate blood flow throughout the body due to catastrophic fall in arterial BP
How do you calculate mean arterial BP?
Mean arterial BP = CO x TPR
Mean arterial BP = DBP + 1/3 PP
How to calculate pulse pressure?
SBP-DBP
What two things can shock be due to?
Fall in CO
Fall in TPR
Beyond capacity of heart to cope
What can a fall in cardiac output be due to?
Mechanical - pump can’t fill
Pump failure
Loss of blood volume
What can a fall in peripheral resistance be due to?
Excessive vasodilation
What types of shocks are due to fall in cardiac output?
Cardiogenic shock
Mechanical shock
Hypovolaemic shock
What is cardiogenic shock?
Failure of heart to maintain CO due to:
- Pump failure
- Ventricle cannot empty properly
Heart fills but fails to pump effectively
Potential causes of cardiogenic shock
- After a MI - damage to LV
- due to serious arrhythmias
- acute worsening on heart failure
What are poorly perfused in cardiogenic shock?
Coronary arteries»_space; makes issue worse
Kidneys
What is asystole?
Loss of electrical and mechanical activity
What is cardiac arrest?
Unresponsiveness associated with lack of pulse
What is the most common form of cardiac arrest?
Ventricular fibrillation - inadequate contraction
What can ventricular fibrillation be due to?
- After MI
- Electrolyte imbalance
- Some arrhythmia e.g. long QT + Torsades de Pointes
What would you do to a patient in cardiac arrest?
Basic life support - CPR + ventriltion
Advanced life support - defibrillation
Adrenaline
Why is adrenaline given in cardiac arrest?
- high conc so act on alpha receptors > vasoconstriction > increases peripheral resistance
- Enhances myocardial function
How does defibrillation help in cardiac arrest?
1- electric current delivered to heart
2- depolarises all cells - puts them into refractory period
3- allows coordinated electrical activity to restart
What is a cardiac tamponade?
Blood or fluid build up in pericardial space which leads to a decrease in arterial blood pressure
Effect of cardiac tamponade
- Heart is compressed
- Restricts filling of heart volume - limits EDV
- Affects left + heart sides of heart
- High central venous pressure»_space; distended neck veins
- Low arterial blood pressure
Why are distended neck veins seen in cardiac tamponade?
High central venous pressure due to restricted filing of heart
Causes of mechanical shock
Cardiac tamponade
Massive pulmonary embolism
What is mechanical shock?
Acute failure of heart to maintain cardiac output due to ventricles cannot fill properly
How does a pulmonary embolism cause mechanical shock?
- embolus occludes large pulmonary artery
- pulmonary artery pressure is high
- RV cannot empty
- CVP high
- reduced return of blood to left heart
- limits filling of left heart
- left atrial pressure low
- arterial BP low
- shock (+chest pain + dyspnoea)
How would an embolus typically reach the lungs?
Deep vein thrombosis
- portion of thrombus breaks off
- travels in venous system to right side of heart
- pumped out via pulmonary artery to lungs
What is hypovolaemic shock?
Failure of heart to maintain cardiac output due to reduced blood volume
What is hypovolaemic shock most commonly due to?
Haemorrhage
How does the body cope with a haemorrhage?
- venous pressure falls
- CO falls
- arterial pressure falls
- detected by baroreceptors
- increased sympathetic stimulation
- tachycardia
- increased force of contraction
- peripheral vasoconstriction
- venoconstriction
Causes of hypovolaemic shock
Haemorrhage - most common
Severe burns
Severe diarrhoea/vomiting + loss of Na+
Signs + symptoms of hypovolaemic shock
Tachycardia
Weak pulse
Pale skin
Cold, clammy extremities
What is the danger of compensation of haemorrhage?
- peripheral vasoconstriction impairs tissue perfusion
- tissue damage due to hypoxia
- release of chemical mediators > vasodilators
- TPR falls
- BP falls
- lack of blood flow to vital organs
- multi organ failure
What shocks are due to low resistance (normvolaemic)?
Toxic/septic shock
Anaphylactic shock
How can sepsis lead to septic shock?
- endotoxins released by circulating bacteria
- excessive inflammatory response
- causes excessive vasodilation
- fall in TPR
- fall in arterial pressure
- impaired perfusion of vital organ
-capillaries become leaky > reduced blood volume
What is septic shock?
A subset of sepsis where profound circulatory, cellular + metabolic abnormalities substantially increased mortality
Signs + symptoms of septic shock
Tachycardia
Warm, red extremities initially»_space; later vasoconstriction > localised hypo-perfusion
What happens in anaphylactic shock?
- severe allergic reaction
- release of histamine from mast cells
- vasodilator effect
- fall in TPR
- drop in arterial pressure
- impaired perfusion of vital organs
- mediators also cause bronchoconstriction + laryngeal oedema»_space; difficulty breathing
Drop in BP > increase in sympathetic response > increased CO - not enough to overcome vasodilation
Signs + symptoms of anaphylaxis shock
Difficulty breathing
Collapse
Rapid heart rate
Red, warm extremities
What type of shock can haemorrhage cause?
Hypovolaemic shock
What type of shock can a MI cause?
Cardiogenic shock
What type of shock can a cardiac tamponade cause?
Mechanical shock
What type of shock can pulmonary embolisms cause?
Mechanical shock
