5. Haemodynamic Shock Flashcards
What is haemodynamic shock?
Acute condition of inadequate blood flow throughout the body, catastrophic fall in arterial blood pressure leads to circulatory shock.
How can mean AP be calculated?
SV x HR x TPR
A fall in which 2 values will lead to shock?
CO or TPR
What are the 3 types of shock due to a fall in CO?
- Cardiogenic shock
- Mechanical shock
- Hypovolaemic shock
What is cardiogenic shock?
Pump failure - ventricle cannot empty properly
What is mechanical shock?
Obstructive - ventricle cannot fill properly
What is hypovolaemic shock?
Reduced blood volume leads to decreased venous return.
What are potential causes of cardiogenic shock?
- Following MI - damage to LV
- Serious arrythmia - bradycardia or tachycardia
- Acute worsening of HF
What would you expect the central venous pressure to be in cardiogenic shock?
Normal or raised due to backlog of blood in venous system- look at JVP in neck.
What is the most common form of cardiac arrest?
Ventricular fibrillation
What form of cardiac arrest will appear normal on an ECG?
Pulseless electrical activity
What is asystole?
Cardiac arrest due to loss of electrical and mechanical activity
What conditions increase the risk of ventricular fibrillation?
Following MI
Electrolye imbalance - K+
Arrythmias - lengthened AP
Why is adrenaline given to treat cardiac arrests?
- Increases TPR
- Increases contractility of the heart
What are possible causes of mechanical shock (ventricle cannot fill)?
Cardiac tamponade
Pulmonary embolism
How can cardiac tamponade lead to mechanical shock?
Limits EDV, decreased SV leads to a decrease in CO.
What would you expect CVP to be in cardiac tamponade?
High - backlog in venous system
How can a massive PE lead to mechanical shock?
Embolus occludes a large pulmonary artery, PA pressure is high, RV cannot empty, reduced filling of LV.
What percentage blood loss is likely to cause hypovolaemic shock?
20-30% might cause some signs of shock
30-40% will cause a serious shock response
What happens to the Starling’s forces during hypovolaemia shock to cause ‘internal transfusion’?
Increased peripheral resistance reduces capillary hydrostatic pressure and causes net movement INTO capillaries to try and maintain blood volume and pressure.
What signs will be present in a patient with hypovolaemic shock?
Tachycardia
Weak pulse
Pale skin
Cold, clammy extremities
What is the danger of decompensation in hypovolaemic shock?
Peripheral vasoconstriction causes hypoxia and tissue damage, release of vasodilator chemical mediators which cause a fall in TPR and another dramatic fall in BP.
Vital organs cannot be perfused - > Multi-system organ failure.
What is distributive shock?
Shock due to a decrease in TPR - blood volume remains constant
What are 2 type of distributive shock?
Toxic shock/ Sepsis
Anaphylactic shock
How does sepsis cause distributive shock?
Excessive inflammatory response -> vasodilation, decrease in TPR and arterial pressure -> impaired perfusion of vital organs.
Vasoconstriction response overridden by vasodilators.
What is septic shock?
Persisting hypotension requiring treatment to maintain blood pressure despite fluid resuscitation.
How will the patient present differently in septic shock compared to hypovolaemic shock?
Warm, red extremities initially
What is anaphylactic shock?
Severe allergic reaction causing release of histamine from mast cells.
Powerful vasodilator which causes decrease in TPR and massive drop in arterial BP.
Why will patients suffering from anaphylactic shock have difficulty breathing?
Mediators also cause bronchoconstriction and laryngeal oedema
What is given to treat anaphylactic shock?
Adrenaline
