Shock Flashcards
What is the difference between regional and general poor diffusion?
- regional e.g. limbs or heart
- generalised e.g insufficient cardiac output to meet all the body’s needs – affects some tissues more (kidneys, brain)
What can cause poor regional perfusion?
Arterial occlusion:
– peripheral artery disease
– coronary artery disease
Venous congestion:
– varicose veins
– deep vein thrombosis
What is arterial occlusion?
- Most commonly affects lower limbs
- Due to partial occlusion of arteries (e.g atheromatous plaque)
How do superficial vessels drain into deep vessels?
via perforating veins
How much of the bodies blood do the veins contain?
approximately 70% at any time
What are varicose veins?
Varicose veins (dilated, torturous superficial veins)
– can be asymptomatic
– venous ulcers
Describe features of cardiac arrest
• Unresponsiveness associated with lack of pulse:
- Heart has stopped or has ceased to pump effectively
- Asystole (loss of electrical and mechanical activity)
- Pulseless Electrical Activity (PEA)
• Ventricular fibrillation (uncoordinated electrical activity)
– most common form of cardiac arrest
– often following MI
– or electrolyte imbalance
– or some arrhythmias (eg long QT and Torsades de Pointes)
How would you treat cardiac arrest?
Basic life support:
– chest compression and external ventilation
Advanced life support:
– defibrillation
– electric current delivered to the heart
– depolarises all the cells – puts them into refractory period
– allows coordinated electrical activity to restart
Adrenaline:
– enhances myocardial function
– increases peripheral resistance
What is haemodynamic shock?
Acute condition of inadequate blood flow throughout the body
A catastrophic fall in arterial blood pressure leads to circulatory shock
Mean arterial BP = CO x TPR
- Shock can be due to fall in CO
- Or fall in TPR beyond capacity of the heart to cope
What are some possible reasons for shock due to a fall in cardiac output?
- Cardiogenic shock (pump failure) – ventricle cannot empty properly
- Mechanical shock (obstructive) – ventricle cannot fill properly
-Hypovolaemic shock
– reduced blood volume leads to poor venous return
What are some potential causes of cardiogenic shock?
following myocardial infarction, damage to left ventricle
- due to serious arrhythmias
- acute worsening of heart failure
What are some features of cardiogenic shock?
Heart fills, but fails to pump effectively
- Central venous pressure (CVP) may be normal or raised
- Dramatic drop in arterial BP
- Tissues poorly perfused
– coronary arteries
• exacerbates problem
– kidneys
• reduced urine production - oliguria
How can cardiac tamponade cause 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
• Low arterial blood pressure
• Heart attempts to beat – continued electrical activity
How can a pulmonary embolism cause mechanical shock?
Embolus occludes a large pulmonary artery, typically due to DVT
– 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 – Also chest pain, dyspnoea
What is hypovolaemic shock?
-Reduced blood volume
- Most commonly due to haemorrhage
- can result from severe burns or severe vomiting/diarrhoea causing Na+ loss
Patient has tachycardia, weak pulse, pale skin, cold and clammy extremities.
What are the consequences of haemorrhage?
– venous pressure falls
– cardiac output falls (Starling’s Law)
– arterial pressure falls
– detected by baroreceptors
Compensatory response:
– increased sympathetic stimulation – tachycardia – increased force of contraction – peripheral vasoconstriction – venoconstriction
How does hypovolaemic shock cause net movement of fluid into the capillaries?
- Increased peripheral resistance reduces the capillary hydrostatic pressure
- Net movement of fluid into capillaries
What are some possible consequences of decompensation in hypovolaemic shock?
- Peripheral vasoconstriction (shutdown) impairs tissue perfusion
- Tissue damage due to hypoxia
- Release of chemical mediators (vasodilators)
- TPR falls
- Blood pressure falls dramatically
- Vital organs can no longer be perfused
- Multi system failure
What are the bodies longer term responses to restore blood volume, following hypovolaemic shock?
- Renin-angiotensin-aldosterone system
- Anti-diuretic hormone
When there is 20% blood volume loss, restoration of body fluid volumes in about 3 days, if salt and water intake are adequate
What is distributive shock?
- Low resistance shock (normovolaemic)
- Profound peripheral vasodilation (decreased TPR)
- blood volume constant, but volume of the circulation has increased
- Toxic shock
- Anaphylactic shock
What is septic shock and what are the consequences?
Endotoxins released by circulating bacteria:
– cause profound vasodilation – dramatic fall in TPR – fall in arterial pressure – impaired perfusion of vital organs – also -capillaries become leaky
-reduced blood volume
What are symptoms of toxic shock?
Decreased arterial pressure:
– Detected by baroreceptors – increased sympathetic output
– Vasoconstrictor effect overridden by mediators of vasodilation
– Heart rate and stroke volume increased
Patient has:
– Tachycardia
– Warm, red extremities
Later stages of toxic shock - vasoconstriction
What is anaphylactic shock?
-severe allergic reaction (anaphylaxis)
- release of histamine from mast cells
- other mediators
- powerful vasodilator effect, fall in TPR, dramatic drop in arterial pressure
- increased sympathetic response - increases CO, but can’t overcome vasodilation
- impaired perfusion of vital organs
- mediators also cause bronchoconstriction and laryngeal oedema so there is difficulty breathing
