CVS S12 - Shock Flashcards
Give a general definition of shock
Acute condition of inadequate blood flow throughout the body
What are the causes of shock? (not any specific type)
Catastrophic fall in BP
Can be due to fall in:
- TPR
- CO
(BP = CO x TPR)
What types of shock are due to a fall in CO?
What are the general causes for each type?
Cardiogenic shock (pump failure): - Ventricle cannot empty properly
Mechanical shock (obstructive): - Ventricles cannot fill properly
Hypovolaemic shock
- Reduced blood volume leads to poor venous return
What are some of the causes of cardiogenic shock?
Following massive MI (>40% of myocardium infarcted)
Serious arrhythmia
Acute worsening of heart failure
What are some of the features of cardiogenic shock?
Central venous pressure can be raised or normal
Dramatic drop in arterial BP
Tissues poorly perfused:
- Coronary artery ischaemia exacerbates problem
- Kidney GFR drop = oliguria
Give 2 examples of conditions that can cause mechanical shock
Cardiac tamponade:
- Blood/fluid in pericardial space builds up
- Restricts right heart filling, limits end diastolic volume
- Affects left and right heart
Pulmonary embolism:
- Embolus occludes a large pulmonary artery
Describe the features of mechanical shock due to cardiac tamponade
High central venous pressure
Low arterial BP
Heart attempts to beat despite compression
Describe the features of mechanical shock due to pulmonary embolism
Raised PA pressure
Right ventricle cannot empty
Central venous pressure high
Reduced filling of left heart
Left atrial pressure and arterial blood pressure low
(Also chest pain dyspnoea)
Describe the features of hypovolaemic shock
What are the most common causes?
Reduced blood volume
What mechanisms help compensate for or correct hypovolaemia?
Baroreceptor response
Internal transfusion
Describe the nervous response to haemorrhage
Low venous pressure due to haemorrhage
CO and arterial pressure fall
Detected by baroreceptors which increase SNS stimulation
Tachycardia, increased contractile force and peripheral vasoconstriction/venoconstriction result
Describe how Starling’s forces are affected by hypovolaemic shock
Increased peripheral resistance due to vasoconstriction (baroreceptor response) causes:
- Reduced capillary hydrostatic forces
- Net movement of fluid into capillaries
What are the symptoms of hypovolaemic shock?
Tachycardia
Weak pulse
Pale skin
Col, clammy extremities
What is decompensation in hypovolaemic shock?
Peripheral vasoconstriction imparis tissue function
Tissue is damaged due to hypoxia
Release of chemical vasodilators causes TPR to fall
BP falls
Vital organs no longer perfused
Multi-system failure
What is distributive shock?
Also known as low resistance (normovolaemic) shock
Profound peripheral vasodilation
Volume is constant but volume of circulation increased
What are the two types of distributive shock?
Toxic shock
Anaphylactic shock
Describe how toxic shock comes about
Septicaemic patient
Endotoxins released by circulating bacteria
Cause profound vasodilation and dramatic fall in TPR
Fall in aBP
Impaired perfusion of organs (leading to multi-system failure)
Also, capillaries become leaky (reduce blood volume)
Describe the SNS response to toxic shock
Decreased aBP detected by baroreceptors
Increased SNS output
Vasoconstrictor effect over-riden by local vasodilators
Heart rate and stroke volume increase
Describe how a patient in toxic shock presents
Tachycardia
Warm, red extremities
Describe how anaphylactic shock comes about
Severe allergic reaction causes release of histamine from mast cells
Powerful vasodilatory effect, TPR falls
Drop in aBP
Increased SNS output cannot overcome vasodilation
Impaired perfusion
Mediators also cause bronchoconstriction and laryngeal oedema (difficulty breathing)
Describe how a patient in anaphylactic shock presents
Difficulty breathing
Collapsed
Tachycardia
Red, warm extremities
What is the treatment for anaphylactic shock?
Adrenaline:
- Causes vasoconstriction via A1 adrenoceptors
