CVS S12 - Shock Flashcards Preview

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Flashcards in CVS S12 - Shock Deck (22):

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:
- 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?

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

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
Red, warm extremities


What is the treatment for anaphylactic shock?

- Causes vasoconstriction via A1 adrenoceptors