Shock

Question 1

What is the difference between regional and general poor diffusion?

Answer 1

• 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)

Question 2

What can cause poor regional perfusion?

Answer 2

Arterial occlusion:
– peripheral artery disease
– coronary artery disease

Venous congestion:
– varicose veins
– deep vein thrombosis

Question 3

What is arterial occlusion?

Answer 3

• Most commonly affects lower limbs

- Due to partial occlusion of arteries (e.g atheromatous plaque)

Question 4

How do superficial vessels drain into deep vessels?

Answer 4

via perforating veins

Question 5

How much of the bodies blood do the veins contain?

Answer 5

approximately 70% at any time

Question 6

What are varicose veins?

Answer 6

Varicose veins (dilated, torturous superficial veins)

– can be asymptomatic
– venous ulcers

Question 7

Describe features of cardiac arrest

Answer 7

• 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)

Question 8

How would you treat cardiac arrest?

Answer 8

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

Question 9

What is haemodynamic shock?

Answer 9

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

Question 10

What are some possible reasons for shock due to a fall in cardiac output?

Answer 10

• 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

Question 11

What are some potential causes of cardiogenic shock?

Answer 11

following myocardial infarction, damage to left ventricle

• due to serious arrhythmias
• acute worsening of heart failure

Question 12

What are some features of cardiogenic shock?

Answer 12

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

Question 13

How can cardiac tamponade cause mechanical shock?

Answer 13

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

Question 14

How can a pulmonary embolism cause mechanical shock?

Answer 14

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

Question 15

What is hypovolaemic shock?

Answer 15

-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.

Question 16

What are the consequences of haemorrhage?

Answer 16

– 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

Question 17

How does hypovolaemic shock cause net movement of fluid into the capillaries?

Answer 17

• Increased peripheral resistance reduces the capillary hydrostatic pressure
• Net movement of fluid into capillaries

Question 18

What are some possible consequences of decompensation in hypovolaemic shock?

Answer 18

• 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

Question 19

What are the bodies longer term responses to restore blood volume, following hypovolaemic shock?

Answer 19

• 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

Question 20

What is distributive shock?

Answer 20

• Low resistance shock (normovolaemic)
• Profound peripheral vasodilation (decreased TPR)
• blood volume constant, but volume of the circulation has increased
• Toxic shock
• Anaphylactic shock

Question 21

What is septic shock and what are the consequences?

Answer 21

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

Question 22

What are symptoms of toxic shock?

Answer 22

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

Question 23

What is anaphylactic shock?

Answer 23

-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