Haemodynamic Shock

Question 1

Describe the essential characteristics of haemodynamic shock

Answer 1

used to describe acute circulatory failure with either inadequate or inappropriately distributed tissue perfusion, resulting in generalised lack of oxygen supply to cells.

Question 2

Describe the characteristics of hypovolaemic, cardiogenic,
mechanical and distributive shock

Answer 2

Cardiogenic shock - Inability of the heart to eject enough blood - ventricle cannot empty properly - affects CO (e.g. in ischaemic cardiac damage)

• Mechanical shock - ventricle cannot fill properly - affects SV and CO (e.g. Cardiac tamponade)

• Hypovolaemic shock - Due to loss of circulating fluid volume -leads to poor venous return
Affects CO and TPR (e.g. haemorrhage)

• Normovolaemic(distributive) shock - affects TPR - Due to uncontrolled falls in peripheral resistance
(e.g. in Sepsis or Anaphylaxis)

o Obstruction to blood flow through the lungs (e.g. Pulmonary embolism)

Question 3

Predict the type of shock involved from the range of signs

Answer 3

Cardiogenic shock
Causes - MI damages LV
worsening of heart failure
serious arrhythmias
Signs
CVP normal or raised
Drop in arterial BP
Tissues poorly produced so kidneys may be affected so dec urine production - oliguria.

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 CVP
Low ABP
Attempts to beat so continued electrical activity.

PE
occludes a large pulmonary artery so Pulmonary artery pressure is high.
RV cannot empty so CVP high
Reduced return of blood to left heart so limits filling so left atrial pressure low and AP low.
Chest pain, dysponea

Hypovalemic - Tachycardia
– Weak pulse
– Pale skin
– Cold, clammy extremities

Normovolaemic - tachycardia, Warm, red extremities initially BUT Later stages of sepsis – vasoconstriction – localised hypo-perfusion
Persisting hypotension requiring treatment to
maintain blood pressure despite fluid
resuscitation.
Low ABP

Question 4

Describe the general features of management of the various types of shock

Answer 4

Cardiogenic shock- adrenaline - improves myocardial function + vasoconstriction. Defibrillation in certain cardiac arrests.
Mechanical shock - pericardiocentesis for cardiac tamponade- A needle and a a catheter are used to remove the fluid - inserted in 5th left intercostal margin.
Hypovalaemic - RAAS, ADH, if salt and water intake adequate back to normal in 3 days. Also internal transfusion from interstitium into capillaries.
Septic - sepsis 6 - O2, fluids, antibiotics given. Take urine output, blood cultures and lactate.
Anaphylactic shock - Adrenaline– Vasoconstriction via action at α1 adrenoceptors

Question 5

Describe the body’s compensatory responses to hypovolaemia to
maintain arterial blood pressure and how this shock happens

Answer 5

30-40% substantial decrease in mean aBP and serious shock response (haemorrhage, severe burns, severe diarrhoea and vomiting and loss of Na+)
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 - hydrostatic pressure drops, inc plasma oncotic pressure so movement of fluid into capillaries.
– venoconstriction
RAAS and ADH

Restore in 3 days

Question 6

Explain how prolonged peripheral vasoconstriction in response to
hypovolaemia can lead to decompensation.

Answer 6

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 7

Cardiac arrest - Cardiogenic shock

Answer 7

What is it
Unresponsiveness associated with lack of pulse • Heart has stopped or has ceased to pump effectively

Types
Asystole (loss of electrical and mechanical activity)
• Pulseless Electrical Activity (PEA)
• Ventricular fibrillation (uncoordinated electrical
activity) - following MI, electrolyte imbalance and some arrhythmias eg long QT and Torsades de Pointes

Question 8

Septic shock - distributive

Answer 8

Endotoxins released by circulating bacteria
– Profound inflammatory response (excessive)
– Causes profound vasodilation
– Dramatic fall in TPR
– Fall in arterial pressure
– Impaired perfusion of vital organs
– also - capillaries become leaky so dec BV

Inc coagulation and localised hypo-perfusion

Compensatory:
Decreased arterial pressure – Detected by baroreceptors – increased sympathetic
output – Vasoconstrictor effect overridden by mediators of
vasodilation – Heart rate and stroke volume increased

Question 9

Distributive- anaphylactic

Answer 9

severe allergic reaction (anaphylaxis) – release of histamine from mast cells

vasodilator effect – fall in TPR – dramatic drop in arterial pressure - increased sympathetic response - ↑ CO, but can’t overcome vasodilation

– impaired perfusion of vital organs

– mediators also cause bronchoconstriction and laryngeal oedema - difficulty breathing