S11: haemodynamic shock

Question 1

Describe the essential characteristics of haemodynamic shock

Answer 1

Acute condition of inadequate blood flow throughout the body
Catastrophic fall in arterial BP leads to circulatory shock (mean aBP = CO x TPR)
Shock can be due to fall in CO or fall in TPR beyond capacity of the heart to cope

Question 2

Define the three different types of shock due to fall in cardiac output

Answer 2

Cardiogenic shock = ventricle cannot empty properly
Mechanical shock = ventricle cannot fill properly
Hypovolaemic shock = reduced blood volume leads to poor venous return

Question 3

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

Answer 3

Distributive shock: sepsis 6, adrenaline EpiPen
Mechanical shock: pericardiocentesis
Hypovolaemic shock: blood transfusion
Cardiogenic shock: vasopressors, aspirin, blood-thinning medication

Question 4

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

Answer 4

Impairs tissue perfusion
Tissue damage due to hypoxia
Release of chemical mediators -> vasodilators
TPR falls, BP falls
Vital organs can no longer be perfused -> multi system failure

Question 5

List the causes of cardiogenic shock

Answer 5

Acute failure of the heart to maintain cardiac output – pump failure

1) Following MI – damage to the left ventricle
2) Due to serious arrhythmias
3) Acute worsening of heart failure

Question 6

Describe cardiogenic shock

Answer 6

Heart fills, but fails to pump effectively
CVP may be normal/raised
Dramatic drop in arterial BP
Tissues poorly perfused:
1) Coronary arteries may be poorly perfused – exacerbates problem
2) Kidneys may be poorly perfused – reduced urine production = oliguria

Question 7

Describe the management of a cardiac arrest

Answer 7

Basic life support – chest compression & external ventilation
Advanced life support – defibrillation
Adrenaline – enhances myocardial function & increases peripheral resistance

Question 8

Describe mechanical shock – cardiac tamponade

Answer 8

Cardiac tamponade – blood/fluid build up in pericardial space
Restricts filling of the heart – limits EDV
High CVP
Low aBP
Heart attempts to beat – continued electrical activity

Question 9

Describe mechanical shock – pulmonary embolism

Answer 9

Embolus occludes a large pulmonary artery – increases pressure in the artery
RV can’t empty -> CVP high
Reduced return of blood to left heart -> limits filling of left heart (left atrial pressure low)
SHOCK, also chest pain & dyspnoea

Question 10

How can an embolus reach the lungs?

Answer 10

Due to deep vein thrombosis
Portion of thrombus breaks off
Travels in venous system to right side of the heart
Pumped out via pulmonary artery to lungs

Question 11

What is hypovolaemic shock?

Answer 11

Reduced blood volume (haemorrhage)
30-40% substantial decrease in mean aBP = serious shock response
Severity of shock related to amount and speed of blood loss
Can also result from: severe burns & severe diarrhoea/vomiting

Question 12

Describe hypovolaemic shock – haemorrhage

Answer 12

Venous pressure falls, CO falls (Starling’s law)
Arterial pressure falls
Detected by baroreceptors

Question 13

Describe the compensatory response in hypovolaemic shock

Answer 13

Increased sympathetic stimulation 
Tachycardia 
Increased force of contraction 
Peripheral vasoconstriction
Venoconstriction 
Increased peripheral resistance reduces the capillary hydrostatic pressure – net movement of fluid into capillaries

Question 14

Describe the clinical presentation of hypovolaemic shock

Answer 14

Tachycardia
Weak pulse
Pale skin
Cold, clammy extremities

Question 15

What is distributive shock?

Answer 15

Low resistance shock
Profound peripheral vasodilation – decreased total peripheral resistance
Blood volume is constant, but volume of the circulation has increased

Question 16

Describe distributive shock – sepsis

Answer 16

Septic shock
Endotoxins are released by circulating bacteria -> profound vasodilation
Dramatic fall in TPR
Fall in arterial pressure
Impaired perfusion of vital organs
Capillaries also become leaky -> reduced blood volume

Question 17

Describe the body’s response to septic shock

Answer 17

Decreased arterial pressure is detected by baroreceptors
Increased sympathetic output
Vasoconstrictor effect overridden by mediators of vasodilation
Heart rate and stroke volume increased

Question 18

Describe the clinical presentation of septic shock

Answer 18

Tachycardia
Warm, red extremities INITIALLY
-later stages of sepsis, there is vasoconstriction causing localised hypo-perfusion

Question 19

Describe distributive shock – anaphylactic shock

Answer 19

Severe allergic reaction – release of histamine from mast cells -> powerful vasodilator effect
Dramatic drop in arterial pressure – increased sympathetic response but can’t overcome vasodilation
Impaired perfusion of vital organs
Mediators also cause bronchoconstriction & laryngeal oedema – difficulty breathing

Question 20

Describe the clinical presentation of anaphylactic shock

Answer 20

Difficulty breathing
Collapsed
Rapid heart rate
Red, warm extremities