Shock

Question 1

What is haemodynamic shock?

Answer 1

• 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 a fall in CO
• Or fall in TPR beyong capasity of the heart to cope.

Question 2

What is mean arterial BP equal to?

Answer 2

Cardiac Output x Total peripheral resistance

OR

SV x HR x TPR

OR

Diastolic + 1/3 pulse pressure

Question 3

What is CO equal to?

Answer 3

SV x HR

Question 4

What can cause shock?

Answer 4

Fall in cardiac output or a fall in total peripheral resistace

Question 5

What types of shock are due to a fall in cardiac output?

Answer 5

• Cardiogenic shock (pump failure) - ventricle cannot empty properly
• Mechanical shock (obstructive) - ventricle cannot fill properly
• Hypovolaemic shock - reduced blood volume leads to poor venous retutn

Question 6

What causes cardiogenic shock?

Answer 6

• MI - damage to left ventricle
• Serious arrhythmias - low CO so, aBP drops.
• Acute worsening of heart failure

Question 7

What happens in cardiogenic shock?

Answer 7

• Heart fills but it fails to pump effectively
• Central venous pressure (CVP) may be normal or raised
• Dramatic drop in arterial BP
• Tissue poorly perfused
  
  • Coronary arteries may be poorly perfused
    
    • Exacerbates problem
  • Kidneys may be poorly perfused
    
    • Reduced urine production - oliguria (reduced conc) -drop in arterial BP

Question 8

What is cardiac arrest?

Answer 8

• 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 fibrilation (uncoordinated elecrical activity)
  
  • Most common form of cardiac arrest
  • After MI
  • Elecrolyte imbalance
  • Some arrhythmias (long QT, Torsades de Pointes - form of VT)

Question 9

How do you treat cardiac arrest?

Answer 9

• Basic life support
  
  • Chest compression and external ventilation
• Advanced life support
  
  • Defibrilator
  • 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 10

How does cardiac tamponade cause mechanical shock?

Answer 10

• Blood or fluid builds up in pericardial space
• Restricts filling of the heart - limits end diastolic volume
• Affects left and right sides of the heart
• High central venous pressure
• Low arterial pressure
• Heart attemps to beat - continued electrical activity
• Reduced SV so CO cannot be maintained. This means that BP cannot be maintained no matter now much TPR and HR change

Question 11

How does a pulmonary embolism cause mechanical shock?

Answer 11

• Embolus occludes a large pulmonary artery
  
  • Pulmonary artery pressure is high
  • Right ventricle cannot empty
  • Central venous pressure is high
  • Reduced retun of blood to left heart
  • Limits filing of left heart
  • Left atrial pressure is low
  • Arterial blood pressure low
  • Shock
  • Also chec pain, dyspnoea

Question 12

How might an embolus reach the lungs?

Answer 12

• Typically due to deep vein thrombosis
• Portion of thrombus breaks off
• Travels in venous system to right side of the hert
• Pumped out via pulmonary artery to lungs
• The effect will depend on the size of the embolus

Question 13

What is hypovolaemic shock? How much blood loss is likely to cause shock?

Answer 13

• Reduced blood volume
• Most commonly due to haemorrhage
• Less than 20% blood loss is unlikely to cause shock
• 20-30% some signs of shock response
• 30-40% substantal decrease in mean aBP and serious shock response
• Severity of shock is related to amount and speed of blood loss

Question 14

How does hypovolemic shock occur?

Answer 14

• Haemorrhage
  
  • Venous pressure falls
  • Cardiac output falls (Starling’s Law)
  • Arterial pressure falls
  • Detected by baroreceptors
• Compensatory response
  
  • Increased sympathetic stimulation
  • Tachycaridia
  • Increased force of contraction
  • Peripheral vasoconstriction
  • Venoconstriction

Question 15

How does hydrostatic pressure change in hypovolaemic shock?

Answer 15

• Normally at the capillaries you get a small movement of fluid out to the tissue
• This then returns to the venous system via lymphatic drainage
• In hypovolaemic shock this reverses. -You get some internal transfusion
• Increased peripheral resistance reduced the capillary hydrostatic pressure
• Net movement of fluid into capillaries

Question 16

What are the clinical signs of hypovolaemic shock?

Answer 16

• Tachycardia
• Weak pulse
• Pale skin
• Cold, clammy extremities

Question 17

Other than haemorrhage, what can cause hypovolaemic shock?

Answer 17

• Severe burns
• Diarrhoea or vomitting and loss of Na

Question 18

What is the danger in hypovolaemic shock?

Answer 18

• Danger of decompensation
• Peripheral vasoconstriction (shutdown) impairs tissue persusion
  
  • Tissue damage due to hypoxia
  • Release of chemical mediators - vasodilators
  • TPR falls
  • Blood pressure falls dramatically
  • Vital organs can no longer be perfused
  • Multisystem failure

Question 19

What is the long term response of hypovolaemic shock?

Answer 19

• Restores blood volume
• RAAS system
• ADH
• 20% blood volume loss - restoration of blody fluid volume in about 3 days if the salt and water intake are adequate

Question 20

What is distributive shock?

Answer 20

• Low resistance shock
• Profound peripheral vasodilation - decreased TPR
  
  • Blood volume constant, but volume of the circulation has increased
• Toxic shock
• Anaphylactic shock

Question 21

What is toxic (septic) shock?

Answer 21

• Endotoxins released by circulating bacteria
  
  • Profound inflammatory response (excessive)
  • Cause profound vasodilation
  • Dramatic fall in TPR
  • Fall in arterial pressue
  • Impaired perfusion of vital organs
  • Also- capillaries become leaky - reduced blood volume
  • Increased coagulation and localised hypo-perfusion
• Decreased arterial BP
  
  • Detected by baroreceptors - increased sympathetic output
  • Vasoconstrictor effect overriden by mediators of vasodilation
  • Heart rate and stroke volume increased

Question 22

Define septic shock

Answer 22

Persisting hypotension requiring treatment to maintain
blood pressure despite fluid resuscitation

Question 23

What are the clinical signs of septic shock?

Answer 23

• Tachycardia
• Warm, red extremities initially BUT
  
  • Later stages of sepsis - vasoconstriction - localised hypo-perfusion

Question 24

What is anaphalactic shock?

Answer 24

• Severe allergic reaction (anaphalaxis)
  
  • Release of histamine form mast cells
    
    • Other medators
  • Powerful vasodilatory effect - fall i TPR
  • Dramatic drop on arterial pressure
    
    • Increased sympathetic response - increased CO but can’t overcome vasodilation
  • Impaired perfusion of vital organs
  • Mediators also cause bronchoconstriction and laryngeal oedema
    
    • Difficulty breathing

Question 25

What are the clinical signs of anaphylactic shock? What do you do?

Answer 25

* Difficulty breathing * Collapsed * Rapid heart rate * Red, warm extremities Acutely life thretening * Adrenaline * Vasocontriction via action at a1 adrenoreceptors.

Question 26

Summarise Shock

Answer 26