Shock

Question 1

Definition of shock

Answer 1

Inadequate peripheral tissue perfusion resulting in lack of O2 and nutrient supply to cells

Question 2

How many stages of shock are there? What are they?

Answer 2

4: Initial, compensatory, progressive, refractory

Question 3

What happens in the “initial” phase of shock?

Answer 3

Hypoperfusion –> hypoxia –> mitochondria unable to produce ATP –> cell membrane destruction –> ‘leaky’ cells
Anaerobic respiration –> ^^ lactic and pyruvic acid –> metabolic acidosis

Question 4

What happens in the “compensatory” phase of shock?

Answer 4

Neural, hormonal and biochemical mechanisms attempt to reverse changes in the initial phase
Hyperventilation –> vv CO2 –> relieve acidosis
Baroreceptors in arteries detect hypoperfusion –> adrenaline and noradrenaline release –> ^^ HR and vasoconstriction –> ^^ BP (Cushing reflex)
RAAS and ADH release –> conserve H2O –> ^^ BP
Net result: vasoconstriction of GIT, kidneys, skin; diversion to brain, heart, lungs

Question 5

What happens in the “progressive” phase of shock?

Answer 5

Compensatory mechanisms fail –> vv perfusion –> Na influx, K efflux
Continued anaerobic metabolism –> metabolic acidosis –> relaxation of arteriolar smooth muscle and capillary sphincters –> pooling of blood in capillaries
^^ hydrostatic pressure + histamine release –> leakage of fluid and protein into surrounding tissue
Blood [] and viscosity ^^ –> sludging in microcirculation

Question 6

What happens in the “refractory” phase of shock?

Answer 6

Vital organs fail and shock can no longer be reversed

Question 7

What are the types of shock?

Answer 7

Hypovolaemic
Cardiogenic
Distributive: septic, anaphylactic, neurogenic
Obstructive

Question 8

Causes of hypovolaemic shock?

Answer 8

Due to insufficient circulating blood volume, most commonly due to blood loss
(most common type of shock)

Question 9

Causes of cardiogenic shock?

Answer 9

Due to failure of heart to pump effectively

Causes: massive MI, arrhythmias, cardiomyopathy, valve disease

Question 10

Causes of distributive shock?

Answer 10

Relative hypovolaemia due to dilation of blood vessels (vv systemic vascular resistance)

• Septic: overwhelming systemic infection
• Anaphylactic: anaphylactic reaction to an allergen, antigen, drug
• Neurogenic: trauma to spinal cord with loss of autonomic and motor reflexes

Question 11

Causes of obstructive shock?

Answer 11

Due to obstruction of blood flow with subsequent impendence of circulation

• Cardiac tamponade
• Tension pneumothorax
• Massive PE
• Aortic stenosis

Question 12

Definition of severe sepsis vs septic shock?

Answer 12

Severe sepsis: acute organ dysfunction secondary to infection
Septic shock: severe sepsis + hypotension not reversed with fluid resuscitation

Question 13

Diagnostic criteria for septic shock?

Answer 13

• Evidence of infection
• Refractory hypotension: systolic BP20), or PCO2 12000
  + Heart rate >90
  + temperature >38.0 or

Question 14

Pathophysiology of septic shock?

Answer 14

Gram -ve (mostly) bacteria –> LPS released –> binds to LPSbp –> binds to CD14 –> neutrophils, monocytes, macrophages –> ^^ IL-1, TNF –> reduce synthesis of of anticoagulation factors (tissue factor pathway inhibitor, thrombomodulin) by endothelium; systemic vasodilatation; diminished cardiac contractility –> coag cascade and systemic leucocyte adhesion –> DIC –> hypoperfusion –> multiorgan failure

Question 15

Treatment of septic shock?

Answer 15

OVERS:

• O2 and airway support
• Volume resuscitation: target MAP >65mmHg, urine output >0,5ml/kg/hr, central venous O2 saturation >70%, haematocrit >30%
• Early antibiotic administration: IV, ASAP, broad-spectrum, preceded by blood (and other) cultures
• Rapid source identification and control: specific anatomical diagnosis sought/excluded and controlled
• Support major organ dysfunction: ventilation, sedation and analgesia, glucose control. renal replacement therapy, DVT prophylaxis, stress ulcer prophylaxis