Shock Flashcards
What is shock?
An abnormality of the circulatory system resulting in inadequate tissue perfusion and oxygenation
Steps in how shock leads to cellular failure
Shock → inadequate tissue perfusion → inadequate tissue oxygenation → anaerobic metabolism → accumulation of metabolic waste products that are toxic to the cell → cellular failure
What does adequate tissue perfusion depend on?
Adequate blood pressure and adequate cardiac output
What does stroke volume depend on?
Preload, myocardial contractility, afterload
Afterload
The resistance against which the heart is pumping
Myocardial contractility
How well the heart can contract
Hypovolaemic shock
Loss of blood volume
How can hypovolaemic shock lead to inadequate tissue perfusion?
Loss of blood volume → decreased blood volume → decreased venous return → decreased end diastolic volume → decreased stroke volume → decreased CO and BP → inadequate tissue perfusion
Cardiogenic shock
Sustained hypotension caused by decreased cardiac contractility
Example on when cardiogenic shock can occur
When the heart is severely damaged e.g. after a myocardial infarction
How can cardiogenic shock lead to inadequate tissue perfusion?
Decreased cardiac contractility → decreased stroke volume → decreased CO and BP → inadequate tissue perfusion
Obstructive shock
Increased intrathoracic pressure
What can cause obstructive shock?
Tension pneumothorax
How can obstructive shock lead to inadequate tissue perfusion?
Increased intrathoracic pressure → decreased venous return → decreased end diastolic volume → decreased stroke volume → decreased CO and BP → inadequate tissue perfusion
Why does increased intrathoracic pressure cause decreased venous return?
Venous return depends on the pressure gradient outside and inside the chest
Neurogenic shock
Loss of sympathetic tone to blood vessels and heart
What can cause neurogenic shock?
Spinal cord injury
How can neurogenic shock lead to inadequate tissue perfusion?
Loss of sympathetic tone to blood vessels and heart → massive venous and arterial vasodilation causing effect on heart rate → decreased venous return and decreased SVR leads to decreased heart rate → decreased CO and BP → inadequate tissue perfusion
What is different in how neurogenic shock leads to inadequate tissue perfusion compared to other types of shock?
Heart rate decreases
Vasoactive shock
Release of vasoactive mediators
Examples of vasoactive shock
Septic shock, anaphylactic shock
How can vasoactive shock lead to inadequate tissue perfusion?
Release of vasoactive mediators → massive venous and arterial vasodilation and increased capillary permeability (vessels become leaky) → decreased venous return and decreased SVR → decreased CO and BP → inadequate tissue perfusion
Treatment of shock
- ABCDE approach
- High flow oxygen
- Volume replacement
- Call for help early
- Treat the cause as appropriate
For which type of shock would you not give volume replacement as treatment?
Cardiogenic shock
Additional treatment for cardiogenic shock
Inotropes
Treatment for tension pneumothorax
Immediate chest drain
Treatment for anaphylactic shock
Adrenaline
Treatment for septic shock
Vasopressors
Causes of hypovolaemic shock
Haemorrhage e.g. trauma, surgery, GI haemorrhage
Vomiting, diarrhoea, excessive sweating
How can vomiting lead to circulatory shock?
Vomiting leads to decreased extracellular fluid volume → decrease in blood volume → decrease in CO → circulatory shock and decreased MAP
Until what stage in haemorrhagic shock can compensatory mechanisms maintain blood pressure?
Until greater than 30% of blood volume is lost
Compensatory mechanisms to maintain blood pressure in haemorrhagic shock
Increased heart rate, decreased stroke volume → cardiac output may be decreased
Increased systemic vascular resistance
Class I haemorrhagic shock:
- Blood loss (mL and % blood volume)
- Pulse rate
- Blood pressure
- Pulse pressure
- Resp rate
- Urine output
- Central nervous system/mental status
- Up to 750ml, up to 15% blood volume
- <100
- Normal
- Normal or increased
- 14-20 per minute
- > 30 ml/hour
- Slightly anxious
Class II haemorrhagic shock:
- Blood loss (mL and % blood volume)
- Pulse rate
- Blood pressure
- Pulse pressure
- Resp rate
- Urine output
- Central nervous system/mental status
- 750-1500ml, 15-30% blood volume
- 100-120
- Normal
- Decreased
- 20-30 per minute
- 20-30 ml/hour
- Mildly anxious
Class III haemorrhagic shock:
- Blood loss (mL and % blood volume)
- Pulse rate
- Blood pressure
- Pulse pressure
- Resp rate
- Urine output
- Central nervous system/mental status
- 1500-2000ml, 30-40% blood volume
- 120-140
- Decreased
- Decreased
- 30-40 per minute
- 5-15 ml/hour
- Anxious/confused
Class IV haemorrhagic shock:
- Blood loss (mL and % blood volume)
- Pulse rate
- Blood pressure
- Pulse pressure
- Resp rate
- Urine output
- Central nervous system/mental status
- > 2000ml, >40%
- > 140
- Decreased
- Decreased
- > 35 per minute
- Negligible
- Confused/lethargic
