Physiology: Cardiovascular Response to Shock Flashcards
Define shock
An abnormality of the circulatory system resulting inadequate tissue perfusion and oxygenation
How does shock cause cell damage?
Shock (inadequate perfusion) --> Inadequate oxygenation --> Anaerobic metabolism in cells --> Anaerobic metabolic waste products accumulate --> Cell failure
On what does adequate tissue perfusion depend
- Adequate blood pressure
- Adequate cardiac output
Can patients have different forms of shock at the same time?
Yes
List the different types of shock
- Hypovolemic shock (haemorrhagic, non-haemorrhagic)
- Cardiogenic shock
- Obstructive
- Distributive (Neurogenic, Vasoactive)
Define hypovolaemic shock
Shock do to a loss of blood volume
Describe how loss of blood volume causes hypovolaemic shock
Loss of blood volume --> Blood volume decreases --> Decreased venous return --> Decreased end diastolic volume --> Cardiac output and Bp decrease --> Inadequate tissue perfusion
By what mechanism does the decrease in end diastolic volume in hypovolaemic shock cause a decrease in stroke volume
The Frank-Starling mechanism
Define cardiogenic shock
Shock due to sustained hypotension caused by decreased cardiac contractility
How does decreased cardiac contractility cause cardiogenic shock?
Decreased cardiac contractility --> Decreased stroke volume --> Decreased cardiac output and Bp --> Inadequate perfusion
Describe the effect of decreased cardiac contractility on the end diastolic volume in the left ventricle
Decreased contractility = EDV increase
increased contractility = EDV decrease
Define obstructive shock
Shock due to obstruction of the heart or its great vessels
List causes of obstructive shock
- tension pneumothorax
- cardiac tamponade
- pulmonary embolism (big)
- severe aortic stenosis
Describe how a tension pneumothorax causes obstructive shock
Increased intrathoracic pressure --> decreased venous return --> Decreased end diastolic volume --> Decreased stroke volume --> Decreased cardiac output and Bp --> Inadequate perfusion
List the 2 types of distributive shock
- Neurogenic shock
- Vasoactive shock
Describe the mechanism of neurogenic shock
loss of sympathetic tone to the heart and blood vessels
–>
Venous and arterial vasodilation, -ve chronotropic effect
–>
Decreased venous return, decreased SVR, decreased heart rate
–>
Decreased cardiac output and Bp
–>
Inadequate perfusion
Define neurogenic shock
Shock due to a loss of sympathetic tone to the heart and blood vessels
Which is the only type of shock to reduce heart rate?
neurogenic shock
due to the loss of sympathetic tone in the heart
Define vasoactive shock
Shock due to the release of vasoactive mediators
How does the release of vasoactive mediators cause vasoactive shock
Release of vasoactive mediators --> Venous and arterial vasodilation, and increased capillary permeability --> Decreased venous return, and SVR --> Decreased cardiac output and Bp --> Inadequate perfusion
Give a condition that can cause cardiogenic shock
Myocardial infarction
List causes of vasoactive shock`
- Septic shock
- Anaphylactic
Give a cause of neurogenic shock
Spinal chord injury
Are systemic vascular resistance (SVR) and total peripheral resistance (TPR) the same thing?
Yes
List the general treatments for shock
- ABCDE approach
- High flow oxygen
- Volume replacement (except for cardiogenic shock)
Why do you not give volume replacement for cardiogenic shock?
It would put more strain on an already failing heart
What is the immediate treatment for obstructive shock due to a tension pneumothorax?
Chest drain
What is the immediate treatment for an anaphylactic shock?
Adrenaline
What is the treatment for septic shock?
Vasopressors
What is the treatment for cardiogenic shock?
+ve inotropic drugs
Compensatory mechanisms can cope with blood loss until what % of volume is lost?
> 30%
After 30% the Bp starts to drop and haemorrhagic shock occurs
List some of the clinical signs of haemorrhagic shock, and their causes
Tachycardia - due to baroreceptor reflex
Small volume pulse - due to decreased cardiac output
Cool peripheries - Increased systemic vascular resistance via baroreceptor reflex
What corrective mechanism is activated by the acute drop in blood volume seen in haemorrhagic shock?
Baroreceptor reflex
List causes of hemorrhagic shock
Bleeding due to:
- trauma
- surgery
- haemorrhage
List causes of non-hemorrhagic hypovolemic shock
- Vomiting
- Diarrhea
- Excessive sweating
Describe the mechanism of non-hemorrhagic hypovolemic shock
Vomiting, diarrhea etc. --> Decreased ECF volume --> Decreased plasma volume --> EDV decreases --> Stroke volume and CO decrease --> Inadequate perfusion
