Shock and Haemorrhage L17 Flashcards
(33 cards)
What is shock?
state of inadequate perfusion of the body
Example of high output states of shock? (2)
- anaphylactic shock
- sepsis
*states of vasodilation
Examples of low output states of shock? (2)
- cardiogenic shock (heart not contracting strongly enough)
- hypovolaemic (low volume)
name the four types of shock.
- hypovolaemic
- septic
- cardiogenic
- anaphylactic
How does cardiogenic shock lead to an increase in central venous pressure?
- ‘pump’ failure e.g. in MI
- ABP falls
- circulating volume falls
- as heart cannot pump blood, back up of blood in venous system
- increase in central venous pressure (*can see this on examination - JVP)
How does the body respond to cardiogenic shock?
fall in BP activates sympathetic NS:
- baroreceptor reflex > widespread vasoconstriction (except to brain)
- symp drive to kidneys > RAAS activation
What type of receptors or volume receptors?
stretch receptors - detect changes in distension of VEINS (CVP)
Where are volume receptors located?
right atrium
Along which nerve do volume receptor afferents travel and where do they travel to?
- Vagus (CN X)
- to the NTS
what are the effects of an increase in stretch of volume receptors?
- DECREASE in symp activity to kidney > increase renal perfusion
- DECREASE ADH release from post. pituitary > increase urine production > DECREASE BLOOD VOLUME
*decrease in blood volume/ stretch will have opposite effect
what is the Bainbridge reflex?
increase in stretch of volume receptors leads to INCREASE in symp activity to the HEART > INCREASE in heart rate
*don’t really know why but thought to be a protective mechanism
which is faster, effects of baroreceptor reflex on BP or effects of volume receptor reflex on blood volume?
Baroreceptor reflex effects
In cardiogenic shock, do you get an increase or decrease in distension of the atrium?
increase - as you get a rise in CVP
In cardiogenic shock, decreased ABP leads to activation of baroreceptor reflex which increase symp activity to the kidney leading to activation of RAS. Due to increase in CVP, there is increased distension of right atrium leading to activation of volume receptor reflex. This decreases symp activity to kidney leading to increased urine production. These two mechanisms are counter-active. Which one is more important? What would be the resulting effects in a person with a MI?
- most people with MI tend to be able to maintain ABP better than controlling rise in CVP
- so more important to decrease volume i.e. volume reflex more important (don’t want veins to burst)
- therefore decrease in symp activity to kidney overrules
- correct blood pressure through decreasing blood volume.
How is cardiogenic shock different to hypovolaemic shock (in terms of CVP)?
cardiogenic > rise in CVP
hypovolaemic > fall in CVP
What are the commonest causes of hypovolaemic shock? (4)
- haemorrhage
- diarrhoea or vomiting (e.g. in cholera)
- burns
- dehydration
Describe the baroreceptor reflex pathway for a fall in ABP.
-fall in ABP
>decreased stretch
>fall in baroreceptor activity
>fall in afferent activity to NTS (CNS)
>decreased inhibition of RVLM (symp to heart and blood vessels) and decreased excitation of NA (vagal to heart)
>increased stimulation of sympathetic pre-gnglionics and sympathetic post-ganglionic neurones to heart and blood vessels
AND
> decreased activity of afferent fibres to SON and PVN
decreased inhibition of post. pituitary gland
more ADH secretion
> increase in ABP to normal
Describe the baroreceptor reflex pathway for a rise in ABP.
-rise in ABP
>increased stretch
>rise in baroreceptor activity
>rise in afferent activity to NTS (CNS)
>increased inhibition of RVLM (symp to heart and blood vessels) and increased excitation of NA (vagal to heart)
>decreased stimulation of sympathetic pre-gnglionics and sympathetic post-ganglionic neurones to heart and blood vessels
AND
> increased activity of afferent fibres to SON and PVN
increased inhibition of post. pituitary gland
less ADH secretion
> decrease in ABP to normal
What happens to the urine output in haemorrhage?
decreases/more concentrated due to ADH and retention of water
After what percentage loss of circulating blood volume does haemorrhage induce shock?
20%
*below 20% body compensates for low BP through vasoconstriciton
At what percentage loss of circulating blood volume does haemorrhage become fatal and why?
40-50% as BP not maintained so cannot maintain perfusion to head >brain infarction *remember cranial perfusion graph
What effect can lack of adequate tissue perfusion in haemorrhage have on kidneys?
insufficient O2 to tissues > anaerobic respiration > lactic acidosis in renal tissue
What effect can tissue damage in haemorrhage have on kidneys?
release of K+ from damaged tissue > additional load on kidneys
What effect can cardiac hypoxia in haemorrhage have on kidneys?
drops in cardiac output > decreased renal perfusion etc.
