Haemorrhage and shock Flashcards
haemorrhage
loss of blood
type of haemorrhage
external - skin cut
revealed - blood in faeces
concealed - haemorrhage stroke
where is BP highest
artery
where is a dangerous haemorrhage
artery, because BP is so high lots of blood will be lost quickly
symptoms and signs of haemorrhage
- pale, grey or cyanotic with clammy skin
- rapid shallow breathig
- constricted veins
- tachycardia but weak pulse giving low stroke volume
- intense thirst
- reduced urin output
- nausea
- muscular weakness
- reduced mental awareness
how does body responds to haemorrhage (overview)
arterial blood pressure is reduced.
Cascade of passive events that are counteracted by reflexes
CV resposes to haemorrhage
- decrease in arterial BP determined by decrease in stoke volume and CO
- increase in HR and TPR to help stroke volume, CO and MAPB return to normal
what is altered directly by blood volume loss in haemorrhage
stroke volume, cardiac output and MABP
what is altered by reflex responses to haemorrhage
heart rate and TPR
- neural or integrated changes
stages of relfex response to haemorrhage
survival: seconds to minutes, by the baroreceptors
returning to normal: hours to days, absorption to restore blood
role of baroreceptors in haemorrhage
survival reflex response that occurs within seconds
what happens to vagal tone after haemorrhage
decreased parasympathetic stimulation in order to increase HR
what happens to sympathetic tone after haemorrhage
increases to:
- increase vasoconstriction,
- increase HR and cardiac contractility
- increase release of renin angiotensin-aldosterone
How does CNS respond to haemorrhage
- decreased parasympathetic/vagal tone
- increased sympathetic tone
- increased cortisol and ADH
what responds to change in blood volume after haemorrhage
cardiopulmonary receptors in the atria ventricles.
send signals to CNS
What responds to change in arterial BP after haemorrhage
baroreceptors in the aortic arch & carotid sinuses signal to CNS
why does vasoconstriction occur after haemorrgahe
- to increase central venous pressure
- to increase TPR
what reduces excretion of Na+ and water, and increases thirst
- cortisol
- ADH
- renin angiotensin-aldosterone
role of renin angiotensin-aldosterone post haemorrhage
- reduces excretion of Na+ and water
- increases thirst
- causes vasoconstriction
3 main response systems immediately after haemorrhage
- baroreceptors
- chemoreceptors
- CNS
main response to haemorrhage after days
renal blood volume pressure control
role of baroreceptor reflex in haemorrhage
contributes to maintaining arterial BP close to normal range
- allows each vascular bed to change its flow without lowering arterial BP
where is renin released and when
released from the kidneys stimulated by drop in blood pressure
what does renin do
renin contributes to production angiotensin
what does angiotensin do
powerful vasoconstrictor
- reduces excretion of salt and water by the kidney
what is a more powerful vasoconstrictor than angiotensin
ADH
what is released from pituitary in severe blood loss
ADH, a very powerful vasoconstrictor
where is ADH released
anterior pituitary
what happens when capillary pressure is reduced by 2mmHg
a 11%r reduction of capillary pressure = 7x more absorption
= net inward force of -2.3
what is maintained better - CO or ABP?
arterial blood pressure is maintained near normal levels during haemorrhage for longer than CO
which is maintained better during haemorrhage and why? CO or ABP
- sympathetic reflexes have a greater vasoconstrictor effect on arterioles than veins
- plateau occurs at 50% of ABP from activation of CNS - ischaemic response
what kicks in when ABP drops to ~50%
CNS as part of ischaemic response
- causes profound vasoconstriction
how does a 10% blood loss affect CO and ABP
virtually no effect, similar to blood donation of 500ml
blood volume of average 70kg man
5.4L
blood volume in men
77ml/kg
blood volume women
67ml/kg
effects of % blood loss
- 10% - virtually no effect on CO and BP
- 20% unlikely to elicit shock
- 20-30% can induce shock. BP may drop
- 20-50% causes severe shock and profound fall in ABP and BP that may be irreversible
- more than 50% death generally inevitable
what has an effect of severity of volume of blood loss
the rate at which the blood is lost
e.g rapid loss of 30% fatal, but 50% loss over 24 hours could be survived
circulatory shock
acute failure of the CV system to perfuse the tissues of the body adequately
type of circulatory shock
- cardiogenic
- septic
- hypovolaemic
cardiogenic shock
caused by acute impairment of cardio function
- myocardial infarction
- myocarditis
85% mortality
septic shock
caused by bacteraemia, especially endotoxin
what is endotoxin
powerful CV toxin that causes septic shock
hypovolaemic shock
caused by fall in blood or plasma volume
- diarrhoea
- vomiting
- dehydration
- haemorrhage most common
stages of shock
- non-progressive
- progressive
- irreversible shock
which stage of shock is reversible
- non- progressive
- progressive with therapy
which stage of shock is irreversible
irreversible shock
no form of therapy is adequate to save person’s life
what is non-progressive shock
shock will not progress because the sympathetic reflexes and other factors compensate enough to the loss of blood, which prevents further deterioration of circulation
how is compensation achieved in non-progressive shock
- baroreceptor reflex
- CNS ischaemic response
- formation of angiotensin in the kidneys by renin
- release of ADH by pituitary
- absorption of fluid from GI and interstitial space of body into capillaries
what is the golden hour
when body tried to compensate. if fails, transfusion will happen at 1 hour and either progressive shock will occur which can be treated, or irreversible shock which cannot be treated
what time frame is reversible shock
30-60 mins post haemorrhage
what % blood loss is reversible and irreversible shock
45%
what can cause progression of shock
positive feedback
how does positive feedback cause progression of shock
- APB becomes excessive low, so coronary blood flow decreases well below level required for adequate nutrition of the myocardium
- lack of nutrition weakens the heart muscle
- weaken heart muscle = even more reduced CO
- reduced CO reduces coronary blood flow even more
= shock becomes more and more severe
what causes shock to become more severe
positive feedback cycle
