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renal > Shock and Haemorrhage L17 > Flashcards

Shock and Haemorrhage L17 Flashcards

1
Q

What is shock?

A

state of inadequate perfusion of the body

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2
Q

Example of high output states of shock? (2)

A
  • anaphylactic shock
  • sepsis

*states of vasodilation

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3
Q

Examples of low output states of shock? (2)

A
  • cardiogenic shock (heart not contracting strongly enough)

- hypovolaemic (low volume)

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4
Q

name the four types of shock.

A
  • hypovolaemic
  • septic
  • cardiogenic
  • anaphylactic
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5
Q

How does cardiogenic shock lead to an increase in central venous pressure?

A
  • ‘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)
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6
Q

How does the body respond to cardiogenic shock?

A

fall in BP activates sympathetic NS:

  • baroreceptor reflex > widespread vasoconstriction (except to brain)
  • symp drive to kidneys > RAAS activation
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7
Q

What type of receptors or volume receptors?

A

stretch receptors - detect changes in distension of VEINS (CVP)

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8
Q

Where are volume receptors located?

A

right atrium

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9
Q

Along which nerve do volume receptor afferents travel and where do they travel to?

A
  • Vagus (CN X)

- to the NTS

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10
Q

what are the effects of an increase in stretch of volume receptors?

A
  • 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

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11
Q

what is the Bainbridge reflex?

A

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

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12
Q

which is faster, effects of baroreceptor reflex on BP or effects of volume receptor reflex on blood volume?

A

Baroreceptor reflex effects

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13
Q

In cardiogenic shock, do you get an increase or decrease in distension of the atrium?

A

increase - as you get a rise in CVP

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14
Q

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?

A
  • 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.
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15
Q

How is cardiogenic shock different to hypovolaemic shock (in terms of CVP)?

A

cardiogenic > rise in CVP

hypovolaemic > fall in CVP

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16
Q

What are the commonest causes of hypovolaemic shock? (4)

A
  • haemorrhage
  • diarrhoea or vomiting (e.g. in cholera)
  • burns
  • dehydration
17
Q

Describe the baroreceptor reflex pathway for a fall in ABP.

A

-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

18
Q

Describe the baroreceptor reflex pathway for a rise in ABP.

A

-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

19
Q

What happens to the urine output in haemorrhage?

A

decreases/more concentrated due to ADH and retention of water

20
Q

After what percentage loss of circulating blood volume does haemorrhage induce shock?

A

20%

*below 20% body compensates for low BP through vasoconstriciton

21
Q

At what percentage loss of circulating blood volume does haemorrhage become fatal and why?

A

40-50% as BP not maintained so cannot maintain perfusion to head >brain infarction *remember cranial perfusion graph

22
Q

What effect can lack of adequate tissue perfusion in haemorrhage have on kidneys?

A

insufficient O2 to tissues > anaerobic respiration > lactic acidosis in renal tissue

23
Q

What effect can tissue damage in haemorrhage have on kidneys?

A

release of K+ from damaged tissue > additional load on kidneys

24
Q

What effect can cardiac hypoxia in haemorrhage have on kidneys?

A

drops in cardiac output > decreased renal perfusion etc.

25
Q

What effect can renal hypoxia in haemorrhage have on kidneys?

A

leads to acute renal failure

26
Q

What is the renal response to shock?

A 
-fall in venous pressure activates ADH release
>water retention 
>transient hyponatraemia
>aldosterone release (RAAS)
>maintian water and Na+
27
Q

What is the main reason for an increase in lactate concentrations during shock?

A
  • shock stimulates release of adrenaline
  • acts via beta-adrenoceptors in muscle cells, heart, renal etc.
  • works to increase AEROBIC metabolism
  • during aerobic metabolism some of the pyruvate is converted into lactate, even in presence of O2
  • therefore increase in lactate concentrations is a marker of adrenaline release, not tissue hypoxia
28
Q

How can shock be treated?

A

give a fluid that has same osmolality as blood and that stays within circulation to increase circulating volume of blood which is the main effect in shock.

Therefore give colloid or crystalloid

29
Q

Why are blood transfusions not usually given for haemorrhage?

A
  • disease risk
  • limited supply of blood to give
  • other fluids preferred unless haemoglobin is very low
30
Q

What is a colloid?

A

a large molecule that remains within intravascular space to mainatin intravascular volume at the expense of interstitial volume

31
Q

Give examples of colloids used.

A

albumin, gelatins, dextrans, hydroxyethyl starches

32
Q

What is a crystalloid?

A

saline solution at normal osmolality

33
Q

Which is better - collids or crystalloids?

A

relatively similar effects

renal (16 decks)

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