cardiovascular responses to shock (CVS 12) Flashcards Preview

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Flashcards in cardiovascular responses to shock (CVS 12) Deck (22):
1

different types of shock

-hypovolaemic (haemorrhagic, non-haemorrhagic)
-cardiogenic (eg. acute myocardial infarction)
-obstructive (eg.cardiac temponade, tension pneumothorax, pulmonary embolism, severe aortic stenosis)
-distributive (neurogenic eg.spinal cord injury, vasoactive eg.septic shock, anaphylactic shock)

2

what is shock

an abnormality of the cirulatory system resulting in inadequate tissue perfusion and oxygenation

3

what is the effect of inadequate tissue perfusion and oxygenation during shock

inadequate tissue perfusion -> inadequate tissue oxygenation -> anaerobic metabolism -> accumulation of waste products -> cellular failure

4

MAP

-mean arterial pressure
-MAP = cardiac output (CO) x total peripheral resistance (TPR)

5

CO

-cadiac output
-the volume of blood pumped by each ventricle of the heart per minute
-CO = stroke volume (SV) x heart rate (HR)

6

stroke volume (SV)

= volume of blood pumped by each ventricle of the heart per heart beat

7

adequate tissue perfusion

-adequate tissue perfusion depends on adequate blood pressure and adequate cardiac output
-> MAP= CO x TPR
-> CO = HR x SV
-> factors that affect stroke volume: preload (affected by venous return), myocardial contractility, afterload

8

hypovolaemic shock

->haemorrhagic
->non-haemorrhagic
-loss of blood volume -> decreased bood volume -> decreased venous return -> decreased end diastolic volume -> decreased stroke volume -> decreased cardiac output and blood pressure -> inadequate tissue perfusion

9

effect of end diastolic volume (EDV) on stroke volume (SV) - frank starling curve

-as end diastolic volume (ml) increases, as does stroke volume (ml)
-stroke volume = tension
-EDV = fibre length = preload

10

cardiogenic shock

->eg. acute myocardial infarction
-decreased cardiac contractility -> decreased stroke volume -> decreased cardiac output and blood pressure -> inadequate tissue perfusion

11

obstructive shock

-can be due to cardiac temponade, tension pneumothorax, pulmonary embolism, severe aortic stenosis
-> in this case = tension pneumothorax
-increased intrathoracic pressure -> decreased venous return -> decreased end diastolic volume ->decreased stroke volume ->decreased cardiac output and decreased blood pressure -> inadequate tissue perfusion

12

neurogenic shock (type of distributive shock)

-type of distributive shock
-can be due to injury to spinal cord
-loss of sympathetic tone -> massive venous and arterial vasodilation -> decreased venous return and decreased TPR -> decreased stroke volume (as a result of decreased venous return as it decreases end diastolic volume) -> decreased cadiac output and decreased TPR -> decreased blood pressure -> inadequate tissue perfusion

13

vasoactive shock (type of distributive shock)

-type of distributive shock
-eg. septic shock
-release of vasoactive mediators -> massive venous and arterial vasodilation, and also increased capillary permeability -> decreased venous return and decreased TPR -> decreased cardiac output and decreased blood pressure -> inadequate tissue perfusion

14

vasoactive

affecting the diameter of blood vessels (and hence blood pressure)

15

outlines of treatment of shock

-ABCDE approach
-high flow oxygen
-volume replacement
-inotropes for cardiogenic shock
-immediate chest drain for tension pneumothorax
-adrenaline for anaphylactic shock
-vasopressors for septic shock

16

vasopressors

a drug or other agent which causes the constriction of blood vessels

17

anaphylactic shock

-an extreme, often life-threatening allergic reaction to an antigen to which the body has become hypersensitive
-anaphylaxis = an acute allergic reaction to an antigen (e.g. a bee sting) to which the body has become hypersensitive.

18

cardiovascular responses to hypovolaemic shock

-compensatory mechanisms can maintain blood pressure until >30% of blood volume is lost
->autoregulation of cerebral blood flow (myogenic response)
->baroreceptors reflex (response to decreased blood pressure)

19

hypovolemia

hypovolemia (also hypovolaemia, oligemia or shock) is a state of decreased blood volume; more specifically, decrease in volume of blood plasma

20

causes of hypovolaemic shock

-haemorrhage (eg. trauma, surgery or GI haemorrhage) -> causes decreased blood volume -> which causes decreased cardiac output -> causing circulatory shock (decreased MABP causing inadequate tissue perfusion)
OR
-vomiting/diarrhea/excessive sweating -> causes decreased ECFV (including plasma) -> causing decreased blood volume -> causing decreased cardiac output -> which causes circulatory shock (decreased MABP causing inadequate tissue perfusion)
->loss of blood volume -> decreased bood volume -> decreased venous return -> decreased end diastolic volume -> decreased stroke volume -> decreased cardiac output and blood pressure -> inadequate tissue perfusion

21

regulation of cerebral blood flow

-autoregulation of cerebral blood flow (myogenic response)
-By definition, the myogenic response is the contraction of a blood vessel that occurs when intravascular pressure is elevated and, conversely, the vasodilation that follows a reduction in pressure
-therefore if there is blood loss, cerebral blood flow decreases and therefore the myogenic response causes vasoconstriction following a decrease in blood pressure

22

baroreceptors reflex in response to decreased blood pressure

-decreased ABP -> decreased baroreceptor discharge -> which is detected by the cardiovascular/ CV integrating centre (medulla) ->this does three things in response
1. decreases vagal activity which -> increases HR
2. decreases cardiac sympathetic activity which -> increases HR and SV
3.increases sympathetic constrictor tone which causes -> venoconstriction which also increases SV, and causes vasoconstriction which increases TPR
->the increase in HR and SV cause an increase in cardiac output as CO= HR x SV
-> and as TPR and CO increase, this increases MAP again as MAP = CO x TPR
-as hemorrhagic shock leads to decreased MAP and CO and therefore inadequate tissue perfusion, this acts as a control mechanism