cardiovascular responses to shock (CVS 12) Flashcards
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)
what is shock
an abnormality of the cirulatory system resulting in inadequate tissue perfusion and oxygenation
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
MAP
- mean arterial pressure
- MAP = cardiac output (CO) x total peripheral resistance (TPR)
CO
- cadiac output
- the volume of blood pumped by each ventricle of the heart per minute
- CO = stroke volume (SV) x heart rate (HR)
stroke volume (SV)
= volume of blood pumped by each ventricle of the heart per heart beat
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
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
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
cardiogenic shock
- > eg. acute myocardial infarction
- decreased cardiac contractility -> decreased stroke volume -> decreased cardiac output and blood pressure -> inadequate tissue perfusion
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
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
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
vasoactive
affecting the diameter of blood vessels (and hence blood pressure)
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
vasopressors
a drug or other agent which causes the constriction of blood vessels
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.
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)
hypovolemia
hypovolemia (also hypovolaemia, oligemia or shock) is a state of decreased blood volume; more specifically, decrease in volume of blood plasma
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
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
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
