Shock Flashcards
what is shock?
condition of inadequate perfusion to sustain normal organ function
what are the 5 main classes of shock?
hypovolaemic cardiogenic (MI dysfunction) obstructive distributive cytotoxic
what is hypovolaemic shock?
insufficient circulating volume to fill the circuit
can be from loss of blood, interstitial fluid or pure water (rare)
clinical features of hypovolaemic shock?
depend on the degree of hypovolaemia
why is hypovolaemic shock so dangerous in young people?
as they compensate very well for a longer time and then suddenly deteriorate
4 main compensatory mechanisms in maintaining circulating volume?
baroreceptor reflex
sympathetic chronotropy/inotropy
capillary absorption of interstitial fluid
hypothalamo-pituitary-adrenal response
describe the baroreceptor reflex?
Stretch sensitive receptors in the carotid sinus (CNIX) and aortic arch (CNX)
Decreased stretch > decreased afferent input to medullary CV centres
Inhibition of parasympathetic (CNX) and enhanced sympathetic output > results in constriction of blood vessels to maintain BP
describe the sympathetic chronotropy/inotropy compensatory mechanism?
Release of circulating vasoconstrictors (adrenaline, angiotensin, noradrenaline, vasopressin)
Redirects fluid from peripheral and secondary organs
Resulting lactic acidosis drives chemoreceptors to enhance response
Circulating vasodilators also increased (involved decompensatory stages)
describe capillary absorption of intetstitial fluid?
reduced capillary hydrostatic pressure = inward net filtration
how can Cardiac output (CO) be increased?
increase HR
increase SV (inotropy)
increase both
why cant young children increase SV?
immature muscle
how does giving fluids change stroke volume?
should increase SV
greater volume loading during diastole increases SV
inotropy increases contractility
how is the frank starling curve affected in heart failure?
decreased contractility = curve shifted downwards
what is cardiogenic shock?
where heart doesnt work effectively as a pump to meet circulatory demands
most common cause of cardiogenic shock?
- Most commonly a complication of MI but may also follow acute valve dysfunction
○ E.g acute mitral prolapse, myocarditis, cardiomyopathy etc
clinical signs of cardiogenic shock?
Poor forward flow, heart cant pump blood forward (hypotension/shock, fatigue, syncope)
Backpressure (pulmonary oedema, elevated JVP, hepatic congestion)
how is cardiogenic shock managed?
focused on increasing CO
give drugs which stimulate sympathetic NS and shift curve upwards
- dobutamine, adrenaline
- dopamine, dopexamine
- others (milrinone, levosimendan)
if heart is so impaired that drugs cant sort CO then use an intra-aortic balloon pump
how does an intra-aortic balloon pump work?
Provides counterpropulsion
® Inflation during ventricular diastole (increased diastole = increased perfusion of coronary arteries)
® Deflation during ventricular systole (reduces afterload and systolic pressure = decreased force that heart has to pump against)
why arent fluids given in cardiogenic shock?
there is often already oedema so fluids would make it worse
what is obstructive shock?
where there is a physical obstruction to either the heart or the great vessels
(mainly affects filling of the heart rather than cardiac ejection)
what can cause obstructive shock?
PE
pericardial effusion/tamponade
tension pneumothorax
basically anything blocking filling of the heart
how is obstructive shock managed?
treat underlying cause
- PE = anticoagulation +/- thrombolysis
- tamponade = pericardial drainage
- tension pneumothorax = decompression and chest drainage
how is obstructive shock diagnosed?
ECHO (point of care testing)
- PE = dilated and non-mobile right ventricle, bowing of IV septum due to pressure difference between ventricles
- pericardial effusion/tamponade = fluid in pericardial sac compressing each chamber, impaired filling and contraction
what is distributive shock?
circuit is dilated (too big) so blood volume si normal but bc the circuit is increased its not not enough to perfuse and BP drops
AKA vasodilatory/warm shock
3 subtypes of ditributive shock?
Septic (bacterial endotoxin mediated capillary dysfunction)
Anaphylactic (inappropriate release of histamine from mast cells)
Neurogenic (loss of thoracic sympathetic outflow following spinal injury)
describe septic shock management
Raising lactate levels can indicate hypoperfusion before hypotension occurs
Every hour delay of antibiotics increases mortality by 7.5%
Early use of vasopressors (vasoconstrictors) improves perfusion and minimises excessive fluid volumes
what causes anaphylactic shock?
Uncontrolled activation of mast cells and degranulation
Release of histamine = vasodilation
what is given in anaphylactic shock?
Adrenaline acts as a mast cell stabliser (stops degranulation) and also is a vasoconstrictor
Serum mast cell tryptase levels confirm the diagnose
neurogenic shock vs spinal shock?
neurogenic = caused by spinal cord damage, spinal cord not attached, due to loss of sympathetic tone
spinal shock = also die to spinal injury but spinal cord still attached, loss of spinal reflexes, will recover?
what causes neurogenic shock?
hypotension due to loss of descending sympathetic tone
inappropriate bradycardia occurs due to unopposed vagal tone (can be exacerbated by suction etc)
mainstays of treatment for neurogenic shock?
dopamine alongside vasopressors
4 Hs and 4 Ts causing cardiac arrest?
- hypoxia
- hypotension
- hypothermia
- hypo/hyperkalaemia
- toxins
- tamponade
- thrombosis
- tension pneumothorax
how does CPR work?
- Cyclical changes in intrathoracic pressure alternately pushes blood out of and sucks blood back into the chest
○ Hence importance of allowing recoil between compressions
what rhythms are shockable?
VF
pulseless VT
describe VF?
chaotic and unrecognisable ECG with no recognisable QRS complexes
can occur after MI, toxins, electrolyte abnormality etc
describe pulseless VT?
can be monomorphic (rapid, broad QRS with constant QRS morphology) or polymorphic (torsades de pointes)
what rhythms arent shockable?
pulseless electrical activity
asystole
what usually causes pulseless electrical activity?
usually hypovolaemia
usually almost normal rhythm but just not enough blood
how is pulseless electrical activity managed?
adrenaline 1mg IV every 3-5 mins
how us asystole managed?
same as pulseless electrical activity
