Physiology of Shock Flashcards
define shock
condition of inadequate perfusion to sustain normal organ function
name the 5 classes of shock
hypovolaemic cardiogenic obstructive distributive cytotoxic
what is the cause of hypovolaemic shock?
loss of circulating volume -> reduced preload and cardiac output
what causes hypovolaemic shock?
bleeding
third space losses
severe dehydration
clinical features of hypovolaemic shock
> pulse and RR
< BP and PP
< urine output
anxiety, confusion, lethargy
describe baroreceptors
stretch sensitive receptors in carotid sinus and aortic arch
describe baroreceptor reflex
decreased stretch -> decreased afferent input to medullary CV centres -> inhibition of parasympathetic and enhanced sympathetic output
what is the sympathetic mediated neurohormonal response?
release of circulatory vasoconstrictors
redirects fluid from peripheral and secondary organs
resulting lactic acidosis drives chemoreceptors to enhance response
name circulatory vasoconstrictors
adrenaline
angiotensin
norad
vasopressin
what is the role of capillary absorption of interstitial fluid?
reduced capillary hydrostatic pressure -> inward net filtration
what is the hypothalamo-pituitary-adrenal response?
intrarenal baroreceptors mediate renin release from JGA
resulting Ang II enhances vasoconstriction and ADH secretion
enhances renal absorption of sodium and water
what are the 3 options to increase CO?
increase HR
increase SV
increase both
what causes cardiogenic shock?
myocardial dysfunction causing reduction in systolic function and cardiac output
what usually causes cardiogenic shock?
MI or acute valve lesion
what are more unusual causes of cardiogenic shock?
myocarditis
cardiomyopathy
myocardial contusion
clinical signs of cardiogenic shock
poor forward flow - hypotension - fatigue - syncope backpressure - pulmonary oedema - elevated JVP - hepatic congestion
what is +ve inotropy?
increase in force of cardiac contraction for any given preload
how is inotropy achieved normally and pharmacologically?
by the SNS
B and dopaminergic stimulation
what is the function of an intra-aortic balloon pump?
to provide counterpulsation
- inflation during diastole
- deflation during systole
what is the cause of obstructive shock?
Physical obstruction to filling of the heart caused by an obstruction in the heart itself or great vessels
what is the result of obstructive shock?
reduced preload and cardiac output
what is the usual cause of obstructive shock?
cardiac tamponade
PE
how do you treat a PE?
anticoagulation +/- thrombolysis
how do you treat cardiac tamponade?
pericardial drainage
how do you treat a tension pneumothorax?
decompression and chest drainage
what causes distributive shock?
Significant reduction in SVR beyond the compensatory limits of increased cardiac output
what is the result of distributive shock?
initial high CO but insufficient to maintain forward perfusion
what causes distributive shock?
septic shock
anaphylaxis
neurogenic causes
what causes shock from sepsis?
bacterial endotoxin mediated capillary dysfunction
how do you treat sepsis to prevent shock?
early abs
vasopressors
what causes shock in anaphylaxis?
mast cell release of histaminergic vasodilators
what causes neurogenic distributive shock?
spinal cord or central trauma causes loss of thoracic sympathetic outflow
how do you treat shock caused by neurogenic reasons?
dopamine
vasopressors
what causes cytotoxic shock?
Uncoupling of tissue oxygen delivery and mitochondrial oxygen uptake
Caused by CO poisoning and CN- poisoning
shockable cardiac rhythms
ventricular fibrillation
pulseless ventricular tachycardia
non shockable cardiac rhythms
pulseless electrical activity
asytole
