cardiology cards Flashcards
Define Shock
life-threatening generalised form of acute circulatory failure with inadequate oxygen delivery to , and consequently oxygen utilisation by the cells.
often defined by low bp (mean arterial pressure <65mmHg), evidence of tissue hypoperfusion, raised serum lactate.
Investigations for shock
Assess using ABCDE
capillary refill time: takes more than 3 seconds to turn pink after 5 second of compression: earliest and most accurate sign of shock
additional ix based on suspected underlying cause: ecg, troponin, cxr
clinical manifestations of anaphylactic shock
-warm and flushed skin
- itching
-sweating
-may be breathlessness and wheeze
-cyanosis
-low bp
-tachycardia
-pulmonary oedema
clinical manifestations of septic shock
- warm and flushed skin
-pyrexia and rigors - nausea and vomiting
- bounding pulse
clinical manifestations of cardiogenic shock
- signs of heart failure eg : raised jvp, pulmonary oedema
clinical manifestations of hypovolaemic shock
- cold and clammy skin
-confusion and drowsiness - increased sympathetic tone
-tachycardia or bradycardia: depending on stage - initially narrow pulse pressure and weak pulse until there is compensation, and then again when there is failure of compensation
General signs and symptoms of shock
- tachycardia
-tachypnoea
-pulse is weak: pulse pressure reduced - mean arterial pressure (MAP) may be maintained until a very large amount of blood has been lost! - skin is warm and flushed - in warm shock
skin is cold and clammy: in cold shock - reduced urine output
-weakness
-confusion
-collapse
-coma
pathophysiology/ aetiology of shock
bp is key determinant of tissue perfusion:
bp = co * resistance to blood flow
co= sv *hr
shock is basically ischaemia on global scale - circulatory failure of whole body.
blood flow to tissues is dangerously low, leading to cellular injury, damage of multiple organs and even lead to multiple organ failure if not treated immediately.
pathophysiology of hypovolaemic shock
induced by a low fluid volume of blood. loss of around 20% of total blood volume can be enough to induce hypovolaemic shock. can be haemorrhagic or non-haemorrhagic :
non - loss of fluid volume isnt from bleeding eg dehydration, burns
haemoragic - loss of blood volume through ruptured blood vessels (loss of blood volume from bleeding ) - eg gi bleeding, trauma, peri/post-operative
results in total volume filling of heart going down which causes stroke volume to go down. causes decreased cardiac output and thend ecreased blood pressure.
when cardiac output goes down, catecholamines eg : epinephrine and norepinephrine, adh, and angiotensin 2 are released. cause vasoconstriction of blood vessels, increases vascular resistance and heart rate, in turn increases cardiac output. combined effects increase bp.
an indicator that tissues arent getting enough oxygen due to hypovolemia is a decreased mixed venous oxygen saturation (MVO2). this is the amount of oxygen bound to haemoglobin in the blood coming to the right side of the heart from the tissues. if blood volume is down, then oxygen is down, and so MVO2 will be donw.
as blood flow also give sheart to tissues, when its down, skin feels cool and clammy.
COlD SHOCK.
pathophysiology of cardiogenic shock
shock related to pathology of the heart, prevents it from pumping enough blood to tissues.
most common cause: acute MI. when cardiac myocytes die, it cant contract as hard, sv and co is reduced.
another cause is due to obstruction which doesnt allow the heart to fill properly with blood : eg pericardial effusion/cardiac tamponade physically constricts the ventricles and prevents the heart from expanding and contracting normally, reducing the sv and co..
other causes: arrhythmias, pulmonary embolus, tension pneumothorax, myocarditis, valvular disease, aortic dissection.
body releases vasoconstrictors to increase vascular resistance and help maintain bp. MVO2 will also be down since theres less oxygen being pumped out. - reduction in cardiac o utput leads to lowered blood flow, so skin gets cool and clammy: COLD SHOCK.
pathophysiology of neurogenic shock
the nervous system gets damaged and cant control the bodys bp
eg : spinal cord injury, epidural or spinal anaesthesia
pathophysiology of anaemic shock
not enough oxygen being carried in blood
pathophysiology of cytotoxic shock
cells are poisoned
pathophysiology of anaphylactic shock
an allergic reaction that causes dangerously low bp. massive release of histamine and other vasoactive mediators causes haemodynamic collapse.
distributive shock types
septic, anaphylactic , neurogenic
what is distributive shock
typically leakiness of blood vessels and excessive amount of arteriole vasodilation.
if arteriole dilate, vascular resistance to blood flow goes down, bp goes down, less perfusion, distribution of blood to organs and tissues.
pathophysiology of septic shock
endotoxins found on pathogens (usually gram negative) in the blood cause a cascade of events leading to lowered perfusion. they directly damage endothelial cells and cause release of vasodilators. they then activate the complement pathway, which stimulates mast cell release and activates other immune cells producing inflammatory cytokines. these help to destory the pathogen but also results in release of further inflammatory molecules eg platelet activating factor and ROS. these damage the endothelial cells and increase vascular permeability making the vessels leaky.
endothelial cells also express a procogaulant called tissue factors. these combined with decrease in anti-coagulants create net increase in coagulation and clotting in microvasculature. clotting creates further blockages and adds to decreased perfusion.
in this case, MVO2 may be normal or increased as blood doesnt have a chance to unload its oxygen to tisses.
also an increase in flow in the peripheral blood vessels, so skin becomes warm and flushed , therefore distributive shock is WARM shock.
management of shock
depends on cause
abc:
airways - intubation if needed
breathing: give o2
circulation: establish iv access, raise legs if hypovolemic, fluid resus and blood transufsion if necessary, ensure haemostasis
medications that increase heart contractility, cause vasoconstriction and retain fluid can nbe administered
manage underlying causes eg:
septic shock may require abx
anaphylactic shock: remove causative agent _+ adrenaline, chlorphenamine and hydrocortisone
cardiogenic shock: may require revascularisation
complications of shock
organ failure due to prolonged hypotension
kidneys - acute tubular necrosis
lung - acute respiratory distress syndrome (ARDs)
heart - Myocardial ischaemia and infarction
brain - confusion - irritability and coma
what is acute respiratory distress syndrome
life-threatening condition wher elungs cant provide the bodys vital organs with enough oxygen.
