Physiology and management of shock Flashcards
What is shock?
Condition of inadequate perfusion to sustain normal organ function
What are the 5 main classes of shock?
Hypovolaemic; loss of circulating volume resulting in reduced preload and cardiac output
Cardiogenic; myocardial dysfunction causing reduction in systolic function and cardiac output
Obstructive; physical obstruction to the filling of the heart; reduced preload and cardiac output
Distributive; significant reduction in SVR beyond the compensatory limits of increased cardiac output
Cytotoxic; uncoupling of tissue oxygen delivery and mitochondrial oxygen uptake
What can cause hypovolemic shock?
Blood loss
Interstitial fluid loss
Pure water deficit (rare)
How does the baroreceptor reflex compensate for hypovolemic shock?
Sense stretch in cartoid sinus (CN 9) and aortic arch (CN 10)
Decreased stretch results in decreased afferent input to medullary CV centers via CN 9
Inhibit parasympathetic outflow resulting in increased sympathetic output
How will sympathetic output compensate for hypovolemic shock?
Sympathetic chronotropy and inotropy
Release of vasoconstrictors; adrenaline, angiotensin, NA, vasopressin
Redirects fluid from peripheral and sensory organs
Resulting lactic acidosis drives chemoreceptors to enhance the response
Circulating vasodilators will increase in the decompensatory stages
How will capillary absorption of interstitial fluid compensate for hypovolemic shock?
Reduced capillary hydrostatic pressure
Inward net filtration
How will the hypothalamo-pituitary-adrenal response compensate for hypovolaemic shock?
Intrarenal baroreceptors mediate renin release from JGA
Resulting angiotensin 2 enhances vasoconstriction and ADH secretion
Enhances renal reabsorption of sodium and water
Very simplistically, what are the 3 ways to increase cardiac output?
Heart rate
Stroke volume (inotropy)
Both
What does the frank starling relationship state?
The greater the end diastolic volume (preload), the greater the ventricular ejection in systole and therefore the greater the SV
What effect will inotropy have on the frank starling curve?
Increased contility; curve shift upwards
Why will a failing heart result in pulmonary congestion?
Decreased contractility of heart
EDV will increase to maintain SV
Backwards pressure resulting in pulmonary congestion
What are some tips surrounding fluid prescribing?
Remember its a drug
Consider the individual patient
Consider fluid AND electrolyte requirements
Consider difference between resuscitation and maintenance fluids
What can cause cardiogenic failure?
Acute MI Valve dysfunction; acute mitral prolapse Myocarditis Cardiomyopathy Myocardial contusion
What are the clinical signs of cardiogenic shock?
Poor forward flow; hypotension/ shock, fatigue, syncope
Backpressure; pulmonary oedema, elevated JVP, hepatic congestion
What physiological mechanisms will increase inotropy?
Sympathetic nervous system
How can we pharmacologically increase inotropy?
Beta and dopaminergic stimulation
Dobutamine, adrenaline
Dopamine, dopexamine
Milrinone/ levosimendan
Should you give fluids in cardiogenic shock?
No; will likely result in pulmonary congestion
Fluids will shift the frank starling curve to the right
How is cardiogenic shock managed?
Inotropic agents
Inotropes will shift the frank starling curve upwards
What is the function of an intra-aortic balloon pump?
Counter pulsation
Inflation during ventricular diastole (augmented diastole) to increase coronary artery filling
Deflation during ventricular systole to reduce afterload and reduce oxygen demand of the heart
What phase of the cardiac cycle will obstructive shock affect?
Filling rather than ejection
How is obstructive shock treated?
PE; anticoags +/- thrombolysis
Tamponade; pericardial drainage
Tension pneumothorax; decompression and chest drainage
What are the ultrasound appearances of a massive PE resulting in obstructive shock?
Dilated, hypokinetic RV
Bowing of interventricular septum
Hyperkinetic RV at apex (McConnells sign)
What are the ultrasound appearances of a cardiac tamponade resulting in obstructive shock?
Fluid accumulation in pericardial sac
Compressess each chamber
Impaired cardiac filling and contraction
What is the physiology of distributive shock?
Vasodilatory
Initially, high cardiac output but insufficient to maintain forward perfusion due to massive dilation of vessels
Then, due to reduced venous return, cardiac output will fall
What are the 3 main subtypes of distributive shock?
Septic; bacterial endotoxin mediated capillary dysfunction
Anaphylactic; mast cell release of histaminergic vasodilators
Neurogenic; loss of sympathetic outflow following spinal injury