Pathology and physiology Flashcards
Name the reversible causes of cardiac arrest
4 H’s, 4 T’s
- hypoxia
- hypovolaemia
- hypo / hyperkalaemia / metabolic
- hypothermia
- thrombosis; coronary or pulmonary
- tamponade
- toxins
- tension pneumothorax
Wischnewski ulcers can be associated with what mode of death?
Hypothermia
Corneal arcus are associated with what?
Coronary artery atherosclerosis
Define shock
A condition of inadequate perfusion to sustain normal organ function - i.e. oxygen concentration cannot meet the metabolic demands of the major organs systems
Name the 5 classes of shock
- hypovolaemic shock
- cardiogenic shock
- obstructive shock
- distributive shock
- cytotoxic shock
Describe cytotoxic shock
- blood flow to tissues is maintained but cellular hypoxia occurs either due to a failure of oxygen delivery via haemoglobin or failure of mitochondrial respiration and use of oxygen
- examples include CO poisoning, CN poisoning
Describe the physiology of hypovolaemic shock
- failure of forward cardiac output due to insufficient circulating volume to fill the circuit
- this leads to reduced preload and cardiac output
- end organ hypoperfusion
Hypovolaemic shock can occur when?
Can be from;
- blood loss
- interstitial fluid loss
- or pure water (rare) deficit
Describe the clinical features of hypovolaemic shock
- young fit people tend to compensate well until they dont
- dependent on the degree of hypovolaemia
- early; modest tachycardia, pulse pressure may widen, sweaty
- as it continues; tachycardia increases, pule pressure narrows, tachypnoeic, urine output maintained initially
- hypotension is a late sign of haemorrhage
- increasingly end organ hypoperfusion becomes apparent e.g. confusion, falling urine output is also a later sign
Name the compensatory mechanisms for hypovolaemic shock
- baroreceptor reflexes
- sympathetic mediated neurohormonal response
- capillary absorption of interstitial fluid
- hypothalamo-pituitary-adrenal response
Describe the baroreceptor reflex in hypovolaemic shock
- stretch sensitive receptors in carotid sinus (CNIX) and aortic arch (CNX)
- shock causes decrease arterial stretch which leads to decreased stimulation of baroreceptors which leads to reduction of affterent input to medullary CV centres
- inhibition of parasympathetic and enhanced sympathetic output
- results in the increase in CO, increase inotropic and chronotropic effect
Describe the sympathetic mediated neurohormonal response in hypovolaemic shock
- sympathetic chronotropy and inotropy
- release of circulating vasoconstrictors e.g. adrenaline, noradrenaline, angiotensin, norad, vasopressin
- this raises vasomotor tone and redirects fluid from peripheral and secondary organs
- the resulting lactic acidosis chemoreceptors to enhance response
Describe the capillary absorption of interstitial fluid in hypovolaemic shock
- reduced capillary hydrostatic pressure, inward net filtration
- starlings forces favour net inward filtration
Describe the hypothalamo-pituitary-adrenal response in hypovolaemic shock
- the combined effects of hypotension and sympathetic activation results in increased secretion of renin from JGA
- this increases conc. of angiotensin 2 which acts as a stimulus to release aldosterone and vasopressin
- this enhances vasoconstriction, thirst and the renal reabsorption of sodium and water
- this all aims to restore blood volume
What are the 3 options the heart has to increase its cardiac output?
- increase HR (tachycardia)
- increase stroke volume (inotropy)
- increase both
Greater volume loading of the ventricle during diastole results in what?
Greater ventricular ejection in systole
How does inotropy and heart failure affect the Frank-Starling curve?
- inotropy results in an upward shift of the curve due to increased contractility
- HF results in a downward shift of the curve due to decreased contractility
Describe the physiology of cardiogenic shock
- inability of the heart as a pump to meet circulatory demands
- most commonly a complication of acute MI but may also follow acute valve dysfunction
- other causes include myocarditis, cardiomyopathy, myocardial contusion
Name clinical signs of cardiogenic shock
- poor forward flow; hypotension / shock, fatigue, syncope
- backpressure; pulmonary oedema, elevated JVP, hepatic congestion
Positive inotropic effects are achieved through what?
Adrenergic stimulation
Positive inotropic effects can be replication pharmacologically using what?
- beta and dopaminergic stimulation
- dobutamine, adrenaline
- dopamine, dopexamine
- others e.g. milrinone, levosimendan
What is the aim of an intra-aortic balloon pump and how does it do this?
Aim; provides counterpulsation to provide mechanical support of CV system
- inflation during ventricular diastole (augmented diastole)
- deflation during ventricular systole (reduced afterload)
Describe obstructive shock and its treatment
- involves a physical obstruction to either the heart or great vessels
- mainly affects cardiac filling rather than cardiac ejection
- treatment involves removing the underlying cause; pulmonary embolism, cardiac tamponade, tension pneumothorax
Describe the physiology of distributive shock
- aka vasodilatory / warm shock
- generally initial high cardiac output but insufficient to maintain forward perfusion
- inadequate oxygen delivery and organ perfusion due to failure of endothelial cells in the micro-circulation to vasoconstrict and direct blood flow correctly resulting in pooling in the larger vessels
