Shock And Haemorrhage Flashcards
What is shock
State of inadequate perfusion to the vital organs
What are the 2 states shock can be divided into
High output state- anaphylaxis and sepsis - there is a systemic vasodilation that lowers TPR the heart compensates by raising cardiac output to try to maintain ABP
Low output state- carcinogenic and hypovolaemic shock
Carcinogenic is a failure of the pumping heart
Hypovolaemic - lack of blood
What does the drop in ABP activate via what and what does this lead to
Sympathetic NS by the baroreceptor reflex
This leads to widespread vasoconstriction everywhere but the brain
What else does the strong synthetic drive activate
Kidneys - renin angiotensin system
What receptors are in the kidney that respond to the increased sympathetic activation
Beta1 cells on the granular cells
How else is the RAS activated in shock
The sympathetic constriction of vessels leads to decreased renal perfusion which activates the JGA
What is hypovolaemia caused by
Loss of blood volume
- dehydration, diarrhoea and vomiting
- haemorrhage
- burns
How is hypovolaemia and cardiogenic shock different
Hypovolaemia causes a drop in CVP
Cardiogenic shock inc the CVP this leads to an increase in hydrostatic pressure of the vasa recta, reducing the rate of fluid reabsorption
What is losing less than 20% of blood volume
Not shock but hypovolaemia- cause tiredness, thirst
What are the severities of shock
20% loss mild
30% loss moderate - blood pressure will fall below 90mmHg and HR will rise above 90 to compensate
40% loss severe
50% loss rapidly fatal
Drop in cardiac output causes
A lack of adequate perfusion causes hypoxia of the tissues, enforcing a switch to anaerobic respiration
This leads to a lactic acidosis from the resulting H+ increase which must be cleared by the kidney
What does tissue damage from hypoxia cause the release of from cells
Inc k+ release
Puts additional strain on the kidneys
What can the prolonged hypotension and renal hypoxia lead to
Acute renal failure which is acute kidney injury
This is due to the death of renal tissue but also due to a fall in GFR causing blockage of the tubules
Which part of the kidney does AKI have the most affect
Medulla
Already perfused you a secondary capillary bed so is already slightly hypoxia
And there is high metabolic activity in the medulla
What happens in acute renal failure AKI
Fall in GFR even when bP and perfusion return to normal and the kidneys remain anuric
What does fall in venous pressure act on the posterior pituitary gland
Release ADH
Lead to water retention via AQP
Also resultant transient hyponatraemia
Hyponatraemia is a trigger for aldosterone release - rare usual triggers are hyperkalaemia and AT2
RAS then helps to retain both Na+ and water
This tends the body towards metabolic acidosis
What is the treatment of hypovolaemia
Administer fluids
Which fluid isn’t given and why
Blood
It is a commodity - don’t want to use it when there is not a lack of Hb
And it reduces the risk of donor recipient infection
What are the most commonly applied fluids and what are they
Crystalloids
Simple isotonic salt solution
That distribute through the extracellular fluid
What is argued to be the most effective treatment in haemorrhage and why
Fluid that will remain entirely intravascular called colloids
As the reduction in circulating volume not extracellularly
So colloids maintain intravascular volume at the expense of interstitial volume
E.g. Collagen derived gelatins, polysaccharide dextrins, hydroxyethyl starches and albumin these substances have a high enough molecular mass to prevent passage through the endothelium
