CR3 EOYS3 Flashcards
Explain three examples that could cause obstructive shock xx [2]
PE
Tension pneuomothorax air gets trapped in pleural space: compresses against vena cava and heart: stops blood flow into right side of heart: reduced preload: reduced CO
Cardiac tamponade :accumulation of pericardial fluid: causes increas in intrapericardial pressure which reduceds cardiac filling
Explain 3 examples of distributive shock x
Sepsis: dysregulated host response to infection where bacteria in blood release chemicals causing uncontrolled hypotension
Anaphylactic shock: allergic response to antigen: IgE mediated mass degranulation releasing histamines: vasodilation and capillary leaking
Neurogenic shock: loss of sympathetic tone and thus unopposed parasympathetic response driven by the vagus nerve. Consequently, patients suffer from instability in blood pressure,
What is cardiogenic shock?
Name 4 causes of cardiogenic shock xx [4]
Failure of the heart to pump blood
Occurs as a result of ventricular dysfunction (esp. LV)
Causes:
* Acute myocardial infarction leading to ventricular dysfunction
* Arrhythmias
* Valvular rupture
* Decompensated heart failure
Explain 4 causes of hypovolaemic shock xx
- Haemorrhage
- GI losses: severe diarrhoea and vomiting
- Surgery: exposure of internal structures to heat
- Burns: fluid shift into extravasuclar space due to inflam response
Explain the compensatory mechanisms for haemorrhagic shock [3]
Baroreceptors detect drop in arterial pressure
Activates sympathetic stimulation:
- Constriction of small arterioles increasing total peripheral resistance thereby maintaining BP
- Veins and venous reservoirs constrict, maintaining venous return
- Increased heart rate and contractility to maintain cardiac output
CNS ischaemia results in increased noradrenaline and adrenaline secretion from adrenal medulla
How does RAAS system work to compensate shock? [3]
- Water retention and salt reabsorption
- Vasomotor centre in the medulla signals to the hypothalamus to release vasopressin (ADH)
- Urine flow and sodium excretion decrease
Name 3 long term compensatory mechanisms of shock [3]
- There is (by an unknown mechanism) stimulation of albumin and other plasma protein synthesis in the liver.
- Increased fluid absorption from GI tract
- Fibroblasts surrounding the kidney tubules are sensitive to hypoxia and release increased amounts of erythropoietin: Red cell production
CO = [] X []?
BP = [] x []?
CO = HR X SV
BP = CO x Systemic vascular resistance
Vasodilation is mediated by the activation of which two compounds? [1]
Explain their basic mechanism [1]
Nitric oxide and prostacyclin [1]
MoA: Through cGMP and cAMP respectively, secondary messengers cause decrease in calcium and smooth muscle relaxation
Vasoconstriction is predominately activated by which molecule on which receptors? [2]
Name two alternative compounds that can cause vasoconstriction [2]
Vasoconstriction is predominately activated by which molecule on which receptors? [2]
Noradrenaline on alpha 2 recptors
Name two alternative compounds that can cause vasoconstriction [2]
Angiotensin
Vasopressin
What are the overall physiological consequences of shock ? [3]
- Increased afterload
- Reduced systemic vascular resistance (Failure to maintain peripheral vasoconstriction)
-
Decreased CO
i) reduced preload
ii) reduced contactility
Name and describe the 4 stages of shock
What are the signs of shock?
- Pulse is weak and rapid
- Pulse pressure reduced - mean arterial pressure (MAP) may be maintained - NOTE; ARTERIAL BP is NOT A GOOD INDICATOR OF SHOCK since it will be maintained until a very large amount of blood loss
- Reduced urine output
- Reduced pH
- Confusion, weakness, collapse and coma
Describe the 4 classes of haemorrhagic shock
x
Explain which of HR or BP falls first in major haemorrhage stroke :)
Cardiac output can accommodate c. 10% blood loss before change in CO
Between 10-20% fall in blood loss, arterial pressure compensates by vasoconstriction
SO you see a raise in HR to compensate fall in SV BEFORE you see a fall in BP