CVS 21 - Haemodynamic Shock Flashcards
What are the equations for: … MAP (should be 2) + CO
Therefore how is arterial blood pressure controlled?
MAP = CO x TPR
MAP = Diastolic BP + 1/3 Pulse Pressure
CO = HR x SV
- aBP controlled via control of CO + TPR (e.g.: vasoconstriction increases BP)
What is haemodynamic shock?
What are the 2 main causes? (remember BP = CO x TPR)
- Acute condition of inadequate blood flow through the body, due to catastrophic fall in arterial BP.
BP = CO x TPR
1) Fall in CO - mechanical obstruction (heart cannot fill), loss of blood volume (bleeding) or pump failure.
2) Fall in TPR - excessive vasodilation
What are the 3 types of shock caused by a fall in cardiac output?
1) Cardiogenic shock (pump failure) - ventricle cannot empty properly
2) Mechanical shock (obstructive) - ventricle cannot fill properly
3) Hypovolaemic shock - reduced blood volumes leads to poor venous return.
What is cardiogenic shock + its potential causes?
What are the signs/complications?
- Failure to maintain CO as pump fails, unable to empty ventricles properly
- Following MI, a serious arrhythmias or worsening of HF
- Central Venous Pressure (CVP) normal or raised
- Coronary arteries + kidneys poorly perfused, exacerbates problem + leads to oliguria (reduced urine)
How does cardiac tamponade cause mechanical shock?
What are the associated signs?
- Blood or fluid fills up in pericardial space, restricting filling of the heart and reducing EDV.
- High CVP, low arterial BP, rapid HR, bulging neck veins
- SV reduced, therefore CO reduced.
How do pulmonary embolisms cause mechanical shock?
What are the associated signs + symptoms?
- Embolus occludes large pulmonary artery (increasing pressure), RV can’t empty and reduced return to LA.
- LA pressure low, arterial BP low … shock
- Chest pain + dyspnoea (shortness of breath)
What is hypovolaemic shock?
What is the compensatory response that occurs in response?
- Reduced blood volume, typically haemorrhage (typically 30-40% loss of blood, under that unlikely to cause shock
- Venous pressure falls, CO falls, arterial BP falls … detected by baroreceptors
- Increased sympathetic stimulation - tachycardia, force of contraction, vasoconstriction + venoconstriction (thus maintaining HR + SV and thus CO)
Why does filtration reverse to capillary reabsorption in hypovolaemic shock?
What are the patient signs/symptoms?
- Increased peripheral resistance reduces capillary hydrostatic pressure, net movement of fluid into capillaries.
- Tachycardia, weak pulse, pale skin + cold clammy extremities (all explained by sympathetic response and drop in SV).
There is a danger of decompensation during hypovolaemic shock, what is this?
- Peripheral vasoconstriction (sympathetic response) impairs tissue perfusion, leading to hypoxia + damage.
- This causes release of vasodilatory mediators, TPR drops and BP drops dramatically
- Leads to multi-system/organ failure.
Which systems in the body are responsible for the long-term restoration of blood volume in hypovolaemia?
1) RAAS
2) ADH
What are the 2 types of distributive (normovolaemic) shock that cause excessive peripheral vasodilation (decreased TPR)?
1) Toxic (septic) shock
2) Anaphylactic shock
How is toxic (septic) shock caused?
What are the signs/symptoms?
- Endotoxins released by circulating bacteria cause profound vasodilation + dramatic fall in TPR/arterial BP.
- Detected by baroreceptors, but mediators of vasodilation override vasoconstriction effect
- Tachycardia, warm/red extremities initially, hypo-perfusion of vital organs in later stages … FUCKED.
How is anaphylactic shock caused?
What are the signs/symptoms?
- Severe allergic reaction, release of histamine and other vasodilators from mast cells, leading to fall in TPR + aBP
- Sympathetic response overriden by vasodilatory
effects, difficulty breathing as mediators cause bronchoconstriction + laryngeal oedema. - Difficulty breathing, collapsed, rapid HR, red/warm extremities. Treat with adrenaline (epipen).
