Flashcards in Physiology and Treatment of Shock Deck (27)
How is "shock" defined?
Inadequate perfusion to sustain normal organ function
What are the 5 main categories of Shock?
Hypovolaemic - loss of circulating volume
Cardiogenic - inefficient pump
Obstructive - physical blockage to heart filling/outflow
Distributive - circuit too big (vasodilation)
Cytotoxic - reduced oxygen delivery/ uptake
Loss of what components can cause hypovolaemic shock?
RARE = pure water deficit
Why should we be aware of young patients who may go into hypovolaemic shock?
They compensate incredibly well before crashing
- BP can be maintained for longer than in older patients
How do our bodies attempt to compensate in hypovolaemic shock?
- Baroreceptor reflex => detects less stretch and inhibits parasympathetic outflow => HR increases
- Sympathetic neurohormonal => releases vasoconstrcitors => redirects blood away from peripheries to the heart
- Capillaries absorb interstital fluid
- Hypothalamo-Pituitary Response => vasoconstriction and ADH secretion to retain Na and water
When do our bodies begin to decompensate?
When circulating vasodilators increase
How can the heart increase its cardiac output?
- Increase rate
- Increase Stroke Vol. (children cant do this)
- Increase both
How do we attempt to increase cardiac output in a patient who is hypovolaemic?
- Frank Starling curve shows this will have large effect on stroke volume and increase BP
Why should excess fluid be carefully monitored in patients with heart failure?
Can result in pulmonary congestion
- if the heart cant pump as well, it increases its end diastolic volume to increase the stroke volume
- this causes back pressure => pulmonary congestion
What are the principles of prescribing fluids to patients in shock?
1. Fluids are a drug => do you know what's in it? Dose?
2. Consider individual patient (e.g. small/elderly dont need 3 litres maintenance saline)
3. Consider the fluid AND electrolyte requirements
4. Consider the difference between resuscitation and
(i.e. dont give 500ml fluid challenge as maintenance)
What is the most common cause of cardiogenic shock?
- acute MI
but may also follow acute valve dysfunction (e.g. if papillary muscles are ruptured during MI)
WHat are the clinical signs of cardiogenic shock?
Poor forward flow
=> Pulmonary oedema
=> elevated JVP
=> hepatic congestion
If the main issue of cardiogenic shock is an inefficient pump, how can this be treated pharmacologically?
- drugs given to improve contractility of pump i.e. INOTROPES
=> β and dopaminergic stimulation
– Dobutamine, adrenaline
– Dopamine, Dopexamine
What can be inserted to help treat cardiogenic shock?
- Intra aortic balloon pump
- Inflates during ventricular diastole (allows coronary arteries to perfuse heart better)
- Deflation during ventricular systole (reduced afterload => reduces pressure that heart needs to pump against)
Causes of obstructive shock usually cause a problem with the heart filling rather than emptying. Give examples of this and how we treat it
– Pulmonary embolism – Anticoag. +/- thrombolysis
– Cardiac tamponade – Pericardial drainage
– Tension pneumothorax – Decompression/ chest drainage
How can a PE be identified on an ECHO?
– Dilated RV - not much movement
– Bowing of interventicular septum into LV
– RV apex is moving lots
What are the 3 main subtypes of distributove shock and how do they make the circuit "too big"?
Septic – Bacterial toxins mediate vasodilation
Anaphylactic – Mast cell release of histamine = vasodilation
Neurogenic – Loss of thoracic sympathetic outflow following spinal injury = unopposed vasodilatation from parasympathetics
What treatments should be given early in septic shock?
Early use of antibiotics and vasopressors
What treatment is given in anaphylactic shock and why?
- Acts as both a vasoconstrictor and a mast cell stabiliser
What test can be done to check if a patient is in anaphylactic shock?
Serum mast cell tryptase levels
(Tryptase is released from mast cells when they degranulate)
Why do patients in neurogenic shock normally experience BRADYcardia?
Occurs due to unopposed vagal tone
- if thoracic sympathetic outflow is compromised, this will not oppose parasympathetics
What should clinicians be aware of if they think a patient is in neurogenic shock?
- dont perform any examinations/procedures which increase vagal tone (e.g. PR exam, suction)
- this could exacerbate bradycardia, making patient less likely to survive
HOw is neurogenic shock normally treated?
Dopamine and vasopressors (to squeeze dilated vessels)
What are the 8 reversible causes of cardiac arrest?
Hypo/Hyper- kalaemia (OR other metabolic causes)
What is the importance of allowing the chest to recoil during CPR?
decreases the intra-thoracic pressure
=> allows more venous return to the heart
What Cardiac Arrest Rhythms are Shockable?
Ventricular Fibrillation (VF)
Pulseless Ventricular Tachycardia (pVT)