Physiology and Treatment of Shock

Question 1

How is “shock” defined?

Answer 1

Inadequate perfusion to sustain normal organ function

Question 2

What are the 5 main categories of Shock?

Answer 2

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

Question 3

Loss of what components can cause hypovolaemic shock?

Answer 3

blood
interstitial fluid
RARE = pure water deficit

Question 4

Why should we be aware of young patients who may go into hypovolaemic shock?

Answer 4

They compensate incredibly well before crashing

- BP can be maintained for longer than in older patients

Question 5

How do our bodies attempt to compensate in hypovolaemic shock?

Answer 5

• 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

Question 6

When do our bodies begin to decompensate?

Answer 6

When circulating vasodilators increase

Question 7

How can the heart increase its cardiac output?

Answer 7

• Increase rate
• Increase Stroke Vol. (children cant do this)
• Increase both

Question 8

How do we attempt to increase cardiac output in a patient who is hypovolaemic?

Answer 8

Fluid challenge

- Frank Starling curve shows this will have large effect on stroke volume and increase BP

Question 9

Why should excess fluid be carefully monitored in patients with heart failure?

Answer 9

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

Question 10

What are the principles of prescribing fluids to patients in shock?

Answer 10

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
   maintenance
   (i.e. dont give 500ml fluid challenge as maintenance)

Question 11

What is the most common cause of cardiogenic shock?

Answer 11

• acute MI

but may also follow acute valve dysfunction (e.g. if papillary muscles are ruptured during MI)

Question 12

WHat are the clinical signs of cardiogenic shock?

Answer 12

Poor forward flow
=> Hypotension/shock
=> fatigue
=> syncope

Backpressure
=> Pulmonary oedema
=> elevated JVP
=> hepatic congestion

Question 13

If the main issue of cardiogenic shock is an inefficient pump, how can this be treated pharmacologically?

Answer 13

• drugs given to improve contractility of pump i.e. INOTROPES

=> β and dopaminergic stimulation
– Dobutamine, adrenaline
– Dopamine, Dopexamine

Question 14

What can be inserted to help treat cardiogenic shock?

Answer 14

• 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)

Question 15

Causes of obstructive shock usually cause a problem with the heart filling rather than emptying. Give examples of this and how we treat it

Answer 15

– Pulmonary embolism – Anticoag. +/- thrombolysis
– Cardiac tamponade – Pericardial drainage
– Tension pneumothorax – Decompression/ chest drainage

Question 16

How can a PE be identified on an ECHO?

Answer 16

– Dilated RV - not much movement
– Bowing of interventicular septum into LV
– RV apex is moving lots

Question 17

What are the 3 main subtypes of distributove shock and how do they make the circuit “too big”?

Answer 17

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

Question 18

What treatments should be given early in septic shock?

Answer 18

Early use of antibiotics and vasopressors

Question 19

What treatment is given in anaphylactic shock and why?

Answer 19

Adrenaline

- Acts as both a vasoconstrictor and a mast cell stabiliser

Question 20

What test can be done to check if a patient is in anaphylactic shock?

Answer 20

Serum mast cell tryptase levels

Tryptase is released from mast cells when they degranulate

Question 21

Why do patients in neurogenic shock normally experience BRADYcardia?

Answer 21

Occurs due to unopposed vagal tone

• if thoracic sympathetic outflow is compromised, this will not oppose parasympathetics

=> bradycardia

Question 22

What should clinicians be aware of if they think a patient is in neurogenic shock?

Answer 22

• dont perform any examinations/procedures which increase vagal tone (e.g. PR exam, suction)
• this could exacerbate bradycardia, making patient less likely to survive

Question 23

HOw is neurogenic shock normally treated?

Answer 23

Dopamine and vasopressors (to squeeze dilated vessels)

Question 24

What are the 8 reversible causes of cardiac arrest?

Answer 24

4Hs
Hypovolaemia
Hypoxia
Hypothermia
Hypo/Hyper- kalaemia (OR other metabolic causes)

4Ts
Thrombosis
Tamponade
Tension Pneumothorax
Toxins

Question 25

What is the importance of allowing the chest to recoil during CPR?

Answer 25

decreases the intra-thoracic pressure

=> allows more venous return to the heart

Question 26

What Cardiac Arrest Rhythms are Shockable?

Answer 26

Ventricular Fibrillation (VF)
Pulseless Ventricular Tachycardia (pVT)

Question 27

What cardiac arrest rhythms are NON-shockable?

Answer 27

Pulseless Electrical Activity

Asystole