Chapter 6 Shock

Question 1

Define shock

Answer 1

Clinical picture observed when tissue oxygen delivery or utilisation is compromised.

Question 2

How so the classical compensatory mechanisms manifest in a patieint with shock?

Answer 2

1. Tachycardia
2. Tachypnoea
3. Peripheral vasoconstriction
4. Mental depression

Question 3

List the four types of shock and give an example of each

Answer 3

1. Hypovolemic e.g. haemorrhage
2. Hypoxic e.g. anaemia, hypoxemia, toxins like acetaminophen in cats
3. Distributive e.g. sepsis, anaphylaxis
4. Cardiogenic e.g pericardial effusion N.B. includes extracardiac causes acting through compression on heart or great vessels.

Question 4

List four changes that would shift the oxygen-haemoglobon curve to the left (resulting in delivery of less oxygen)

Answer 4

1. Reduced temperature
2. Reduced PCO₂
3. Reduced 2,3-DPG
4. Increased pH

The oxygen-hemoglobin dissociation curve. Note that for a normal oxygen tension of 90 to 100 mm Hg, the hemoglobin saturation is 100%. Hemoglobin saturations less than 94% are on the steep portion of the curve; therefore a small decrease in saturation leads to a large decrease in O2 tension. Decreases in temperature, PCO2, or 2,3-diphosphoglycerate (DPG) and increases in pH shift the curve to the left, resulting in delivery of less oxygen. Dissolved oxygen contributes only a small amount to the total oxygen content (volume %), even with high fractional inspired oxygen. PCO2, Partial pressure of carbon dioxide.

Question 5

Formula for CO

Answer 5

CO = SV x HR

Question 6

What are the three factors affecting SV?

Answer 6

Pre-load, afterload and contractility

Question 7

What is the Frank Starling mechanism?

Answer 7

I

Question 8

List 5 categories of defects of oxygen uptake

Answer 8

1. Diffusional shunting (e.g. due to prolonged transit time)
2. Diffusional resistance (e.g. oedema)
3. AV shunting (e.g. capillary obstruction)
4. Perfusion/metabolism mismatch (e.g. tachycardia –> reduced coronary perfusion due to shortened diastole but increased demand)
5. Cytopathic hypoxia (mitochondrial dysfunction, usually with sepsis)