Ch 6 - Shock

Question 1

List and briefly describe the 4 main types of shock

Answer 1

• Hypovolaemic - Reduction in curculating intravascular volume
• Cardiogenic - Inability of heart to propel blood through circulation. Includes obstructive shock by decreasing to preload
• Distributive - Maldistribution of vascular volume and massive vasodilation resulting in relative hypovolaemia. Sepsis and SIRS, anaphylaxis, drugs, severe CNS damage
• Hypoxic - Adequate perfusion but inadequate arterial oxygen content or cellular oxygen utilisation

Question 2

What are the basic factors determining oxygen delivery?

Answer 2

• Cardiac output
• Arterial oxygen content

Question 3

What is the Frank-Starling mechanism?

Answer 3

In an intact heart, an increase in end-diastolic volume (pre-load) augments the strength of cardiac contractions

Question 4

What factors influence the affinity of Hb for Oxygen

Answer 4

pH, temperature, 2,3-DPG, CO2

Question 5

List the ALTS (Advanced Trauma Life Support) classed of haemorrhage

Answer 5

• Class 1 - loss of up to 15% blood volume. Clinical signs absent or mild
• Class 2 - Loss 15-30%. Tachycardia, tachypnoea, weak pulses
• Class 3 - Loss 30-40%. mms pale, CRT prolonged, arterial hypotension
• Class 4 - Loss of >40%. Severe and immediately life-threatening. Cold extremities, altered mentation, profound hypotension

Question 6

List the possible defect of oxygen uptake in which the central venous oxygen saturation can be normal but tissue oxygenation can be impaired

Answer 6

• Diffussional shunting - slow blood velocity cause diffusion of oxygen from arterial into venous blood instead of into the tissues
• Diffusional resistance - Tissue oedema increases diffusion distance and limits oxygen availability
• AV shunting - Loss of capillary bloodflow due to SIRS/sepsis, thrombi etc
• Perfusion/metabolic mismatch - increased metabolic oxygen demands
• Cytopathic hypoxia - mitochondrial dysfunction such as in sepsis

Question 7

What is the normal resting oxygen extraction ratio?

Answer 7

20%

Can increase to 60-70% in cases of increased metabolic demand or decreased oxygen delivery

Question 8

What are the three main hypotheses to explain acute coagulopathy of trauma?

Answer 8

• A fibrinolytic variant fo DIC
• Enhance thrombomodulin-thrombin protein C pathway (decreased thrombin degradation and increased activation of anticoagulant and profibrinolytic protein C)
• Neurohumoral response (Catecholamine induced glycocalyx damage and expression of prothrombotic phenotype. Counterregulatory increase in anticoagulants and fibrinolytics leads to systemic anticoagulation and hyperfibrinolysis

Question 9

What are considered the shock organs in the dog and cat?

Answer 9

dog - GIT
cat - Lungs

Question 10

Over what MAP ranges will perfusion be maintained to the kidneys, myocardium and the brain?

Answer 10

Kidneys - 70-130mmHg
Myocardium - 60-140mmHg
Brain - 50-180mmHg

Question 11

What is the recommended blood pressure cuff width?

Answer 11

40% limb circumference in dogs, 30-40% in cats

Question 12

What is considered physiologic central venous pressure for dogs and cats?

Answer 12

0-5cmH20

Question 13

What is a Swan-Ganz catheter?

Answer 13

A pulmonary artery catheter for the measurement of cardiac output

Question 14

What factors effect lactate measurement?

Answer 14

• Liver and kidney clearance can cause normal lactate in hypoperfusion
• Severe hepatic failure can cause hyperlactataemia with normal production
• Inadequate collection and handling

Question 15

What are the 2 types of lactic acidosis?

Answer 15

• Type A - inadequate oxygen delivery
• Type B - mitochondrial dysfuntion with normal oxygen delivery (sepsis, DM, neoplasia, drugs, toxins)

Prolonged hypoxia can lead to mitochondrial damage leading to complex (Type A and B) lactic acidosis

Question 16

List some methods of evaluating regional perfusion

Answer 16

• Rectal temperature
• Gastric tonometry
• Sublingual capnometry
• Near-infrared spectroscopy

Question 17

What is considered normal Pa02 on room air? With supplemental O2?

Answer 17

Normal PaO2 >90mmHg on room air
When supplemental O2, Pa02 should be 5x the % of FiO2 (PaO2/FiO2 ratio should be approx 500)