41. Shock

Question 1

Shock

Answer 1

inadequate cellular ATP

• multifactorial syndrome
• due to inadequate tissue perfusion and cellular oxygenation, affecting multiple organ systems

Question 2

Shock can be caused by what 2 general deficiencies?

Answer 2

deficiency in:

• delivery of oxygen/substrates to cells
• utilization of oxygen/substrates by cells

Question 3

Oxygen delivery

Answer 3

transport of oxygen to the tissues

DO2 (oxygen delivery) = CO (cardiac output) x CaO2 (oxygen content of arterial blood)

CO = HR x SV
CaO2 = [hgb] x 1.34 x SaO2 + (0.003 x PaO2)

Question 4

What contributes to reduced oxygen delivery to the tissues?

Answer 4

loss of:

• blood volume
• hemoglobin
• oxygen saturation

Question 5

What are the 6 forms of shock?

Answer 5

1. hypovolemic
2. distributive
3. cardiogenic
4. obstructive
5. hypoxic
6. metabolic

*often more than one mechanism of shock is at play

Question 6

What forms of shock prevent blood from getting to the cells (CV dysfunction)?

Answer 6

• hypovolemic shock
• distributive shock
• cardiogenic shock
• obstructive shock

Question 7

What forms of shock cause a lack of substrate?

Answer 7

• hypoxic shock

- metabolic shock

Question 8

What form of shock involves dysfunctional cells (unable to utilize oxygen)?

Answer 8

metabolic shock

Question 9

What is the most common form of shock?

Answer 9

hypovolemic

Question 10

Hypovolemic shock leads to decreases in which 4 parameters?

Answer 10

• preload
• SV
• CO
• DO2

Question 11

What are 2 broad causes of hypovolemic shock?

Answer 11

• abnormal external losses

- third space losses

Question 12

What are some examples of abnormal external losses that can lead to hypovolemic shock?

Answer 12

• GI: diarrhea, vomit, reflux
• urinary: polyuria from diabetes mellitus or insipidus
• respiratory - increased ventilation
• acute blood loss

Question 13

What are some examples of third space losses that can lead to hypovolemic shock?

Answer 13

• systemic inflammation: capillary losses –> interstitial fluid accumulation
• body cavity effusions

Question 14

What clinical findings point toward a diagnosis of hypovolemic shock?

Answer 14

• decreased mentation
• tachycardia
• decreased pulse quality
• increased CRT
• pale MM
• cold extremities
• decreased jugular refill time (large animal)
• hypotension
• decreased urine production with high USG
• increased blood/plasma lactate concentration (reflects anaerobic glycolysis, has other possible causes like sepsis)
• increased oxygen extraction ratio

Question 15

oxygen extraction ratio

Answer 15

OER = (SaO2 - SvO2)/SaO2

• increases when cells extract more oxygen per unit blood flow due to less overall flow
• when venous oxygen saturation decreases relative to arterial oxygen saturation –> ratio increases
• normal = (100-70)/100 = 30%

Question 16

What are normal blood volumes in a dog, horse, and cat?

Answer 16

• dog, horse = 8-10% of body weight
• cat = 5% of body weight
• ruminants - somewhere in between

Question 17

What are 2 examples of hypovolemic shock?

Answer 17

• hemorrhage

- fluid deficits

Question 18

What is distributive shock?

Answer 18

inappropriate vasodilation

Question 19

What are 3 examples of distributive shock?

Answer 19

• septic shock / SIRS shock (SIRS = systemic inflammatory response syndrome)
• anaphylactic shock
• neurogenic shock

Question 20

What are the mediators of distributive shock due to sepsis?

Answer 20

• NO (most potent vasodilator in physiology)
• adrenomedullin
• prostaglandins
• cytokines

Question 21

What are the mediators of distributive shock due to anaphylaxis?

Answer 21

• histamine

- bradykinins

Question 22

What is the mechanism of distributive shock due to neurogenic causes?

Answer 22

• autonomic dysfunction from spinal cord injury cranial to thoracic level
• loss of sympathetic tone –> vasodilation, bradycardia

Question 23

What is cardiogenic shock?

Answer 23

• cardiac dysfunction: “pump failure”

- inadequate cell metabolism secondary to cardiac dysfunction despite adequate intravascular volume

Question 24

What are 2 broad causes of cardiogenic shock?

Answer 24

• decreased HR

- decreased SV

Question 25

What are some examples of systolic dysfunction leading to cardiogenic shock?

Answer 25

systolic dysfunction = decreased contractility or flow: - DCM (dilated cardiomyopathy) - sepsis-induced myocardial failure

Question 26

What are some examples of diastolic dysfunction leading to cardiogenic shock?

Answer 26

diastolic dysfunction = inadequate fill: - cardiac tamponade physical restriction, also fits with obstructive shock - HCM (hypertrophic cardiomyopathy) - inability to relax

Question 27

What are some examples of dysrhythmias leading to cardiogenic shock?

Answer 27

- severe bradyarrhythmias | - severe tachyarrhythmias

Question 28

What clinical findings point toward a diagnosis of decompensated heart failure that could lead to cardiogenic shock?

Answer 28

- signs of hypoperfusion (perfusion parameters, lactate) - arterial hypotension (poor perfusion) - ECG abnormalities - murmurs - secondary volume overload (pulmonary and peripheral edema, cardiomegaly)

Question 29

What is obstructive shock?

Answer 29

extra-cardiac mechanical obstruction to cardiac output --> decrease in systemic perfusion ("forward flow" reduced)

Question 30

What are some examples of obstructive shock?

Answer 30

- pulmonary thromboembolism (also fits with hypoxic shock) - tension pneumothorax (decreased venous return and increased pleural pressures limit forward flow, also fits with hypoxic shock) - cardiac tamponade (also fits with cardiogenic shock)

Question 31

What is the mechanism of obstructive shock due to pulmonary thromboembolism?

Answer 31

- cardiac output is restricted by mechanical obstruction of pulmonary vessels or obstruction induced by pulmonary hypertension - examples: fat or septic emboli, metastatic neoplasia, heart worm, blood clots

Question 32

What is the mechanism of obstructive shock due to tension pneumothorax?

Answer 32

- continuous leakage of air into pleural space from airway or lung --> increased intrapleural pressures --> collapse of the cranial and caudal vena cava --> inadequate venous filling - treatment: emergency decompression of pleural air, continuous

Question 33

What is hypoxic shock?

Answer 33

blood volume/flow normal, but deficient of oxygen - low PaO2 or SaO2 - low hemoglobin concentration (severe anemia) remember: CaO2 = [hgb] x 1.34 x SaO2 + (0.003 x PaO2)

Question 34

What are the 5 causes of hypoxemia that could lead to hypoxic shock?

Answer 34

- low PIO2 (partial pressure of inspired oxygen; e.g. high altitude) - V/Q mismatch (e.g. pneumonia) - diffusion impairment (e.g. smoke inhalation or fibrosis --> replacement of type I pneumocytes with thicker type II pneumocytes) - hypoventilation (look for hypercapnia on blood-gas) - right-to-left shunt (e.g. VSD, PDA, shunt within lung itself)

Question 35

What are the 2 main categories of metabolic shock?

Answer 35

- mitochondrial dysfunction --> impaired oxygen utilization | - severe hypoglycemia --> inadequate energy substrate for normal metabolism

Question 36

What are 2 causes of mitochondrial dysfunction?

Answer 36

- cytopathic hypoxia due to cytokines associated with sepsis/SIRS (systemic inflammatory response syndrome) - cyanide toxicity

Question 37

How does cyanide toxicity cause mitochondrial dysfunction leading to metabolic shock?

Answer 37

- disrupts mitochondrial cytochrome oxidative phosphorylation - cytochrome c oxidase inhibited (last enzyme in ETT - electron transport chain) - cells unable to utilize oxygen

Question 38

What are some causes of severe hypoglycemia leading to metabolic shock?

Answer 38

neonates: - not nursing on top of low body stores of glycogen/fat - sepsis adults: - sepsis - hypoadrenocorticism - liver failure - insulinoma - (diabetic ketoacidosis)