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VET 415 > 41. Shock > Flashcards

41. Shock Flashcards

1
Q

Shock

A

inadequate cellular ATP

  • multifactorial syndrome
  • due to inadequate tissue perfusion and cellular oxygenation, affecting multiple organ systems
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2
Q

Shock can be caused by what 2 general deficiencies?

A

deficiency in:

  • delivery of oxygen/substrates to cells
  • utilization of oxygen/substrates by cells
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3
Q

Oxygen delivery

A

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)
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4
Q

What contributes to reduced oxygen delivery to the tissues?

A

loss of:

  • blood volume
  • hemoglobin
  • oxygen saturation
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5
Q

What are the 6 forms of shock?

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

*often more than one mechanism of shock is at play

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6
Q

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

A
  • hypovolemic shock
  • distributive shock
  • cardiogenic shock
  • obstructive shock
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7
Q

What forms of shock cause a lack of substrate?

A
  • hypoxic shock

- metabolic shock

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8
Q

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

A

metabolic shock

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9
Q

What is the most common form of shock?

A

hypovolemic

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10
Q

Hypovolemic shock leads to decreases in which 4 parameters?

A
  • preload
  • SV
  • CO
  • DO2
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11
Q

What are 2 broad causes of hypovolemic shock?

A
  • abnormal external losses

- third space losses

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12
Q

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

A
  • GI: diarrhea, vomit, reflux
  • urinary: polyuria from diabetes mellitus or insipidus
  • respiratory - increased ventilation
  • acute blood loss
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13
Q

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

A
  • systemic inflammation: capillary losses –> interstitial fluid accumulation
  • body cavity effusions
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14
Q

What clinical findings point toward a diagnosis of hypovolemic shock?

A
  • 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
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15
Q

oxygen extraction ratio

A

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%
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16
Q

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

A
  • dog, horse = 8-10% of body weight
  • cat = 5% of body weight
  • ruminants - somewhere in between
17
Q

What are 2 examples of hypovolemic shock?

A
  • hemorrhage

- fluid deficits

18
Q

What is distributive shock?

A

inappropriate vasodilation

19
Q

What are 3 examples of distributive shock?

A
  • septic shock / SIRS shock (SIRS = systemic inflammatory response syndrome)
  • anaphylactic shock
  • neurogenic shock
20
Q

What are the mediators of distributive shock due to sepsis?

A
  • NO (most potent vasodilator in physiology)
  • adrenomedullin
  • prostaglandins
  • cytokines
21
Q

What are the mediators of distributive shock due to anaphylaxis?

A
  • histamine

- bradykinins

22
Q

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

A
  • autonomic dysfunction from spinal cord injury cranial to thoracic level
  • loss of sympathetic tone –> vasodilation, bradycardia
23
Q

What is cardiogenic shock?

A
  • cardiac dysfunction: “pump failure”

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

24
Q

What are 2 broad causes of cardiogenic shock?

A
  • decreased HR

- decreased SV

25
Q

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

A

systolic dysfunction = decreased contractility or flow:

  • DCM (dilated cardiomyopathy)
  • sepsis-induced myocardial failure
26
Q

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

A

diastolic dysfunction = inadequate fill:

  • cardiac tamponade physical restriction, also fits with obstructive shock
  • HCM (hypertrophic cardiomyopathy) - inability to relax
27
Q

What are some examples of dysrhythmias leading to cardiogenic shock?

A
  • severe bradyarrhythmias

- severe tachyarrhythmias

28
Q

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

A
  • signs of hypoperfusion (perfusion parameters, lactate)
  • arterial hypotension (poor perfusion)
  • ECG abnormalities
  • murmurs
  • secondary volume overload (pulmonary and peripheral edema, cardiomegaly)
29
Q

What is obstructive shock?

A

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

30
Q

What are some examples of obstructive shock?

A
  • 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)
31
Q

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

A
  • 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
32
Q

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

A
  • 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
33
Q

What is hypoxic shock?

A

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)

34
Q

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

A
  • 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)
35
Q

What are the 2 main categories of metabolic shock?

A
  • mitochondrial dysfunction –> impaired oxygen utilization

- severe hypoglycemia –> inadequate energy substrate for normal metabolism

36
Q

What are 2 causes of mitochondrial dysfunction?

A
  • cytopathic hypoxia due to cytokines associated with sepsis/SIRS (systemic inflammatory response syndrome)
  • cyanide toxicity
37
Q

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

A
  • disrupts mitochondrial cytochrome oxidative phosphorylation
  • cytochrome c oxidase inhibited (last enzyme in ETT - electron transport chain)
  • cells unable to utilize oxygen
38
Q

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

A

neonates:

  • not nursing on top of low body stores of glycogen/fat
  • sepsis

adults:

  • sepsis
  • hypoadrenocorticism
  • liver failure
  • insulinoma
  • (diabetic ketoacidosis)

VET 415 (4 decks)

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