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Principles I > Oxygen Therapy > Flashcards

Oxygen Therapy Flashcards

1
Q

What formula is used to determine oxygen delivery to the tissues?

A

DO2 = CO x arterial O2 content

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2
Q

How do you calculate cardiac output?

A

HR x SV

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3
Q

How do you calculate arterial O2 content?

A

Hgb x SaO2 x 1.34 + PaO2 + 0.003

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4
Q

What does failure to oxygenate the tissues result in?

A

Hypotension
Acidosis
Coagulopathy

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5
Q

What is the oxygen extraction ratio?

A

represents the ratio of O2 consumption to O2 delivery

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6
Q

What is the normal oxygen extraction ratio?

A

about 25%, 4x O2 needed is delivered to tissues

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7
Q

What is the equation to calculate O2 use? (VO2)

A

VO2 = cardiac output x O2a - O2v

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8
Q

What is the primary goal regarding oxygen therapy under anesthesia?

A

maintain ventilation and oxygenation; prevention and correction of hypoxemia and tissue hypoxia

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9
Q

What is hypoxemia?

A

deficiency of O2 in the blood

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10
Q

What is hypoxia?

A

O2 delivery to tissues is not sufficient to meet metabolic needs

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11
Q

What are the different types of hypoxia?

A 
Hypoxic hypoxia
Circulatory hypoxia
Hemic hypoxia
Demand hypoxia
Histotoxic hypoxia
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12
Q

What are some causes of hypoxic hypoxia?

A
  • low barometric pressure or FiO2 <21% (altitude, equipment error)
  • alveolar hypoventilation (drug overdose, COPD exacerbation)
  • pulmonary diffusion defect (emphysema, fibrosis)
  • pulmonary mismatch (asthma, pulmonary emboli)
  • R L shunt (atelectasis, cyanotic congenital heart disease)
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13
Q

What is a cause of circulatory hypoxia?

A

reduced cardiac output (congestive heart failure, MI, dehydration, too much inhaled agents)

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14
Q

What are some causes of hemic hypoxia?

A

Reduced Hgb content (anemias)

Reduced Hgb function (carboxyhemoglobinemia, metHgb)

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15
Q

What is a cause of demand hypoxia?

A

increased O2 consumption (fever, seizures)

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16
Q

What is a cause of histotoxic hypoxia?

A

inability of cells to utilize oxygen (cyanide toxicity)

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17
Q

What are some s/s of hypoxia?

A 
vasodilation
tachycardia
tachypnea
cyanosis
confusion
lactic acidosis
organ-related changes (Ex: decreased urine output)
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18
Q

What are some methods to improve oxygenation?

A

Increase VE (hypoxic hypoxia)
Increase cardiac output (circulatory hypoxia)
Increase O2 carrying capacity (hemic hypoxia)
Optimize VQ relationships (hypoxic hypoxia)
Decrease O2 consumption (demand hypoxia)
Increase FiO2

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19
Q

What are some methods for supplemental O2 for non-intubated patients?

A

nasal cannulas
simple face masks
face masks with reservoirs
venturi masks

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20
Q

How much flow and FiO2 can you use with a nasal cannula?

A

Flow rates 1-6 L/min (flows >6 L/min uncomfortable to patient)
FiO2 increases about 4% per L/min

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21
Q

How much O2 can you deliver with a simple face mask?

A

40-60% FiO2
Need minimum of 5 L flow to prevent CO2 rebreathing
(usually used to transfer patients to PACU)

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22
Q

How much FiO2 can you deliver with a face mask with a reservoir?

A

60-100% FiO2

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23
Q

How much FiO2 can you deliver with a venturi mask?

A

more precise FiO2 from 24-50% FiO2

24
Q

If the non-rebreathing facemask doesn’t help with oxygenation, what would be the next step?

A

intubate with ETT

25
Q

How many L of O2 do you use with a simple mask?

A

5-8 L

26
Q

How many L of O2 can you use with a non-rebreathing mask?

A

7-15 L

27
Q

What are some hazards of O2 therapy?

A 
oxygen toxicity
absorption atelectasis
induced hypoventilation
fire hazard
retinopathy of prematurity
28
Q

What are some adverse effects of oxygen toxicity?

A

acute tracheobronchitis
decreased ciliary movement
alveolar epithelial damage
interstitial fibrosis

29
Q

What causes oxygen toxicity?

A

high FiO2 over long periods of time, detrimental to lung tissue; dependent on partial pressure of O2 in inspired gases, duration of exposure, and patient susceptibility

30
Q

How long is it safe to administer 100% FiO2?

A

10-20 hours

31
Q

How long does it take for oxygen toxicity to develop?

A

> 50-60% FiO2 for >24-72 hours

32
Q

Who is at high risk for oxygen toxicity?

A

> 70 yo
Hx of radiation to lung or chest
Antineoplastic drugs: bleomycin

33
Q

What is the exact pathophysiology behind O2 toxicity?

A

intracellular generation of oxygen metabolites (free radicals) are cytotoxic as they react with cellular DNA; inflammation in alveoli leads to membrane disruption

34
Q

What are some s/s of O2 toxicity?

A 
Similar to ARDS:
cough
dyspnea
rales
hypoxemia
decreased diffusion capacity
increased A:a gradient
pulmonary fibrosis
35
Q

What is absorption atelectasis?

A
  • Insoluble nitrogen is replaced by O2
  • Under-ventilated alveoli have decreased volume due to greater uptake of oxygen
  • Causes increase in pulmonary shunting
  • FiO2 of 60% is safe
36
Q

What is induced hypoventilation?

A

Chronic CO2 retainers rely on hypoxic drive to breathe so their peripheral chemoreceptors are triggered better by hypoxemia (CO2 receptors desensitized to increase in CO2)

37
Q

What is retinopathy caused by oxygen therapy in pediatrics?

A

O2 therapy in neonates with immature retinas can lead to disorganized vascular proliferation, fibrosis, retinal detachment, and blindness secondary to retinal hyperoxia

38
Q

What pediatric populations are at risk for retinopathy?

A

<1500 gm
Neonates up to 44 weeks gestational age are considered high risk
Other contributing factors: anemia, infection, acidosis

39
Q

What is the recommended PaO2 for safe O2 administration to neonates?

A

PaO2 of 60-80 mmHg

40
Q

What is hypercapnia?

A

CO2 >45 mmHg

41
Q

What are some causes of hypercapnia?

A
  • increased inspired CO2 concentration or increased CO2 production
  • increased alveolar dead space (VQ mismatching, ventilation without perfusion)
  • decreased alveolar ventilation
42
Q

What is the most common cause of hypercapnia in the immediate post-op period?

A

decreased alveolar ventilation from narcotics

43
Q

What are some clinical manifestations of hypercapnia?

A
  • direct effect vasodilation of peripheral vessels
  • indirect effect of increasing HR after catecholamine release
  • produces effects as a consequence of an acidotic state
44
Q

What are some symptoms of hypercapnia in the awake patient?

A 
Headache
N/V
sweating
flushing
shivering
restlessness
dysrhythmias
hallucinations
unconsciousness
seizure activity
45
Q

What does hypercapnia cause in the brain?

A

increased cerebral blood flow/cerebral vasodilation

46
Q

How much does the cerebral blood flow increase with an increase in PaCO2?

A

CBF increases 1-2 mL/100 gm/min for every 1 mmHg increase in PaCO2 within a range of 20-80 mmHg

47
Q

What are some cardiovascular considerations with hypercapnia?

A
  • Depression of vascular and smooth muscle
  • Increased catecholamine release increases CO and HR with decreased peripheral vascular resistance
  • Vasodilation (with sympathetic blockade) vs. vasoconstriction (with intact SNS)
48
Q

What are some pulmonary considerations with hypercapnia?

A

Increased RR
Increased pulmonary vascular resistance
RIghtward shift of oxyhemoglobin dissociation curve

49
Q

How much can hypercapnia increase PA pressures?

A

Can produce up to 60% increase

50
Q

What are some treatments to hypercapnia?

A

Tailor treatment to cause**
Increase minute ventilation
Check integrity of anesthesia machine

51
Q

What is hypocapnia?

A

CO2 <35 mmHg

52
Q

What is usually the cause of hypocapnia in the OR?

A

iatrogenic, fast RR

53
Q

What are some CNS considerations with hypocapnia?

A

Decrease in CBF and spinal cord blood flow
Directional change in CBF with PaCO2
May be beneficial with intracranial surgery and increased ICP

54
Q

What are some cardiovascular considerations with hypocapnia?

A
  • CO decreases with hyperventilation due to increased intrathoracic pressure which decreases preload
  • Decrease in sympathetic stimulation
  • Coronary vasoconstriction
  • Alkalosis decreases concentration of ionized calcium
55
Q

What are some pulmonary considerations with hypocapnia?

A
  • Alkalosis produces leftward shift in oxy-hgb curve

- hypoxemia may result from body’s compensatory hypoventilation

Principles I (5 decks)

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