Oxygen Therapy

Question 1

oxygen delivery

Answer 1

-DO2 = CO x arterial oxygen content (CaO2)

Question 2

failure of oxygen delivery leads to

Answer 2

• hypotension
• acidosis
• coagulopathy

Question 3

oxygen use

Answer 3

VO2 = CO x (PaO2 - PvO2)

• oxygen extraction ratio; normal is about 25%
• heart has very high demand

Question 4

why is oxygen therapy important in surgical patients?

Answer 4

they are at increased risk for hypoxia and hypoxemia

Question 5

hypoxemia

Answer 5

deficiency of oxygen in the blood

Question 6

hypoxia

Answer 6

oxygen delivery to the tissues is not sufficient to meet the metabolic demand

Question 7

anesthesia goal

Answer 7

maintain oxygenation and ventilation that is sufficient to meet the metabolic demand

Question 8

oxygen therapy goal

Answer 8

prevent and correct hypoxemia and tissue hypoxia

Question 9

hypoxic hypoxia

Answer 9

shunting or pulmonary diffusion defect; can be caused by a drug OD, COPD exacerbation, asthma, atelectasis, or emphysema

Question 10

circulatory hypoxia

Answer 10

decrease in CO to the point where oxygen delivery to the tissues is inadequate; common causes are CHF or MI

Question 11

hemic hypoxica

Answer 11

a decreased Hgb content (such as anemia) and/or decreased function of Hgb; anemia, carboxy-hemoglobinemia, methemoglobinemia

Question 12

demand hypoxia

Answer 12

an increase in the metabolic rate or oxygen demands of the body such that insufficient oxygen is delivered to the body; fever, seizure, MH

Question 13

histotoxic hypoxia

Answer 13

inability of the cells themselves to use oxygen such as in cyanide poisoning

Question 14

hypoxia S/S

Answer 14

• vasodilation
• tachycardia
• tachypnea
• cyanosis
• confusion
• lactic acidosis

Question 15

improving oxygenation in mechanically ventilated patients

Answer 15

• treatment tailored to cause
• increase VE
• increase CO
• increase O2 carrying capacity
• optimize V/Q relationship
• decrease O2 consumption
• increase FiO2

Question 16

nasal cannula

Answer 16

• flow rates 1-6 L/min

- FiO2 increases about 4% per L/min

Question 17

simple face mask

Answer 17

• FiO2 40-60%
• min 6L flow required to prevent rebreathing; min is essentially whatever the patient’s minute ventilation is to prevent rebreathing of CO2

Question 18

face masks with reservoirs

Answer 18

-FiO2 60-100%

Question 19

Venturi Masks

Answer 19

• more precise FiO2 24-50%

- Bernoulli’s Principle

Question 20

oxygen toxicity

Answer 20

• high FiO2 over long period of time can be harmful to lung tissue
• decrease ciliary movement, so lungs can’t get rid of mucous or debris as easily
• alveolar epithelial damage
• interstitial fibrosis
• dependent upon - FiO2, duration, and patient susceptibility

Question 21

what is generally considered a “safe” amount of oxygen?

Answer 21

100% for up to 10-20 hours

Question 22

what has been shown to have oxygen toxicity?

Answer 22

50-60% for more than 24-72 hours

Question 23

high risk populations for oxygen toxicity?

Answer 23

• older than 70 years
• history of radiation to the lungs/chest
• bleomycin (used to treat various types of cancer)

Question 24

s/s of oxygen toxicity

Answer 24

• cough
• dyspnea
• rales
• hypoxemia
• increased A:a (alveolar to arterial) gradient
• decreased diffusion diffusion capacity

Question 25

absorption atelectasis

Answer 25

- nitrogen (insoluble so normally stays in lungs to keep them open) replaced by oxygen - under-ventilated alveoli have decreased volume, due to a greater uptake of oxygen - increases pulmonary shunting; widen A-a gradient

Question 26

induced hypoventilation

Answer 26

- chronic CO2 retainers rely on hypoxic drive - peripheral chemoreceptors are triggered by hypoxemia - increased O2 can lead to hypoventilation

Question 27

fire hazard

Answer 27

- oxygen supports combustion | - use extreme caution with head and neck cases

Question 28

retinopathy

Answer 28

- oxygen therapy in neonates can lead to vascular proliferation, fibrosis, retinal detachment, and blindness - safe O2 administration --> PaO2 60-80 mmHg

Question 29

population at risk for oxygen induced retinopathy

Answer 29

- <36 weeks gestational age; but actually can happen up to 44 weeks gestational age - weight <1500 gm - up to 44 weeks gestational age are considered high risk

Question 30

hypercapnia

Answer 30

- increased PaCO2 > 45 mmHg | - causes --> increased CO2 concentration, increased CO2 production

Question 31

causes of hypercapnia

Answer 31

- increased alveolar dead space --> decreased alveolar perfusion, interruptions in pulmonary circulation, pulmonary disease - decreased alveolar ventilation --> can be central or peripheral, resp depression most common cause in immediate postoperative period

Question 32

clinical manifestations of hypercapnia

Answer 32

- directly produces vasodilation of peripheral vessels - indirectly increases HR after catecholamine release - produces effects due to an acidotic state - non-specific signs --> HA, N/V, sweating, flushing, shivering, restlessness

Question 33

CNS considerations with hypercapnia

Answer 33

- regulation of ventilatory drive --> increased CO2 makes you want to breath more - cerebral blood flow --> increases 1-2 mL/100g/min for every 1 mmHg increase in PaCO2

Question 34

CV considerations with hypercapnia

Answer 34

- depression of smooth muscle and cardiac muscle - increased catecholamine release - vasodilation versus vasoconstriction - because of the increased catecholamine release; might see initial vasodilation then vasoconstriction from SNS activation; HOWEVER if SNS blockade, vasodilation will prevail

Question 35

pulmonary considerations with hypercapnia

Answer 35

- increased RR - increased PVR (b/c CO2 increases vasoconstriction of pulmonary vessels) - R shift of oxy-Hgb dissociation curve

Question 36

treatment for hypercapnia

Answer 36

- adjust treatment to cause | - increase Ve

Question 37

hypocapnia

Answer 37

- CO2 < 35 mmHg | - cause usually iatrogenic

Question 38

clinical manifestations of hypocapnia

Answer 38

- decreased CBF, decreased ICP - decreased CO, coronary constriction - hypoxemia may result from hypoventilation

Question 39

hypocapnia treatment

Answer 39

-decrease minute ventilation