15: Oxygen Therapy

Question 1

What is the difference between hypoxia and hypoxemia?

Answer 1

• hypoxia means decreased O2 supply to the tissues
• hypoxemia means decreased oxygenation of arterial blood

Question 2

Explain how there can by hypoxemia without hypoxia and hypoxia without hypoxemia.

Answer 2

• Oxygen delivery relies on CO and CaO2 → if CaO2 is lower (hypoxemia) increased CO may compensate for this to a degree
• If perfusion is compromised (e.g, shock, anemia, etc.) there may be tissue hypoxia without hypoxemia

Question 3

List 5 causes for hypoxemia

Answer 3

• Hypoventilation
• Ventilation/Perfusion mismatch
• decreased O2 content of inspired air (e.g., high altitude)
• Diffusion impairment
• intrapulmonary shunt

Question 4

Whast are the 3 main causes for tissue hypoxia?

Answer 4

• Hypoxemia
• Perfusion impairment (i.e., circulatory shock)
• Anemia

Question 5

If you use non-humidified air for oxygen supplementation what are the 4 complications this can lead to?

Answer 5

• Drying and irritation of the nasal mucosa
• Respiratory epithelial degeneration
• Impaired mucociliary clearance
• Increased risk of infection

Question 6

How much FiO2 can be achieved with flow-by oxygen?

Answer 6

2-3 L/min will provide 25-40% FiO2

(if within 2 cm of nostrils and no panting)

Question 7

How much FiO2 can be achieved with an oxygen mask?

Answer 7

with a tight fitting mask and high flow rate about 50-60%

Question 8

What is the recommended flow-rate for nasal cannula oxygen administration and what FiO2 ratio can be achieved?

Answer 8

50-150 mL/kg/min

30-70% FiO2

Question 9

What is the advantage of 2 nasal cannulas over just 1

Answer 9

• higher flow rates can be administered without causing as much discomfort as letting it flow through just one cannula
• can therefore administer higher flow rates
• same flow rate, however, will not achieve higher FiO2

Question 10

Between which tracheal rings should you place the tracheostomy tube?

Answer 10

between 4th and 5th tracheal rings

Question 11

What muscle must be bluntly dissected to place a tracheostomy tube?

Answer 11

sternohyoid muscle (between 3th and 5th tracheal ring

Question 12

By how much will the hyperbaric oxygen chamber treatment increase the % of dissolved O2 in the blood?

Answer 12

from 10 to 20 %

Question 13

Explain how oxygen supplementation may cause hypoventilation and which patient population is predisposed to this?

Answer 13

in a normal animal hypercapnia is the main drive for respiration

in animals with disease (e.g., chronic pulmonary disease, BAS) causing chronic hypercapnia the CO2 devels do not drive respiration and hypoxemia is the main drive

When giving these animals supplemental oxygen they may lose their drive to ventilate leading to hypoventilation and respiratory failure

Question 14

What are the 5 phases of oxygen toxicity?

Answer 14

1. Initiation phase
2. Inflammatory phase
3. Destruction phase
4. Proliferative phase
5. Fibrosis phase

Question 15

Which phase of oxygen toxicity has the highest mortality?

Answer 15

The destruction phase

Question 16

Explain the pathophysiology of oxygen toxicity

Answer 16

Oxygen is directly toxic to the pulmonary epithelium

Oxygen ⇒ O2-derived free radical species ⇒ cellular antioxidant stores become depleted ⇒ epithelial cell damage ⇒ recuitment of inflammatory cells and release of inflammatory mediators ⇒ increased endothelial permeability and edema formation

⇒ severe tissue destruction

⇒ increased accumulation of type II pneumocytes and monocytes

⇒ collagen deposition and interstitial fibrosis

Question 17

What is recommended to avoid oxygen toxicity

Answer 17

Do not administer and FiO2 > 50% for longer than 24-72 hours