Hypoxemia - Chapter 15 - Haskins

Question 1

Define hypoxemia

Answer 1

An arterial partial pressure of oxygen (PaO2)

Question 2

Arterial blood is used for assessment of ______ _______, while venous blood (coming from the tissues) is more a reflection of ________ __________.

Answer 2

Arterial blood is used for assessment of pulmonary function, while venous blood (coming from the tissues) is more a reflection of tissue function than lung function.

Question 3

What is PaO2?

Answer 3

PaO2 is the partial pressure (the vapor pressure) of oxygen dissolved in solution in the plasma of arterial blood and is measured with a blood gas analyzer. The arterial PO2 (PaO2) is a measure of the ability of the lungs to move oxygen from the atmosphere to the blood.

Question 4

What is normal PaO2 at sea level?

Answer 4

80-110 mmHg

Question 5

What drives oxygen diffusion down to the mitochondria?

Answer 5

The partial pressure of oxygen in plasma (NOT Hgb saturation)

Question 6

What does cyanosis (grayish to bluish coloration of mm) commonly signal?

Answer 6

The presence of deoxygenated Hgb in the observed tissues

Question 7

What are the three basic causes of hypoxemia? What is a fourth potential cause?

Answer 7

(1) Low inspired oxygen concentration
(2) Hypoventilation
(3) Venous admixture
(4) Reduced venous oxygen content - secondary to low CO or slugglish peripheral blood flow (shock) or high oxygen extraction by the tissues (seizures)

Question 8

What are some examples of low inspired oxygen?

Answer 8

Apparatus that patient is attached to is improperly functioning; depleted oxygen supply; altitude

Question 9

What are some examples of global hypoventilation?

Answer 9

(1) Elevated PaCO2, ETCO2 or PvCO2
(2) Neuromuscular dysfunction
(3) Airway Obstruction
(4) Abdominal Distension
(5) Chest wall dysfunction
(6) Pleural Space disease

Question 10

Define hypoventilation

Answer 10

An elevated PaCO2 > or equal to 45 mmHg OR ETCO2

Question 11

Name the four gases in the alveoli

Answer 11

Oxygen
Carbon Dioxide
Water Vapor
Nitrogen

Question 12

What is the normal alveolar composition of gases when breathing room air at sea level is _____

Answer 12

• Water vapor 50 mmHg (fixed; alveolar gases are always 100% saturated at body temp)
• Carbon Dioxide 40 mmHg (regulated by the brainstem respiratory control center)
• Oxygen 105 mmHg
• Nitrogen 560 mmHg

Question 13

What is venous admixture?

Answer 13

All the ways in which venous blood can get from the right side to the left side of the circulation without being properly oxygendated

Question 14

What are four causes of venous admixture?

Answer 14

(1) Low ventilation-perfusion regions
(2) Small airway and alveolar collapse (atelectasis or zero ventilation but perfused lung units)
(3) Diffusion defects
(4) Anatomic R to L shunts

Question 15

Name a cause for LOW V/Q regions and give 3 examples. Is it responsive to oxygen therapy? If not, what is it responsive to?

Answer 15

Moderate to severe diffuse lung disease (i.e. edema, pneumonia, hemorrhage) – responsive to oxygen therapy

Question 16

Name a cause for atelectasis (Zero V/Q regions) and give 3 examples. Is it responsive to oxygen therapy? If not, what is it responsive to?

Answer 16

Severe to very severe diffuse lung disease (i.e. edema, pneumonia, hemorrhage) – NOT responsive to oxygen but responsive to PPV.

Question 17

Name a cause for diffusion defects and give 3 examples.Is it responsive to oxygen therapy? If not, what is it responsive to?

Answer 17

Moderate to severe diffuse lung disease (i.e. oxygen toxicity, smoke inhalation, ARDS); partially responsive to oxygen therapy.

Question 18

Name a cause for R to L shunts and give 3 examples. Is it responsive to oxygen therapy? If not, what is it responsive to?

Answer 18

R to L PDA and VSD; intrapulmonary A-V anatomic shunts; NOT responsive to oxygen therapy or PPV; surgery possible

Question 19

What is the equation for Alveolar-Arterial PO2 Gradient (A-a gradient)?

Answer 19

The difference between the calculated alveolar partial pressure of oxygen (PAO2) and the measured arterial partial pressure of oxygen (PaO2). At sea level, breathing 21%, the alveolar air equation can be shortened to: PAO2 = 150 - PaCO2

Question 20

What is the normal A-a gradient when breathing room air?

Question 21

When the A-a gradient is > ____ mmHg, you worry that it may represent decreasing oxygenating efficiency (venous admixture).

Answer 21

20 mmHg