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Pharmacology · chapter 23 · Introduction to the Respiratory System

Oxygenation and Gas Exchange

The 13 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.

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Key points

  1. How oxygen reaches the tissues

    When a person breathes in, oxygen diffuses and is picked up by the hemoglobin of the red blood cells. It is then transported and distributed to the organs and tissues of the body.

  2. What oxygen saturation measures

    The amount of oxygen bound to hemoglobin can be measured using oxygen saturation. This describes the percentage of hemoglobin currently bound to oxygen.

  3. Normal oxygen saturation

    Normal oxygen saturation is between 95% and 100% for a client breathing only room air.

  4. Hypoxemia needs treatment

    Hypoxemia is lower-than-normal oxygen levels in the blood and often requires the client to receive concentrated oxygen. This condition can be fatal if not treated (Landry, 2022).

  5. Three conditions for gas exchange

    For gas exchange to happen, the alveoli must be ventilated, gases must be diffused, and perfusion must take place.

  6. Path of blood through the lungs

    The pulmonary arteries bring venous blood from the right side of the heart to be oxygenated, and the gas exchange occurs in the pulmonary capillaries.

  7. Ventilation and blood pH

    The ventilation process also helps to maintain blood pH in the normal range by regulating the amount of carbon dioxide in the body.

  8. Chemoreceptors set the breathing rate

    Chemoreceptors sense changes in the levels of carbon dioxide, hydrogen ions, and oxygen in the blood. These receptors adjust the rate of ventilation in response to the amount of carbon dioxide in the blood.

  9. High carbon dioxide speeds breathing

    When carbon dioxide levels are too high, the respiratory rate increases to “blow off” the excess carbon dioxide. This, in turn, raises the pH level of blood because carbon dioxide is acidic.

  10. Low carbon dioxide slows breathing

    On the other hand, if carbon dioxide levels are too low, the respiratory rate will decrease to “hold on to” the carbon dioxide, thereby lowering the pH level (Landry, 2022).

  11. Gases move from high to low pressure

    Diffusion of oxygen and carbon dioxide depends on the concentration or partial pressure of gases. The movement of gases always occurs from a high-pressure area to a low-pressure area.

  12. Where perfusion happens in the lungs

    In the lungs, perfusion takes place through the capillaries that surround the alveoli.

  13. What reduces perfusion

    Perfusion can be affected by poor circulation, which reduces the amount of oxygen that is transported to the tissues and organs. Other factors that can affect perfusion are low circulating volume, the pumping ability of the heart, and low blood pressure (Dezube, 2023).

Terms to know

Oxygenation
Oxygenation is the process of supplying oxygen to body cells.
Hypoxemia
Hypoxemia is lower-than-normal oxygen levels in the blood and often requires the client to receive concentrated oxygen.
Ventilation
Ventilation is the process of moving air into and out of the lungs.
Diffusion
Diffusion is the spontaneous movement of gases between the alveoli and capillaries in the lungs.
Perfusion
Perfusion is the process of blood flowing to tissues and organs, which is crucial for delivering oxygen and nutrients and removing waste products.

Practice questions

Stuck on select-all-that-apply? How to take them one option at a time.

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Every question here, with the answer

  1. A client breathing room air has an oxygen saturation of 89%. How should the nurse interpret this?

    1. Higher than normal
    2. Normal for room air
    3. Lower than normal; the client may have hypoxemia
    4. Normal only during sleep

    Answer: Lower than normal; the client may have hypoxemia

    Normal oxygen saturation on room air is 95% to 100%, so 89% is low and suggests hypoxemia, which often requires concentrated oxygen. The other interpretations do not match the normal range.

  2. A client's blood carbon dioxide level rises. What change in breathing should the nurse expect?

    1. Breathing stops briefly to reset pH.
    2. Breathing stays exactly the same.
    3. The respiratory rate decreases to hold on to carbon dioxide.
    4. The respiratory rate increases to blow off carbon dioxide.

    Answer: The respiratory rate increases to blow off carbon dioxide.

    When carbon dioxide levels are too high, chemoreceptors increase the respiratory rate to blow off the excess, which raises blood pH. A slower rate is the response to low carbon dioxide.

  3. Which factors can reduce perfusion to tissues and organs? Select all that apply.

    1. Low blood pressure
    2. Poor circulation
    3. Reduced pumping ability of the heart
    4. Normal oxygen saturation
    5. Low circulating volume

    Answer: Low blood pressure, Poor circulation, Reduced pumping ability of the heart, Low circulating volume

    Poor circulation, low circulating volume, the heart's pumping ability, and low blood pressure all affect perfusion. A normal oxygen saturation does not reduce perfusion.

  4. A student nurse lists what must happen for gas exchange to occur. Which items are correct? Select all that apply.

    1. Gases must diffuse.
    2. Gases must move from low pressure to high pressure.
    3. The alveoli must be ventilated.
    4. Perfusion must take place.
    5. The body must spend energy to move gases.

    Answer: Gases must diffuse., The alveoli must be ventilated., Perfusion must take place.

    Gas exchange requires ventilation of the alveoli, diffusion of gases, and perfusion. Gases always move from high to low pressure, and diffusion does not require energy.

  5. A client asks what the pulse oximeter number means. Which explanation is accurate?

    1. The blood pressure in the lungs
    2. The amount of carbon dioxide in the blood
    3. The percentage of hemoglobin currently bound to oxygen
    4. The number of breaths per minute

    Answer: The percentage of hemoglobin currently bound to oxygen

    Oxygen saturation describes the percentage of hemoglobin currently bound to oxygen. It is not a breathing rate, a pressure, or a carbon dioxide level.

  6. A client's carbon dioxide level falls too low. How will the body respond?

    1. Breathing slows to hold on to carbon dioxide, lowering the pH.
    2. Oxygen saturation drops to zero.
    3. Breathing speeds up to blow off more carbon dioxide.
    4. The heart rate stops changing.

    Answer: Breathing slows to hold on to carbon dioxide, lowering the pH.

    If carbon dioxide levels are too low, the respiratory rate decreases to hold on to carbon dioxide, which lowers the pH. Faster breathing is the response to high carbon dioxide.

Where every quote comes from

Section 23.3 Oxygenation and Gas Exchange of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.

The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.