Thoracic Anatomy and the Physiology of Ventilation and Oxygenation Practice Questions

25 multiple-choice questions on Thoracic anatomy and the physiology of ventilation and oxygenation for paramedic and EMT students, from Chapter 36 (Chest Trauma). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. The bony thoracic cage is made up of 12 pairs of ribs, the sternum, and the:

   1. A. Cervical vertebrae
   2. B. Thoracic vertebrae
   3. C. Clavicles and scapulae
   4. D. Lumbar vertebrae
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   Answer: B. Thoracic vertebrae

   The ribs articulate posteriorly with the 12 thoracic vertebrae and most attach anteriorly to the sternum. The clavicles and scapulae form the shoulder girdle, which sits on top of the cage but is not part of it.

2. To locate the second intercostal space, you palpate the sternal angle (angle of Louis), which marks where the sternum joins the:

   1. A. First rib
   2. B. Fourth rib
   3. C. Fifth rib
   4. D. Second rib
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   Answer: D. Second rib

   The sternal angle is the ridge where the manubrium meets the sternal body, and the second rib attaches there; the space just below it is the second intercostal space. The first rib lies under the clavicle and is hard to feel, so counting from it leads to errors.

3. Ribs 1 through 7 are called true ribs because they:

   1. A. Attach directly to the sternum by their own cartilage
   2. B. Attach to the sternum through one shared costal cartilage
   3. C. Have no anterior attachment to the sternum
   4. D. Attach to the vertebrae without any cartilage
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   Answer: A. Attach directly to the sternum by their own cartilage

   Ribs 1 to 7 each have their own costal cartilage joining the sternum. Ribs 8 to 10 join through shared cartilage (false ribs), and ribs 11 and 12 have no anterior attachment (floating ribs).

4. When a needle or chest tube is passed between the ribs, it is placed just over the top of the lower rib mainly because:

   1. A. The upper edge of each rib is thicker
   2. B. The lung is farther away at that point
   3. C. Vessels and nerve run under each rib
   4. D. The pleura is absent over the rib tops
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   Answer: C. Vessels and nerve run under each rib

   Each intercostal artery, vein, and nerve runs in a groove along the lower border of its rib, so entering just above the rib below avoids them. Rib thickness, lung position, and pleural coverage do not differ in this way; the pleura lines the whole chest wall.

5. Under normal conditions, the pleural space contains:

   1. A. About 150 mL of air
   2. B. A thin film of serous fluid
   3. C. Several hundred mL of blood
   4. D. Loose fat and connective tissue
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   Answer: B. A thin film of serous fluid

   The pleural space is a potential space with only a few milliliters of lubricating fluid, which lets the pleural layers slide during breathing. Any air or blood there is abnormal and is what defines a pneumothorax or hemothorax.

6. A patient with rib fractures is using the muscles of his neck to help each breath. This finding indicates:

   1. A. A flail segment on that side
   2. B. Respiratory alkalosis from pain
   3. C. Normal effort with rib pain
   4. D. Increased work of breathing
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   Answer: D. Increased work of breathing

   Quiet breathing uses mainly the diaphragm. Recruiting accessory muscles such as the sternocleidomastoids and scalenes means the patient is working hard to breathe and may be tiring, which warrants close monitoring and possible ventilatory support. Accessory muscle use does not identify a flail segment or a blood gas change, and it is not a normal baseline for rib pain; it signals strain.

7. In a patient with a worsening chest injury, which monitor usually shows inadequate ventilation first?

   1. A. Capnography (ETCO2)
   2. B. Pulse oximetry (SpO2)
   3. C. Blood pressure cuff
   4. D. Cardiac rhythm strip
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   Answer: A. Capnography (ETCO2)

   ETCO2 changes breath by breath, so hypoventilation shows up as a rising ETCO2 or a changing waveform right away. SpO2 may stay normal for minutes, especially on supplemental oxygen, before falling. Blood pressure and rhythm changes are late and nonspecific.

8. The lung stays expanded against the chest wall mainly because of:

   1. A. Positive pressure in the pleural space
   2. B. Cartilage rings throughout the bronchioles
   3. C. Negative pressure in the pleural space
   4. D. Muscle tone within the visceral pleura
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   Answer: C. Negative pressure in the pleural space

   The chest wall tends to spring outward and the lung tends to recoil inward, creating a slight vacuum between the pleural layers. Once air enters that space, the negative pressure is lost and the lung collapses.

9. A patient with rib fractures is breathing 32 times/min with a tidal volume of 200 mL. Assuming a dead space of 150 mL, his alveolar ventilation is about:

   1. A. 6,400 mL/min
   2. B. 4,800 mL/min
   3. C. 1,600 mL/min
   4. D. 11,200 mL/min
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   Answer: C. 1,600 mL/min

   Alveolar ventilation is (tidal volume minus dead space) × rate, or (200 − 150) × 32 = 1,600 mL/min. 6,400 mL/min is the total minute volume, which looks adequate but ignores that most of each shallow breath only fills dead space.

10. When ventilating an adult chest trauma patient with a bag-valve device, the best guide to an appropriate breath size is:

    1. A. Squeezing the bag fully each time
    2. B. As much air as the bag will hold
    3. C. The loudest sound from the mask
    4. D. Enough volume to see chest rise
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    Answer: D. Enough volume to see chest rise

    Breaths of about 6 to 8 mL/kg, enough to produce visible chest rise, oxygenate without excessive pressure. Oversized breaths raise intrathoracic pressure, reduce venous return, worsen air leaks and barotrauma, and inflate the stomach. Mask noise does not measure volume.

11. A 30-year-old with chest trauma is breathing fast, is anxious, and says his hands are tingling. Before calling this anxiety hyperventilation, you should:

    1. A. Rule out hypoxia and chest injury
    2. B. Have him breathe into a paper bag
    3. C. Tell him to calm down and slow down
    4. D. Withhold oxygen until he relaxes
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    Answer: A. Rule out hypoxia and chest injury

    Rapid breathing after chest trauma may be the body's response to hypoxia, pneumothorax, pulmonary contusion, or blood loss. Assess SpO2, breath sounds, and perfusion, and give oxygen. Paper-bag rebreathing is dangerous if hypoxia is present, and dismissing the symptoms risks missing a life-threatening injury.

12. A 35-year-old who fell 15 feet (4.5 m) has a normal rate and depth of breathing but an SpO2 of 86% on oxygen. A pulmonary contusion is suspected. The best explanation is that:

    1. A. Her minute volume is too low to clear her CO2
    2. B. Blood is passing alveoli that cannot exchange gas
    3. C. Carbon dioxide is filling the alveoli on that side
    4. D. The pulse oximeter is reading carboxyhemoglobin
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    Answer: B. Blood is passing alveoli that cannot exchange gas

    In a contusion, blood and fluid fill alveoli that are still perfused, so blood passes through without picking up oxygen (shunt). Her rate and depth are normal, so low minute volume does not explain the hypoxia.

13. A stab wound at the level of the sixth intercostal space anteriorly should be assumed to involve:

    1. A. Both the chest and the abdominal cavity
    2. B. The chest cavity but not the abdomen
    3. C. The abdominal cavity but not the chest
    4. D. The chest wall muscles without the pleura
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    Answer: A. Both the chest and the abdominal cavity

    The diaphragm rises as high as the fourth or fifth intercostal space on exhalation, so a wound below the nipple line may cross both cavities. Assuming a chest-only injury misses liver, spleen, and diaphragm injuries.

14. A 26-year-old was kicked in the left lower chest and has tenderness over ribs 9 through 11. You should be most concerned about injury to the:

    1. A. Liver
    2. B. Aorta
    3. C. Spleen
    4. D. Bladder
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    Answer: C. Spleen

    The lower left ribs overlie the spleen, so fractures there should raise suspicion of splenic bleeding. The liver lies under the lower right ribs, so it is the tempting but wrong choice for a left-sided injury.

15. Alveoli that are ventilated but not perfused represent:

    1. A. Intrapulmonary shunting
    2. B. Dead space ventilation
    3. C. Alveolar hypoventilation
    4. D. Diffusion impairment
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    Answer: B. Dead space ventilation

    Ventilated alveoli with no blood flow add to dead space, as in a pulmonary embolism or severe hypovolemia. Shunt is the opposite: perfused alveoli that are not ventilated, as in pulmonary contusion.

16. Inspiration occurs because enlarging the thoracic cavity:

    1. A. Raises the pressure inside the lungs
    2. B. Pushes the diaphragm up into the chest
    3. C. Raises the surface tension of the alveoli
    4. D. Lowers the pressure inside the lungs
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    Answer: D. Lowers the pressure inside the lungs

    By Boyle's law, increasing the volume of the chest lowers the pressure inside it, so air flows in from the atmosphere. Raising lung pressure is what happens during exhalation, or during positive-pressure ventilation.

17. A patient with a flail chest on a nonrebreather mask has an SpO2 of 99% and an ETCO2 of 62 mmHg. The best interpretation is:

    1. A. Ventilation is adequate but oxygenation is not
    2. B. Both ventilation and oxygenation are adequate
    3. C. The capnometer reading is almost certainly false
    4. D. Oxygenation is adequate but ventilation is not
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    Answer: D. Oxygenation is adequate but ventilation is not

    High-flow oxygen can keep the SpO2 normal even while CO2 builds up from hypoventilation. The ETCO2 of 62 mmHg shows inadequate ventilation, so the SpO2 alone would falsely reassure you.

18. A 25-year-old has lost about 2 L of blood into his chest. On high-flow oxygen, his SpO2 is 98%. His oxygen delivery to the tissues is most likely:

    1. A. Normal, since his SpO2 shows full saturation
    2. B. Reduced, since he has less hemoglobin for O2
    3. C. Increased, since he is breathing high-flow O2
    4. D. Normal, since dissolved O2 makes up the loss
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    Answer: B. Reduced, since he has less hemoglobin for O2

    Almost all oxygen in blood travels bound to hemoglobin, and SpO2 reports only the percentage of the remaining hemoglobin that is saturated, not how much hemoglobin there is. After a 2-L loss, oxygen content and cardiac output both fall, so delivery is reduced even at 98%. A normal SpO2 therefore does not mean delivery is normal. High-flow oxygen cannot raise delivery above normal when the carrier is lost; it adds only a little dissolved oxygen. Dissolved oxygen is about 0.3 mL per 100 mL of blood per 100 mmHg of PaO2, far too little to replace lost hemoglobin; only blood and bleeding control restore delivery. (PHTLS 10th ed., shock and thoracic chapters.)

19. During forceful exhalation, such as coughing, the muscles that contract include the:

    1. A. External intercostals and the diaphragm
    2. B. Scalenes and the sternocleidomastoid muscles
    3. C. Internal intercostals and abdominal muscles
    4. D. Diaphragm and pectoralis minor
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    Answer: C. Internal intercostals and abdominal muscles

    Quiet exhalation is passive, but forced exhalation uses the internal intercostals and abdominal wall to squeeze the chest. The external intercostals, scalenes, and diaphragm all enlarge the chest and work during inspiration.

20. A patient with painful rib fractures takes only small breaths and will not cough. The main danger of this splinting is:

    1. A. Shallow breathing that leads to atelectasis
    2. B. Deep breathing that leads to respiratory alkalosis
    3. C. Bronchospasm that leads to wheezing
    4. D. Pleural fluid that leads to effusion
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    Answer: A. Shallow breathing that leads to atelectasis

    Small, guarded breaths let alveoli collapse and secretions pool, leading to hypoxia and pneumonia. Pain prevents deep breathing, so alkalosis from overbreathing is the opposite of what happens.

21. While you bag a patient with a large pulmonary contusion, each breath takes more squeezing pressure than it did earlier. This mainly reflects:

    1. A. Decreased lung compliance
    2. B. An increase in lung compliance
    3. C. Normal recovery of the lung
    4. D. A leak in the bag's valve
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    Answer: A. Decreased lung compliance

    Blood and edema filling the contused lung make it stiffer (less compliant), so more pressure is needed to deliver the same volume, and this can worsen over hours. Rising resistance should also prompt a check for tension pneumothorax and tube problems. Increased compliance would make bagging easier, and a valve leak makes the bag feel loose, not stiff.

22. A patient with a rib fracture has a sharp, stabbing pain that worsens with each deep breath. This pleuritic pain arises from the:

    1. A. Visceral pleura
    2. B. Alveolar walls
    3. C. Parietal pleura
    4. D. Bronchial mucosa
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    Answer: C. Parietal pleura

    The parietal pleura has somatic pain fibers, so irritation produces sharp, localized pain with breathing. The visceral pleura and lung tissue lack pain fibers, which is why a lung injury itself may be painless.

23. A patient with a large pulmonary contusion stays hypoxic despite a nonrebreather mask at 15 L/min. The main reason oxygen helps so little is that:

    1. A. The mask cannot deliver enough oxygen
    2. B. Blood passes fluid-filled alveoli
    3. C. Carbon dioxide displaces the oxygen
    4. D. The bruised lung has lost its perfusion
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    Answer: B. Blood passes fluid-filled alveoli

    In pulmonary contusion, blood and fluid fill alveoli, so blood flowing past them picks up no oxygen (an intrapulmonary shunt); raising inspired oxygen helps little, while positive end-expiratory pressure (CPAP or PEEP) can reopen alveoli. The mask delivers high oxygen, carbon dioxide is not crowding oxygen out of the alveoli, and the problem is perfused alveoli that are not ventilated (shunt), not ventilated alveoli that have lost their blood flow (dead space).

24. After a high-speed crash, a driver has a fracture of the first rib. The main significance of this finding is that it:

    1. A. Is a common low-energy seat belt injury
    2. B. Usually signals a flail segment there
    3. C. Means the patient has osteoporotic bones
    4. D. Implies great force, vessel injury
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    Answer: D. Implies great force, vessel injury

    The first and second ribs are short, thick, and protected by the shoulder girdle, so fracturing them takes substantial force, raising concern for injury to the subclavian vessels, aorta, brachial plexus, and lungs. It is not a low-energy injury, a single upper rib fracture does not make a flail segment, and it suggests energy, not weak bone.

25. For ventilation to occur, the bellows system of the chest requires an:

    1. A. Intact pericardium, aorta, and esophagus
    2. B. Intact sternum, clavicles, and scapulae
    3. C. Intact chest wall, diaphragm, and pleura
    4. D. Intact bronchioles, alveoli, and capillaries
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    Answer: C. Intact chest wall, diaphragm, and pleura

    Air moves in only if the chest wall and diaphragm can create negative pressure and the pleural seal transmits it to the lung. Chest trauma that breaks any part of this system (flail chest, open pneumothorax, diaphragm rupture) impairs ventilation; the alveoli and capillaries handle gas exchange, not bellows action.