Diving and Pressure Injuries: Gas Laws, Barotrauma, Arterial Gas Embolism, and Decompression Sickness Practice Questions

25 multiple-choice questions on Diving and pressure injuries: gas laws, barotrauma, arterial gas embolism, and decompression sickness for paramedic and EMT students, from Chapter 39 (Environmental Emergencies). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. Two divers who filled their tanks from the same portable compressor both develop headache and confusion at depth. You should suspect:

   1. A. Carbon monoxide in the air
   2. B. Nitrogen narcosis at depth
   3. C. Sinus barotrauma in each diver
   4. D. Oxygen toxicity from the tank air
   Show answer

   Answer: A. Carbon monoxide in the air

   A compressor whose intake draws in engine exhaust can contaminate tank air with carbon monoxide, and the higher partial pressure at depth makes toxicity worse. Symptoms in several divers using the same air source are a clue. Give high-flow oxygen and consider hyperbaric treatment. Nitrogen narcosis impairs judgment and clears on ascent without headache, sinus squeeze causes facial pain rather than confusion, and air at recreational depths does not reach a toxic oxygen pressure.

2. Each 10 m (33 ft) of seawater adds about how much pressure?

   1. A. 2 atmospheres
   2. B. 0.1 atmosphere
   3. C. 1 atmosphere
   4. D. 5 atmospheres
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   Answer: C. 1 atmosphere

   At 10 m (33 ft) the total pressure is 2 atmospheres absolute: one from air and one from water. At 30 m (99 ft) it is 4 atmospheres absolute.

3. The greatest relative change in gas volume occurs between:

   1. A. 20 m and 30 m (66 and 99 ft)
   2. B. The surface and 10 m (33 ft)
   3. C. 30 m and 40 m (99 and 132 ft)
   4. D. 40 m and 50 m (132 and 165 ft)
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   Answer: B. The surface and 10 m (33 ft)

   Pressure doubles from 1 to 2 atmospheres in the first 10 m (33 ft), halving gas volume, so the shallowest water carries the highest relative risk of barotrauma. Deeper 10-m steps produce smaller proportional changes.

4. Henry's law explains decompression sickness because it states that the amount of gas dissolved in a liquid:

   1. A. Depends mainly on the temperature of the liquid
   2. B. Falls as the surrounding pressure rises
   3. C. Is fixed regardless of the gas pressure
   4. D. Is proportional to the gas partial pressure
   Show answer

   Answer: D. Is proportional to the gas partial pressure

   At depth, more nitrogen dissolves into tissues; if a diver ascends too quickly, the gas comes out of solution as bubbles, like opening a soda bottle. This bubble formation is decompression sickness.

5. After a dive, a diver has red spots on the face and bleeding in the whites of both eyes. He forgot to exhale into his mask while descending. This is most likely:

   1. A. Decompression illness
   2. B. Arterial gas embolism
   3. C. Mask squeeze
   4. D. A carbon monoxide leak
   Show answer

   Answer: C. Mask squeeze

   If a diver does not exhale through the nose into the mask during descent, the air space in the mask becomes negative pressure, causing facial petechiae and subconjunctival hemorrhages (mask squeeze). It is usually benign, though vision changes need evaluation. It is not decompression illness or gas embolism.

6. A diver who has a cold descends and develops severe ear pain, then sudden vertigo and nausea underwater. The most likely cause is:

   1. A. Tympanic membrane rupture
   2. B. Nitrogen narcosis
   3. C. Decompression sickness
   4. D. An oxygen toxicity seizure
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   Answer: A. Tympanic membrane rupture

   Congestion prevents equalization, and on descent the eardrum can rupture; cold water entering the middle ear causes vertigo, which is dangerous underwater. Nitrogen narcosis does not cause ear pain.

7. A diver feels pain over the maxillary sinus during descent. This is:

   1. A. Arterial gas embolism
   2. B. Sinus barotrauma
   3. C. Decompression sickness
   4. D. Nitrogen narcosis
   Show answer

   Answer: B. Sinus barotrauma

   Blocked sinus openings trap air that contracts on descent, causing pain and sometimes bleeding into the sinus. Decompression sickness typically appears after surfacing, not during descent.

8. Pulmonary overpressurization syndrome is most often caused by a scuba diver who:

   1. A. Exhales steadily while ascending
   2. B. Descends too slowly to the bottom
   3. C. Holds the breath while ascending
   4. D. Stays too long at a shallow depth
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   Answer: C. Holds the breath while ascending

   Compressed air in the lungs expands as the diver rises; if it cannot escape, alveoli rupture and cause pneumothorax, mediastinal emphysema, or arterial gas embolism. Exhaling during ascent prevents this.

9. Arterial gas embolism typically produces symptoms:

   1. A. 12 to 24 hours after a dive
   2. B. Within minutes of surfacing
   3. C. Mainly after flying home
   4. D. Several days after diving
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   Answer: B. Within minutes of surfacing

   AGE usually appears immediately or within about 10 minutes of surfacing as air enters the pulmonary veins and travels to the brain or heart. Decompression sickness typically appears later, often within hours.

10. A 30-year-old diver surfaces rapidly from 18 m (60 ft) after running out of air. Within 2 minutes she is confused with right-sided weakness. The most likely diagnosis is:

    1. A. Decompression sickness
    2. B. Nitrogen narcosis
    3. C. Ear barotrauma
    4. D. Arterial gas embolism
    Show answer

    Answer: D. Arterial gas embolism

    Sudden stroke-like signs within minutes of a rapid ascent strongly suggest cerebral AGE. Decompression sickness typically presents later with joint pain or spinal signs.

11. The prehospital priorities for arterial gas embolism are:

    1. A. High-flow oxygen and early recompression
    2. B. Aspirin and transport to a stroke center
    3. C. Nitrous oxide and transport to the nearest ED
    4. D. Rest on scene until symptoms resolve fully
    Show answer

    Answer: A. High-flow oxygen and early recompression

    Give 100% oxygen by nonrebreathing mask or demand valve whatever the SpO2: it speeds removal of nitrogen from the bubbles, shrinks them, and improves oxygen delivery to ischemic tissue. Then arrange recompression early through Divers Alert Network or medical direction, since recompression in a hyperbaric chamber is the definitive treatment. AGE looks like a stroke, but the blockage is a gas bubble, not a clot; a stroke center without a chamber cannot give the definitive treatment, and aspirin is not a substitute for oxygen and recompression. Nitrous oxide diffuses into gas bubbles and enlarges them, so it is contraindicated. Waiting on scene delays recompression, and symptoms that improve with oxygen often return. (UHMS best practice guidelines; DAN.)

12. Decompression sickness (the bends) is caused by:

    1. A. Nitrogen bubbles forming in tissues and blood
    2. B. Air entering the arteries from the torn alveoli
    3. C. Carbon dioxide building up in the regulator
    4. D. Water aspirated from a leaking face mask
    Show answer

    Answer: A. Nitrogen bubbles forming in tissues and blood

    Dissolved nitrogen comes out of solution during or after ascent and forms bubbles that block vessels and trigger inflammation. Torn alveoli releasing air into arteries describe arterial gas embolism.

13. A diver develops a deep, aching pain in the shoulder 3 hours after a series of deep dives. This most likely represents:

    1. A. Type II decompression sickness
    2. B. Cerebral arterial gas embolism
    3. C. Type I decompression sickness
    4. D. Nitrogen narcosis
    Show answer

    Answer: C. Type I decompression sickness

    Joint pain, often in the shoulders or elbows, is the most common symptom of mild (type I) DCS. Type II DCS involves the nervous system, lungs, or circulation, and AGE appears within minutes of surfacing, not hours.

14. Which finding indicates serious (type II) decompression sickness?

    1. A. Itching of the skin on the forearms
    2. B. Numbness and weakness of the legs
    3. C. Joint pain in the elbow
    4. D. Ear pain that began during descent
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    Answer: B. Numbness and weakness of the legs

    Neurologic signs, especially spinal cord signs such as leg numbness, weakness, or urinary retention, define serious (type II) DCS, as do cerebral signs, respiratory "chokes", and shock; these patients need oxygen and urgent recompression. Itching of the skin without marbling is a mild skin bend (type I). Elbow or shoulder joint pain is the classic type I symptom, although it can coexist with serious signs. Ear pain that began on descent is middle ear barotrauma from failure to equalize, not decompression sickness, which develops after ascent. Note that a mottled or marbled skin rash (cutis marmorata) is not a mild finding: it can precede serious DCS and should be treated as such. (U.S. Navy Diving Manual Rev 7, ch. 20; Vann 2011; DAN.)

15. Decompression sickness can be triggered by:

    1. A. Drinking water before diving
    2. B. Diving to a depth of 3 m
    3. C. Exhaling during the ascent
    4. D. Flying soon after diving
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    Answer: D. Flying soon after diving

    Lowered cabin pressure lets residual nitrogen bubble out, so divers should wait at least 12 to 24 hours before flying. Exhaling during ascent prevents pulmonary barotrauma but does not affect nitrogen loading.

16. A diver with suspected decompression sickness should be transported by air:

    1. A. At the highest possible altitude to shorten the flight time
    2. B. After symptoms have resolved on scene with oxygen
    3. C. At low altitude or in a cabin pressurized to sea level
    4. D. With the cabin at the aircraft's cruising altitude
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    Answer: C. At low altitude or in a cabin pressurized to sea level

    Ascending to altitude lowers ambient pressure and enlarges bubbles, worsening DCS or AGE, so helicopters fly low and fixed-wing aircraft pressurize to sea level. Air transport is often the fastest route to a chamber.

17. The definitive treatment for decompression sickness and arterial gas embolism is:

    1. A. Surgical removal of the trapped gas bubbles
    2. B. Diuretics to reduce tissue swelling
    3. C. Rapid warming in a warm water bath
    4. D. Recompression in a hyperbaric chamber
    Show answer

    Answer: D. Recompression in a hyperbaric chamber

    Recompression shrinks bubbles and hyperbaric oxygen speeds nitrogen elimination and tissue oxygenation. Diuretics would worsen dehydration, which contributes to DCS.

18. Fluids for a diver with decompression sickness should be:

    1. A. Oral or IV isotonic fluids
    2. B. Avoided to prevent edema
    3. C. Hypotonic D5W at 500 mL/h
    4. D. Withheld until recompression
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    Answer: A. Oral or IV isotonic fluids

    Divers are often dehydrated from immersion diuresis, sweating, and breathing dry gas, and dehydration slows the removal of nitrogen and worsens the microcirculation. Give isotonic oral fluids to an alert diver who can protect the airway, or IV normal saline or lactated Ringer's otherwise. Avoiding fluids for fear of edema leaves the diver volume depleted, and DCS does not cause fluid overload. Glucose-only solutions such as D5W act as free water and can worsen neurologic injury. Waiting for the chamber to start fluids leaves the diver dry during what may be hours of transport. (UHMS best practice guidelines; DAN.)

19. Nitrogen narcosis, or "rapture of the deep," typically:

    1. A. Begins after the diver has surfaced
    2. B. Resolves with ascent to shallower depth
    3. C. Requires immediate recompression
    4. D. Causes ear pain on the way down
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    Answer: B. Resolves with ascent to shallower depth

    Nitrogen at high partial pressure has an anesthetic effect below about 30 m (100 ft), causing euphoria and poor judgment that resolve when the diver ascends. Its danger is the errors and accidents it causes at depth.

20. A diver who was impaired at 40 m (130 ft) and now feels normal on the boat most likely had:

    1. A. Oxygen toxicity
    2. B. Arterial gas embolism
    3. C. Nitrogen narcosis
    4. D. Decompression sickness
    Show answer

    Answer: C. Nitrogen narcosis

    Narcosis clears on ascent and needs no specific treatment unless it led to injury or a rapid ascent. AGE and DCS present or persist after surfacing.

21. A diver surfaces with chest pain, a voice change, and crackling under the skin of the neck. This most likely represents:

    1. A. Mediastinal and subcutaneous emphysema
    2. B. Decompression sickness of the large joints
    3. C. Nitrogen narcosis from a deep dive
    4. D. Sinus squeeze from a blocked sinus
    Show answer

    Answer: A. Mediastinal and subcutaneous emphysema

    Ruptured alveoli leak air along the bronchi into the mediastinum and neck, causing crepitus, chest pain, and hoarseness. Watch closely for pneumothorax and AGE.

22. A diver with suspected pneumothorax from ascent barotrauma is being considered for recompression. Before recompression, the pneumothorax:

    1. A. Will resolve with recompression
    2. B. Is not a concern at depth
    3. C. Should be watched until it grows
    4. D. Must be decompressed first
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    Answer: D. Must be decompressed first

    On decompression in the chamber, any trapped pleural air will expand, so a pneumothorax must be treated with a chest tube or needle decompression first. Recompression alone does not fix a pneumothorax.

23. Which resource helps paramedics locate a hyperbaric chamber and get dive medicine advice 24 hours a day?

    1. A. Poison control center
    2. B. Divers Alert Network
    3. C. National Weather Service
    4. D. Local lifeguard tower
    Show answer

    Answer: B. Divers Alert Network

    The Divers Alert Network runs an emergency hotline that provides consultation and helps find recompression facilities. Poison control does not coordinate dive emergencies.

24. A diver who had joint pain after a dive felt better after 20 minutes of oxygen. You should:

    1. A. Stop the oxygen and release him from care now
    2. B. Give aspirin and release him to rest
    3. C. Continue oxygen and still arrange evaluation
    4. D. Watch him for 1 hour and release him
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    Answer: C. Continue oxygen and still arrange evaluation

    Symptoms often improve with oxygen but can recur, and recompression is still recommended for DCS. Releasing him after a short period of observation or with aspirin skips the evaluation he needs, and he should not dive or fly until he has been assessed.

25. In a diver with suspected arterial gas embolism, the recommended position is:

    1. A. Head-down tilt
    2. B. Sitting upright
    3. C. Prone
    4. D. Supine
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    Answer: D. Supine

    Current guidance places patients supine, since the head-down Trendelenburg or left lateral head-down position does not keep bubbles out of the brain and can worsen cerebral edema. Sitting upright may encourage bubbles toward the brain.