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ABEM UHM practice questions

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Question 1Undersea Medicine

A scuba diver breathing compressed air at depth absorbs extra nitrogen because the partial pressure of nitrogen in the breathing gas rises with ambient pressure. Which principle best explains this increased nitrogen loading?

  1. Dalton's law, in which total pressure equals the sum of partial pressures
  2. Boyle's law, in which gas volume is inversely proportional to pressure
  3. Graham's law, in which gas diffusion rate is inversely proportional to molecular weight
  4. Henry's law, in which gas solubility in a liquid rises with its partial pressure Correct answer.

Explanation

Henry's law governs how much dissolved gas a liquid holds at equilibrium, and dissolved nitrogen rises in proportion to its partial pressure at depth. Dalton's law describes how the partial pressure is calculated but not the resulting tissue solubility.

Question 2Undersea Medicine

Which gas is added to breathing mixtures specifically to reduce the risk of nitrogen narcosis and oxygen toxicity at depth?

  1. Carbon dioxide
  2. Helium Correct answer.
  3. Argon
  4. Carbon monoxide

Explanation

Helium is used in trimix and heliox because it is essentially non-narcotic and allows lowering the nitrogen and oxygen fractions at depth. It also has low density, which reduces breathing resistance.

Question 3Undersea Medicine

A diver ascends while holding their breath after breathing compressed air at depth. What is the principal mechanism of pulmonary barotrauma in this setting?

  1. Expanding gas in the lungs exceeds the elastic limit of lung tissue Correct answer.
  2. Cold water triggers laryngospasm and negative-pressure pulmonary edema
  3. Increased gas density causes turbulent flow and alveolar rupture
  4. Dissolved nitrogen comes out of solution within the pleural space

Explanation

As ambient pressure falls during ascent, gas trapped in the lungs expands according to Boyle's law and can overdistend and rupture alveoli. This is why divers must never hold their breath on ascent.

Question 4Undersea Medicine

Which finding most strongly suggests arterial gas embolism rather than decompression sickness in a diver who surfaces and collapses within minutes?

  1. Immediate loss of consciousness with focal neurologic deficits Correct answer.
  2. Gradual onset of unilateral knee pain over several hours
  3. Itchy rash over the trunk after a long dive
  4. Progressive fatigue developing the next morning

Explanation

Arterial gas embolism typically presents within seconds to minutes of surfacing with sudden neurologic or cardiac collapse from gas in the arterial circulation. Decompression sickness more often evolves over minutes to hours with joint pain or other symptoms.

Question 5Undersea Medicine

A diver with suspected decompression illness is conscious, breathing spontaneously, and has no signs of airway compromise. What is the most appropriate initial field management?

  1. Place supine, give 100% oxygen, and arrange urgent recompression Correct answer.
  2. Have the patient sit upright and give oral fluids only
  3. Encourage a rapid return to depth to equalize symptoms
  4. Give nitroglycerin and observe for one hour before transport

Explanation

High-flow oxygen and supine positioning with urgent transport to a hyperbaric chamber are the cornerstones of initial decompression-illness care. Oxygen reduces bubble-driven ischemia and accelerates inert-gas elimination.

Question 6Undersea Medicine

What is the primary pathophysiologic effect of nitrogen narcosis on a diver at depth?

  1. Progressive impairment of judgment and cognition resembling alcohol intoxication Correct answer.
  2. Hemolysis of red blood cells causing anemia
  3. Acute airway obstruction from laryngeal edema
  4. Direct thermal injury to the tympanic membrane

Explanation

Nitrogen narcosis produces reversible cognitive and motor impairment that worsens with depth and resolves with ascent. It impairs judgment, which is why it contributes to diving accidents.

Question 7Undersea Medicine

A diver ascends rapidly and develops a choking sensation with hemoptysis and subcutaneous emphysema in the neck. Which diagnosis is most likely?

  1. Pneumothorax from pulmonary barotrauma Correct answer.
  2. Carbon monoxide poisoning
  3. Hypothermia
  4. Inner ear barotrauma

Explanation

Overexpansion of trapped lung gas during ascent can cause alveolar rupture with pneumothorax, pneumomediastinum, and subcutaneous emphysema. Hemoptysis and neck crepitus point to this barotrauma spectrum.

Question 8Undersea Medicine

Which gas is most commonly implicated in oxygen toxicity when a diver breathes a high-oxygen mixture at depth?

  1. Helium
  2. Oxygen Correct answer.
  3. Nitrogen
  4. Argon

Explanation

Elevated oxygen partial pressure is the direct cause of central nervous system and pulmonary oxygen toxicity. The risk rises with both the fraction of oxygen and the ambient pressure.

Question 9Undersea Medicine

A diver using a rebreather with a faulty oxygen sensor develops muscle twitching, visual disturbance, and a seizure underwater. Which complication is most likely?

  1. Hypoxic encephalopathy
  2. Carbon dioxide narcosis
  3. Decompression sickness from nitrogen
  4. Central nervous system oxygen toxicity Correct answer.

Explanation

Central nervous system oxygen toxicity can present with twitching, visual changes, and seizures when the oxygen partial pressure is excessive. In a rebreather, a sensor fault can raise the inspired oxygen fraction dangerously.

Question 10Undersea Medicine

At what approximate oxygen partial pressure does central nervous system oxygen toxicity typically become a significant concern for divers?

  1. 0.2 atmospheres
  2. 1.6 atmospheres Correct answer.
  3. 3.0 atmospheres
  4. 0.5 atmospheres

Explanation

Most diving agencies set a maximum working oxygen partial pressure near 1.4 to 1.6 atmospheres to limit central nervous system toxicity. Below that range the risk is much lower for typical exposures.

Question 11Undersea Medicine

A free diver performs repeated deep breath-hold dives with short surface intervals and develops cough, chest tightness, and hemoptysis. Which process best explains these findings?

  1. Pulmonary squeeze from lung volume reduction below residual volume Correct answer.
  2. Nitrogen narcosis from compressed air
  3. Arterial gas embolism from breath-hold ascent
  4. Oxygen toxicity from enriched air

Explanation

Breath-hold divers can suffer pulmonary squeeze when lung gas compresses below residual volume, causing capillary stress and hemorrhage. Symptoms include cough, chest pain, and hemoptysis after deep or repetitive dives.

Question 12Undersea Medicine

A diver with a history of asthma wants to begin scuba diving. Which concern most appropriately guides counseling?

  1. Greater risk of oxygen toxicity at surface pressure
  2. Increased risk of air trapping and pulmonary barotrauma during ascent Correct answer.
  3. Reduced risk of decompression sickness from bronchodilation
  4. Higher susceptibility to nitrogen narcosis at shallow depths

Explanation

Asthma can promote airway obstruction and regional air trapping, which raises the risk of pulmonary barotrauma and arterial gas embolism during ascent. Fitness-to-dive decisions weigh disease control and exercise-induced symptoms.

Question 13Undersea Medicine

Which clinical scenario is most consistent with immersion pulmonary edema?

  1. A healthy swimmer develops dyspnea and frothy sputum during a cold-water surface swim Correct answer.
  2. A diver develops a focal seizure at 40 meters on air
  3. A snorkeler develops vertigo and vomiting after a forceful Valsalva maneuver
  4. A diver has delayed shoulder pain twelve hours after a dive

Explanation

Immersion pulmonary edema occurs in otherwise healthy individuals during immersion, often with cold water or exertion, producing dyspnea, cough, and pink frothy sputum. It is not explained by gas embolism or decompression sickness.

Question 14Undersea Medicine

A diver develops vertigo, nausea, and nystagmus after a forceful Valsalva maneuver during descent. Which structure is most likely injured?

  1. Round window of the inner ear Correct answer.
  2. Eustachian tube orifice
  3. Tympanic membrane only
  4. External auditory canal

Explanation

A forceful Valsalva during descent can raise inner ear pressure and rupture the round or oval window, causing vertigo and nystagmus. This is inner ear barotrauma and requires urgent otolaryngology evaluation.

Question 15Undersea Medicine

Which statement about decompression sickness is most accurate?

  1. It is prevented by breathing pure oxygen throughout the dive
  2. It occurs only when divers exceed 100 meters of depth
  3. It is caused by oxygen bubbles forming in venous blood
  4. It results from inert gas bubbles forming when tissue supersaturation exceeds safe limits Correct answer.

Explanation

Decompression sickness arises when dissolved inert gas, chiefly nitrogen, comes out of solution as bubbles during or after ascent. Symptom onset and severity depend on depth, time, and ascent profile.

Question 16Undersea Medicine

A diver with suspected decompression sickness is being transported by air. Which transport consideration is most important?

  1. Maintain cabin altitude as low as possible or use ground transport to limit further bubble growth Correct answer.
  2. Give supplemental carbon dioxide to stimulate breathing
  3. Keep the patient upright to reduce cerebral blood flow
  4. Fly at the highest feasible altitude to speed arrival

Explanation

Lowering ambient pressure during flight can enlarge existing bubbles and worsen symptoms, so transport should minimize altitude exposure. Ground transport or a pressurized cabin at low altitude is preferred.

Question 17Undersea Medicine

Which finding is most characteristic of middle-ear barotrauma during descent?

  1. Profuse watery diarrhea
  2. Unilateral ptosis and miosis
  3. Petechial rash over the abdomen
  4. Ear pain with a retracted, congested tympanic membrane Correct answer.

Explanation

Failure to equalize middle-ear pressure on descent causes a pressure gradient that stretches the tympanic membrane and produces pain with a retracted, congested drum. Severe cases may involve hemotympanum or membrane rupture.

Question 18Undersea Medicine

A diver breathing air at 30 meters of seawater (4 atmospheres absolute) has an inspired oxygen partial pressure closest to which value?

  1. 0.21 atmospheres
  2. 4.0 atmospheres
  3. 0.84 atmospheres Correct answer.
  4. 1.68 atmospheres

Explanation

At 4 atmospheres absolute, the oxygen partial pressure is 0.21 times 4, or about 0.84 atmospheres. Partial pressure equals the gas fraction multiplied by ambient pressure.

Question 19Undersea Medicine

Which measure most directly reduces the risk of decompression sickness on a repetitive dive series?

  1. Ascending within the allowed rate and observing surface intervals Correct answer.
  2. Descending faster to reach the target depth sooner
  3. Breathing a helium-rich mixture at shallow depths
  4. Skipping safety stops to shorten total bottom time

Explanation

Controlled ascent rates and adequate surface intervals allow inert gas to be eliminated gradually and keep tissue supersaturation within safe limits. Dive tables or computers operationalize these principles.

Question 20Undersea Medicine

A diver is found unconscious at the surface after an emergency ascent. Which action should be prioritized first?

  1. Give intravenous fluids before any airway assessment
  2. Immediately place the patient in Trendelenburg position
  3. Apply a cervical collar before opening the airway
  4. Assess and secure the airway while providing 100% oxygen Correct answer.

Explanation

Airway, breathing, and circulation take precedence in any unresponsive diver, with high-flow oxygen to address possible gas embolism. Recompression is arranged after stabilization.

Question 21Undersea Medicine

Which statement about carbon monoxide contamination of scuba air is most accurate?

  1. It is detected reliably by the diver's sense of smell
  2. It is harmless because it is exhaled unchanged
  3. It causes symptoms only after surfacing
  4. It binds hemoglobin avidly and can cause headache, confusion, and loss of consciousness at depth Correct answer.

Explanation

Carbon monoxide in compressed air binds hemoglobin with high affinity, reducing oxygen delivery and causing neurologic and cardiac symptoms that may appear at depth. Compressor maintenance and air testing prevent contamination.

Question 22Undersea Medicine

A diver with a patent foramen ovale is at increased risk for which diving-related complication?

  1. Middle-ear squeeze
  2. Nitrogen narcosis at shallow depth
  3. Cold-induced urticaria
  4. Paradoxical gas embolism with neurologic symptoms Correct answer.

Explanation

A right-to-left shunt such as a patent foramen ovale can allow venous gas bubbles to reach the arterial circulation, producing paradoxical embolism and neurologic decompression illness. Divers with unexplained neurologic symptoms after diving are sometimes evaluated for a shunt.

Question 23Undersea Medicine

Which pathophysiologic mechanism best explains the benefit of hyperbaric oxygen therapy in decompression illness?

  1. Increasing nitrogen partial pressure to re-dissolve bubbles faster
  2. Causing systemic vasodilation to flush bubbles through the circulation
  3. Shrinking bubble volume and improving tissue oxygenation while accelerating inert gas washout Correct answer.
  4. Suppressing hemoglobin production to reduce blood viscosity

Explanation

Hyperbaric oxygen reduces bubble size according to Boyle's law, hyperoxygenates ischemic tissue, and creates a gradient that speeds inert gas elimination. These combined effects treat both the mechanical and ischemic consequences of bubble disease.

Question 24Undersea Medicine

A commercial diver breathing heliox at great depth develops nausea, tremor, and slowed thinking. Which complication of the breathing mixture should be considered?

  1. Nitrogen narcosis
  2. High-pressure nervous syndrome Correct answer.
  3. Oxygen toxicity seizure
  4. Carbon dioxide retention from a scrubber failure

Explanation

High-pressure nervous syndrome occurs with deep heliox exposures and produces tremor, nausea, and cognitive changes. It is distinct from inert-gas narcosis and from oxygen toxicity.

Question 25Undersea Medicine

Which physiologic change during immersion in cold water most contributes to the risk of drowning in the first minutes after accidental entry?

  1. Sudden bradycardia with asystole from the diving reflex
  2. An involuntary gasp and hyperventilation that can lead to aspiration Correct answer.
  3. Rapid onset of decompression sickness from dissolved gas
  4. Immediate loss of consciousness from nitrogen narcosis

Explanation

Cold-water immersion triggers a gasp reflex and hyperventilation, which can cause aspiration and drowning if the head is submerged. This cold-shock response is a leading early hazard in immersion incidents.

Question 26Undersea Medicine

A scuba diver descends to 20 meters of seawater (3 atmospheres absolute) breathing air. What is the approximate partial pressure of nitrogen in the breathing gas at that depth?

  1. 3.2 atmospheres
  2. 2.4 atmospheres Correct answer.
  3. 0.8 atmospheres
  4. 1.6 atmospheres

Explanation

At 20 msw the ambient pressure is 3 ATA, and air is approximately 79% nitrogen, so the nitrogen partial pressure is about 0.79 x 3 = 2.4 ATA. This is why narcosis becomes noticeable at this depth.

Question 27Undersea Medicine

Which tissue is most commonly injured in a diver who develops barotrauma of the middle ear during descent?

  1. The round window membrane
  2. The eustachian tube cartilage
  3. The ossicular chain
  4. The tympanic membrane Correct answer.

Explanation

During descent the gas-filled middle ear is compressed, and if the eustachian tube cannot equalize the pressure gradient, the tympanic membrane is stretched and may rupture. This is the most frequent structure injured in middle-ear barotrauma.

Question 28Undersea Medicine

A diver surfaces after a deep dive and develops pruritus, a blotchy rash over the trunk, and mild fatigue. Which form of decompression sickness is this most consistent with?

  1. Type II decompression sickness
  2. Type I decompression sickness Correct answer.
  3. Immersion pulmonary edema
  4. Arterial gas embolism

Explanation

Type I decompression sickness is the milder form, classically producing skin manifestations such as cutis marmorata, pruritus, and localized limb pain without neurologic or cardiopulmonary involvement. Type II disease involves the nervous, respiratory, or cardiovascular systems.

Question 29Undersea Medicine

What is the principal mechanism by which hyperbaric oxygen therapy improves tissue oxygenation in decompression illness?

  1. It stimulates erythropoietin release
  2. It raises the dissolved oxygen content of plasma Correct answer.
  3. It dilates systemic arteries
  4. It increases the solubility of nitrogen in blood

Explanation

At hyperbaric pressures, oxygen dissolved physically in plasma rises substantially and can supply tissue needs even when hemoglobin carriage and perfusion are compromised. This also creates gradients that accelerate inert gas elimination and reduce bubble size.

Question 30Undersea Medicine

Which finding best distinguishes arterial gas embolism from decompression sickness shortly after surfacing?

  1. Bilateral knee aching after a long dive
  2. Immediate neurologic deficit after a rapid ascent Correct answer.
  3. Gradual onset of joint pain over several hours
  4. Localized rash over the abdomen

Explanation

Arterial gas embolism results from pulmonary barotrauma with gas entering the arterial circulation, producing abrupt neurologic or cardiac symptoms within minutes of surfacing. Decompression sickness typically has a more gradual onset of limb pain or neurologic symptoms over minutes to hours.

Question 31Undersea Medicine

Which gas is added to a breathing mixture to reduce the risk of nitrogen narcosis and gas density during deep commercial diving?

  1. Carbon dioxide
  2. Argon
  3. Nitrous oxide
  4. Helium Correct answer.

Explanation

Helium is much less narcotic than nitrogen and produces a lower-density gas mixture, which reduces work of breathing at depth. Heliox is therefore used for deep commercial diving.

Question 32Undersea Medicine

A diver breathing air at 40 meters of seawater develops sudden loss of consciousness with no warning. Which cause should be considered first?

  1. Hypothermia
  2. Oxygen toxicity
  3. Nitrogen narcosis Correct answer.
  4. Hypercapnia

Explanation

At 40 msw (5 ATA) the nitrogen partial pressure approaches 4 ATA, a level at which narcosis can cause severe impairment and loss of consciousness. The absence of warning signs and the depth make narcosis the leading concern.

Question 33Undersea Medicine

Which statement best describes the relationship between depth and the volume of a gas-filled space in a diver's body, assuming constant temperature?

  1. Volume decreases linearly with depth in meters
  2. Volume is directly proportional to absolute pressure
  3. Volume is inversely proportional to absolute pressure Correct answer.
  4. Volume is unaffected by depth

Explanation

Boyle's law states that at constant temperature the volume of a gas is inversely proportional to absolute pressure. This principle underlies all barotrauma during descent and the risk of overexpansion during ascent.

Question 34Undersea Medicine

A diver who has been breathing air at 30 meters of seawater ascends rapidly while holding his breath and collapses on the surface. Which is the most appropriate initial management priority?

  1. Give aspirin and discharge if symptoms resolve
  2. Administer oral fluids and observe
  3. Place supine, provide 100% oxygen, and arrange urgent transport Correct answer.
  4. Apply a heating blanket and encourage ambulation

Explanation

Suspected arterial gas embolism requires immediate high-flow oxygen, supine positioning, and urgent transport to a hyperbaric facility. Oxygen reduces bubble size and treats ischemia while definitive recompression is arranged.

Question 35Undersea Medicine

A diver is diagnosed with decompression sickness and is being prepared for transport. Which factor most strongly determines the choice of transport altitude?

  1. The cabin pressure of the aircraft and the risk of bubble expansion Correct answer.
  2. The diver's insurance coverage
  3. The diver's age and body mass index
  4. The availability of in-flight meals

Explanation

Aircraft cabins are typically pressurized to an altitude equivalent of 2000 to 2500 meters, lowering ambient pressure and allowing bubbles to expand. Transport should use the lowest feasible cabin altitude or a ground ambulance when practical.

Question 36Undersea Medicine

Which physiologic change during head-out water immersion most directly promotes a positive fluid balance and contributes to immersion pulmonary edema?

  1. Reduced cardiac preload
  2. Decreased intrathoracic blood volume
  3. Increased glomerular filtration rate
  4. Increased venous return from peripheral compression Correct answer.

Explanation

Hydrostatic pressure during immersion displaces blood from the extremities to the thorax, increasing central blood volume and pulmonary capillary pressure. This central fluid shift is a key mechanism in immersion pulmonary edema.

Question 37Undersea Medicine

A diver presents with vertigo, hearing loss, and tinnitus after a dive with difficulty equalizing. Which diagnosis should be considered?

  1. Pulmonary barotrauma
  2. Decompression sickness of the shoulder
  3. Inner-ear barotrauma Correct answer.
  4. Carbon dioxide retention

Explanation

Inner-ear barotrauma results from a pressure gradient transmitted to the inner ear, often after forceful Valsalva or failed equalization, and produces vertigo, hearing loss, and tinnitus. It requires urgent evaluation because of the risk of permanent hearing loss.

Question 38Undersea Medicine

Which infection-control or fitness consideration most appropriately delays return to diving after a tympanic membrane rupture?

  1. The need for lifelong antibiotic prophylaxis
  2. The need to avoid all physical activity
  3. The need to abstain from air travel permanently
  4. The need to avoid water entry until the membrane heals Correct answer.

Explanation

An unrepaired tympanic membrane perforation allows water into the middle ear and impairs pressure equalization, so diving should be deferred until healing is confirmed. Otoscopic clearance and equalization testing guide return to diving.

Question 39Undersea Medicine

A diver breathing a nitrox mixture with 36% oxygen plans a dive. What is the maximum operating depth if the oxygen partial pressure is limited to 1.4 ATA?

  1. About 18 meters of seawater
  2. About 50 meters of seawater
  3. About 29 meters of seawater Correct answer.
  4. About 40 meters of seawater

Explanation

The maximum depth is calculated from the oxygen fraction and the chosen partial pressure limit. At 1.4 ATA with 36% oxygen, the ambient pressure limit is about 3.9 ATA, corresponding to roughly 29 msw.

Question 40Undersea Medicine

A diver reports joint pain and fatigue several hours after a dive and is found to have a patent foramen ovale. Which mechanism best explains the increased risk of decompression sickness in this diver?

  1. Reduced cardiac output at depth
  2. Right-to-left shunt allowing venous gas emboli to bypass the pulmonary filter Correct answer.
  3. Increased pulmonary oxygen uptake
  4. Enhanced nitrogen solubility in arterial blood

Explanation

A patent foramen ovale permits paradoxical embolism of venous nitrogen bubbles into the arterial circulation, bypassing the pulmonary capillary filter. This increases the risk of neurologic and systemic decompression sickness.

Question 41Undersea Medicine

Which symptom pattern most suggests carbon monoxide contamination of a scuba air supply?

  1. Localized joint pain relieved by recompression
  2. Vertigo with nystagmus during descent
  3. Headache, confusion, and cherry-red skin after a dive Correct answer.
  4. Blotchy rash over the trunk

Explanation

Carbon monoxide binds hemoglobin avidly and produces headache, confusion, and impaired oxygenation; cherry-red skin is an inconsistent but classically described finding. The history of a contaminated fill source supports the diagnosis.

Question 42Undersea Medicine

Which measure most effectively prevents nitrogen narcosis during a deep dive?

  1. Limiting depth and using a helium-based mixture Correct answer.
  2. Descending more rapidly
  3. Using a larger cylinder
  4. Increasing the breathing rate

Explanation

Narcosis is driven by the partial pressure of the narcotic gas, so reducing depth and substituting helium for nitrogen lowers the narcotic load. These are the primary preventive strategies.

Question 43Undersea Medicine

A diver with a history of pneumothorax asks about diving. Which recommendation is most appropriate?

  1. Diving is safe if the diver uses nitrox
  2. Diving may be permitted after complete resolution and specialist clearance Correct answer.
  3. Diving is safe if the diver limits depth to 10 meters
  4. Diving is contraindicated only for commercial divers

Explanation

Prior pneumothorax raises concern for recurrent pneumothorax and pulmonary barotrauma during pressure changes. Clearance requires documented resolution, evaluation of underlying lung disease, and specialist assessment.

Question 44Undersea Medicine

A diver develops sudden hearing loss and tinnitus after a forceful Valsalva during descent. Which additional finding would most increase concern for inner-ear barotrauma?

  1. Vertigo with nystagmus Correct answer.
  2. Neck pain
  3. Chest tightness
  4. Abdominal bloating

Explanation

Inner-ear barotrauma commonly produces cochleovestibular symptoms, including vertigo and nystagmus, alongside hearing loss and tinnitus. The combination raises concern for a perilymphatic fistula and warrants urgent evaluation.

Question 45Undersea Medicine

Which statement about oxygen toxicity in diving is most accurate?

  1. Oxygen toxicity does not occur below 2.0 ATA
  2. Pulmonary toxicity occurs only with convulsions
  3. Pulmonary toxicity is associated with prolonged exposure to moderately elevated oxygen partial pressures Correct answer.
  4. CNS toxicity is prevented by breathing air

Explanation

Pulmonary oxygen toxicity results from cumulative exposure to elevated oxygen partial pressures over time and is distinct from CNS toxicity. Both are managed by limiting oxygen partial pressure and exposure duration.

Question 46Undersea Medicine

A diver is rescued unconscious from the water and has no palpable pulse. Which action should be performed first?

  1. Perform a focused neurologic examination
  2. Begin rescue breathing and chest compressions Correct answer.
  3. Remove the diving suit and apply warming blankets
  4. Administer intravenous fluids

Explanation

Cardiac arrest in a drowning or diving victim requires immediate initiation of CPR with rescue breaths, because hypoxemia is a common cause. Standard resuscitation takes precedence over other interventions.

Question 47Undersea Medicine

Which physiologic effect of immersion in cold water most increases the risk of drowning in the first minutes after entry?

  1. An involuntary gasping reflex and hyperventilation Correct answer.
  2. Rapid onset of decompression sickness
  3. Immediate loss of consciousness
  4. Progressive bradycardia with asystole

Explanation

Sudden cold-water immersion triggers the cold shock response, with involuntary gasping and hyperventilation that can lead to aspiration and drowning. This occurs within the first minute, before hypothermia develops.

Question 48Undersea Medicine

A diver breathing heliox at great depth develops nausea, tremor, and slowed thinking. Which complication of the breathing mixture is most likely?

  1. Nitrogen narcosis
  2. High-pressure nervous syndrome Correct answer.
  3. Oxygen toxicity
  4. Carbon dioxide excess

Explanation

High-pressure nervous syndrome occurs with rapid compression on helium-oxygen mixtures at great depth and produces tremor, nausea, and cognitive slowing. Slower compression and gas selection reduce its severity.

Question 49Undersea Medicine

A diver with suspected decompression sickness has a history of congestive heart failure. Which consideration most affects the decision to use hyperbaric oxygen therapy?

  1. The need to avoid all fluids before treatment
  2. The inability to use a monoplace chamber
  3. The risk of oxygen-induced pulmonary and cardiovascular stress at pressure Correct answer.
  4. The need for general anesthesia

Explanation

Hyperbaric oxygen increases systemic vascular resistance and can stress a failing heart, and prolonged oxygen exposure may cause pulmonary irritation. Patients with heart failure require individualized risk assessment and monitoring during treatment.

Question 50Undersea Medicine

Which pattern of injury best fits pulmonary barotrauma from breath-holding during ascent?

  1. Diffuse alveolar hemorrhage without pneumothorax
  2. Alveolar rupture with gas tracking into the mediastinum and pleural space Correct answer.
  3. Progressive alveolar collapse with hypoxemia
  4. Isolated bronchospasm without gas leak

Explanation

Ascending while holding the breath allows expanding gas to overdistend alveoli until they rupture, with gas dissecting into the mediastinum, pleural space, and systemic circulation. This can produce pneumomediastinum, pneumothorax, and arterial gas embolism.