100+ Free ABEM UHM Practice Questions

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Question 1

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Which gas law best describes why an undrained pneumothorax is an absolute contraindication to hyperbaric oxygen therapy?

Boyle's law — gas volume is inversely proportional to pressure, so trapped gas expands during decompression

Dalton's law — the total pressure of a gas mixture equals the sum of partial pressures

Henry's law — gas dissolves in liquids in proportion to partial pressure

Charles's law — gas volume is directly proportional to absolute temperature

to track

2026 Statistics

Key Facts: ABEM UHM Exam

~200

Exam Questions

ABEM/ABPM

$2,215

Total Exam Cost

ABEM 2026

1 year

Required UHM Fellowship

ACGME

UHMS Approved Indications

UHMS 14th Edition

2.8 ATA

Navy Table 6 Depth

U.S. Navy Diving Manual

Every 2 years

Exam Frequency

ABEM Subspecialty

The ABEM UHM exam is an ABEM subspecialty certification for emergency physicians practicing undersea and hyperbaric medicine. Candidates must complete a 1-year ACGME UHM fellowship after primary ABEM/AOBEM certification. The exam costs $470 application + $1,745 exam fee and is administered via ABPM in even-numbered years. It tests gas laws, dive medicine, UHMS-approved HBO2 indications, Navy Treatment Tables, chamber operations, and contraindications.

Sample ABEM UHM Practice Questions

Try these sample questions to test your ABEM UHM exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which gas law best describes why an undrained pneumothorax is an absolute contraindication to hyperbaric oxygen therapy?

A.Boyle's law — gas volume is inversely proportional to pressure, so trapped gas expands during decompression

B.Dalton's law — the total pressure of a gas mixture equals the sum of partial pressures

C.Henry's law — gas dissolves in liquids in proportion to partial pressure

D.Charles's law — gas volume is directly proportional to absolute temperature

Explanation: Boyle's law (P1V1 = P2V2) explains why a pneumothorax is the only absolute contraindication to HBO2: at depth (compression) the gas volume shrinks, but upon decompression (ascent), the trapped air expands in inverse proportion to the decreasing ambient pressure, converting a simple pneumothorax into a tension pneumothorax. The pneumothorax must be drained with a chest tube before compression. Dalton and Henry laws are important for gas mixture partial pressures and inert gas kinetics, respectively, but are not the mechanism for pneumothorax expansion.

2A diver descends to 33 feet of seawater (fsw). What is the approximate absolute ambient pressure?

A.2 atmospheres absolute (ATA)

B.1 ATA

C.3 ATA

D.0.5 ATA

Explanation: At sea level, ambient pressure is 1 ATA. Each 33 fsw (or 10 msw) of seawater adds an additional 1 ATA of pressure. Therefore 33 fsw corresponds to 2 ATA total (1 atmospheric + 1 hydrostatic). This relationship is fundamental to all dive and hyperbaric medicine calculations. Freshwater adds 1 ATA per 34 ft due to lower density.

3According to Dalton's law, what is the partial pressure of oxygen (PO2) when breathing 100% oxygen at 2.4 ATA?

A.2.4 ATA (1,824 mmHg)

B.0.21 ATA

C.1.0 ATA (760 mmHg)

D.2.0 ATA

Explanation: Dalton's law of partial pressures states that the partial pressure of a gas equals its fraction of the mixture multiplied by the total pressure. Breathing 100% oxygen (FiO2 = 1.0) at 2.4 ATA yields PO2 = 1.0 × 2.4 = 2.4 ATA, approximately 1,824 mmHg. This is roughly 10-15 times the PaO2 achievable at sea level on 100% oxygen and drives the therapeutic effects of HBO2 including hyperoxygenation of poorly perfused tissues.

4Which gas law explains the uptake of nitrogen into tissues during a dive (nitrogen saturation) and its subsequent release leading to decompression sickness?

A.Henry's law — the amount of gas dissolved in a liquid is proportional to its partial pressure above the liquid

B.Boyle's law — volume and pressure are inversely related

C.Graham's law — rate of diffusion is inversely proportional to the square root of molecular weight

D.Charles's law — volume and temperature are directly related at constant pressure

Explanation: Henry's law states that at a given temperature, the amount of a gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. During a dive, the increased PN2 drives nitrogen into tissue (saturation); on ascent, the partial pressure drops and nitrogen comes out of solution. If ascent is too rapid, nitrogen exceeds its solubility limit and forms bubbles, causing decompression sickness. Slow, staged ascent allows controlled offloading below the critical supersaturation threshold.

5Which of the following is NOT currently among the 14 UHMS-approved indications for hyperbaric oxygen therapy?

A.Autism spectrum disorder

B.Carbon monoxide poisoning

C.Necrotizing soft tissue infection

D.Idiopathic sudden sensorineural hearing loss

Explanation: Autism spectrum disorder is NOT a UHMS-approved indication for hyperbaric oxygen therapy. Despite marketing claims by some off-label clinics, there is no high-quality evidence supporting HBO2 for autism. The 14 UHMS-approved indications include: air/gas embolism, CO poisoning (with cyanide adjunct), clostridial myonecrosis, crush injury/compartment syndrome, decompression sickness, arterial insufficiencies (CRAO, enhancement of problem wounds), severe anemia, intracranial abscess, NSTI, refractory osteomyelitis, delayed radiation injury, compromised grafts/flaps, acute thermal burn, and ISSNHL.

6A 45-year-old male presents with a COHb of 28%, transient loss of consciousness at the scene, and mild confusion. Which is the strongest indication for HBO2?

A.History of loss of consciousness combined with COHb >25%

B.Headache alone

C.COHb of 10% with nausea

D.Asymptomatic COHb of 15%

Explanation: UHMS/ACMT criteria for HBO2 in CO poisoning include: any loss of consciousness, neurologic signs/symptoms other than headache, cardiac ischemia or arrhythmia, pregnancy (with COHb >15%), or COHb >25%. This patient meets TWO criteria (LOC AND COHb >25%), making HBO2 strongly indicated. The primary mechanism is accelerated dissociation of CO-hemoglobin (half-life ~20 min at 2.5-3 ATA vs ~320 min on room air) and reduction in delayed neurologic sequelae.

7What is the typical treatment pressure for carbon monoxide poisoning in a hyperbaric chamber?

A.2.5-3.0 ATA for 90-120 minutes

B.1.5 ATA for 30 minutes

C.6.0 ATA for 60 minutes

D.Atmospheric pressure with 100% oxygen

Explanation: Standard CO poisoning protocols treat at 2.5-3.0 ATA for 90-120 minutes total, with alternating oxygen and brief air breaks to minimize CNS oxygen toxicity. The Weaver protocol uses 3 ATA initially, stepping down to 2 ATA. The half-life of carboxyhemoglobin decreases from ~320 minutes on room air, to ~74 minutes on 100% NBO, to ~20 minutes at 2.5-3 ATA HBO2. HBO2 also reduces CO binding to cytochrome oxidase and may reduce delayed neurologic sequelae.

8A diver surfaces from a 100 fsw / 40-minute dive and develops shoulder pain (the 'bends') 30 minutes later. How is this classified?

A.Type I decompression sickness — musculoskeletal (joint/skin)

B.Type II decompression sickness — neurologic

C.Arterial gas embolism

D.Inner ear barotrauma

Explanation: Decompression sickness is classified as Type I (pain-only, including joint/limb pain known as 'the bends', skin itch or cutis marmorata, and lymphatic) or Type II (serious — neurologic, spinal cord, vestibular/inner ear, cardiopulmonary 'chokes', or CNS). This patient with isolated joint pain has Type I DCS. Even Type I DCS warrants recompression per current UHMS guidelines, typically on U.S. Navy Treatment Table 5 or 6. 'Staggers' refers to vestibular DCS (Type II), and 'chokes' refers to cardiopulmonary DCS (Type II).

9What is the immediate pre-hospital treatment for a diver with suspected decompression sickness after surfacing?

A.100% surface oxygen via tight-fitting non-rebreather mask, supine positioning, and IV fluids while arranging transport to a recompression chamber

B.Recompress the diver underwater by sending them back down

C.Aspirin 325 mg and observation

D.Immediate intubation regardless of symptoms

Explanation: Surface oxygen is first-line emergency treatment for suspected DCS or AGE. A tight-fitting non-rebreather mask with 100% O2 washes out nitrogen from tissues and accelerates bubble resolution by steepening the nitrogen gradient. Place the patient supine (modern teaching; historical head-down Trendelenburg is no longer recommended because it increases cerebral edema). Give IV fluids to improve perfusion. Arrange emergent transport — do NOT send the diver back down ('in-water recompression' is dangerous without trained teams). Definitive treatment is recompression in a chamber on a Navy treatment table.

10U.S. Navy Treatment Table 6 is used for what indication and at what initial depth?

A.Serious decompression sickness and arterial gas embolism — 60 fsw (2.8 ATA)

B.Type I DCS only — 30 fsw (1.9 ATA)

C.Routine chronic wound treatment — 45 fsw (2.4 ATA)

D.Oxygen toxicity prophylaxis — 165 fsw (6.0 ATA)

Explanation: U.S. Navy Treatment Table 6 is the standard initial treatment for serious decompression sickness (Type II) and arterial gas embolism. It compresses to 60 fsw (2.8 ATA), delivers alternating 20-minute O2 / 5-minute air periods for 75 minutes at depth, then slowly decompresses to 30 fsw for a prolonged O2 phase, totaling approximately 4 hours 45 minutes. Extensions may be added at 60 fsw or 30 fsw for persistent/recurrent symptoms. Treatment Table 5 is a shorter profile for pain-only (Type I) DCS with complete resolution at depth.

About the ABEM UHM Exam

The ABEM Undersea and Hyperbaric Medicine (UHM) Subspecialty Exam certifies emergency physicians in the practice of hyperbaric oxygen therapy and diving medicine. The exam is sponsored by the American Board of Emergency Medicine (ABEM) and administered by the American Board of Preventive Medicine (ABPM). Candidates must hold primary ABEM or AOBEM certification and have completed an ACGME-accredited 1-year UHM fellowship. The exam is offered in even-numbered years (October-November testing window).

Questions

200 scored questions

Time Limit

Approximately 4 hours (computer-based)

Passing Score

Scaled criterion-referenced passing score

Exam Fee

$470 application + $1,745 exam fee (American Board of Emergency Medicine (administered by ABPM))

ABEM UHM Exam Content Outline

15-20%

Hyperbaric Physics & Physiology

Boyle, Dalton, and Henry's gas laws; partial pressures; inert gas kinetics; mechanisms of hyperbaric oxygen (vasoconstriction, angiogenesis, neutrophil inhibition, bactericidal effect).

20-25%

Diving Medicine

Decompression sickness (Type I joint/skin vs Type II neurologic/cardiopulmonary), arterial gas embolism, barotrauma (ear, sinus, pulmonary), nitrogen narcosis, and oxygen toxicity.

30-35%

UHMS Approved HBO2 Indications

CO poisoning, necrotizing soft tissue infection, osteoradionecrosis, DFU Wagner 3+, chronic osteomyelitis, crush injury, burns, compromised flaps, ISSNHL, CRAO, severe anemia, gas gangrene, intracranial abscess, AGE.

15-20%

Chamber Operations & Treatment Tables

Monoplace vs multiplace chambers, U.S. Navy Treatment Tables 5 and 6, NFPA 99 fire safety, tender roles, and emergency procedures.

10-15%

Contraindications & Complications

Absolute (untreated pneumothorax) and relative contraindications (bleomycin, cis-platinum, doxorubicin, disulfiram, mafenide, COPD), middle ear barotrauma, seizures, confinement anxiety, progressive myopia.

How to Pass the ABEM UHM Exam

What You Need to Know

Passing score: Scaled criterion-referenced passing score
Exam length: 200 questions
Time limit: Approximately 4 hours (computer-based)
Exam fee: $470 application + $1,745 exam fee

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ABEM UHM Study Tips from Top Performers

1Memorize U.S. Navy Treatment Table 6 (60 fsw / 2.8 ATA) for serious DCS and AGE — it is the single most tested protocol on the exam

2Know all 14 UHMS-approved HBO2 indications cold, including the Wagner classification cutoff (Grade 3 or higher) for diabetic foot ulcers

3Master the gas laws — apply Boyle's law to barotrauma and expanding gas, Dalton's law to partial pressures at depth, and Henry's law to inert gas saturation and decompression sickness

4Differentiate CNS oxygen toxicity (>1.6 ATA threshold, seizures, Paul Bert effect) from pulmonary oxygen toxicity (prolonged exposure, Lorrain-Smith effect, tracked via OTU/UPTD)

5Understand CO poisoning HBO criteria: loss of consciousness, cardiac ischemia, neurologic symptoms, pregnancy, or COHb >25% (>15% in pregnancy) — know 2.5-3 ATA protocols and cyanide adjunct therapy

Frequently Asked Questions

Who is eligible for the ABEM UHM subspecialty exam?

Candidates must hold primary ABEM or AOBEM certification in Emergency Medicine, successfully complete an ACGME-accredited Undersea and Hyperbaric Medicine fellowship of at least 1 year, maintain active unrestricted medical licensure, and be actively participating in ABEM continuing certification or AOBEM OCC. Unlike some other subspecialties, there is no current practice-pathway alternative for ABEM candidates — the ACGME fellowship is required.

How often is the ABEM UHM exam offered?

The ABEM UHM subspecialty exam is offered every two years in even-numbered years. The 2026 exam is scheduled for October 12 - November 1, 2026, with applications open May 18 - June 23, 2026.

How many questions are on the ABEM UHM exam?

The exam contains approximately 200 multiple-choice questions delivered via computer-based testing. The content blueprint covers hyperbaric physics and physiology, diving medicine, UHMS-approved indications for HBO2, chamber operations, and contraindications/complications.

How much does the ABEM UHM exam cost?

The total cost is $2,215: a $470 non-refundable application fee plus a $1,745 examination fee. These fees are paid to ABEM (application) and ABPM (exam administration).

What are the UHMS-approved indications for hyperbaric oxygen therapy?

UHMS recognizes 14 approved indications: air or gas embolism, carbon monoxide poisoning (with cyanide adjunct), clostridial myonecrosis (gas gangrene), crush injury/compartment syndrome, decompression sickness, arterial insufficiencies (CRAO and enhancement of healing in select problem wounds such as DFU Wagner 3+), severe anemia, intracranial abscess, necrotizing soft tissue infection, refractory osteomyelitis, delayed radiation injury (osteoradionecrosis and soft-tissue radionecrosis), compromised skin grafts/flaps, acute thermal burn injury, and idiopathic sudden sensorineural hearing loss (ISSNHL).

What is U.S. Navy Treatment Table 6?

Navy Treatment Table 6 is the standard treatment protocol for serious decompression sickness (Type II) and arterial gas embolism. It compresses the patient to 60 feet of seawater (fsw, equivalent to 2.8 ATA), delivers alternating 20-minute oxygen and 5-minute air breaks for 75 minutes at depth, then decompresses stepwise over approximately 4 hours 45 minutes total. Extensions may be added at 60 fsw or 30 fsw for persistent symptoms.

What is the only absolute contraindication to hyperbaric oxygen therapy?

Untreated pneumothorax is the only absolute contraindication to hyperbaric oxygen therapy. During decompression (ascent), trapped gas expands per Boyle's law, which can convert a simple pneumothorax into a tension pneumothorax. The pneumothorax must be drained with a chest tube before treatment. Relative contraindications include concurrent bleomycin, cis-platinum, doxorubicin, disulfiram, and topical mafenide.

How do I maintain ABEM UHM certification?

Diplomates maintain UHM certification by actively participating in ABEM's continuing certification (MOC) program or AOBEM's OCC program. This includes completing required CME, passing periodic assessments (MyEMCert longitudinal assessment for ABEM), paying annual fees, and maintaining active licensure. The subspecialty certificate is valid for 10 years with continuous MOC.