DMT common mistakes
DMT · Understand the traps and how to avoid them.
When asked to assess fitness to dive, the candidate clears or disqualifies the diver based only on the named diagnosis, without working through the required sequence of history, examination, investigation, and the specific risk the condition poses in the hyperbaric environment.
Candidates memorize lists of absolute and relative contraindications and then try to pattern-match the diagnosis to a list. The exam instead tests whether the candidate can reason about gas trapping, reduced consciousness, thermal balance, medication effects, and the physical demands of rescue at depth. Pure recall feels faster under time pressure.
What to do instead
For every fitness question, write a short structured answer: what the condition is, how it behaves under pressure and in cold water, whether the diver can tolerate a mask and regulator, whether the diver can perform a self-rescue and assist a buddy, and what monitoring or restriction would make diving acceptable. Practice with common conditions such as asthma, epilepsy, diabetes, cardiac disease, pregnancy, and implanted devices until the sequence is automatic.
The candidate applies surface oxygen and basic first aid to a suspected decompression illness case but omits the decisive actions: stopping further diving, lying the casualty flat or in a comfortable position without a head-down tilt, giving high-flow oxygen with a tight-fitting mask, maintaining hydration and warmth, avoiding air travel or further pressure exposure, and arranging urgent referral to a hyperbaric facility.
The candidate focuses on the diagnostic question and treats management as an afterthought. Real-world exposure is often to protocols that emphasize transport, and the exam rewards complete early management because outcome depends on time to recompression and on avoiding additional bubble load.
What to do instead
Memorize a fixed management checklist and rehearse it in order: remove from diving and pressure, high-flow oxygen via a non-rebreather or demand valve, supine or recovery position, fluids if conscious, keep warm, record a full neurological examination, contact a hyperbaric unit and a diving physician, and avoid flying or driving to altitude until cleared. State each element explicitly in every management answer.
The candidate describes hyperbaric oxygen therapy as a generic treatment and cannot state which indications it is actually accepted for, nor distinguish an accepted indication from an investigational or unproven one.
Marketing material and patient forums list dozens of conditions, and candidates absorb these lists without checking which ones have evidence and which societies endorse them. The exam tests the boundary between accepted, adjunctive, and unproven indications, and the candidate who has only seen promotional lists cannot draw that line.
What to do instead
Learn the accepted indications in groups: decompression illness and gas embolism, carbon monoxide poisoning, problem wounds, compromised grafts and flaps, necrotizing soft tissue infections, osteomyelitis, radiation injury, crush injury and compartment syndrome, and a small number of others. For each, know whether hyperbaric oxygen is primary or adjunctive therapy and what the mechanism of benefit is. Treat any indication you cannot justify mechanistically and by evidence as unproven.
The candidate explains the physiology of hyperbaric oxygen therapy only in terms of increased oxygen carriage by hemoglobin, and cannot explain dissolved oxygen, the relationship to ambient pressure, oxygen toxicity mechanisms, or the effect on bubble size and gas exchange.
Surface-level revision reduces oxygen therapy to 'more oxygen in the blood'. The exam asks quantitative and mechanistic questions, such as how dissolved oxygen changes with pressure, why vasoconstriction coexists with improved oxygenation, and why oxygen can be both therapeutic and toxic.
What to do instead
Work through the numbers: at 1 atmosphere, dissolved oxygen is small compared with hemoglobin-bound oxygen; at 2 to 3 atmospheres absolute on 100 percent oxygen, dissolved oxygen becomes clinically significant. Link this to the mechanisms tested: hyperoxygenation, vasoconstriction and edema reduction, enhanced neutrophil killing, fibroblast and collagen activity, angiogenesis, and reduction of bubble volume by pressure. Then explain oxygen toxicity as a dose-and-time effect on the central nervous system and lungs.
When asked to calculate a dose, depth, or pressure, the candidate mixes gauge and absolute pressure, forgets to add atmospheric pressure to depth, or confuses feet of seawater with meters of seawater and atmospheres absolute.
The candidate has learned formulas by rote and applies them without tracking units. Hyperbaric and diving calculations almost always require absolute pressure, and a single missed addition of one atmosphere produces a plausible but wrong answer that looks correct.
What to do instead
Adopt a habit: convert everything to absolute pressure first, state the conversion explicitly, and only then substitute into the formula. Memorize the standard equivalences (one atmosphere absolute equals about 10 meters or 33 feet of seawater and about 1 bar) and check every answer against a sanity estimate, such as whether the calculated pressure is greater than one atmosphere. Show the unit at each step.
The candidate describes a chamber operation, a treatment table, or an emergency procedure without sequencing it, omitting the pre-compression checks, the attendant and inside observer roles, the compression and decompression rate limits, the air breaks, and the criteria for aborting a treatment.
Procedural knowledge is often learned as a diagram or a list of components rather than as an ordered script. Under exam conditions the candidate recalls the components but not their order, and misses the safety-critical steps that only make sense in sequence.
What to do instead
Turn each procedure into a timed script and rehearse it aloud: patient assessment and consent, equipment and gas checks, fire safety and ignition source control, staffing roles, compression with equalization checks, oxygen periods and air breaks, observation for oxygen toxicity, decompression, and post-treatment review. For each step, know the reason and the abort criterion. Practice writing the script from memory until the order is stable.
The candidate treats chamber fire safety as a single fact, such as 'no smoking', and cannot list the full set of ignition controls, the role of the inside attendant, the permitted materials, the grounding and electrical requirements, and the emergency suppression procedure.
Fire safety is taught as a memorable slogan rather than as a system of controls. The exam probes the details because a pressurized oxygen-enriched environment turns small ignition sources into catastrophic events, and because the controls are the main thing a candidate can actually influence.
What to do instead
Build a checklist organized by source of ignition and fuel: patient clothing and cosmetics, prohibited devices, approved materials, grounding, electrical equipment classification, gas purity and analysis, chamber atmosphere monitoring, and the written safety program. Then learn the emergency sequence for a chamber fire and the reason each step exists. Anchor each item to the physics of oxygen-enriched atmosphere flammability.
The candidate answers a question about a standard, guideline, or code by citing a general principle and cannot name the type of document involved, what it covers, or how it differs from a clinical guideline.
Candidates often study clinical content only and skim the standards domain, so they know that 'there is a standard' but not which body issues it, whether it is mandatory or advisory, or what it governs. The exam distinguishes standards from guidelines and tests the scope of each.
What to do instead
Make a short table of the document landscape: international and national standards for hyperbaric chambers and pressure vessels, codes for chamber design and operation, clinical practice guidelines from hyperbaric and diving medicine societies, and training and competency frameworks. For each, record the issuing body, whether it is a requirement or a recommendation, and the topics it covers. Revise the table until you can place a new document in the right category.
The candidate confuses the safety of the patient inside the chamber with the safety of the attendant, or assumes that because the patient is receiving therapy, routine pressure-vessel and gas-supply checks can be relaxed.
Attention naturally focuses on the clinical task, and the technical and safety domain is treated as background. The exam tests whether the candidate understands that the chamber is a pressure system and that the attendant is exposed to the same pressure, oxygen, and fire risks, sometimes with less protection.
What to do instead
For every scenario, ask two questions in parallel: what does the patient need, and what does the pressure system and the staff need. Learn the attendant's exposure limits, the decompression obligations of staff, the monitoring of chamber atmosphere and gas supplies, and the maintenance and inspection regime. Frame safety checks as prerequisites to treatment, not as optional extras.
The candidate presents a differential diagnosis or a management plan as a flat list of possibilities without ranking them by likelihood and urgency, and without stating what finding would change the plan.
Lists are easy to memorize and feel comprehensive, so candidates reproduce them instead of reasoning. The exam rewards prioritization, especially where a time-critical diagnosis such as gas embolism, pneumothorax, or oxygen toxicity must be acted on before a less urgent one is investigated.
What to do instead
Structure every clinical answer as a ranked differential with the reasoning for the ranking, then state the immediate actions, the investigations that discriminate between the leading options, and the triggers that would change management. Practice by taking a presentation such as sudden neurological deficit after a dive and arguing explicitly why the dangerous options come first.