DMT cheat sheet

Decompression sickness (DCS) is classified as Type I (musculoskeletal pain only, cutaneous, lymphatic) or Type II (neurological, cardiopulmonary, vestibular); Type II and any cardiopulmonary symptoms mandate urgent recompression.

Arterial gas embolism (AGE) typically presents within seconds to minutes of surfacing with focal neurological deficits, seizure, or loss of consciousness; DCS usually develops over 15 minutes to hours, though onset can be delayed 24-48 hours.

Inert gas load follows Haldane-style exponential kinetics: tissue tension approaches ambient inspired inert gas pressure with a half-time specific to each tissue compartment; the fastest compartments (e.g., ~5-10 min) govern short, deep exposures.

Oxygen toxicity: CNS toxicity (Paul Bert effect) is risked by high PO2 and manifested by seizures, visual disturbance, tinnitus, nausea, and twitching; pulmonary toxicity (Lorrain Smith effect) follows prolonged lower-level hyperoxia.

A PO2 above 1.4 atm during working dives and above 1.6 atm at rest is the conventional upper limit; 1.6 atm is the usual maximum for hyperbaric oxygen therapy sessions.

Nitrogen narcosis becomes clinically relevant at depths around 30 m and deeper on air; it impairs judgment and reaction time and resolves on ascent without residual deficit.

Hypoxia from a low-PO2 breathing gas is assessed by alveolar oxygen partial pressure, not by fraction of oxygen alone; a 21% mix at depth can be hypoxic if the absolute pressure is insufficient.

Immersion pulmonary edema and sudden cardiac events are recognized causes of in-water death that can mimic drowning; autopsy findings may be minimal, so scene and dive-profile history are essential.

Standard HBOT session: 2.0-3.0 atm abs (commonly 2.0-2.5 atm abs), 60-120 minutes of oxygen breathing, with air breaks (e.g., 5 minutes air every 20-30 minutes) to limit oxygen toxicity.

Indications per the Undersea and Hyperbaric Medical Society include carbon monoxide poisoning, decompression sickness, arterial gas embolism, gas gangrene, crush injury/compartment syndrome, compromised flaps and grafts, osteoradionecrosis, and delayed radiation injury.

HBOT mechanism in CO poisoning: displaces carboxyhemoglobin (half-life falls from roughly 4-6 hours on room air to about 20-30 minutes at 2.5-3 atm abs) and reduces lipid peroxidation and reperfusion injury.

HBOT is contraindicated in untreated pneumothorax; relative risks include poorly controlled asthma, seizure disorders, claustrophobia, and some implanted devices not rated for pressure.

Oxygen delivery per unit blood improves roughly 10- to 15-fold in plasma at 3 atm abs because dissolved oxygen rises about 0.003 mL O2/dL per mmHg PO2 (Henry's law), independent of hemoglobin.

Eustachian tube dysfunction is the most common barrier to compression; middle-ear barotrauma is managed with equalization techniques, decongestants, or tympanostomy when necessary.

Fire risk is the defining safety hazard: chambers use 100% oxygen atmospheres only in multiplace settings with strict ignition control; cotton, wool, and petroleum products are excluded and conductive fabrics/electronics are restricted.

Neurological examination in suspected DCS/AGE includes cranial nerves, motor strength, sensation, coordination, Romberg, and a mental status assessment; serial exams document progression and response to recompression.

Rapid neurological assessment tools (e.g., the fast neurological exam used in diving medicine) screen for motor weakness, sensory change, and gait instability within minutes of symptom onset.

Tympanic membrane examination with otoscopy distinguishes barotrauma (hemorrhage, retraction, perforation) from middle-ear effusion; Valsalva and Toynbee maneuvers are the standard equalization techniques.

A diver's dive profile (depth-time, repetitive dives, surface intervals, ascent rate) is the primary data for recompression decisions; missing or unreliable profiles should be reconstructed with conservative assumptions.

Chest auscultation, pulse oximetry, and end-tidal CO2 support assessment of respiratory compromise; arterial blood gas and carboxyhemoglobin measurement are indicated in CO poisoning.

In-water recompression is not a routine substitute for chamber treatment and is reserved for remote settings with trained support; standard of care is surface oxygen and transport to a hyperbaric facility.

Immersion and pressure effects on devices (catheters, cuffs, drains) must be planned: gas-filled cuffs expand on ascent and can rupture; fluid-filled lines compress and may occlude.

Pre-dive checks include gas analysis and labeling, regulator function, BCD and drysuit integrity, weight release, and a buddy/team briefing on hand signals and emergency procedures.

Ascent rate is limited to 9-10 m/min (roughly 30 ft/min) in recreational diving; a safety stop of 3-5 minutes at 3-6 m (10-20 ft) reduces bubble formation after no-decompression dives.

Out-of-gas and lost-buddy procedures: signal, ascend no faster than the standard rate, and use a backup gas source; never hold breath during ascent because of pulmonary barotrauma risk.

Enriched air (nitrox) requires oxygen-clean equipment, oxygen analysis before each dive, and depth limits based on maximum PO2 (commonly 1.4 atm working).

Oxygen fire safety in chambers: limit flammable materials, enforce electrical safety, and maintain a fire-suppression plan; chamber atmospheres are monitored for oxygen fraction and contaminants.

Emergency action plans must include nearest hyperbaric facility, transport time, and a communication chain; the DAN emergency hotline and local coast guard are typical first contacts.

Dive computers assume a specific ascent rate and gas mix; a diver using a computer must not exceed its limits and must plan for a backup depth/time source.

Hyperbaric chamber design and operation are governed by standards such as ASME PVHO-1 (pressure vessels for human occupancy) and NFPA 99 (health care facilities, hyperbaric chapter) in the United States.

ASME PVHO-1 covers design, fabrication, inspection, and testing of pressure vessels, including viewports and penetrators; periodic inspection and testing are required.

NFPA 99 addresses fire safety, electrical classification, and oxygen handling in hyperbaric facilities, including limits on combustibles in oxygen-enriched atmospheres.

Diving operations are guided by consensus standards such as the Diving Medical Advisory Committee (DMAC) and the International Marine Contractors Association (IMCA) for commercial diving, and by national recreational training standards.

The Undersea and Hyperbaric Medical Society (UHMS) publishes the recognized list of hyperbaric indications and facility accreditation criteria.

Pressure vessel and gas system regulations vary by jurisdiction; operators must verify local requirements for chamber certification, gas purity, and operator competency.

Diver medical fitness is assessed against published fitness standards (e.g., recreational and occupational diving medical guidelines) that address cardiovascular, respiratory, neurological, and ENT conditions.