Decompression Sickness and Arterial Gas Embolism First Aid: What Boat Captains, Divemasters, and First Responders Need to Do Before the Chamber

A diver surfaces on your charter, sits on the swim step, and within twenty minutes cannot lift her right arm. Another comes up hot after a computer-guided ascent and slurs her first sentence. A third, a spearfisher who never went past forty feet, blacks out on the ladder. If you are the captain, divemaster, or first responder standing there — not a diver, not a hyperbaric physician — the next five minutes decide whether that diver walks off the boat later that day or leaves in a helicopter. This is the field-first-aid guide almost no one writes for the non-diver: what to recognize, what to do, what not to do, and who to call before you burn thirty minutes making the wrong call. Every recommendation below is drawn from primary sources — the Undersea and Hyperbaric Medical Society (UHMS) best-practice guidelines, the Divers Alert Network (DAN) medical reference, the German S2k diving accident guideline, and ILCOR's 2024 first aid scoping review.

What is decompression sickness (DCS) versus arterial gas embolism (AGE), and why does the difference matter for first aid?

The two conditions share a common downstream story — gas bubbles in the vasculature — but they arrive there by different roads, and that changes what the diver looks like when they surface. DCS Type I usually presents with joint pain (the classic "bends" ache in the shoulder, elbow, knee, or hip), mottled skin, or fatigue. DCS Type II is the neurological variant: paresthesias, weakness, ataxia, bladder or bowel dysfunction, altered mentation, or the pulmonary "chokes" — substernal chest pain and a dry cough. Symptoms of DCS most commonly appear within one hour of surfacing but can develop up to 24 hours later, and rarely beyond.

AGE is the more time-critical entity. Bubbles introduced into the arterial circulation lodge in cerebral vessels within seconds and typically produce sudden neurological symptoms — loss of consciousness, seizure, focal weakness, aphasia, cortical blindness — within ten minutes of surfacing. The 2024 StatPearls chapter on arterial gas embolism is explicit that "sudden neurologic or cardiopulmonary collapse in a setting where gas could have entered the circulation" is the diagnostic centerpiece (Malik & Regina, StatPearls, 2024). AGE can occur after a dive as shallow as four to six feet if a breath-hold breaks a lung on ascent — a fact that catches spearfishers, freedivers, and inexperienced open-water students who panic and hold their breath during a bolt to the surface.

What are the first ten minutes of DCS or AGE first aid on a boat?

The sequence matters because in a real event the boat gets busy fast. A workable memory sequence for a two- or three-person crew:

1. Get the diver on deck and horizontal. Remove wet gear as tolerated but do not delay oxygen or supine positioning to strip a wetsuit. If the diver is unconscious but breathing, place them in the recovery position (left lateral) to protect the airway; the UHMS guidance is explicit on the recovery position as the airway-protective default for unconscious divers with suspected DCI (UHMS Best Practice, DCS & AGE).
2. Deliver 100% oxygen immediately. A tight-fitting non-rebreather at 15 L/min, a demand valve, or a MTV/BVM with reservoir at 15 L/min or higher. If a proper mask is not available, a nasal cannula at maximum flow is better than nothing until better delivery arrives. The 2019 S2k German diving accident guideline states plainly: "administration of 100% oxygen shall be continued without pause until the HBOT chamber is reached" (S2k Guideline, GMS 2023).
3. ABC check. Airway patent, breathing effective, pulse present. Any answer of "no" escalates to standard BLS/ALS with high-flow oxygen continued.
4. Fluids by mouth if fully conscious. One to two liters over the first two to four hours of clear, non-carbonated, non-alcoholic, non-caffeinated fluid. Oral rehydration solution (WHO ORS, Pedialyte, LMNT, DripDrop) is preferred over plain water; water is acceptable. Do not give fluids to an unconscious diver, a vomiting diver, or a diver with airway concerns.
5. Call DAN. +1 (919) 684-9111 in English, +52 557 100 0540 in Spanish. DAN medics coordinate consultation, chamber location, and MEDEVAC logistics 24/7/365 and accept collect calls from anywhere in the world.
6. Call USCG on VHF Channel 16. If you are offshore and the diver has neurological symptoms or is unstable, MEDEVAC is likely faster than driving. The USCG Aeromedical Technical Bulletin process routes to a duty flight surgeon who makes the flyable-diagnosis decision with you.
7. Baseline neuro exam and document. Level of consciousness, cranial nerves, motor strength in all four extremities, sensation, coordination (finger-to-nose, heel-to-shin), gait if safe, deep tendon reflexes. Repeat every 15 to 30 minutes. Document time-stamped changes on paper — the receiving hyperbaric physician needs the trend, not just the current snapshot.

Why is 100% oxygen the single most important pre-hospital intervention?

The physiology is worth understanding because it drives the delivery choices. At normal sea-level pressure, breathing room air produces an alveolar oxygen partial pressure of roughly 100 mmHg. Breathing 100% oxygen at sea level raises that to roughly 673 mmHg — the entire alveolar space is now oxygen, and the diffusion gradient for nitrogen out of the bloodstream is at its maximum. Every bubble in the diver is a nitrogen bubble; every unit of oxygen delivered pulls nitrogen out of that bubble faster.

The clinical evidence is consistent across four decades. The most-cited DAN study on first aid oxygen documented 14% complete resolution and 51% partial resolution of symptoms in recreational divers treated with normobaric oxygen alone before recompression. A more recent CDC/DAN publication concluded that first aid oxygen "increased recompression efficacy and decreased the number of recompression treatments required if given within four hours after surfacing" (CDC/DAN, First Aid Oxygen). The 2019 UHMS DCS Best Practice guideline lists normobaric 100% oxygen as recommended in every case of DCS, starting as soon as possible after symptom onset (UHMS DCS Recommendations, 2019).

The delivery decision — which mask, which flow rate — comes down to matching the diver's respiratory pattern:

Two operational notes that catch new dive-medical responders:

• You cannot cause acute oxygen toxicity at the surface breathing 100% O2. The partial pressure is far below the toxic threshold (which is a hyperbaric-chamber concern, not a surface concern). Do not take "air breaks" out of a misplaced concern about seizures — the UHMS guidance is explicit that surface oxygen therapy in DCS should be continuous until reaching the chamber (Moon et al., cited in DCS reviews).
• Do not run out. A single "M6" pony bottle at 15 L/min lasts under 30 minutes. A serious dive boat carries enough oxygen to cover transport to the nearest chamber-capable ED plus a 100% margin. This is the single most common failure mode on charter boats — plenty of oxygen for the first ten minutes, none for the next three hours of transport.

Should you put a suspected DCS or AGE victim in the Trendelenburg or head-down position?

This is one of the most common lay-first-aid mistakes still taught by outdated open-water manuals: "if the diver has the bends, tilt them head-down to keep the bubbles in the legs." The evidence base has moved away from that position over the last twenty years, and the guidance is consistent across UHMS, DAN, the S2k German diving accident guideline, and Canada Hyperbarics' 2026 referral guide:

• Supine (flat on the back, horizontal) for the awake, breathing diver.
• Recovery position (left lateral) for the unconscious diver, to protect the airway.
• Sitting or semi-recumbent only if the diver has significant respiratory compromise or "chokes" that is worse when flat — comfort in that specific case outranks strict horizontal positioning.

The historical rationale for Trendelenburg — that head-down positioning would keep cerebral gas bubbles from reaching brain tissue — does not hold up. Gas bubbles distribute by pressure and flow, not gravity, and head-down positioning raises intracranial pressure, worsens cerebral edema in an already ischemic brain, and impairs ventilation in a diver who may already have pulmonary symptoms. The Canada Hyperbarics 2026 physician referral guide states the current position in plain terms: "Keep the patient supine (lying flat). Current guidance does not recommend the head-down Trendelenburg position for arterial gas embolism, as it can worsen cerebral oedema" (Canada Hyperbarics, 2026).

When do you drive to the ED versus activate a USCG MEDEVAC for a suspected diving casualty?

The decision is a math problem with a clinical modifier. The math is oxygen supply, transport time, and hyperbaric window. The clinical modifier is what the diver actually looks like right now.

The hyperbaric window matters. Ideal time from surfacing to recompression is under six to eight hours; delays beyond that are associated with slower and less complete recovery, and multiple guidelines emphasize that "the six-hour window" for inner-ear DCS in particular is associated with permanent inner ear damage in up to 90% of casualties if missed (EUBS/DHM Vol 48 No 3). AGE has an even tighter window — the earlier the better, with most sources treating the first eight hours as the operational goal. That is not the same as "delayed treatment is useless" — case series document good outcomes with hyperbaric therapy days after the event — but earlier is materially better.

The USCG MEDEVAC framework:

• Range. USCG rotary-wing MEDEVAC has typical hoist range of 100 to 300 nautical miles under favorable conditions. Offshore charter and dive-boat operations routinely fall within this envelope.
• Contact. VHF Channel 16 (156.8 MHz) is the international distress and calling frequency. HF distress: 2182 kHz or 4125 kHz. Once contact is made you will be routed to the sector command center and, depending on the case, to a flight surgeon.
• Decision authority. The USCG flight surgeon or sector duty surgeon makes the fly/no-fly determination based on your patient description, sea state, aircraft availability, and receiving facility. DAN's on-call physicians frequently coordinate with USCG surgeons on diving cases.
• Prep for hoist. Clear the deck of loose objects, illuminate at night without pointing at the helicopter, communicate on Channel 16 or as directed, do not tie the hoist line or trail line to the vessel, and follow the rescue swimmer's instructions once on scene. The USCG Auxiliary Emergency Medical Assistance procedure document walks through the full sequence (USCG Auxiliary, Section 4.7).
• NOAA option. For scientific and government dive teams, the NOAA Dive Medical Officer line is (855) 822-DIVE (3483). NOAA's diving emergency assistance plan routes through DAN when the NOAA DMO cannot be reached within 15 minutes (NOAA DEAP).

What common mistakes still show up in boat-based DCS and AGE first aid?

The correction table maps each mistake to the current guideline-backed alternative:

The aspirin mistake in particular deserves emphasis because it is still taught in older diver-first-aid materials. The U.S. Navy Diving Manual, Chapter 17, section 12.1.4 addresses aspirin and NSAIDs directly: "Routine use of antiplatelet agents in patients with neurological DCS is not recommended, due to concern about worsening hemorrhage in spinal cord or inner ear decompression illness" (National Hyperbaric Centre, "Aspirin and the Manual"). The historical rationale for aspirin — that it might reduce platelet aggregation on bubble surfaces — has never been supported by outcome data. The bleeding risk is real. Acetaminophen (paracetamol) is a safer choice for pain relief if the diver is awake and can swallow.

What should a serious offshore vessel actually carry for a diving emergency?

Diving emergencies do not happen in the parking lot of a hospital. They happen at the offshore wreck, the reef, the wall — and the equipment on board is what you have. A charter operating twenty miles offshore that carries a single pony bottle of oxygen has committed to a maximum thirty minutes of first-aid response and no margin. That is not a plan; that is a wish. The MED-TAC oxygen delivery equipment collection stages the components — cylinders, regulators, demand valves, non-rebreathers, adjunctive airway management — that a serious vessel needs to actually complete the transport.

The complementary equipment matters too. Divers who have a DCS or AGE event often have concurrent problems: seasickness that limits oral fluid intake, thermal stress from cold water and wet exposure, lacerations from a rapid ladder recovery, and the operational chaos of coordinating a MEDEVAC on a rolling deck. A comprehensive maritime watertight trauma kit should be within arm's reach of the helm on any offshore-capable vessel, and the crew should have completed a wilderness or dive-medical first-aid course within the last two years.

All products sourced from the actual brand manufacturer or authorized master distributors. CoTCCC recommendation status verified where applicable. Ships from MED-TAC International, Pembroke Pines, FL — clinician-founded, veteran-led, SDVOSB-certified.