Undersea and hyperbaric medicine is a medical subspecialty focused on two related areas: treating conditions caused by diving and underwater environments, and using pressurized oxygen as a therapeutic tool for a range of serious medical conditions. Physicians in this field apply the physics of pressure and gas behavior to both prevent and treat illness, from decompression sickness in divers to chronic wounds that won’t heal with standard care.
What the Specialty Covers
The field splits into two overlapping domains. The “undersea” side deals with the physiology and hazards of working or diving in high-pressure underwater environments. This includes conditions like decompression sickness (the “bends”), arterial gas embolism, nitrogen narcosis, barotrauma to the ears, sinuses, and lungs, and oxygen toxicity at depth. The “hyperbaric” side focuses on using pressurized chambers to deliver pure oxygen at levels far above what normal breathing provides, treating conditions that range from carbon monoxide poisoning to radiation injuries.
These two sides share fundamental science. The same gas laws that explain why a diver gets the bends also explain why breathing pure oxygen under pressure can force healing in damaged tissue. Physicians in this subspecialty need to understand both.
How Pressurized Oxygen Works in the Body
At sea level, you breathe air that’s roughly 21% oxygen at normal atmospheric pressure (1 ATA). During hyperbaric oxygen therapy, you breathe 100% oxygen at pressures typically between 2 and 3 ATA. This dramatically increases the amount of oxygen dissolved directly in your blood plasma and tissues, well beyond what red blood cells alone can carry.
Two gas laws drive most of what happens in the chamber. First, higher pressure shrinks gas bubbles. If someone has nitrogen bubbles trapped in their blood and joints after a diving accident, raising the ambient pressure physically compresses those bubbles and pushes the gas back into solution, like squeezing carbonation back into a soda bottle. Second, higher pressure forces more gas to dissolve in liquid. This means oxygen saturates tissues that would otherwise be starved, reaching areas where damaged or swollen blood vessels can’t deliver enough on their own.
The combination creates conditions that promote healing in several ways: it drives oxygen into tissues with compromised blood flow, helps the body fight certain infections by creating an environment hostile to bacteria that thrive without oxygen, and stimulates the growth of new blood vessels in irradiated or otherwise damaged tissue.
Approved Medical Uses
Hyperbaric oxygen therapy is a recognized standard of care for a specific set of conditions, not a general wellness treatment. The approved indications include decompression sickness, arterial gas embolism, carbon monoxide poisoning, gas gangrene, necrotizing fasciitis (flesh-eating infections), diabetic foot ulcers that haven’t responded to conventional treatment, delayed radiation injury to soft tissue or bone, refractory osteomyelitis (bone infections that resist standard antibiotics), compromised skin grafts and flaps, crush injuries, severe burns, and sudden hearing loss.
Treatment protocols vary significantly depending on the condition. Gas gangrene, for example, may require sessions at 3 ATA for 90 minutes, three times in the first 24 hours. Diabetic foot ulcers typically involve daily 90-minute sessions at 2.0 to 2.4 ATA for 30 to 40 days. Radiation injuries can require 30 to 60 treatments. The common thread is that sessions last roughly 90 to 120 minutes, with pressures usually between 2 and 2.5 ATA.
Chronic Wounds and Diabetic Ulcers
One of the most common reasons patients encounter hyperbaric medicine is wound care, particularly diabetic foot ulcers. These ulcers are recommended for hyperbaric treatment when they haven’t improved after 30 days of conventional care, especially more severe wounds classified as Wagner grade 3 or higher (meaning the ulcer has penetrated deeper tissue or bone).
The evidence is mixed but generally favorable. A systematic review of multiple clinical trials found that in four of six studies, hyperbaric therapy reduced major amputation rates, with one trial showing a 13% improvement in limb preservation. Across several studies, about 50% of patients receiving hyperbaric therapy achieved complete ulcer healing, compared to 29% with conventional treatment alone. One smaller study found that patients receiving hyperbaric therapy were 44 times more likely to achieve at least a 30% reduction in wound size. Not every trial has shown dramatic benefits, though. One large study found no significant difference in amputation rates or healing between treated and untreated groups, highlighting that results depend on patient selection and wound severity.
Diving Medicine
The undersea side of the specialty manages the unique hazards of breathing compressed gases at depth. Decompression sickness occurs when dissolved nitrogen forms bubbles in the blood and tissues during ascent, causing joint pain, neurological symptoms, and potentially life-threatening complications. Arterial gas embolism happens when expanding gas enters the bloodstream, often from holding breath during ascent or from lung injury. Both conditions are treated by placing the diver in a hyperbaric chamber to recompress the gas and allow it to safely dissolve back into the blood.
Nitrogen narcosis, sometimes called “rapture of the deep,” impairs judgment and coordination at depths beyond about 30 meters. It resolves completely within minutes of ascending to shallower depth. For dives beyond 50 meters, divers substitute helium or helium-nitrogen mixtures for regular air to avoid narcosis entirely. Other conditions undersea specialists manage include sinus and ear barotrauma from pressure changes, pulmonary overpressurization injuries, and oxygen toxicity from breathing high concentrations of oxygen at depth.
What Treatment Looks Like
Hyperbaric treatments take place in one of two types of chambers. Monoplace chambers are small acrylic tubes designed for a single patient. They’re less expensive, easier to install, and require less staffing since no attendant sits inside with you. The tradeoff is patient isolation. If you need intensive monitoring or IV medications during treatment, monoplace chambers present logistical challenges because all equipment must operate from outside through special pass-throughs.
Multiplace chambers are larger rooms that can hold several patients and a medical attendant simultaneously. These are better suited for critically ill patients because standard monitoring equipment and hands-on care can continue inside the chamber. Patients in multiplace chambers breathe oxygen through a mask or hood rather than having the entire chamber filled with pure oxygen.
A typical session involves gradual pressurization over several minutes (similar to the pressure change during an airplane descent, but more pronounced), followed by the treatment period at target pressure, then slow depressurization. The most common side effect is difficulty equalizing ear pressure, similar to what you feel on a plane. Some people experience temporary changes in vision after repeated treatments, and claustrophobia can be a barrier for some patients in monoplace chambers.
Risks and Limitations
The only condition that absolutely rules out hyperbaric treatment is an untreated collapsed lung (pneumothorax). Pressure changes inside the chamber could turn it into a life-threatening tension pneumothorax. Patients with gas trapped in the eye from recent surgery are also excluded from non-emergency treatment, as pressure shifts could cause vision loss.
Several conditions require careful evaluation before treatment. People with COPD face a risk of breathing complications from high oxygen levels. Asthma or lung cysts can trap air and cause lung injury during pressure changes. Difficulty equalizing ear or sinus pressure, whether from a cold or prior surgery, increases the risk of painful barotrauma. High fevers and seizure disorders can lower the threshold for oxygen toxicity, which in rare cases causes seizures.
The FDA has specifically warned against clinics promoting hyperbaric therapy for conditions it hasn’t been proven to treat, including AIDS, heart disease, stroke, depression, and spinal cord injuries. Pursuing unproven uses risks not only wasted money but delayed treatment for the actual condition.
Training and Certification
Undersea and hyperbaric medicine is a board-certified subspecialty recognized by the American Board of Medical Specialties. Physicians must first complete a primary residency, then undertake a one-year fellowship in the subspecialty. Two pathways exist: emergency medicine physicians can pursue certification through the American Board of Emergency Medicine, while physicians from any ABMS-certified specialty can pursue it through the American Board of Preventive Medicine. This means the field draws practitioners from emergency medicine, surgery, internal medicine, and other backgrounds, reflecting the diverse conditions it treats.