State-by-State HBOT Clinic Regulations

Last updated: April 2026

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before starting any treatment.

Affiliate Disclosure: We may earn a commission when you purchase through our links. This does not affect our editorial independence.

Quick Answer

The Undersea & Hyperbaric Medical Society (UHMS) lists 14 primary indications for HBOT, including carbon monoxide poisoning and decompression sickness.
The FDA recommends UHMS-accredited facilities for specific illnesses, highlighting the importance of proper accreditation.
Arterial gas embolism can occur after an ascent of as little as one meter in divers, or from causes like mechanical ventilation.
The 14th edition of the UHMS Hyperbaric Oxygen Therapy Indications report provides current recommendations for treatment.

Hyperbaric oxygen therapy (HBOT) is a specialized medical treatment with specific guidelines and recognized uses. The Undersea & Hyperbaric Medical Society (UHMS) is a leading authority in this field, defining what HBOT is and outlining its approved medical applications. The UHMS lists 14 primary conditions for which hyperbaric oxygen therapy is considered an effective treatment. These conditions range from air or gas embolism, which can occur after an ascent of as little as one meter in divers, to carbon monoxide poisoning and certain types of problem wounds. The UHMS also plays a critical role in ensuring quality and safety through its accreditation program for hyperbaric facilities. In fact, the FDA recommends that patients seek treatment at UHMS-accredited facilities for specific illnesses, underscoring the importance of these standards. This guidance helps ensure patients receive care that meets established medical protocols.

What is Hyperbaric Oxygen Therapy (HBOT)?

Hyperbaric oxygen therapy, or HBOT, involves breathing 100% oxygen while inside a special chamber where the air pressure is increased. This increased pressure allows the body to take in much more oxygen than it would at normal atmospheric pressure. The Undersea and Hyperbaric Medical Society (UHMS) provides the widely accepted definition of HBOT and maintains a comprehensive list of its recognized medical uses. The UHMS publishes detailed reports on these indications, with the 14th edition of their "Hyperbaric Oxygen Therapy Indications" serving as a key resource for practitioners and patients alike. This document outlines the accepted medical conditions that can benefit from HBOT.

Defining Hyperbaric Oxygen

The core principle of HBOT is to deliver oxygen at higher-than-normal pressures. This process dramatically increases the amount of oxygen dissolved in the blood plasma, allowing it to reach areas of the body where blood flow might be poor or blocked. This extra oxygen can help damaged tissues heal, fight certain infections, and reduce swelling. The UHMS has a dedicated committee that regularly reviews and updates the scientific evidence supporting these treatments. Their work ensures that the definition and application of HBOT remain consistent with the latest medical research. The UHMS is located at 631 US Highway 1, Suite 307, North Palm Beach, FL 33408, USA, serving as a central hub for hyperbaric medicine expertise UHMS 14th Edition Reference Material.

The Role of the UHMS in HBOT Standards

The UHMS is not just an informational body; it sets the standards for hyperbaric medicine. Its "Hyperbaric Oxygen Therapy Indications" reports, such as the 14th Edition, are critical documents. These reports provide detailed guidance on when and how HBOT should be used. They cover the background of HBOT, its precise definition, and the process for reviewing and accepting new indications. This rigorous approach means that any condition listed in their report has been thoroughly vetted by medical experts. The society also provides resources like online continuing education portals and introductory 40-hour training courses for medical professionals, ensuring high standards of practice across the field. This commitment to education and evidence-based practice is fundamental to the safe and effective delivery of HBOT.

Understanding the 14th Edition

The 14th Edition of the UHMS "Hyperbaric Oxygen Therapy Indications" is a foundational text in hyperbaric medicine. It details the current recommendations for treating various conditions with HBOT. This edition, like its predecessors, serves as a comprehensive guide for medical professionals. It organizes the indications into specific chapters, ensuring that each condition is discussed thoroughly with its unique considerations for HBOT. For example, the report starts with Chapter 1, "Hyperbaric Treatment of Air or Gas Embolism: Current Recommendations," and covers a wide range of conditions through Chapter 14, "Adjunctive Hyperbaric Oxygen Therapy in the Treatment of Thermal Burns." This structured approach helps ensure that treatments are applied consistently and effectively based on the most up-to-date medical understanding.

What are the UHMS-Approved Indications for HBOT?

The UHMS has identified a specific list of conditions for which hyperbaric oxygen therapy (HBOT) is recognized as an effective treatment. These indications are detailed in comprehensive publications like the 14th Edition of "Hyperbaric Oxygen Therapy Indications." This document serves as the authoritative guide for medical professionals, outlining the conditions that have strong scientific evidence supporting the use of HBOT. Conditions on this list include critical emergencies like air or gas embolism and carbon monoxide poisoning, as well as chronic issues like certain types of problem wounds and delayed radiation injuries.

The Comprehensive List of 14 Indications

The 14th Edition of the UHMS "Hyperbaric Oxygen Therapy Indications" lists 14 primary indications for HBOT. This list represents the consensus of medical experts within the Undersea and Hyperbaric Medical Society. The conditions include:

Air or Gas Embolism
Arterial Insufficiencies (including Central Retinal Artery Occlusion and Selected Problem Wounds)
Carbon Monoxide Poisoning
Clostridial Myonecrosis (Gas Gangrene)
Compromised Grafts and Flaps
Acute Traumatic Ischemias
Decompression Sickness
Delayed Radiation Injuries (Soft Tissue and Bony Necrosis)
Sudden Sensorineural Hearing Loss
Intracranial Abscess
Necrotizing Soft Tissue Infections
Refractory Osteomyelitis
Severe Anemia
Adjunctive Hyperbaric Oxygen Therapy in the Treatment of Thermal Burns

These indications are consistent across different editions of the UHMS report. For instance, the 13th edition also listed these same indications, demonstrating a consistent medical consensus over time regarding the efficacy of HBOT for these specific conditions UHMS HBO Indications (2020).

Why These Conditions Are Approved

The UHMS approves these conditions based on rigorous scientific review. Each indication is backed by research showing that HBOT can significantly improve patient outcomes. For example, in conditions like carbon monoxide poisoning, HBOT helps remove carbon monoxide from the blood much faster than breathing normal air, reducing the risk of long-term neurological damage. For problem wounds, the increased oxygen delivery promotes healing in tissues that might otherwise struggle to repair themselves due to poor circulation. The UHMS committee, including experts like Lindell K. Weaver MD, Chair and Editor of the 13th Edition, carefully evaluates studies and clinical data before adding or confirming an indication. They state, "No responsibility is assumed by the Publisher or Editor for any injury and or damage to persons or property as a matter of product liability, negligence or otherwise, or from any use or operation of any methods, product, instructions, or ideas contained in the material herein." This highlights the importance of professional judgment and independent verification in medical practice.

The Importance of a Defined List

Having a clearly defined list of approved indications is crucial for several reasons. First, it guides healthcare providers on when to appropriately prescribe HBOT. Second, it helps patients understand when HBOT might be a viable treatment option for their condition. Third, it helps ensure that HBOT is used for conditions where its benefits are established, rather than for experimental or unproven uses. This focus on evidence-based medicine is a hallmark of the UHMS's approach. The detailed chapters in the "Hyperbaric Oxygen Therapy Indications" provide specific recommendations for each of these 14 conditions, ensuring that treatment protocols are standardized and effective. This standardization is vital for patient safety and for achieving the best possible clinical results.

How Does HBOT Treat Air or Gas Embolism?

Hyperbaric oxygen therapy (HBOT) is a critical treatment for air or gas embolism, a condition that occurs when gas bubbles enter arteries or veins, potentially blocking blood flow and causing severe damage. HBOT works by reducing the size of these gas bubbles and increasing oxygen delivery to affected tissues. This dual action helps to clear the obstruction and support the recovery of cells that have been deprived of oxygen. The effectiveness of HBOT in these cases is well-documented and is one of the primary indications listed by the Undersea and Hyperbaric Medical Society (UHMS).

Understanding Air and Gas Embolism

Gas embolism occurs when gas bubbles enter arteries or veins. Richard E. Moon, an expert on hyperbaric oxygen therapy indications for air or gas embolism, explains that arterial gas embolism (AGE) was first described in relation to submarine escape training. In these situations, pulmonary barotrauma, which is lung injury from pressure changes, happened during free ascent after breathing compressed gas at depth. This type of injury and gas embolism can occur after an ascent of as little as one meter, even with breath holding. AGE has also been linked to normal ascents in divers who have lung conditions like bullous disease or asthma. Pulmonary barotrauma can also result from blast injuries, mechanical ventilation, penetrating chest trauma, chest tube placement, and bronchoscopy.

Venous gas embolism (VGE) is common after compressed gas diving. Normally, VGE bubbles get trapped in the tiny capillaries of the lungs and do not cause symptoms. However, if the volume of gas is large, VGE can cause coughing, difficulty breathing, and pulmonary edema. It can also overwhelm the lung's filtering capacity, allowing bubbles to enter the arterial circulation. VGE can directly enter the left side of the heart through an atrial septal defect or a patent foramen ovale, which are small openings in the heart.

Various Causes of Gas Embolism

Beyond diving, many other situations can lead to gas embolism. These include accidental intravenous air injection, accidents during cardiopulmonary bypass surgery, needle biopsies of the lung, hemodialysis, and the placement or disconnection of central venous catheters. Gastrointestinal endoscopy, irrigation or ingestion of hydrogen peroxide, arthroscopy, cardiopulmonary resuscitation, and percutaneous hepatic puncture are also known causes. Even non-medical scenarios like blowing air into the vagina during orogenital sex or sexual intercourse after childbirth can cause air embolism.

Procedures where the surgical site is under pressure, such as laparoscopy, transurethral surgery, vitrectomy, endoscopic vein harvesting, and hysteroscopy, can also lead to air embolism. Massive VGE can occur when air passively enters surgical wounds that are elevated above the heart, causing pressure in adjacent veins to drop below atmospheric levels. This has been observed in sitting craniotomy, cesarean section, prostatectomy, spine surgery, hip replacement, liver resection, liver transplantation, and dental implant insertion.

How HBOT Reverses the Effects

HBOT treats gas embolism primarily in two ways. First, the increased pressure in the hyperbaric chamber physically shrinks the gas bubbles, reducing their size and helping them pass through blood vessels or dissolve. This is crucial because even small volumes of air injected into arteries can cause clinical problems. Second, breathing 100% oxygen at high pressure increases the amount of oxygen dissolved in the blood plasma. This extra oxygen helps tissues that were starved of oxygen due to the embolism to recover and function properly.

In experimental animals, intravenous injection of up to 0.5-1 mL/kg of air has been tolerated. In humans, continuous intravenous infusion of oxygen at 10 mL/min has been reported as well tolerated, while 20 mL/min caused symptoms. Compared with constant infusions, injections of air are more likely to cause clinical abnormalities. HBOT rapidly increases the partial pressure of oxygen in the blood, which helps to displace the inert gas (like nitrogen) from the bubbles and replace it with oxygen, which can then be metabolized. This process helps to resolve the embolism more quickly and effectively than other treatments.

Why is UHMS Accreditation Important for HBOT Facilities?

UHMS accreditation is a vital benchmark for quality and safety in hyperbaric oxygen therapy (HBOT) facilities. The FDA specifically recommends that patients seek hyperbaric treatment at UHMS-accredited facilities for certain illnesses. This recommendation underscores the importance of proper accreditation, which signifies that a facility meets rigorous standards for patient safety, quality of care, and adherence to established medical protocols. Choosing an accredited facility ensures that patients receive care from trained professionals using appropriate equipment and following best practices.

FDA's Endorsement of UHMS Accreditation

The U.S. Food and Drug Administration (FDA) has publicly recommended UHMS-accredited hyperbaric facilities for the treatment of specific illnesses FDA Recommendation for UHMS Accreditation. This is a strong statement about the reliability and quality of care provided by these accredited centers. The FDA's recommendation is not made lightly; it reflects a recognition that UHMS accreditation ensures a level of oversight and expertise that is crucial for a specialized and potentially complex therapy like HBOT. Patients can have greater confidence that they are receiving care that aligns with the highest medical standards when they choose an accredited facility. This guidance helps patients navigate the landscape of HBOT providers and make informed decisions about their treatment.

What UHMS Accreditation Means

Accreditation by the UHMS Hyperbaric Facility Accreditation Program means that a clinic has undergone a thorough evaluation of its operations. This evaluation covers several key areas:

Patient Safety Protocols: Ensuring that all procedures are designed to protect patients from risks associated with high-pressure oxygen therapy.
Staff Competency: Verifying that physicians, nurses, and technicians are appropriately trained and experienced in hyperbaric medicine. The UHMS offers resources like "Introductory 40-Hour Training Courses" and a "Fellow of Undersea & Hyperbaric Medicine" designation to ensure a high level of expertise.
Equipment Maintenance: Checking that hyperbaric chambers and associated equipment are properly maintained and meet safety standards. Different types of hyperbaric chambers exist, and their proper use is critical for safety and efficacy.
Quality of Care: Assessing whether the facility follows evidence-based guidelines for treatment, as outlined in the UHMS's "Hyperbaric Oxygen Therapy Indications" reports.
Emergency Preparedness: Ensuring the facility is equipped and staff are trained to handle any emergencies that might arise during HBOT.

The UHMS accreditation process is not a one-time event; facilities must regularly renew their accreditation, which involves ongoing monitoring and periodic re-evaluations. This continuous oversight helps maintain consistent quality and safety standards over time.

The Importance of Rigorous Standards

For patients, choosing a UHMS-accredited facility offers several benefits. It provides assurance that the treatment they receive is based on established medical science and delivered by qualified professionals. This is particularly important for HBOT, as it is a specialized therapy with potential risks if not administered correctly. Unaccredited facilities might not adhere to the same stringent safety and operational standards, potentially putting patients at risk or providing ineffective treatment. The UHMS provides resources on "How to Prepare for Accreditation Workshop," demonstrating their commitment to guiding facilities toward meeting these high standards. This rigorous approach to accreditation ultimately protects patients and upholds the integrity of hyperbaric medicine. When considering HBOT, verifying a facility's accreditation status with the UHMS is a crucial step for ensuring safe and effective care.

What Other Conditions Does UHMS Recognize for HBOT?

Beyond treating air or gas embolism, the Undersea and Hyperbaric Medical Society (UHMS) recognizes hyperbaric oxygen therapy (HBOT) for a range of other significant medical conditions. These recognized indications are carefully selected based on strong scientific evidence demonstrating the benefits of HBOT in improving patient outcomes. The UHMS 14th Edition of "Hyperbaric Oxygen Therapy Indications" serves as the definitive guide, detailing these various conditions and the recommended protocols for their treatment. This comprehensive document ensures that HBOT is applied judiciously and effectively across diverse medical needs.

Arterial Insufficiencies and Problem Wounds

One category of conditions for which HBOT is recognized includes arterial insufficiencies, such as central retinal artery occlusion. This is a severe eye condition where blood flow to the retina is blocked, potentially leading to sudden and significant vision loss. HBOT can help by increasing oxygen delivery to the deprived retinal tissues, potentially preserving vision. Additionally, HBOT is approved for the enhancement of healing in selected problem wounds. These are chronic wounds that do not heal with conventional treatments, often due to poor circulation or infection. Examples include diabetic foot ulcers, which are a major concern for individuals with diabetes. The increased oxygen levels delivered by HBOT can stimulate new blood vessel growth, reduce inflammation, and improve the body's ability to fight infection, all crucial factors in wound healing. The UHMS 14th Edition dedicates specific chapters to these issues, with "Central Retinal Artery Occlusion" discussed in Part I, Section 2A, and "Hyperbaric Oxygen Therapy for Selected Problem Wounds" in Section 2B.

Infections, Grafts, and Traumatic Injuries

HBOT also plays a vital role in treating serious infections and certain types of injuries. Clostridial myonecrosis, commonly known as gas gangrene, is a rapidly progressing and life-threatening bacterial infection that produces gas in tissues. HBOT is an essential adjunctive treatment for gas gangrene because the high oxygen levels create an environment that is toxic to the anaerobic bacteria causing the infection, while also helping to preserve tissue. Similarly, compromised grafts and flaps, often used in reconstructive surgery, can fail if their blood supply is insufficient. HBOT can enhance the survival of these tissues by improving oxygenation and promoting healing.

Acute traumatic ischemias, which involve severe reduction in blood flow to tissues following injury, are another key indication. Conditions like crush injuries or compartment syndrome can benefit from HBOT by reducing swelling and improving oxygen delivery to damaged areas, potentially preventing amputation or severe tissue loss. The UHMS 14th Edition covers these indications in detail, including "Clostridial Myonecrosis (Gas Gangrene)" in Chapter 4, "The Effect of Hyperbaric Oxygen on Compromised Grafts and Flaps" in Chapter 5, and "The Role of Hyperbaric Oxygen for Acute Traumatic Ischemias" in Chapter 6. See the crush injury and compartment syndrome evidence atlas for the full study-by-study evidence breakdown.

Radiation Injuries, Hearing Loss, and Other Conditions

The UHMS also recognizes HBOT for delayed radiation injuries, which can manifest as soft tissue and bony necrosis. These injuries can occur months or even years after radiation therapy for cancer, causing significant pain and dysfunction. HBOT helps by promoting healing in these damaged tissues and improving blood flow to the affected areas. Sudden sensorineural hearing loss, an abrupt loss of hearing often without a clear cause, is also an approved indication. HBOT can improve oxygen delivery to the inner ear, potentially aiding in recovery.

Other conditions on the UHMS list include intracranial abscess, a collection of pus within the brain, where HBOT can support antibiotic treatment by improving tissue oxygenation and immune function. Necrotizing soft tissue infections, severe bacterial infections that rapidly destroy tissue, also benefit from HBOT as an adjunctive therapy. Refractory osteomyelitis, a persistent bone infection that doesn't respond to standard treatments, can be treated with HBOT to enhance the effects of antibiotics and promote bone healing. Severe anemia, where the body lacks enough healthy red blood cells to carry oxygen, can be managed with HBOT when blood transfusions are not possible or are contraindicated, as HBOT delivers oxygen directly dissolved in plasma. Finally, adjunctive hyperbaric oxygen therapy in the treatment of thermal burns is also recognized, helping to reduce swelling, promote healing, and fight infection in severe burn cases. The UHMS 14th Edition covers indications from "Air or Gas Embolism" (Chapter 1) to "Adjunctive Hyperbaric Oxygen Therapy in the Treatment of Thermal Burns" (Chapter 14), providing comprehensive guidance for each. See the intracranial abscess evidence atlas for the full study-by-study evidence breakdown.

Are There Different Types of Hyperbaric Chambers?

Yes, there are different types of hyperbaric chambers used for delivering hyperbaric oxygen therapy (HBOT). While not directly related to clinic regulations themselves, understanding these chamber types is crucial because the choice of chamber impacts the delivery of treatment, patient experience, and the specific medical applications possible. The safety and effectiveness of HBOT are intrinsically linked to the proper use, maintenance, and operational protocols of these chambers. Different chambers are designed for specific medical applications and patient needs, influencing how HBOT is administered in a clinical setting.

Monoplace Chambers

Monoplace chambers are designed to treat one patient at a time. These chambers are typically cylindrical and transparent, allowing the patient to see outside and the medical staff to monitor the patient inside. The entire chamber is pressurized with 100% oxygen. Patients lie down comfortably inside the chamber for the duration of their treatment. This type of chamber is often used for a wide range of UHMS-approved indications, including problem wounds, sudden hearing loss, and preparing for or recovering from surgery. The individualized nature of monoplace chambers allows for precise control of pressure and oxygen delivery for each patient. They are a common sight in many hyperbaric medical solutions clinics, as highlighted by resources discussing "Types of Hyperbaric Chambers" and "The Complete Guide to HBOT" from hyperbaric medical solutions.

Multiplace Chambers

Multiplace chambers are larger, room-sized chambers that can accommodate several patients simultaneously, along with medical staff. In these chambers, patients breathe 100% oxygen through masks or hoods, while the chamber itself is pressurized with compressed air. The presence of medical staff inside the chamber with the patients allows for direct monitoring, intervention, and care during the treatment session. This setup can be particularly beneficial for critically ill patients or those who require constant attention. Multiplace chambers are often found in larger hospitals or specialized hyperbaric centers, especially when treating conditions like carbon monoxide poisoning or decompression sickness, where immediate medical intervention might be necessary. The ability to treat multiple patients at once can also be more efficient for certain clinical workflows.

Hard Chambers vs. Soft Chambers

The terms "hard" and "soft" chambers refer to the materials and pressure capabilities of the hyperbaric units.

Hard Chambers: Both monoplace and multiplace chambers are typically "hard" chambers. They are made of rigid materials like steel or acrylic and can withstand higher pressures, usually up to 3 atmospheres absolute (ATA) or more. These higher pressures are often necessary for treating severe conditions like air or gas embolism, decompression sickness, and carbon monoxide poisoning, as recommended by the UHMS. The ability to achieve and maintain these higher pressures is critical for the therapeutic effects of HBOT for many of its approved indications.
Soft Chambers: Also known as mild hyperbaric chambers, soft chambers are made of flexible, inflatable materials. They operate at much lower pressures, typically around 1.3 to 1.5 ATA. While these chambers are sometimes marketed for various health benefits, it is important to note that the UHMS-approved indications for HBOT generally require pressures of 2.0 ATA or higher. Therefore, soft chambers are not typically used for the UHMS-approved medical conditions. Patients seeking treatment for UHMS-approved indications should ensure they are receiving therapy in a hard chamber capable of reaching the necessary pressures.

Importance of Chamber Selection and Maintenance

The selection of the appropriate hyperbaric chamber type is a critical decision made by medical professionals based on the patient's condition and the specific UHMS-approved indication. Regardless of the type, proper maintenance, calibration, and safety protocols for all hyperbaric chambers are paramount. Clinics must ensure their equipment is regularly inspected and meets all safety regulations. This includes the integrity of the chamber itself, the oxygen delivery systems, and the monitoring equipment. The UHMS accreditation process includes a thorough review of a facility's equipment and maintenance practices, reinforcing the importance of these aspects for patient safety and treatment efficacy.

Frequently Asked Questions

What is the primary role of the UHMS in HBOT?

The Undersea & Hyperbaric Medical Society (UHMS) serves as the leading authority in hyperbaric oxygen therapy. Its primary role is to define HBOT, establish evidence-based indications for its use, and set standards for facility accreditation and practitioner training. The UHMS publishes comprehensive reports, such as the 14th Edition of "Hyperbaric Oxygen Therapy Indications," which lists 14 specific medical conditions for which HBOT is recognized as an effective treatment. This guidance ensures that HBOT is applied safely and effectively across the medical community.

How many conditions are approved for HBOT by the UHMS?

The UHMS currently approves 14 primary conditions for hyperbaric oxygen therapy. These conditions are detailed in the society's authoritative publications, including the 14th Edition of "Hyperbaric Oxygen Therapy Indications." This list includes serious medical issues such as air or gas embolism, carbon monoxide poisoning, decompression sickness, and various types of problem wounds. The consistency of this list, as seen in both the 13th and 14th editions, reflects a strong medical consensus on these specific applications of HBOT.

Can HBOT be used for conditions not on the UHMS approved list?

While HBOT may be explored for conditions not on the UHMS approved list, such uses are considered experimental or off-label. The UHMS list represents conditions for which there is strong scientific evidence and medical consensus for HBOT's effectiveness. The FDA recommends seeking treatment at UHMS-accredited facilities for specific illnesses, implying that treatment for unapproved conditions may not have the same level of oversight or proven efficacy. Patients should discuss any potential off-label uses thoroughly with their healthcare provider, understanding that such treatments might not be covered by insurance and may lack robust clinical evidence.

What are some common causes of gas embolism that HBOT can treat?

Gas embolism, which HBOT effectively treats, can arise from various causes. Beyond diving-related incidents like pulmonary barotrauma from an ascent of as little as one meter, common causes include accidental intravenous air injection during medical procedures, complications from mechanical ventilation, and certain surgical procedures like laparoscopy or craniotomy. Venous gas embolism is also frequent after compressed gas diving, though it often remains asymptomatic unless large volumes overwhelm the pulmonary capillaries. HBOT helps by shrinking the gas bubbles and increasing oxygen delivery to affected tissues.

Why does the FDA recommend UHMS-accredited facilities?

The FDA recommends UHMS-accredited facilities because accreditation signifies that a clinic meets stringent standards for patient safety, quality of care, and adherence to established medical protocols. This recommendation helps patients identify facilities that follow best practices in hyperbaric medicine. The UHMS accreditation process thoroughly evaluates staffing, equipment, and safety procedures, ensuring that treatments like breathing 100% oxygen in a pressurized chamber are administered by qualified professionals in a safe environment. This endorsement from the FDA provides a crucial layer of assurance for patients seeking HBOT.