Hyperbaric oxygen therapy (HBOT) An upcoming Medical Technology for Innovative Healing

Introduction

Hyperbaric oxygen therapy (HBOT) is a medical treatment that facilitates the body’s natural healing process by inhalation of 100% oxygen in a total body chamber, where atmospheric pressure is increased by a factor of 2-3 times. Under normal circumstances, oxygen is transported throughout the body only by RBCs in the blood. With HBOT, oxygen is dissolved into all the body’s fluids, the plasma, the central nervous system fluids and the lymph, and can be carried to areas where circulation is diminished or blocked. The increased oxygen greatly enhances the ability of WBCs to kill bacteria, reduces oedema and facilitates angiogenesis. With repeated scheduled treatments, the temporary extra high oxygen levels encourage normal tissue oxygen levels; even after the therapy is completed. It is important to understand that oxygen is not absorbed trans-dermally; the only transport mechanism is through the pulmonary system.

Mechanism of action

HBOT has two primary mechanisms of action – Hyperoxygenation and a decrease in bubble size. Hyperoxygenation results from an increase in dissolved oxygen in plasma as a result of increased partial pressure of arterial oxygen (pAO2). Decrease in bubble size is an application of Boyle’s law according to which the volume of a bubble decreases directly in proportion to increasing pressure. This is how HBOT helps in the management of decompression sickness and arterial gas embolism.

Secondary mechanisms of action of HBOT include Vasoconstriction, Angiogenesis, Fibroblast proliferation, Leukocyte oxidative killing, Toxin inhibition and antibiotic synergy. Hyperoxia in normal tissues causes vasoconstriction which reduces post-traumatic tissue oedema (contributing to treatment of crush injuries, compartment syndromes and burns). This vasoconstriction, however, does not cause hypoxia as this is more than compensated by increased plasma oxygen content and microvascular flow. This is important when considering concussion and brain injuries as we can potentially reduce swelling and further damage while promoting neuroplasticity to restore normal brain activity and reduce potential for long-term neurological sequelae.

Hypoxia is a vital stimulant for angiogenesis, but development of adequate capillary network requires adequate amounts of tissue oxygen concentration. HBOT increases the oxygen gradient between the center and periphery of the wound, thus creating a strong angiogenic stimulus. This along with fibroblastic proliferation leads to increased neovascularisation and promotes wound healing.

Types of HBOT

There are two different types of HBOT chambers as per NFPA – Class A (multiple occupancy/ Multiplace) and Class B (single occupancy/ Monoplace). Both are equally effective but Multiplace chambers are considered safer with the added advantage of treating several patients at one time. Depending on the underlying condition, the estimated duration of session varies from 1.5 to 2 hours and may be performed from one to three times daily, being given among 20 to 60 therapeutical doses.

Indications for HBOT

Hyperbaric oxygen therapy (HBOT) is well known for treating decompression sickness in scuba and deep-sea divers. In the last decade, HBOT has been used to treat several medical conditions, of which the FDA approved indications are listed here.

1. 1. Decompression Sickness or Gas Embolism

   2. Crush Injury, Compartment Syndrome & Acute Traumatic Ischemia

   3. Clostridial Myositis & Myonecrosis (Gas gangrene)

   4. Exceptional anaemia when blood transfusion cannot be used

   5. Non-healing wounds (e.g. Diabetic wounds that have not resolved after 30 days of conventional wound care and antibiotics)

   6. Necrotizing soft tissue infections

   7. Refractory Osteomyelitis

   8. Intracranial Abscess / Traumatic brain injury

   9. Osteoradionecrosis

   10. Compromised skin flaps or grafts

   11. Thermal burns

   12. Radiation Necrosis

   13. Carbon Monoxide poisoning

   14. Idiopathic sudden sensorineural hearing loss

1. Vision loss due to Central retinal artery occlusion

Osteoradionecrosis (ORN) of the mandible is a severe iatrogenic disease of devitalized bone caused by radiation therapy of oral and oropharyngeal cancers. The bone lies exposed with a non-healing ulcer despite conventional wound management for three to six months

Contra-Indications for HBOT and Possible Side effects

Absolute contraindications include untreated pneumothorax, recent treatment with drugs like Bleomycin (pulmonary toxicity, at least 3-4 months gap recommended), Cisplatin (delayed wound healing, gap of 3 months is recommended), Doxorubicin (cardiotoxicity, at least 3-4 days gap recommended), Disulfiram (blocks superoxide dismutase, to be discontinued) and Sulfamylon (impaired wound healing, to be discontinued).  All patients are screened with a Chest X Ray prior to starting HBOT. Relative contraindications are COPD/ asthma, Low ejection fraction on 2D Echo (<35%), seizures, claustrophobia, pregnancy, hereditary spherocytosis, Eustachian tube dysfunction, high fever, pacemaker, epidural pain pump and recent upper respiratory tract infection.

Possible side effects of HBOT are temporary near-sightedness (myopia) which usually resolves in 3-6 months, middle ear injury and rupture of ear drum, barotrauma to lungs, seizures due to oxygen toxicity in the CNS, fire outbreak due to oxygen rich environment of the HBOT chamber. Minor side effects most commonly experienced by patients are popping in ears and ear pain due to pressure changes similar to that experienced in a flight. This can easily be alleviated by teaching the patients how to perform Valsalva manoeuvre. All fire safety measures are followed including prohibition of inflammable substances and use of only 100% cotton clothing within the chamber.

Conclusion

There is a lot of literature on the beneficial effects of HBOT in approved indications and active research is currently underway for several newer off-label and experimental indications. Overall it appears to be highly beneficial in improving tissue oxygenation and enhance wound healing.

Dr. Shalini Mishra

Consultant – Pediatric Surgical Oncology, RGCIRC, Delhi