Hyperbaric oxygen therapy is a useful tool in the management of certain chronic nonhealing wounds. Nonhealing wounds are those that have become stagnant within the pathway to wound healing, particularly the proliferative phase. By definition, hyperbaric oxygen therapy involves a patient breathing 100% oxygen while in a chamber or vessel that is compressed to pressures greater than sea level.
At the most basic level, hyperbaric oxygen therapy (HBOT) does 2 things:
1. Decrease bubble size
2. Increase the dissolved content of oxygen in the plasma
The first is useful for the emergent indications for HBOT, including decompression sickness, arterial or venous gas embolism, and gas gangrene. However, the second action is what most of us in the wound healing arena will be counting on when we prescribe HBOT for our patients. At sea level, in normal healthy individuals, our hemoglobin is completely saturated with oxygen. When we increase the pressure around a patient, such as in a hyperbaric chamber, while the patient is breathing 100% oxygen, we can increase the dissolved content of oxygen in the plasma.
At sea level, we live with a column of air around us that exerts 14.7 pounds per square inch absolute or 1 atmosphere absolute (ATA). At 3 ATA, or 3 times the pressure at sea level, HBOT can increase the dissolved amount of oxygen about 2 volume% per atmosphere so that there is enough dissolved oxygen in the plasma to sustain life. This was proven by Ite Boerema, who in 1959 performed exchange transfusions on pigs with dextran/saline solution to reduce hemoglobin levels to near zero. Although quite pale, the pigs survived at 3 ATA.
At this concentration, hyperbaric oxygen begins to exert beneficial effects, such as angiogenesis that can help increase the delivery of oxygen to hypoxic wounds. Other effects include:
· Reducing edema
· Increasing the oxygen level in hypoxic wounds
· Fighting infection (eg, can stop exotoxin production in clostridial infections)
· Reducing the hypoxic impairment of oxygen-dependent leukocyte killing of anaerobes
· Providing increased oxygen to hypoxic wounds for the oxygen-dependent hydroxylation of proline (collagen formation).
The current approved indications for HBOT as defined by the Hyperbaric Oxygen Therapy Committee and as listed on the Undersea and Hyperbaric Medical Society website (www.uhms.org) are:
· Air or gas embolism
· Carbon monoxide poisoning/cyanide poisoning
· Clostridial myositis and myonecrosis (gas gangrene)
· Decompression sickness
· Crush injury, compartment syndrome, and other acute ischemias
· Arterial insufficiencies
a. Central retinal artery occlusion
b. Enhancement of healing in selected problem wounds
· Severe anemia
· Intracranial abscess
· Necrotizing soft tissue infections
· Osteomyelitis (refractory)
· Delayed radiation injury (soft tissue and bony necrosis)
· Compromised flaps and grafts
· Acute thermal burn injury
· Idiopathic sudden sensorineural hearing loss
When used for the right indications, HBOT can be a useful adjunctive therapy to assist in the healing of chronic wounds.