The Undersea and Hyperbaric Medical Society (UHMS) currently recognizes hyperbaric oxygen therapy (HBO) as an approved therapy for 13 pathologic entities.1 These are conditions for which HBO has substantial scientific support demonstrating therapeutic benefit. Hyperbaric oxygen is currently considered a primary treatment modality for carbon monoxide poisoning, cerebral arterial gas embolism, osteoradionecrosis, decompression sickness, and clostridial gas gangrene. It is also considered an adjunctive therapy for acute exceptional blood loss anemia, acute thermal burns, compromised skin grafts or skin flaps, crush injury, compartment syndrome, necrotizing soft-tissue infections, non-clostridial gas gangrene, radiation tissue damage, refractory osteomyelitis, selected problem wounds, and intracranial abscesses.1 Treatment of frostbite injuries with HBO is considered experimental in the United States. In several published case reports, patients with frostbite appear to have had a favorable clinical outcome in comparison with the expected course of their condition.2–7 Case studies point to reduced tissue loss and enhanced healing when HBO is used as an adjunct to standard therapies. The authors describe a case of severe peripheral frostbite injury in a hiker presenting for HBO 22 days after injury. Case Report The patient, a 28-year-old woman, was hiking on Mount Rainier, Wash, and became trapped in a snowstorm for 3 days. She climbed with 4 companions from 6,000 feet to 10,000 feet to a hut and spent the night there. The group’s progress was slow due to darkness and weather conditions. The patient described the hut as “a pit, very cold and damp.” She slept that evening wearing her ice climbing gloves, which were frozen with ice. She recalls shivering uncontrollably through the night. The next day the group started to descend the mountain, but the snow became heavier and limited visibility to 20 feet. The group became lost and stopped in the late afternoon to build a snow cave. The patient noted that the fingers on her right hand were grey-blue in color by the time they finished building the snow cave. The group was not eating or drinking much at this time, and she urinated a small amount on a single occasion only. It continued to snow, and after they started their descent the next morning, they were forced to return to their snow cave. The patient slept that day and night intermittently in a sleeping bag but noticed that she could no longer feel her fingers or hands. At this point, the patient put on a dry pair of fleece gloves but did not look at her fingers. The group remained inside the cave the rest of the day. As the temperature increased during the day, the patient began to feel pain in her hands and fingers. The next morning (the third day) the weather had cleared, and at this time, the patient checked her hands and noted that the fingertips of both hands had a blackened/grey appearance. A group of telemark skiers crossed paths with the group on the morning of the third day and contacted emergency services. The skiers helped the group of climbers descend, and they reached the base camp after dark. At this time, the patient was experiencing severe pain in both hands and was taken by ambulance to a local hospital. The emergency department documented that upon arrival the patient’s hands were thawed but all 10 fingers were grey/blue in color. She was provided with topical aloe vera gel, gauze dressings, and morphine sulfate for pain. Recommendations to stop or reduce smoking, which can affect peripheral circulation, were unnecessary because the patient was a nonsmoker. The patient was not admitted to the hospital. None of the other climbers required hospital admission. The patient was seen for follow-up the next day and was advised to continue use of the aloe vera gel. A day later she developed hemorrhagic blisters on the fingertips of both hands. She spoke with another climber who advised her that he was receiving outpatient wound care and whirlpool treatments. A few days later she took this information to her primary care physician who referred her to orthopedics and the authors’ hyperbaric medicine department (located at the wound care center of the hospital). Her referral to hyperbaric medicine was not expedited because of the orthopedic referral and the perceived nonemergent nature of her injury. On examination at the authors’ facility, the patient’s involved fingertips were blackened and hard to the touch. Erythema and tenderness were noted proximal to each area of black discoloration (Figures 1 and 2). She was diagnosed with Grade III frostbite (involving the dermal and deeper layers) to the third and fourth fingers of the right hand and fourth finger of the left hand. Initial orthopedic prognosis was that amputation of the involved fingertips would be necessary based on external appearance and abnormal bone scan results. Hyperbaric oxygen treatments were initiated 22 days after the patient’s initial presentation at the emergency room. Initially, it was thought that HBO would only be of benefit in preventing secondary infection this long after the original insult. Wound care consisted of debridement of sloughing tissue as needed with use of antibiotic ointments and various wound care products commonly used to assist with epithelization and reduce bioburden. Her fingers were wrapped at each visit with ADAPTIC™ Non-Adhering Dressing (Johnson & Johnson Wound Management, Somerville, NJ) and tube gauze. The patient required a 10-day course of cephalosporin for an early cellulitis at her fingertips. By the time of her third HBO treatment, the necrotic tissue at her fingertips was demarcating nicely and tissue color had improved in patches at her fingertips. Her skin color and texture continued to improve daily and began to look more viable. Sensation had returned to previously numb areas of the fingertips by the sixth treatment. After receiving 21 hyperbaric and wound care treatments over a 5-week period, the patient had complete recovery with only superficial sloughing of skin at the fingertips. Figures 1–4 illustrate her progress with HBO and wound care treatments. Discussion Frostbite occurs when the tissues freeze. Individuals exposed to temperatures below 0°C are at risk of experiencing frostbite. Frostbite rarely occurs at normal altitudes except in individuals who are inadequately clothed, have concurrent illness or alcoholism, or are accidentally exposed to prolonged cold. Heat production can also fall in cases of illness, injury, or poor physical condition, and in these cases, the extremities will cool to the ambient temperature despite adequate clothing.2 In superficial frostbite (Grades I and II), the skin loses sensation and becomes white. Blister formation may follow. Deep frostbite (Grades III and IV) involves necrosis of the dermal layers and can extend to the muscles and bone in addition to the skin and subcutaneous tissue.2 The degree of damage secondary to frostbite is related to the length of time the tissue remains frozen.8–10 Following frostbite, the affected area may show evidence of vascular occlusion, vasomotor irritability, hyperhidrosis, and partial nerve injury as manifested by numbness and tingling. Disorders of sensation and excessive sweating may persist for months. Once frostbitten, a body part is more susceptible to recurrent cold injury. A variety of treatments have been used for frostbite, including topical aloe vera, vasodilator drugs, sympathectomy, anticoagulants, tissue plasminogen activator, hydrotherapy, ultrasound, pressure dressings, oxygen, dextran, packing the body part in ice, rapid rewarming, antibiotics, cortisone, and any combination of these treatments.2,11 Numerous studies on the mechanism of frostbite injuries have stressed the importance of changes in the microcirculation, especially in the later phases.12–15 Other proposed mechanisms for injury have noted free radical formation3 and leukocyte adherence and aggregation.16 Vascular stasis and edema may effectively damage the local circulation. It has been shown that skin frozen and thawed on the surface of the body underwent necrosis for this reason and not because of individual cell death.2 Ledinham17 first reported the use of HBO for the treatment of frostbite in 1963. Other studies2–7 have reported considerable success with the use of HBO for frostbite injuries. Whether local circulatory effects decrease cellular damage or tissue viability, it appears that an increase in local tissue oxygen tension through the use of HBO improves the viability of tissue and allows vascular and cellular regeneration to occur. The immediate effect of HBO is hyperoxygenation of ischemic tissues, resulting from increased amounts of dissolved oxygen in plasma directly in proportion to the partial pressure of inhaled oxygen.18 Hyperoxia can be of great benefit through numerous mechanisms: improvement of oxygen delivery and preservation of tissue viability in ischemic areas;19,20 vasoconstriction with reduction in local edema with preservation of oxygenation;21,22 prevention of ischemic/reperfusion injury syndrome;23,24 enhancement of host response to local infections;24,25 and enhancement of the wound healing process through stimulation of angiogenesis and tissue growth and support.26 These processes can improve the local circulation and viability of damaged tissues, even when HBO treatments are started 2 weeks or more after the injury.4 The ideal time to initiate HBO for frostbite is during the rewarming period because of the reperfusion component of the injury. Hyperbaric oxygen therapy should be started as soon as possible post injury for maximum efficacy in preventing the ischemia-reperfusion injury complex. Hyperbaric oxygen treatments are usually administered for 90 minutes duration at a pressure of 2.0–2.5 atmospheres absolute for acute injuries. Initial treatments are usually done twice daily for a few days, then reduced to once daily. The authors elected to treat this patient once daily because with the delay in treatment, HBO was only expected to help with control of secondary infection. The patient was not charged for these treatments because she did not meet the current criteria for use of HBO as determined by the Undersea & Hyperbaric Medical Society (UHMS) and the US Food and Drug Administration. Daily treatments should be continued until no further improvement is observed. Improvement can be observed clinically, and laser Doppler flowmetry has been used for patient assessment during therapy.27 Conclusion Hyperbaric oxygen treatment for frostbite injuries is still considered investigational in the US. A frostbite injury is an ischemic injury but, in this case, not an acute ischemic insult. The patient’s wounds may not have been ischemic 22 days post injury. Since this is a case report, it is unknown what outcome this patient would have had without HBO. Timely use of HBO may be beneficial as an adjunctive therapy in the treatment of frostbite injuries. However, controlled studies on the treatment of frostbite with HBO are necessary to further establish the effectiveness of this treatment modality.