HBO Nuggets of the Week
A forum to discuss interesting aspects of hyperbaric medicine.
Tuesday, March 17, 2015
Collagen formation and maturation is a required step in the natural pathway to wound healing. Following injury, a wound goes through several phases in the process of healing. During the proliferation and maturation phases of wound healing, collagen is synthesized and then crosslinked by the hydroxylation of collagen by proline hydroxylase. These are oxygen-dependent steps as seen below in this simplified equation:
proline ---à proline hydroxylase---àhydroxyproline
O2, Fe2+ -----à CO2, Fe3+
Early American Indians noted that wounds that they sustained while living high up in the mountains appeared to heal more quickly in the higher pressure valleys. French divers living in submersible habitats in the 1960’s noted that their wounds healed more quickly in the moist undersea environment with higher oxygen tensions. These observations prompted T.K. Hunt in San Francisco in the early 1970s to perform studies on the effects of varying oxygen tensions on wound healing with relationship to collagen synthesis.1 He observed the rate of collagen synthesis in small cylinders implanted in rabbits with varying concentrations of oxygen. His results demonstrated collagen synthesis was accelerated in response to hyperbaric oxygen.
Hyperbaric oxygen is an adjunctive therapy in the treatment of specific nonhealing wounds; however, we must keep in mind that we should always treat the underlying cause of the wound and not just the wound itself. Peripheral arterial disease and diabetes, eg, may by underlying causes of ulceration that need to be evaluated in the initial workup of patients presenting for hyperbaric oxygen therapy consultation.
1. Hunt TK and Pai MP. The effect of varying ambient oxygen tensions on wound metabolism and collagen synthesis. Surg Gynaecol Obstet 1972;135:561-7.
Tuesday, September 16, 2014
One of the indications for treating patients with hyperbaric oxygen therapy (HBOT) is a Grade III Wagner’s diabetic foot ulcer. This classification was discussed in a previous blog. Treating a patient with diabetes in an HBO chamber requires attention to the patient’s blood glucose (BG) level.
For reasons still unclear, BG levels in patients with diabetes, either type 1 or type 2, tend to drop during HBOT. Patients with type 1 diabetes seem to be affected to a greater degree. Patients without diabetes may experience a drop in BG levels, but to a much lesser degree. Some studies have shown a mean drop in BG of nearly 50 mg/dL at 2.4 ATA. The exact mechanism needs to be understood, but it appears an increased peripheral cellular sensitivity to insulin may occur.
It is important to realize during the initial evaluation of patient candidates for HBOT that certain medications may affect glucose metabolism. These may include:
When undergoing HBOT, patients with diabetes should have their BG levels checked both pre- and post-dives. Each wound care center should establish protocols for patient BG management prior to HBOT. Clinicians may want to treat a patient prior to a dive if his or her BG level is between 110 and 140 mg/dL. During their course of therapy, falls in patients’ BG may increase after the third dive; hence, one must also be cognizant of the patient’s trend in BG levels versus any one individual number.
Wednesday, April 16, 2014
As hyperbaric medicine physicians, we may be asked to evaluate patients with compromised or failing flaps following reconstructive surgical procedures. With improved techniques in vascular and plastic surgery, there are an increasing number of these procedures being performed. Examples include:
· Breast reconstruction flaps
· Procedures to cover tissue defects after trauma
· Oral and maxillofacial procedures
One of the indications for the use of hyperbaric oxygen therapy (HBOT) is that of a failing flap or graft. HBOT can be used to promote flap survival. There are several theories describing how the flaps may benefit. One proposed theory is that there are small arteriovenous shunts that form within the flap and that HBOT may reduce these by causing vasoconstriction, thus increasing flow to more ischemic areas. The other is the well-known effect of migration of fibroblasts into hypoxic areas and induction of angiogenesis.
Typical recommended therapy is 2.0 ATA for 90 minute dives and, in some situations, the frequency could be twice a day. Treatment should always include close communication with the operating surgeon so that progress of the graft can be monitored.
Wednesday, February 26, 2014
One of the approved uses of hyperbaric oxygen therapy (HBOT) is for the treatment of chronic refractory osteomyelitis. This is a chronic condition of infection involving the cortex and medullary portions of the bone. For a patient to be considered a candidate for HBOT, he or she must have failed a course of standard therapy that includes debridement and a course of antibiotics. There is no exact point where one can differentiate between acute and chronic osteomyelitis, however, the accepted guidelines by the Centers for Medicare & Medicaid Services for treatment is generally 3 months.
One of the more common places that we encounter osteomyelitis is in diabetic patients with foot ulcers that penetrate to the bone or with a history of prior extremity trauma. The use of HBOT for osteomyelitis involving the long bones has decreased with the advent of improved surgical techniques for fracture repair and the use of plastic surgical flaps. Healing can be compromised by the interruption of blood supply to the bone either by infection, trauma, or repetitive injury. Physical examination may demonstrate exposed bone, odor, drainage, and tenderness. Although X-rays may be helpful, magnetic resonance imaging has emerged as the diagnostic tool of choice. Bone biopsy may provide pathologic diagnosis and also provide deep wound culture.
The mechanism of action of HBOT is similar to what has been discussed here before: enhancement of angiogenesis, increased leukocyte killing and improved bone healing through increased fibroblastic activity, and deposition of collagen with subsequent osteoblastic bone deposition.
The typical course of therapy for the treatment of chronic refractory osteomyelitis is 2.0-2.5 ATA, 30 dives for 90 minutes each, but the number of treatments may increase based on the severity of the disease.
Wednesday, January 08, 2014
Referring a wound care patient for hyperbaric oxygen therapy requires a commitment of time. Typically, the patient would require 20 to 40 treatments or “dives,” with 30 being the average amount of treatments. The patient must arrive before the treatment can start to have their vital signs taken and their glucose checked if they are diabetic and also be screened for safety. Contraband cannot be allowed in the chamber. Recall that 3 things are required for a fire: fuel, ignition source, and an accelerant. For example, street clothes, hand warmers, cell phones, and hairspray are not permitted in the chamber.
Pressurization, or descent, usually takes about 10 minutes. After arrival at the required depth, the standard treatment time is 90 minutes. The patient must then ascend, or depressurize, which again takes about 10 minutes. Total time in the hyperbaric chamber (monoplace) is usually 110 minutes. Clearly, the amount of time needed exceeds 2 hours. However, for many, the benefits of having a wound healed and closing the door to infection far outweigh any time inconvenience.