Acute Traumatic Ischemia Hyperbaric Evaluation and Treatment

Anatomy and Physiology

After an acute traumatic injury to a limb, injury to blood vessels leads to bleeding into tissues with subsequent coagulation and stasis in the vessels, which leads to hypoxia in the cells and the inability to maintain the metabolic demand important to maintain adequate intra-cellular water. The resulting edema causes increased pressure, causing more ischemia and hypoxia, leading to more cell death and extra-vascular water. Once blood flow is restored, subsequent ischemia-reperfusion injury occurs. The endothelial layer of the vessels becomes injured, and fluid extravasates, causing edema besides progressive obstruction of blood flow caused by neutrophils that adhere to the injured vessel wall.

Hyperbaric oxygen works in multiple ways to help with those acute changes at the cellular level. First, it produces vasoconstriction by about 20%, which means less inflow of fluid (blood and plasma) into the injured area, but since the dissolved oxygen in plasma is at least doubled (from that of breathing 100% oxygen by facemask), there is a net increase in oxygen delivery. This vasoconstriction results in less edema and increased oxygen diffusion distance. Hyperbaric oxygen also reduces the adhesion of neutrophils to the injured endothelium, which blunts the ischemia-reperfusion injury.[3]

Indications

Emergency surgical treatments such as revascularization and fracture stabilization should come before considering hyperbaric oxygen treatments. In some less urgent cases, hyperbaric oxygen treatments may help the surgeon better demarcate viable from dead tissue and thus minimize tissue loss and reduce the risk of amputations. The decision to use and frequency of hyperbaric oxygen should be made in close collaboration with the surgeon and depends on the injury type, the injury severity, and patient host factors. It is best to use an objective grading system such as the Gustillo open-fracture crush injury grading system while adding a host factor function score that includes age, smoking, steroid use, ambulation status, and cardiovascular and kidney function. This improves patient selection and the treatment algorithm, with the idea that even milder type injuries in a compromised host benefit from hyperbaric oxygen as adjuvant therapy.[1] Utilization review of hyperbaric treatments is an important part of the clinical care of those patients and is best done in close collaboration with the surgical and hyperbaric team after a certain number of predetermined hyperbaric treatments.[2][4][5]

Contraindications

There are no direct contraindications to hyperbaric oxygen in acute traumatic peripheral ischemia unless use delays emergency, limb-saving operations such as revascularization or established compartment syndrome. There are few absolute contraindications, such as an unrelieved tension pneumothorax.

Equipment

A pressure vessel and 100% oxygen are the tools to provide the benefits of hyperbaric oxygenation to the body. There are 2 types of pressure vessels: mono-place chambers and multi-place chambers. Mono-place chambers which can hold only 1 person. They are usually made of a transparent acrylic tube with patient access through a metal door on 1 end. In mono-place chambers, 100% oxygen pressurizes the tube while the patient breathes the chamber's ambient oxygen. Some mono-place chambers have a separate breathing mask to provide air when air breaks are used. Mono-place chambers can be outfitted with ventilators, infusion pumps, and physiologic monitoring capabilities to provide high-acuity care. Mono-place chambers can fit into a standard hospital room and get piped into the hospital oxygen and air supply.

Multi-place chambers are steel with acrylic viewing ports and can fit 2 to more than 20 people. They are pressurized with air while the patients breathe oxygen through a tight-fitting mask or a special hood sealed around the neck with a rubber neck dam. For any potential air breaks, the patients breathe the chamber air. These multi-place chambers are often large complexes with large compressors and reserve air and oxygen tanks.

Both chamber types require special manufacturing and installation guidelines governed by special fire protection codes such as NFPA 99 in the United States. Facility accreditation of hyperbaric programs is recommended and available through the Undersea and Hyperbaric Medical Society in the United States and some international locations. A transcutaneous oximeter can help determine the level of tissue oxygen tension on room air and during hyperbaric treatments and has been shown to have a positive predictive value of 0.88 for healing when a level over 200 mm Hg is reached during the treatment.[6]

Personnel

For mono-place chambers, 1 specially trained outside attendant may conduct and supervise up to 2 simultaneous hyperbaric chamber treatments and must be in continuous attendance outside the chambers. Multi-place chamber operations require both outside and inside specialty-trained attendant(s). Those inside attendants are breathing compressed chamber air and can be at risk for decompression illness, just like a scuba diver. Appropriate safety protocols and procedures must be in place to minimize that risk. An outside chamber operator is pressuring the chamber and constantly communicates with the inside attendant.

A safety director must ensure maintenance and safe operations for the hyperbaric facility. A specialty-trained hyperbaric physician prescribes and supervises the pressure, time, and gas profiles of the hyperbaric treatments and examines the patient before and after the treatments. A specialty-trained hyperbaric clinician provides expert wound care, administers medications, and trains and educates the patients.

Preparation

Safety procedures are required to minimize the introduction of static electricity, fuel, and ignition sources into the hyperbaric environment to decrease the fire risk. Everyone inside must wear cotton or cotton blend sheets and scrubs. Oily substances and alcohol must be avoided, and ignition sources are not allowed. In rare cases where the patient has difficulty equalizing their ears during the pressure change, myringotomy tubes may have to be placed.

Depending on the patient's injury, dressing changes and wound debridement may be required before entering the hyperbaric chamber. If patients require monitoring during the hyperbaric treatment, appropriate sensors must be applied and connected to pass-through connectors in the hull. If the patients require medications or infusions, those may need to be prepared for special infusion pumps. Communication between the primary surgical service and the hyperbaric medical team is paramount.

Technique or Treatment

The attending hyperbaric medicine specialist prescribes the time, the pressure, and the breathing gas in a treatment table for the patient (and if the treatment is scheduled in a multi-place chamber, they also plan the dive profile for the inside attendants). Common treatment tables for acute traumatic peripheral ischemia are 2 atmospheres absolute (ATA) for 2 hours or 2.4 ATA for 90 minutes. The number of treatment tables that have been suggested varies by type of injury. For preventing ischemia-reperfusion injury, a single treatment may be sufficient. For crush injuries, a much more aggressive schedule of 8 treatments (1 treatment 3 times a day for 2 days, twice a day for 2 days, followed by once a day for another 2 days) may be required. For an impending compartment syndrome, 3 treatments (2 twice a day on the first day and 1 on the second day) are recommended. While any established compartment syndrome requires a fasciotomy, hyperbaric oxygen may still be useful following the fasciotomy to treat residual concerns such as tissue ischemia, massive swelling, or nerve injury and may require twice daily treatments for up to 7 days.[2]

Complications

Hyperbaric oxygen is usually well tolerated. Occasionally, patients who have difficulty equalizing may develop barotrauma to the ears. This can usually be managed with nasal decongestants and rarely requires myringotomy tubes to be placed by an otolaryngological surgeon. Pulmonary barotrauma is very rare; however, the possibility of pulmonary trauma should be considered when patients develop chest pain on an ascent. Pulmonary and cerebral oxygen toxicity is typically not an issue with the relatively short exposures used for acute traumatic peripheral ischemias, but it can occur.

Clinical Significance

Acute traumatic peripheral ischemia can be devastating and can lead to permanent loss of the limb or function. The cost of amputation with rehabilitation and the resulting loss of productivity far outweighs the cost of salvage and reconstruction, even including appropriate hyperbaric oxygen therapy, which only adds about 10% to the overall cost.[7]  Hyperbaric oxygen therapy is an often overlooked adjunct therapy to surgery and can help reduce the vicious cycle of edema, ischemia, and hypoxia, as well as reduce the deleterious effects of an ischemia-reperfusion injury. Unfortunately, hyperbaric oxygen is often only thought of to mitigate late complications, rather than applying it early helping to reduce tissue loss.[8][9][10][11][12][10]

Enhancing Healthcare Team Outcomes

The management of acute traumatic peripheral ischemia is challenging and complex. While it is in the realm of the trauma surgeon and the orthopedist, other important healthcare team members can offer expertise and skills to improve patient outcomes. Defining the patients who might best benefit from hyperbaric oxygen therapy, the Undersea and Hyperbaric Medical Society has suggested a treatment algorithm that considers the type and severity of trauma based on the Gustillo classification and patient host function factors that may influence the treatment decision.[2] The optimal treatment plan after a severe traumatic injury is best done with an interprofessional approach.