Traumatic brain injury (TBI) or intracranial injury, generally occurs due to a sudden, violent blow or jolt to the head. Air evacuations of soldiers have suffered a TBI may pose a significant added risk, potentially causing more damage to already injured brains, revealed a new study by researchers at the University of Maryland School of Medicine.
Over the past 15 years, more than 330,000 US soldiers have suffered a TBI. It is one of the leading causes of death and disability connected to the country's recent conflicts in Afghanistan and Iraq. Many of these patients were evacuated by air from these countries to Europe and the US for further treatment. In general, these patients were flown quickly to hospitals outside the battle zone, where more extensive treatment was available.
This is the first study to suggest that air evacuation may be hazardous for TBI patients. The study was published in the Journal of Neurotrauma.
About a quarter of all injured soldiers evacuated from Afghanistan and Iraq have suffered head injuries.
Faden and his colleagues tested rats that were subjected to TBI, using a model that simulates key aspects of human brain injury. Animals were exposed to six hours of lowered air pressure, known as hypobaria, at levels that simulated conditions during transport; control animals were exposed to normal pressure. All the animals received extra oxygen to restore normal oxygen concentrations in the blood. In another study, animals received oxygen, either as in the first study or at much higher 100% concentration, which is often used during military air evacuations. On its own, low air pressure worsened long-term cognitive function and increased chronic brain inflammation and brain tissue loss. Pure oxygen further worsened outcomes.
Faden and his colleagues believe the findings raise concerns about the increased use of relatively early air evacuation, and suggest that this potential risk should be weighed against the benefits of improved care after evacuation. Faden said, "It may be necessary to change the current policy for TBI patients and delaying air evacuation in many cases."
Faden and colleagues believe that one of the mechanisms by which hypobaria worsens TBI is by increasing persistent brain inflammation after injury. They are currently examining how this process occurs and have tested treatments that can reduce the risks of air evacuation. Early results are promising. Scientists suspect that breathing pure oxygen could worsen TBI by increasing production of dangerous free radicals in the brain. After brain injury, these free radicals flood the site of injury, and pure oxygen may further boost these levels. Several recent studies from trauma centers, including from the R Adams Cowley Shock Trauma Center at the University of Maryland Medical Center, have found evidence that using 100% oxygen in trauma patients may be counterproductive.