Decompression Sickness, Decompression Illness, and Arterial Gas Embolism from Blast Injury:
Not exactly the same things, but damned close when it comes to treatment.
Each of these conditions is brought about by barotrauma, injury caused by changes in ambient pressure that occur too quickly and/or too intensely for the body’s systems to accommodate. While there are obvious differences in these conditions, they share many of the same features . One of these features is the phenomenon of arterial gas emboli or ,\GE (tiny bubbles in the blood), which are often not immediately apparent but that effects ranging from inconsequential to lethal. Of particular interest is the fact that these bubbles can cause ongoing or permanent neurological impairments of varying degrees of seriousness, and which may often be misdiagnosed and thus incorrectly treated. In these cases of Decompression Sickness (DCS) and Decompression Illness (DCI), there is a much stronger likelihood of a proper diagnosis and effective treatment. In the case of AGE/blast injury, this is not the case. Currently, blast injury is a somewhat common problem in the military engaged in Iraq and Afghanistan, and there is concern that injured soldiers may not be receiving the best treatment available. Similarly, in parts of the world civilian populations are suffering increased cases of AGE/blast injury. Blast injury appears to be a phenomenon that will not soon abate; therefore, it is imperative that it be understood and treated as effectively as possible. This paper attempts to briefly discuss, in very simple language, how similarities in these conditions support the use of hyperbaric oxygen therapy, the established primary treatment for DCS and DCI, in AGE/blast injury.
DCS is the barotrauma most commonly recognized by the general public. Also know as caisson disease or “the bends,” it is universally known and feared by commercial and recreational divers. Basically, DCI is bubbles in the blood. Here’s how it happens. Air (approximately 78% nitrogen, 21 % oxygen, and 1 % other inert gases) is taken into the lungs as we breathe. The lungs pass the air into our blood where the oxygen molecules bond to the red blood cells and are distributed to the cells of our body where they support cell metabolism. Then the lungs expel the nitrogen and the byproduct of the oxygen metabolism, carbon dioxide. These gasses are dissolved into the fluid blood by the lungs and then released from the blood for expulsion after circulation. The amount of gas that can be dissolved into, and maintained in, solution in the blood varies with ambient pressure: the higher the pressure, the more gas held in solution; the lower the pressure, the less gas. When a diver goes under water the ambient pressure on his body increases and more gas (air) is dissolved into his blood. The deeper he goes, and the longer he stays under pressure, the more gas is dissolved into the blood. As he ascends ambient pressure decreases and his blood cannot maintain the volume of gas dissolved in his blood. If he ascends slowly, his lungs are able to accept the gas from the blood and expel it through breathing (“off-gassing”). How slowly he has to ascend to successfully off-gas is based upon the depth and duration of his dive. To the extent that he ascends too quickly, the off-gassing process is incomplete and the gas that is not expelled through breathing is retained in the blood as tiny bubbles. In fact, there are tiny bubbles of gas (nitrogen) in the blood of any diver after any dive, because the off-gassing process is never perfect. In most cases, these tiny bubbles remain tiny and cause no problems until they are eventually off-gassed as they circulate through the system time after time. DCS occurs when the amount of gas in solution is released too fast for adequate off-gassing and too much gas is sent into circulation as bubbles in the blood. These bubbles can actually “foam” the blood in severe cases and cause the heart to be unable to pump the blood adequately; this leads to death. More often, the bubbles are .carried through the system until they lodge somewhere, often in a joint. This is known as a “hit” or “bent” (He took a hit in the elbow, or His shoulder got bent) and is common in minor cases of DCS. “Hits” or “bends” in the nervous system are common, and can be very serious; paresis and paralysis are common, and a “hit” to the brain can be anywhere from subtle to catastrophic. Fortunately, even if the signs and symptoms of DCS are subtle, the history of just having been diving usually leads to implementation of the proper treatment: hyperbaric oxygen therapy (HBOT). HBOT involves breathing pure (or almost pure) oxygen under pressure. The way it works with DCS is that by re-pressurizing the patient, the troublesome nitrogen bubbles are forced back into solution in the blood. They can then be circulated through the lungs and gradually off-gassed. No more nitrogen is dissolved because the patient is breathing oxygen, not air. He is taking in no nitrogen. The primary mechanism of HBOT in DCS is mechanical: the nitrogen bubbles are pressurized back into solution, allowing off-gassing, and no additional nitrogen is taken in during the process. While such procedures as dialysis or total blood
exchange/transfusion could also be employed in DCS, HBOT is the definitive treatment. DCI includes DCS but also encompasses other causes of air embolism. To extend the use of SCUBA diving examples, another type ofbarotrauma seen in diving is AGE/pneumothorax. Pneumothorax occurs when the pressure inside the lung becomes so excessive that the lung ruptures, releasing gas into the chest cavity. Divers experience pneumothorax because they ascend so rapidly that lungs cannot adjust to the changing pressure, or the diver holds his breath on ascent preventing the lung from equalizing pressure. Basically, the lung simply “blows out” or explodes, like an over-inflated tire. The release of gas into the chest cavity can lead to AGE. So, along with the trauma to the lung tissue itself, pneumothorax can lead to AGE. There are other types of injuries that are included in DCI besides DCS and pneumothorax, but they share the common problem of some probability of AGE. In this respect, HBOT remains the definitive treatment.
Blast injury is complex; there are four general types of injury seen:
1. Baro trauma / AGE
2. Penetration/laceration from shrapnel
3. Concussion and impact
4. other; such as burns, toxic chemical exposure, and asphyxia/CO poisoning
The so-called “Primary” type of injury is barotrauma. A blast is, in fact, an intense change in ambient pressure. Beginning with an environment of normal atmospheric pressure, a blast first causes an extremely rapid increase in atmospheric pressure. Then, after the initial over-pressurization, there is a secondary wave of vacuum – a decrease in pressure from normal atmosphere. So, we go from normal atmospheric pressure to many times atmospheric pressure to much less than atmospheric pressure-almost instantaneously. It is sort oflike a diver descending to several atmospheres of depth, then taking an airplane ride and landing again on the ground, all in an instant. In a blast, many of the same factors of compression/decompression seen in DCI and DCS are present. There is AGE. There are bubbles. The bubbles are not nitrogen as in DCS, because the victim of a blast is not breathing; it is not a matter of off-gassing problems. It is more similar to AGE/pneumothorax DCL In fact, “blast Jung” is somewhat equivalent to AGE/pneumothorax as seen in DCI in many respects, with ruptured alveoli Jetting gas into the arterial system leading to bubbling. The bubbles cause ischemia.(decrease of blood because of arterial blockage) and the blood starved downstream cells are either stunned into inactivity or killed outright. Signs include disruption ;it the blood-brain barrier, increased cerebrospinal fluid (CFS) pressure, and inflammation. Neurologic signs and symptoms of AGE/blast injury are many and varied, and include several common to both Traumatic Brain Injury (TBI, unspecified), a presumably physiological condition, as well as Post Traumatic Stress Disorder, considered primarily a psychological disorder. These signs and symptoms include depression, anxiety, cognitive impairment, and other changes in mental status. While blast injury victims may well be susceptible to PTSD and require psychological or psychotropic medical treatment, the AGE/blast injury (tiny bubbles) are also causing or contributing to these signs and symptoms. Both conditions need to be treated, and while PTSD is being diagnosed and addressed aggressively, the AGE is not. Psychotherapy and/or psychotropic medicines are effective for PTSD but they do not shrink bubbles in the bloodstream. While psychological and psychiatric interventions may mask some of the signs and symptoms of AGE/blast injury in the brain, they are neither curative nor maximally effective. The definitive treatment for AGE is HBOT. Blast injury victims are simply not being adequately treated.
HBOT works for DCS, other DCl’s, and is specified as the primary treatment for AGE in the Department of Defense literature. While each of these conditions is different in some ways, they are all very similar in that they share a common problem: tiny bubbles in the blood. They also, then, share a common treatment: HBOT. AGE/blast injury is not exactly the same as DCI or DCS, but “bubbles is bubbles” and bubbles behave the same relative to pressure changes, and wreak the same havoc in the bloodstream, regardless of the label attached to the cause HBOT should be the first line of treatment, and the airlifting of AGE/blast injury victims prior to HBOT should be avoided, because further reductions in ambient pressure make tiny bubbles less tiny, leading to more damage. It is past time for HBOT to be made available for victims of AGE/blast injury.