Incident Insight reprinted from Alert Diver magazine
By Marty McCafferty
Emergency oxygen is only the first step to treating suspected cases of decompression illness.
>The diver was a 44-year-old male recreational scuba diver, certified for more than 10 years, who was active in the sport and had no known medical conditions. During a two-week dive vacation in the South Pacific, he completed 36 dives on air over a 12-day period. His deepest dive in the series was to 100 feet, and his last dive was to 75 feet for 60 minutes. All dives went as planned, and he denied any history of rapid ascents, gear malfunctions or decompression obligations.
>When he surfaced from his 36th and final dive, he lost feeling in his lower back and legs. His condition rapidly progressed to include loss of vision and lower-extremity muscular weakness. He required assistance getting into the boat and was immediately placed on high-concentration oxygen via a demand regulator. He had a brisk response to oxygen and reported feeling normal after 30 minutes of therapy, at which point oxygen treatment was discontinued. Physical examination revealed that he still had weakness and sensory deficits in his legs. Taking no chances, the boat crew arranged transport to the nearest medical facility for evaluation and recompression. The time from developing symptoms until the initiation of hyperbaric treatment was approximately two hours.
>This individual suffered from an acute injury to his nervous system, most likely due to decompression illness. Blindness and weakness of both legs immediately after ascent may have occurred due to arterial gas embolism (AGE) and/or spinal cord decompression sickness (DCS). These two types of injuries can be difficult to distinguish, but the treatment for both is the same. The attending physician diagnosed DCS Type II (neurological). The diver was treated with a single U.S. Navy Treatment Table 6, after which most of his symptoms resolved, but he still suffered from tingling in his feet and experienced generalized fatigue.
>Three days after hyperbaric oxygen treatment, he flew home but continued to experience symptoms. He called DAN® and was referred to a local hyperbaric/dive physician for follow-up care.
>Residual symptoms after treatment are not unusual, especially when the initial injury is severe. Fortunately, the general trend is progressive symptom improvement over time.
>Although this diver participated in a multiple-day/multiple-dive schedule, he reported that he was always within his computer's no-
>decompression limits. Despite this, he wasdiagnosed with a severe case of neurological DCS. This case speaks to the potential for
>DCS even when dives are done within "limits."
>Remember, decompression models vary among dive computers even from the same manufacturer. In addition, some computers let divers modify their safety margins, and thus no-decompression limits do not always represent the same level of safety. In fact, the decompression stress of dives reportedly done within no-decompression limits may vary significantly as an individual's capacity to accommodate decompression stress can vary on any given day or dive.
>Divers must remember that a number of variables can affect our response to decompression stress, not the least of which is our underlying health. Fitness to dive is a combination of our medical history (long- and short-term issues) and physical condition. Another important factor is the level of exertion during a dive. An unexpected long swim back to the boat or shore may push an individual to his or her limits. Dehydration and cold water also influence decompression stress and may contribute to the onset of DCS. All of these factors need to be considered together to maximize safety and minimize risk. Focusing solely on a computer's no-decompression limit does not guarantee an injury-free dive.
>Divers can take a number of important lessons from this case. The first is that numbness and weakness in the legs within minutes of surfacing should be regarded as an emergency requiring immediate medical attention. The diver should be treated with oxygen as soon as possible and put under the care of a knowledgeable physician. Untreated, these symptoms may worsen or result in permanent disability.
>Emergency oxygen is important as it facilitates nitrogen off-gassing and supplies compromised tissues with needed metabolic support. The rate and extent of symptom resolution will vary, but decompression injury cannot be determined solely on the response to emergency oxygen. Divers must be evaluated by a medical professional, even when they say they feel normal or appear to have made a complete recovery. There are subtle signs and symptoms that the diver or first responder may not be aware of that indicate injury and the need for definitive treatment. The strength of a large muscle, for example, may be easier to assess than short-term memory problems. Properly trained personnel seek out these subtle signs during a thorough physical and neurological examination.
>Do not dismiss symptoms that seem to clear with emergency oxygen. There are multiple reports of divers whose symptoms appear to have resolved only to return hours later. The symptoms may even worsen on return. Remember, hyperbaric oxygen (i.e., chamber treatment) is the only definitive treatment for decompression illness.
>When a diver experiences symptoms of decompression illness, follow emergency first aid protocols, which should include oxygen at high concentrations and transportation to the nearest medical facility for further evaluation. The method of oxygen administration should enable the highest concentration of oxygen possible. This can be via a demand valve regulator (preferred) or by mask. If oxygen is delivered by continuous flow, gas supply becomes an issue, and the time/distance from definitive medical care requires consideration when forming an emergency action plan. (The standard oxygen flow rate employed by emergency medical services is 10-15 liters/minute when using a continuous flow mask.) Most important, make sure the diver stays on oxygen either until the supply is exhausted or he is evaluated by a medical professional. DAN is available for medical consultation (+1-919-684-9111) to help guide appropriate care for possible decompression incidents.
>© Alert Diver — Winter 2010