Diving after Decompression Illness: part I

"As with many areas of medicine, there are no hard and fast rules with DCI."

By Dr. Sawatzky

As with many areas of medicine, there are no hard and fast rules in this area and if you ask ten different diving medical experts to evaluate your personal case, you will get ten different answers, ranging all the way from very conservative to very liberal. Therefore, keep asking different doctors and you will eventually find one who says what you want to hear!

I must take some time to comment on this approach as it is very common and exceptionally stupid. First, it assumes that you, the diver, are more knowledgeable than the specialists you are consulting, as you have already determined the only answer you are going to accept! Therefore, why are you consulting the specialists in the first place? The reason is obvious. You are unwilling to take responsibility for making the decision yourself. The only reason you are asking the question is so that you will have someone to blame if the decision turns out to be wrong! Contrary to much of society, I am a very strong believer in individuals being responsible for themselves. I also trust that on every dive course you have taken you were taught that the only person responsible for you, is you. Therefore, it is reasonable to ask an expert for their opinion but it is more important that you ask them to explain how they arrived at that opinion. If the opinion is based on reasonable information and logic, then you should abide by it, whether you like the conclusion or not. If the opinion is simply a personal bias then you are being quite reasonable to consult a second specialist. With this introduction, let's get into the details of how the specialist decides if and when you should return to diving.

In general, they have to determine, in as much detail as possible, exactly what happened to you at an anatomical and physiological level. At this point it might be wise to review the pathophysiology of arterial gas embolism and decompression sickness (DCS, Diver Magazine June, August, September, November 1994, Pulmonary Barotrauma April 1997). It is usually impossible to fully answer this question as we do not completely understand the pathophysiology of DCI but in most cases we can make some pretty reasonable guesses. Let's look at a very simple case.

A diver is doing a 20 foot dive on a warm reef taking pictures. Suddenly they realize that they have completely run out of air. They hold their breath and swim to the surface, where they immediately lose consciousness. They are rescued by their dive companions, taken to the chamber that just happens to be 100 meters away on shore and they are treated immediately.

They fully regain consciousness seconds into the compression and have absolutely no residual signs or symptoms. In this very simple case, the diver almost certainly suffered rupture of some of the alveoli in their lungs from the expanding air as they ascended. The air was forced into the circulation and pumped to the brain where it plugged enough of the arteries so that the brain cells started to starve. Therefore the person lost consciousness. When the person was compressed in the chamber, the air was compressed and moved through the brain, restoring blood flow to the starving cells.

In this case, the person definitely suffered some damage to their lungs and might or might not have suffered some minimal brain damage. What investigations do they need? They should probably have a CT scan of the lungs and brain. If any abnor malities are found, the person should never dive again. But what if the CT is normal (from past experience, I would expect it to be completely normal). This is where the experts disagree. From autopsies on divers who have died, we know that the area of damage in the lungs can be very small. In the literature, we have several cases of divers who suffered pulmonary baro trauma and continued to dive, only to suffer another case of pulmonary barotrauma. In these recurrent cases, the provocation (what the diver did to cause the damage) was much less than the initial incident and the outcome much worse (the diver died or had permanent brain damage). I personally have been involved in two cases of definite pulmonary barotrauma in divers who survived with no signs or symptoms. Both continued to dive and one has since died in a diving accident where recurrent pulmonary barotrauma may have occurred.

In the simple case of arterial gas embolism described above, I would strongly recommend the person never dive again. Some "experts" talk about "earned" vs "unearned" pulmonary barotrauma. They argue that if the person damaged their lungs, even though they had a normal ascent rate and did nothing wrong ("unearned"), the person must have abnormal lungs and therefore they should never dive again. Conversely, if the person did something that explains the damage ("earned", in this case, held their breath while ascending) the lungs were probably normal before the accident and therefore it is OK for the person to return to diving! My response is that regardless of why the lungs were damaged, they were definitely damaged during the incident. Therefore, after the incident the diver has abnormal lungs and is at increased risk of recurrent pulmonary barotrauma. They should not dive again. Whether their lungs were normal or abnormal before the incident is irrelevant.

As you can see, even in simple pulmonary barotrauma, it can be difficult to arrive at a logical and reasonable conclusion as to whether the diver should return to diving! Decompression Sickness is much more complex.

A diver does a dive to 100 feet, stays for 25 minutes, and ascends directly to the surface at 50 feet per minute. Depending upon which tables you are using, this dive is right around the no-decompression limit. Therefore we know that the diver has a fairly large inert gas load at the end of the dive and some chance of developing decompression sickness. Sure enough, as the diver is carrying his equipment up the hill to his car, he develops a mild but constant, deep pain in his left elbow. He stows his gear and drives to the nearest chamber (15 minutes). The chamber staff just happens to be at the chamber and the diver is almost immediately pressurized. His pain disappears at 10 feet during the press and he remains sign and symptom free thereafter.

In this case, the most common form of DCS, we do not actually know what caused his pain! It was probably due to the formation of bubbles in the tissues around the joint although researchers have never been able to document these bubbles. Nevertheless, he had very mild symptoms that were present for a very short period of time and immediately responded to treatment. If he were a commercial diver, he would probably be back diving the next day. If he were in the Canadian Armed Forces, he would be most likely be diving after a week. However, if he develops DCS at any time in the next several months, the DCS will probably present as pain in his left elbow. We know that after frostbite, the microcirculation in the affected area takes up to five years to recover! In DCS, I suspect that the microcirculation is often damaged and also takes a long time to recover. Therefore, after DCS, it seems reasonable to conclude that the diver is at increased risk of DCS for months to years.

In this case, I would suggest that the diver return to diving after a week but that they dive more conservatively for the next year and minimize their risk factors (good advice for all divers). Two easy ways to dive conservatively are to dive nitrox (after taking a course) but use air no-decompression limits or add 25% to your bottom time on every dive (stay 25% inside the no-D limits).

Let's look at some variations in the above case, if the diver had taken several hours to reach the chamber, the response to treatment would most likely have been much slower. It might have taken some time at 60 feet on 100% oxygen before the pain completely resolved. In this case, the diver would have suffered more severe injury and the advice would have to be slightly more conservative.

If the diver had severe pain and took a long time to become pain free in the chamber, they should not dive for at least four to six weeks (the time it takes for a soft tissue injury to heal) and be very conservative (add 50% - 100% to their bottom time) for the next year.

If the diver had only been at 100 feet for 15 minutes and had no known risk factors but still got bent, we could conclude that they might be more susceptible than average to DCS. In this case, they could return to diving in one week but they should dive more conservatively (say add 25% - 50% onto their bottom time) for the rest of their life!

As can be seen, even simple DCS can also be very complicated to analyze! We will continue this discussion in the next column when we look at more complex cases of DCS. However, it should be obvious by now that there can not be simple hard and fast rules for when you can return to diving after DCI. Therefore, you should always dive so that your chance of suffering DCI is minimized and if you do suffer DCI, get the best advice available before you return to diving.