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Decompression Illness

by Philip Greenspun,

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Some things that I learned the hard way about decompression illness ("DCI", "DCS", or "the bends"): Here then is my decompression illness story.

I'm a novice diver, certified with 5 beach dives in Hawaii in 1991 topped up with 11 dives in three days from a liveaboard out of Cairns, Australia in 1992 (see and two more dives in the Caymans in 1994. During those 18 dives, I'd never had any problems of any kind. I never considered myself at any risk of the bends because I tend to consume air rapidly.

Following six years glued to the keyboard, in August 2000, I went out for a 6-day cruise to the Coral Sea out of Townsville, Australia with Mike Ball Dive Expeditions ( There were 19 other divers on the boat. Every one of these 19 people did more dives, longer dives, and deeper dives than I did. Yet I got ill and they did not. Mike Ball requires and supplies dive computers. I used one throughout this trip. At all times the computer showed that I had ample time remaining at my current depth for a no decompression stop ascent.

I felt pretty bad during much of the trip. We started off with a 10-hour drive through rough seas. Even with a Scopalamine patch on, I felt a bit seasick. Several other passengers and crew were vomiting. Few people reporting having slept well. Keep in mind that dive boats aren't luxurious floating cities like the Love Boat. We were on Spoilsport, which is considered Australia's finest liveaboard, staying in a "premium" cabin, and yet the noise of the engines when moving is thunderous. The hull of a powerboat acts as a resonator for all the diesel engine noise and, even if you're wearing earplugs, you might have a tough time sleeping from the noise of the engines alone. This night we had the noise plus the seas were rough enough that we were actually pitched up into the air from the mattress regularly.

Bottom line is that I was a bit tired on the first day of diving but felt good because I wasn't actually green and vomiting like some of the other passengers. While equalizing on the second dive (out of 24 possible), I bruised my right eardrum a bit. Upon visiting a doctor following my return, I learned that I had a wax buildup in this ear and that was probably why it was tough to equalize. Lesson: Get a dive medical or at least a regular physical before any new collection of SCUBA dives.

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By the second day my ear felt better and I enjoyed three dives to about 17-18 meters. After three or four days I found that I was unable to read with my eyeglasses on. I'm nearsighted but normally I read with my glasses. One of the precautions against taking scopalamine is for people with glaucoma so I figured that this was a side effect of the patch, though I'd used these patches 10 or 15 times before with no such effect. Early in the morning on the fifth day of the trip, I had a really bad headache, I felt pressure behind my eyes, and my right arm ached as though I'd had a tetanus shot in the biceps. Was it from the three dives the day before (23m, total bottom time 27 minutes; 20m, 28 min; 17m, 25 min; all multilevel dives)? Headache is not listed as one of the symptoms of DCI in the PADI and SSI books. Or was the headache from the scopalamine patch? And the arm ache a result of a crewman opening a door into my elbow the day before? Jason, the captain, put me on 100% oxygen as a precaution. This is the traditional first-aid given to DCI sufferers. The oxygen did not give me any relief and the Mike Ball staff said that was a sign against it being DCI since a DCI sufferer will usually feel better after 30 minutes of oxygen. Jason also telephoned the hyperbaric chamber at Townsville General Hospital and spoke with a technician there. It was the judgement of the tech that my symptoms could best be accounted for by the scopalamine and the elbow whack. A helicopter ride and treatment in the chamber seemed unnecessary.

I took the scopalamine patch off. The arm ache cleared by mid-morning. My headache cleared by the afternoon. Talking to the crew and the other passengers reassured me. All of them had convinced themselves that they'd gotten bent. They'd felt or imagined twinges and were sure that they needed hyperbaric treatment. But in every case it turned out that they were simply paranoid. There are 1 million people diving every year in Queensland and only 120 are treated in Townsville's hyperbaric chamber. 1 chance in 10,000!

I did a dive to 14 meters for 40 minutes to watch a shark feed and then did a 40-minute multilevel night dive, to a max depth of 14 meters. I suffered from some stress and fatigue at the end of the night dive, however, as we overshot the boat and there was a strong current flowing away from the deco bar. Mike Ball had buddied me up with Kevin, a volunteer divemaster, who'd done about 60 dives before this trip. He saved my butt by helping me fin back to the boat. Some rough times were predicted so I took an English seasickness remedy, Sturgerol, from another diver.

Overnight we drove through rough seas for 10 hours to get to the wreck of the Yongala, a coastal steamer that sank 12 miles off the coast of Queensland in 1911 with 120 lives lost. This is considered one of the world's best wreck dives. However, conditions in the morning were challenging. Few had gotten a good night's sleep. The noise of the engines and the rough water, nearly as bad as the first night's sail out, was enough to wake almost anyone. There was a substantial surface swell, the sky was intermittently gray, and we had reports of a strong current down on the wreck.

One of the good things about diving with a first class outfit like Mike Ball is that they spend a lot of time preparing the site. They dropped two lines to the wreck, one on the stern and one on the bow. So it would be possible to descend and ascend on the lines, important for doing the decompression stops that Mike Ball insisted on even if the computers did not. At the bottom of each line, in about 15 meters of water, the Mike Ball crew had left a spare SCUBA tank and regulator for anyone who was low on air. If you came up on the far line you could just raise your hand to get picked up by a Zodiac rather than pull your way back to the boat.

I was buddied with my girlfriend Eve Andersson, who'd done her open water certification dives on board the Spoilsport. We asked for help from the crew and they sent Kevin, the volunteer divemaster, with us again. My plan was to descend on the line nearest the boat, drift with the current to the second line, then ascend to the surface and ask for a Zodiac pickup. Short, sweet, no finning against the current. I let Kevin overrule me. Pointing to the crashing up and down of the Spoilsport, he said that it was tough to get back onto the boat from the Zodiac and we'd be better off just staying in the neighborhood of the first line and coming back up.

We executed a modified version of Kevin's plan. The current took us fairly quickly all the way to the other end of the boat. Then we proceeded to swim back. I watched my tank pressure gauge drop from 140 bar to 40 sickeningly fast. We were back on the first line but rather than grab the spare tank, Kevin had me breathe from his octopus regulator. He still had more than 100 bar (Lesson: be in really good shape before a challenging dive and work out with your fins doing a bunch of snorkeling.). We did the safety stops with me breathing from his octopus but it wasn't much fun because something about the arrangement kept flooding my mask. We did a 2-minute stop at 10 meters and a 3-minute stop at 5 meters and then ascended. I went back on my own tank to pull myself back to the boat along a surface line. The waves were too rough for me to feel that I could snorkel comfortably so I stayed with the regulator and watched the pressure drop from 30 to less than 10 bar. Just like it says in the books, it became a bit tougher to draw breath. I made it back to the boat but couldn't get on immediately. The swell was causing Spoilsport to crash up and down hard enough to crack anyone's head open. So the crew was on the dive platform telling divers exactly when to approach. I got on with maybe one more breath left in my tank.

There are a whole lot of lessons to be learned from the preceding. One is probably to be more assertive about insisting on an easier dive plan. Second is to not be shy to grab the spare air tank. Third is to wait for a better day (as it happened the second dive that morning on the Yongala had much reduced surface swell and hardly any current).

The PADI and SSI books don't list being scared as a contributing factor to DCI. But they do list "fatigue" and "vigorous exertion". "Weakness" is also listed as a symptom of DCI. So it is possible that I had trouble finning against the current on the Yongala dive because of DCI picked up from previous dives and that the effort of the dive itself made the DCI worse. The poor night's sleep wouldn't have helped either. My profile on the dive was reasonable. I was down at 26 meters only for about 5 minutes then mostly up around 17 meters. My total bottom time would have been about 20 minutes. It was a no-decompression dive by the PADI tables and the dive computer certainly gave me ample margin.

That said, after the Yongala dive, I was finished. I was exhausted and collapsed on my bunk. A terrible headache developed within half an hour and I tried some oxygen (the tank was still in our cabin). I felt a little bit better towards the afternoon as we drove back towards Townsville and managed to come up on deck to gaze out at the horizon. When I got off the boat at 4:00 pm, I was dizzy and had a headache. So I hopped in a taxi to a local dive physician's office and presented my symptoms. His diagnosis:

  1. based on a wax buildup in my right ear, it looked like I'd had a minor ear infection
  2. the pressure of diving had pushed the infection into my sinuses and that was the cause of the headache
  3. the other symptoms were side effects from scopalamine
I was put on a course of antibiotics and sent back to the hotel.

Facing the Music

It was 8:00 am. Twenty four hours after my last dive and three hours before the first of a series of flights that would carry me back to the US, ending my three-week sojourn in Australia. My headache was terrible and I was a bit lightheaded. Not as dizzy as the previous afternoon but it seemed like a reasonable precaution to visit the hyperbaric medicine department at Townsville General Hospital. They were very polite and organized on the phone and agreed to see me immediately at 9:00 so that I could get cleared and proceed direct to the airport for my 11:00 am flight.

Dr. Webb was on duty. He's an anesthesiologist normally but was filling in for the head of hyperbaric medicine. He listened to my report. He tested my balance by making me stand with one foot in front of the other, clasping my hands to opposite shoulders, closing my eyes and seeing how long it took me to topple over (15 seconds; 60 is normal). He tested the comparative sensation in left and right sides using light touch with cotton balls, sharp and dull needles, and cold versus not-cold objects. My right hand was considerably less sensitive than the left one. He tested my mental abilities by timing me count backward by 7s from 100 and by asking me to remember a sentence.

Dr. Webb offered no opinions until the end of the consultation: "You have decompression illness and need treatment in the hyperbaric chamber."

I struggled against this diagnosis as best as my fogged mind could. I cited the fact that my diving was within the limits of the computer. Dr. Webb pulled out a very conservative set of dive tables from a Canadian organization and noted that it recommended longer decompression stops for a 28-minute dive to 26 meters. He put little faith in dive computers, saying that they were based on animal studies. In any case, he'd had patients who got DCI in swimming pools or on their open water certification dives. Headache wasn't on the list of common DCI symptoms. He said that the entire recreational diving industry was deeply confused about what was and what was not a symptom of DCI. In fact, headache and flu-like symptoms were fairly common. Because they aren't listed, a lot of divers get DCI and wrongly attribute it to the flu. I asked him to consider the possibilities that all of my symptoms were explained by a sinus infection or Scopalamine. Finally he crushed my resistance by saying "You don't feel right, do you?"

The chamber was in use that morning for a scheduled 1.5-hour "dive" to benefit wound patients. This is the main use of hyperbaric facilities worldwide. If a wound is poorly supplied with blood, most typically because the patient is diabetic, 30 treatments with pressure and 100% oxygen often help. Divers with DCI are treated initially with a 5-hour "dive" and that was scheduled for 1:00 pm.

During the rest of the morning I found out some more unpleasant facts about DCI. I would be forbidden to fly in a commercial aircraft for three weeks following my last treatment. I tried to make the best of this. I would drive or take the train down to Sydney and work from the bosom of the University of New South Wales's excellent computer science department. Wrong! There was a series of 200-meter high hills between Brisbane and Sydney and the road or train would keep me up there for a total of 20 minutes. That might bring back all the DCI symptoms as the nitrogen bubbles expanded further. I could go north to Cairns or south to Brisbane but not inland or south to Sydney. I couldn't do anything too rugged in this rugged part of Australia, though, because strenuous exercise was forbidden for at least two weeks following the final treatment. Alcohol was prominently restricted as well, something you might expect when there is a huge drive-through liquor store just half a block from the hospital, but I'm not a drinker normally so I wasn't upset about that.

Into the Chamber

Digital photo titled philip-entering-hyperbaric-chamber The basic theory behind DCI is that your body has respired out most of your excess nitrogen. However, it didn't get rid of enough of it quickly enough. The residual nitrogen formed itself into bubbles too large to diffuse through blood and tissues. The objective of recompression is to squeeze the bubbles down small enough that they can diffuse through tissue again. To encourage those bubbles to diffuse out through your lungs, you breathe 100% oxygen in the chamber. I.e., there is no nitrogen in your airways and at least some nitrogen in your tissues. So the diffusion of the nitrogen will all point up and out of your mouth.

Recompression and oxygen is not 100% effective, however. If a bubble is really big it might not be compressed down small enough in the 18m of pressure that you get (they can't bring you down lower because otherwise the oxygen becomes toxic). If a bubble has become coated with protein, it may be more tenacious than a regular bubble and persist. This is why it will take some weeks following treatment for maximum recovery.

Some people get what Dr. Webb called a "fit" from the pure oxygen under pressure. So they stick an IV in you before the first long dive and the treatments are done with one nurse in the chamber and one nurse outside the chamber with the technician. If there is an adverse reaction to the oxygen, they can easily pump drugs into your system to revive you.

During most of the first treatment, I just lay down on the bed, opposite Mardi, one of the nurses. I did a bit of reading towards the end and found that my concentration was considerably improved compared with the morning.

The rest of the week

Digital photo titled hyperbaric-staff Each day for the rest of the week, I would get evaluated in the morning by Dr. David Griffiths, the head of hyperbaric medicine. He tested my pulse, my temperature, my blood, and X-rayed my sinuses to rule out the possibility that some of my symptoms were explained by an infection (all tests were negative). My headaches were slowly getting better and, by the morning of the fourth treatment, I was able to balance for 60 seconds. Hanging around the unit, I learned more about DCI. One patient's had no symptoms other than a personality change: "He became a complete arsehole," said one of the nurses. Over a three month period, this diver lost his wife, his kids, and his job. Even after three months, hyperbaric treatment partially restored his former personality.

Digital photo titled hyperbaric-chamber Townsville is a pleasant place and after three treatments I was able to visit the Billabong Sanctuary, where you can cuddle a koala, hold a python, watch the staff almost hand-feed huge crocodiles, pet kangaroos, and be walked on by Australian parrots. After my fourth treatment I was able to take a ferry out to Magnetic Island and poke around a bit. But basically I was an invalid and this was the sanitorium life a la Mann's Magic Mountain. I had the worst headaches of my life, was worn out and tired from just getting up and walking two blocks to the hospital, and felt like I would never get better. It is extremely depressing. I was only able to get by day to day because my girlfriend Eve rearranged her life and stayed with me for the week of treatment.

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The Future (for me)

I'm back to work officially, remotely supervising some projects back at ArsDigita. I've rented a car and am trying to drive down to Brisbane to give a couple of lectures at the university. Eventually I will make it down to UNSW in Sydney and then home. Dr. Griffiths tells me that I might be headache-free in a week and that I can hope for a complete recovery though it sure seems hard to believe right now.

Liveaboards and Decompression Illness

I built my Web site in order to share what I've learned in the hopes that it would be useful to others. So here is something I think that I've learned about liveaboard diving boats: a liveaboard dive cruise is a great way to get DCI. On a liveaboard trip, there is nothing to do except dive. You will be doing more dives per day than if you were at a beach resort with other options.

Liveaboards tend to move at night. Smallish power boats are extremely noisy. If you are a light sleeper, you won't get much sleep. Fatigue puts you at increased risk of DCI according to the PADI and SSI books. Even more of a problem is that if you are tired after a dive you won't know whether it is due to the sleepless night or the dive itself. Do you have DCI or did you just sleep poorly?

If you've any tendency toward seasickness, you may have some problems. If you actually get sick you'll be dehydrated and that puts you at increased risk for DCI. If you take medication and then feel odd at some point in the trip, you won't know whether the discomfort is a side effect of the medication or related to your dive.

One of the best tests for DCI is the balance test that I had every day in Townsville General Hospital. I think you should test yourself at home to establish a baseline and then on every dive day. If you're on a liveaboard dive boat, you'll never know whether or not an inability to balance is due to the rocking of the boat or a case of DCI.

Patent Foramen Ovale (PFO)

Before taking up SCUBA, it might be worth getting tested by a cardiologist for Patent Foramen Ovale (PFO). The procedure takes about one hour. Depending on whom you ask, PFO afflicts 5-15 percent of the population and increases the risk of DCI by a factor of three. PFO is a disqualifying condition for U.S. Navy divers.

I asked a cardiologist friend to explain this and here is what she said:

A Patent Foramen Ovale (PFO) is a small hole between the right upper chamber of the heart (right atrium) and the left upper chamber of the heart (left atrium). It is covered by a flap of tissue on the right side of the heart so that there is not usually continuous flow. It is a vestigial structure from embryonic development. In the developing fetus, oxygenated blood comes from the mother via the umbilical cord into the venous system of the fetus. In order for the tissues to get adequate oxygen, the blood is shunted from the right atrium (venous side) to the left atrium (arterial side) via the foramen ovale. At birth with the first breath, the abrupt pressure change closes the foramen ovale. However, in 10-15% of the population, this hole does not completely close.

A PFO is diagnosed by a cardiac echocardiogram which is an ultrasound of the heart. Rarely can blood flow be seen across the PFO as it is usually too small, so agitated saline bubbles are injected through an IV catheter in the arm and these tiny bubbles can be seen crossing the PFO on the echocardiogram. There is no risk to the patient with this test.

The majority of people will never know they have a PFO as there are usually no medical consequences. They are at slightly higher risk for having a stroke compared to the general population, but there are no preventative steps taken unless a stroke happens. There may also be an associated with migraines. Current studies are being conducted to determine if closing the PFO with a small closure device will make a difference in these patients.

The one group of patients where a PFO might make a difference is in divers. The danger is in the potential to develop small bubbles in the venous system either during ascension or during decompression. These small bubbles can cross over into the arterial system and cause decompression illness (DCI). It has also been suggested that divers with PFOs can have MRI evidence of multiple brain lesions. Several studies have suggested that divers with DCI have a significantly higher incidence of PFOs than the general population.

If you are a diver with a PFO you should be aware that you are potentially at much higher risk for developing DCI. Some physicians will recommend that you not dive at all. Other recommendations include more conservative dives and certainly no dives that require decompression stops. Also, the newer oxygen-rich gas mixtures [Nitrox] may also help although there is no conclusive data.

After my experience with DCI, I was tested for PFO. The test was negative, i.e., I should have had half the risk of DCI of a person in the general population with an unknown PFO status.


Oh yes, the money

One of the refreshing things about Townsville General Hospital is that they treat the patient first and worry about the money later. It was only after three days that they gently told me that they'd been given the brushoff by Blue Cross when they inquired as to whether my treatment was covered. They made all the phone calls back to the US so that I wouldn't have to be bothered. The total bill was about USD$2500, which I paid by credit card. Lesson: if you're American and want health care, you really do have to be rich, even if you're insured in theory..

More important than the money was the warmth of the staff at Townsville General. They ordered lunch for me the first day without being asked. They anticipated my questions and needs. There were no lengthy bureaucratic waits or procedures. The staff tend to dress casually and don't try to distance themselves from the patients. It sucks to be ill (you can't say "sick" in Australia because it means vomiting) but if you're going to be ill there really isn't a better place than the hyperbaric unit at Townsville General Hospital.

Am I going to dive again?

Dr. Griffiths says that I can SCUBA dive again in six weeks. The people that get DCI on their certification dives are told that diving isn't for them. But there are plenty of people who do hundreds of dives, get DCI randomly, and then go on to do hundreds more dives happily. Do I think I'm prone to DCI? Obviously to some extent. I did not have any of the risk factors mentioned in the SCUBA books except for fatigue. I'm not a drinker. I'm not grossly overweight. I'm not really old (nearly 37). I was careful to drink a lot of fluids throughout my boat trip. On the other hand, I've dived successfully in the past.

Some of the factors in my favor on the 11 dives that I did in 1992:

So if I absolutely had to dive, I'd be willing to risk another full month of hospital treatment, convalescence, and imprisonment in Australia. But who absolutely has to SCUBA dive? Most of the good coral reef sights are within 10 meters of the surface, oftentimes closer to 5 meters. And the shallower they are the more vibrant the colors from sunlight. You can see these sights just floating on the surface with a snorkel and see them well by getting good at free diving (the dive instructors on Spoilsport would regularly free dive down to 15 meters to secure lines and oftentimes to 30 meters or more for fun). I very happily snorkeled a full mile across a bay in Hawaii once and then snorkeled a mile back in the other direction. I saw eagle rays, sea turtles, and a school of dolphins. The beauty of the snorkel is that you can breathe while floating at your natural level. So you can just stop and rest at any time. Still, if you're lazy or out of shape SCUBA is a good crutch for getting below the surface but being out of shape is probably an increased risk for DCI.

SCUBA is essential when you need to remain in a fixed position underwater. If you want to be a great underwater photographer, you'll need to SCUBA dive. To rescue a diver or salvage a sunken item you'll need to SCUBA dive. SCUBA is good when the surface is rough. You can descend to 5 or 10 meters and be out of the surge and also not have to worry about getting water into your snorkel. If you love visiting wrecks (sunken ships), SCUBA is probably going to be required. Most wrecks are fairly deep and most people will have trouble getting good enough at free diving/snorkeling to visit them unaided.

So my plan for future underwater sightseeing is the following:

An ideal fit to this plan is some kind of tropical lagoon where the hotel room is right on the beach and the reef is swimming distance from the beach. If I were to SCUBA dive, I'd want it to also be under these same conditions. I'd do it once or twice on any given day, using Nitrox (see below) and following the most conservative tables that I could find. It would have to be in a place where I could easily get a medi-jet or helicopter flight out to a decompression chamber (it turns out that any jet interior can be compressed to sea level; they just need to fly somewhat lower (burns more fuel) and compressed the interior harder (also burns more fuel)). If I had to be home by a specific date, that decompression chamber would itself have to be in a place with a road or rail link to my home in Boston.


Remember that any dive involves a risk of decompression illness. There is some research that suggests that, based on examination of burst retinal blood vessels, subclinical tissue damage occurs after every SCUBA dive.


October 2000 Epilogue

It is now two months since I left Townsville General Hospital. I think that I'm just about completely recovered. One of the difficulties in recovery has been that the symptoms of DCI are so varied and subtle. Two weeks after leaving the hospital, I caught what I think was either food poisoning or a stomach flu in New South Wales. I had a headache and was tired. Was it from the bug or a relapse of DCI? It was impossible to say and therefore much more worrying than a normal stomach problem.

The flight back was horrible. I did not get any obvious DCI symptoms but I had terrible stomach and body aches by the time the LA to Boston flight was getting close to landing. After a long weekend in Boston I still had headaches. My doctors at the MIT HMO scheduled a brain MRI. It turned out normal and about a week later the headaches subsided.

Bottom line: about six weeks of pain and terror that my mental processes would be permanently compromised.

Reader's Comments

Test message.

-- Philip Greenspun, June 23, 2015
This is an interesting narrative because it points out all of the uncertainty inherent in diagnosing decompression illness. There was no single objective test that proved you had it and I imagine there seldom is. Instead the diagnosis hinged on subjective self reported, vague neurologic signs and a physicians subjective assessment of the same.

I can see how this resulted in non reimbursement from an Insurance company, which is a hazard I never considered.

I think you and the doctor acted with appropriate caution given your history so I think your cautions are good ones. A person should avoid creating such a history.

Its probably best to avoid exhaustion, fatigue, seasickness and too many dives. Its simply not worth the worry.

-- Adam Greenberg, August 30, 2015

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