An event that any SCUBA diver tries their best to avoid. A condition every diver trains to prevent, practises skills to avoid and plans their dives to render the risks of it happening almost nil. Nonetheless, it happened to me; a fully qualified, experienced, Rescue Diver. This is my account of DCS and I hope it serves as a warning and an opportunity to learn for other divers.
We decided on a twin-tank (2x100cf) EAN36 dive with "scooters" (DPVs) to get us out to a favourite site of ours off Bass Point, NSW where sand eels are frequent visitors. The dive calls for a scooter ride about 1.5km off shore (15-20min) down to 28m simply following the bottom contours. After about 30min at 28m move west to "3rd Gutter" and follow the bottom up to 18m. Then a slow ascent back up to the gutter and burn off any remaining decompression time before surfacing. We expected to accrue about 10-12min of decompression time from our time at 28m, but the profile takes that into account.
That was the plan and the first half of the dive went relatively to plan for me. There was a strong SE current running which made navigation on the long scooter transits difficult for everyone, not just the dive master. One member of our entourage was testing some new, more "technical" dive equipment and was coming to grips with the different operation of their gear. Even with these stressors, we arrived at the sand eels and enjoyed exploring and photographing the site. When we reached the upper limit of the planned decompression time, we headed for shallower water.
On the transit to "3rd Gutter", the diver with the unfamiliar gear somehow managed to get into an uncontrolled ascent from 20m! The rest of our dive group were a few body lengths in front of us and unaware of the unfolding drama. I was presented with a difficult decision; chase the distressed diver and bring them back down to the safety of 20m, or leave them to their ascent, then carry out a controlled ascent (with deco stops) and deal with whatever state the other diver was in on the surface? I chose the former, knowing full well I could end up with DCS myself, and rapidly ascended to almost 7m before positive progress was made back towards the bottom. I assisted the other diver to get control of their buoyancy and waited on the bottom for the others to double back. We didn't see the others and doubling back accurately would've been difficult due to the current.
After a suitable waiting period, I decided that with the remaining 100bar in our tanks, we should deal with deco time, execute a controlled ascent and surface. From there we could get a bearing to our shore entry/exit point and proceed back. This is exactly what we did. I shot up my surface marker buoy (SMB) and ascended up the line following all instructions on the most restrictive computer between myself and the other diver. We even added an extra 5min at 5m safety stop before our mandatory deco stop at 3m.
When we had our bearing back t shore, we descended to 3-5m and scooted back to our exit point without incident.
In hindsight, I was experiencing mild symptoms almost immediately as I exited the water. Even though it was a 115min dive, I was surprised at how weak I felt trying to support my own body weight and gear as I climbed out up the rock. I was also a little more unsteady on my feet, which was unusual for me. Both these warnings I dismissed as simply being a result of long, stressful and physically demanding dive. Later during lunch and debrief with the other divers I started feeling "distant" and "disconnected" from the events before me coupled with increasing sense of extreme fatigue. All the while mild discomfort was building behind my knees and in my left elbow.
When I arrive back home, approximately 3hrs after the dive, the mental impairment was starting to be more and more evident. I would walk into a room, and have no idea why I was there. I would look around a room and wonder how the hell do I get to "another room" - this is a house I have lived in for over 12 years! This coupled with the increasing joint pain, and difficulty focussing on anything made me (finally) join the dots and I immediately called the Diver Alert Network (Asia-Pacific) and spoke to one of their doctors. He was confident I was suffering DCS and should get to the nearest hospital immediately. They called ahead and the hospital was expecting me. This was very reassuring.
On arrival in hospital they started me on oxygen therapy and commenced assessment. After assessing my symptoms they contacted the hyperbaric medicine unit at Prince of Wales Hosptial (Randwick, NSW). After being on 100% oxygen at sea level for several hours with a saline drip there was no improvement in my symptoms, and some continued to deteriorate. The decision was made to transfer me to the hyperbaric unit at Prince of Wales. I was conveyed by intensive care ambulance to to Sydney via the most direct route. Unfortunately, this took me up Mt Ousely which tops out at almost 1200ft above sea level (~40hPA pressure drop from sea level). During this portion of the transfer, symptoms escalated significantly and the pain I experienced as a result was excrutiating. I've dislocated my right shoulder 5 times, and I would rather experience all 5 simultaneously than revisit the pain that night! Make no mistake - DCS can hurt. A lot. The medical staff on the ride with me did a great job of managing the situation and I soon arrived at the hyperbaric unit.
Another assessment was done and I was quickly transferred to the hyperbaric chamber and commenced the first treatment which would last 5 hours. Here's where the divers reading this might be a little surprised; the chamber is pressurised to 18m (approx 180kPa) where we spend the whole time breathing 100% oxygen on a demand, non-rebreather mask (I say "we" because another diver was in there with me - unrelated incident). This is well in excess of the 1.4 partial pressure of oxygen we use for dive planning. The good thing is, I got to experience some of the mild effects of oxygen toxicity (specifically nausea, altered sensation/tingling, visual disturbances and auditory anomalies). On about the fourth hour the chamber was depressurised to 140kPa and further to 90kPa before terminating the first treatment at the five hour mark. Lucky for me, I was still pretty wiped out from the morphine I was given in the ambulance and slept or dozed through most of it.
The second treatment was a solid two hours at 14m on 100% oxygen again with occasional "air breaks" where we could remove the masks. Again I had the pleasure of some oxygen toxicity specifically in the form of fairly acute nausea. Thankfully, for both treatments, the medical staff had ondansetron on hand which was very effective in my case.
The third treatment was a carbon copy of the third, except without the air breaks and for me, the oxygen toxicity side-effects (yay).
Luckily all my symptoms were either "cured" or at a the point where no further improvement was experienced. This effectively signals the end of the hyperbaric treatments. However, this is not the end. There are a few things to be aware of after this sort of treatment:
- You are recommended to stay in the Sydney basin for two weeks.
- You cannot fly, go over the mountains, do rigorous exercise or other strenuous activity for the two weeks after treatment.
- You cannot dive again until you have been reviewed by the doctors at the hyperbaric unit.
I live on the south coast which is beyond the mountains I was not supposed to cross - this was a problem. However, I pulled out a topographic map of the Sydney basin, identified the spot heights in the basin then found a route home that kept me under those spot heights. It's called Sydney to Wollongong via the Royal National Park. Whilst this wasn't welcomed by the medical team managing my treatment, they granted me a once-off reprieve to allow me to return home, only on the previso I stopped in the Illawarra coastal fringe for the next seven days. I think that was a workable compromise which was medically safe in my circumstances. It shouldn't be seen as a green light for any South Coast NSW divers to "game" the system.
The dive was well planned and well supervised by the Dive Master involved. I've dived with them many times before and always been impressed by their professionalism and genuine concern for the divers in their care. However, diving with a group of people who are confident in both their own capabilities and the skills of their fellow divers led to a "schooling fish" type situation. We were all safe, as long as we stayed together. When people strayed outside the "group" there wasn't an immediate concern to get them paired back up with their buddy. The buddy system works - use it properly and things go a lot safer and smoother.
Another aspect of the dive that should've been addressed before getting in the water; taking unfamiliar gear (like an entire BCD/tank/harness) on a deep, decompression dive with scooters is probably, in hindsight, a bad idea. I dont care if you're the reincarnated Jacques-Yves Cousteau take your new gear on a shallower, non-technical dive to get familiar with its operation. Scooters are notoriously tricky to get your buoyancy just right and new gear just compounds the problem.
The onset of symptoms, in my case, were apparent when exiting the water (although I didn't recognise them as such). However, the way DCS is taught in the various courses I've done suggest joint pain is one of the first and definitive symptoms. However, for me the joint pain came much later. It was the confusion, disorientation and visual disturbances that really stood out in my case. This again leads to a small piece of advice; pay careful attention to any divers who have had anything other than a "normal" dive - their symptoms could be slow to develop and subtle. Ask them how they're feeling, monitor their behaviour; are they engaged, articulate, alert? Is their behaviour different to "normal"? Your buddy is your responsibility - take it seriously.
You might be wondering what happened to the diver I assisted - they were fine. Absolutely no symptoms of DCS. However, they had been fighting their ascent before I noticed their predicament, and I had to play "catch up" making the rate of my ascent significantly faster than theirs. The doctors in the hyperbaric unit are confident this rapid ascent was the trigger for my DCS. Despite returning to the depth I started at (~20m) the majority of my residual nitrogen was absorbed at 28m. This meant the rapid ascent caused nitrogen to come out of solution but not go back. Everything after this simply reduced the danger but was never going to prevent DCS from developing.
The key thing is, DCS affects people in different ways. What you can get away with, I may not, and visa versa. I followed all the instructions on my computer and added some extra for margin - it wasn't enough. A rapid ascent is a very dangerous thing espeically if you have banked any deco time. Learn from my experience.
Having said all this, as a rescue diver, if I was faced with the same circumstances again, would I do the same thing again? No. Uncontrolled ascent with deco time is a guaranteed recipe for severe injury or death. A rapid ascent is dangerous and can cause DCS. However, the first rule of rescue is: DON'T BECOME THE NEXT CASUALTY! I'd have an injured diver to deal with (or worse), but I am not putting myself in a position where I end up in the pot instead of the person I'm trying to help.
This is not intended as a training guide and shouldn't be used as a prescriptive guide for dealing with dive emergencies or DCS. This is a retrospective for others to see through the eyes of another diver the experience of DCS within the context of how it occurred. Always dive within the limitations of your training, dive tables and/or computers.