Tragic Results of Not Exhaling During Your Ascent


O2 onboard your diving boat can save your life

An Interview with Dean Syme

By Dave Moran

In January 2015 diver Dean Syme developed a Cerebral Arterial Gas Embolism (CAGE – was previously called Air Embolism) which has affected his life dramatically. In the following interview he gives us an insight into his journey from enjoying his love of diving through to his long recovery and his recommendations to all divers and boat owners.

Dave: Dean, how long had you been diving before the accident?
I started diving early October 2014 when I completed a PADI Open Water diver course. I had completed about 12 dives, the last being in the Marlborough Sounds, about two weeks before the accident. All were normal, uneventful dives.

Take us through the day you developed CAGE.
I had been working really long hours harvesting on the farm so had no time for diving. So when a morning came free I was eager to go for a dive. In retrospect, I really was too tired to be diving that day. It hadn’t occurred to me that tiredness was a potential diving risk factor. I was diving with my buddy William Sewell. Mark Butler was boatman. Our first dive was normal to a maximum depth of 18m.

After doing the required surface interval [time] we commenced our second dive, which took us to 19m briefly. We began our ascent from 14m having noticed that we were down to 30 bar. According to both our dive computers, everything was fine.

When did you feel that something was not right?
I was within the last metre before breaking the surface, when I felt my legs were going numb and tingly! I broke the surface and immediately called for help, advising the guys that I could not feel my legs and asked Mark to throw me a rope. Will came over and further inflated my Buoyancy Compensator (BC). The last thing I remember was Will and Mark getting me into the boat.

What action was taken once people realised that you may be suffering CAGE or Decompression Illness (DCI)?
Will and Mark waved down Liquid Asset, a diving and fishing charter boat belonging to Brian Franks. I was transferred to his boat. Brian had just finished a dive safety briefing and was now putting it into practice! He had oxygen on board, administering it immediately. Brian requested the Westpac Rescue Helicopter, which met us in Akaroa.

What was your treatment once you arrived on shore?
I was airlifted to Christchurch hospital. I was responsive to some commands but I was unable to focus or communicate or have the full range of movements in both legs and one arm. I was also suffering hypothermia. I was put into the hyperbaric decompression facility for treatment. The medical team were able to retrieve my dive profile from my dive computer.

The cause of the accident was due to a simple mistake of not exhaling air at some point during my ascent causing the air in my lungs to expand resulting in air bubbles being pushed into the small veins within my lungs. These bubbles passed directly into my arteries and were carried to my brain resulting in my brain injury. During my treatment it was found that I have a Patent Forman Ovale (PFO), a hole in my heart that didn’t close at birth. PFO is present in approximately 20 percent of people. It is not thought this was the cause of my injury but it is another way in which bubbles (formed from dissolved nitrogen in the veins) can enter the arteries in DCI.Bends-1

My first treatment in the decompression chamber was for five and a half hours. I became increasingly agitated during the treatment and was put under a general anaesthetic for a MRI scan of my brain, spine and entire vascular system. The scan showed extensive damage in both sides of my brain with the majority on the left side. The damage indicated that I was cortically blind, likely to have cognitive issues and had significant motor function impairments. I remained sedated in an induced coma and on a breathing ventilator. I received a further four decompression treatments over the next four days.

A week later the sedation was reduced and I woke up. Despite developing a severe infection in my lungs, I was able to take over breathing on my own and stunned the medical staff by my coherence, memory and cognitive functioning. I was able to see, hear, talk and recall the details of the incident until getting into the boat. I was discharged from hospital four days later. I had rehabilitation at Laura Fergusson Centre where I spent three months strengthening my arms and legs, relearning how to move, stand and eventually walk. The staff were supportive, kind and encouraging. They really focused on getting me to be independent in my own home.

Do you have any ongoing problems due to the CAGE?
I have contact with my physiotherapist about once a month, who assesses my improvements and sets goals for me to be able to get back to full-time work on the family farm. I have impaired strength, agility, balance and sensation in my legs, all of which are very slowly improving.

What do you think are the main points that you would like to pass on to divers so that they avoid the experience you had?
My wife Sara and I strongly believe that these things should be taken on board by others, which is why we are sharing this story. Doctors were amazed that they were able to treat me, because most divers in my position do not make it to hospital. My survival will hopefully encourage more people to carry oxygen on board their boats and be trained in its administration. This simple action could help divers suffering from CAGE or DCI for a better chance of survival and long-term recovery.

Further, we believe it is vital to have a thorough understanding of diving practices; knowing what to do and what not to do and understanding how things can develop quickly even when you follow all the rules. Always ascend with plenty of air. Don’t go diving if you are fatigued. Have good reliable equipment. Someone waiting for you to surface.

Oxygen – it is the first and only treatment for diving injuries. I would not be here without it. I was lucky that Liquid Asset had oxygen and the capability to administer it. Radio communications are vital.

Next January Sara is walking from Akaroa to Christchurch with a group of family and friends, to raise money for the Westpac Rescue Helicopter and to raise awareness for safe diving and boating practices. Donations to the Air Rescue helicopter at:


Comments by Associate Professor Simon J. Mitchell, Consultant Anaesthesiologist and Diving Physician

A patent foramen ovale (PFO) can be detected in around 25% of adults. Large PFOs are less common, occurring in around 5–10%. There is an association between severe neurological DCI and large PFO. For example, about 60–80% of divers who suffer this sort of DCI will be found to have a large PFO; a much higher proportion than found in the general diving population. When people consider these sorts of figures at face value it may seem logical to suggest that all diving candidates be screened for a PFO. However, this is an issue that deserves very cautious interpretation. Despite the high prevalence of PFO, serious neurological DCI remains rare; occurring in approximately once out of 20–40,000 dives. This has several implications. First, since PFO is common but serious DCI is rare there must be other contributing factors that need to align to cause a problem. PFO is clearly not the whole story and indeed, serious neurological DCI can occur in divers without a PFO. Second, general screening for a lesion that is a risk factor (and certainly not the sole cause) for a rare problem can be difficult to justify, particularly where the test is invasive and expensive. A PFO test involves having a heart ultrasound while a solution of small bubbles is injected into the veins to see if any cross a PFO when they reach the heart. Can you imagine what would happen to the diving industry if the notion of general screening for PFO before a dive course ever caught on or, even worse, was mandated? A contemporary (2015) review of the evidence and consensus of experts did not consider general screening for PFO to be justified or necessary1. Sufferers of migraines with a neurological aura are more likely to have a large PFO, and consideration could be given to screening diving candidates with this problem1.


  1. SMART D, MITCHELL SJ, WILMSHURST P, TURNER M, BANHAM N. Joint position statement on persistent (patent) foramen ovale and diving. South Pacific Underwater Medicine Society (SPUMS) and the United Kingdom Sports Diving Medical Committee (UKSDMC). Diving Hyperbaric Med. 45, 129-131, 2015.




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