May 2002 newsletter

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Diving incidents

Last week another diver drowned, this time on the West Coast of Scotland. The risks of diving remain ever present while the nature of diving as a sport is gradually changing. Previous incident analyses showed that fatalities usually resulted from technical rather than medical complications. With increasing use of gas mixtures, rebreathers, and dives involving wreck penetration or extreme depths, it is likely that the fatalities will continue.
Looking at the figures from Scapa Flow, it is possible to estimate the frequency of incidents since the dive boat operators record the number of divers. The incident statistics were then compared to the total number of divers, and the number of dives made. This revealed that the incidence of decompression illness requiring treatment was 0.49 per 1000 dives. This may not sound impressive, but further analysis confirmed that 1 in 102 divers was involved in a significant accident. This frequency is unacceptably high and confirms that the main problem is diving training and mistakes made during the ascent. The most common reason for mishap was missed decompression stops.
Scapa is certainly a mecca for divers and there may be pressure on divers to continue diving in conditions which may be outwith their level of experience. Most dives are moderately deep (30-40 m). The Scottish Sub-Aqua Club incident reports for last year confirmed two divers who were involved in recompression therapy– in both cases a midweek break in their diving would probably have been enough to prevent the accident. Neither diver had evidence of an underlying condition likely to increase the chance of decompression illness (both underwent echocardiography with contrast to exclude a patent foramen ovale). The diving organisations therefore need to put their own house in order, and shift focus to improve basic dive training, particularly emphasising safe decompression practice.
Many referees see divers following an episode of decompression illness and this is a good opportunity to reinforce the message. Divers should be advised that they have an increased risk of a further bend, and that they are likely to have caused permanent damage already. A limited number of divers should be considered for further investigation particularly if the incident occurred within recommended limits, if symptoms were mainly neurological or skin bends, and if symptoms started after a short period following surfacing (usually 5 minutes). 60% of such individuals would be expected to have an underlying patent foramen ovale.
Alarmingly, the incident frequency in Scapa Flow has increased significantly from the previous year (1 in 178 divers) and it must be hoped that divers (and the dive boat operators) will take heed of the risks involved.

For more information
Diving accidents in sports divers in Orkney waters. Trevett AJ, Forbes R, Rae CK, Sheehan C, Ross J, Watt SJ, Stephenson R. Scott Med J 2001;46:176-77

Misleading PFO data

A paper published by Wong and Wright in SPUMS journal (2001;36:62-69) reports that a PFO was found in 10 divers out of 36 treated for DCI in 2000. They concluded that the 28% prevalence in their series is close to the incidence of autopsy demonstrated PFO. This was reiterated by Dr Knight in his editorial. The association between PFO’s and DCI looks even less impressive when one reads that in one of their ten cases, the diagnosis of PFO is entirely speculative because the diver did not have contrast echocardiography, and a further two had findings on contrast echocardiography more suggestive of a pulmonary shunt.
To interpret these observations we need to be sure that the other 26 divers had negative echocardiograms, to know the types of DCI they had, and to know the PFO detection rate of contrast echocardiography in normal controls in the hands of the operators involved in this report.
Responding to these points, Dr Wong said “I do not look for PFO in all our patients with DCI, but only in those we suspect to have PFO’s… We check those divers who present predominantly with cerebral or cognitive symptoms, present with spinal symptoms, or who have performed beign profiles which do not normally give rise to DCI. Of the 26 divers, we only tested a few of them. They presented with musculoskeletal symptoms… I have not looked in divers who have not been bent” Clearly one cannot place reliance on the prevalence rates quoted. Because Wong and Wright found right to left shunts (PFO’s or pulmonary shunts) in all nine of the individuals with neurological DCI tested, and the tenth was not tested, the prevalence rate in their small series was 90 or 100% in cases with neurological DCI, but with wide confidence intervals.
It is impossible to draw conclusions about the 26 cases with non-neurological DCI because the majority were not tested. Unfortunately the SPUMS journal will not publish a correction to this paper. The editorial position is clear that PFO’s are not related to DCI.
It is important that referees are aware of the limitations of this paper, and that the conclusions are inconsistent with most of the published evidence in properly controlled studies.

For more information
Please contact Dr Peter Wilmshurst at the Department of Cardiology, Royal Shrewsbury Hospital, Mytton Oak Road, Shrewsbury, SY3 8XQ.

Website changes

The website has been updated recently to include PDF versions of the newsletters. Medical referees can access the full version including anonymised case reports through the registered users section using the password previously issued. If you have forgotten the password please contact the secretary. Please check your contact details on the website or at the end of the newsletter and let us know of any changes. All cases referred to the committee since 1999 have been entered into the database and this can be searched (again in the registered users section). This is updated after every committee meeting.
What else would you like to see in the website? We piloted a forum for a time but there was very little activity seen in this and it has now been withdrawn. There are so many diving message boards on the internet that there seems little point in setting up another one. Each of the diving organisations has an active forum which may be of interest. We have avoided providing an advisory service for divers using the website because of the workload involved, and also because it is rarely possible to assess the nature of the problem adequately. The website is primarily a source of information for the medical referees, and we aim to keep this up to date as frequently as possible.

Images in diving medicine

The images below show a contrast echo performed in a young man interested in taking up diving. Clinical examination suggested evidence of a ventricular septal defect with some signs of right heart strain. Echocardiography confirmed purely right to left flow of bubbles through the VSD with severe pulmonary hypertension. He has been advised not to dive.

Image before injection of contrast

Agitated saline appears in right heart and crosses into left ventricle (right-to-left flow)