When considering a return to diving after an episode of DCS, it is important to consider the following:
- Has there been a good response to treatment?
- Are there any residual symptoms and signs attributable to DCS?
- Was the development of DCS consistent with the diving exposure?
- Does the individual have an increased susceptibility to DCS?
- Was there any evidence of associated pulmonary barotrauma?
Evidence supports the existence of bubbles for some days or weeks after DCS and recompression therapy – a function of the slower rate of gas elimination, especially in the presence of bubbles. For this reason, the authors of this text recommend a minimum period of 4 weeks before a return to diving. Bubble micronuclei may exist indefinitely within the tissues only to re-expand with an exposure to an inert gas load.
Patients with incomplete recovery after recompression should be followed up clinically with appropriate investigations, e.g. brain imaging techniques, electroencephalography (EEG), bone scans and neuropsychological testing as indicated by the clinical condition.
If there has been a less than complete recovery following neurological DCS, the recommendation of the authors of this text is that the individual not dive again. Autopsy evidence suggests that DCS may involve greater areas of the brain and spinal cord than are detected clinically – a characteristic of some degree of neurological redundancy. A further insult may result in this subclinical damage extending to become clinically evident. Therefore, the second episode of neurological DCS may result in a significantly worse outcome.
If the episode of DCS occurs after a relatively trivial exposure, a cause for this increased susceptibility should be actively sought (e.g. pulmonary barotrauma, patent foramen ovale). Evidence of pulmonary barotrauma (see Chapter 6) usually renders the individual permanently unfit to dive.
Many episodes of DCS result from a complete disregard for decompression schedules or from simply stretching accepted computer algorithms to their limits. Rapid and frequent ascents and multiday repetitive diving are commonly reported. Before a return to diving, the patient with DCS should be counseled on safe diving practices. Diving according to published dive tables (e.g. the PADI tables) is now exceedingly rare, and almost all diving is controlled by a personal diving computer. Although greeted with some initial skepticism by dive physicians, these computers do not seem to have been associated with a higher incidence of DCS – if anything, quite the reverse, with DCS numbers falling across most jurisdictions.
Safe diving practices
- Use a decompression schedule that has been tested and has a known and acceptable risk of DCS (e.g. Canadian Defence and Civil Institute of Environmental Medicine [DCIEM] tables; see Appendix A) or a reputable personal diving computer.
- Add a depth/time penalty for future diving; i.e. for a dive to 16 metres for 35 minutes use the decompression limits for a 40-minute, 18-metre dive. With a computer, stay well within the no decompression limit rather than dive to that limit.
- Restrict diving to two dives a day, with a long surface interval.
- Have a rest day after each 3 days of diving.
- Perform slow ascent rates.
- Incorporate a ‘safety stop’ of 3 to 5 minutes at 3 to 5 metres on every dive.
- Ensure conservative flying after any diving exposure.
- Consider substituting nitrox (oxygen enriched air) for air, but dive according to the air tables.
There is a lack of good scientific data on when it is safe to fly or ascend to altitude following an episode of DCS. Recommendations vary from 24 hours to 42 days. The bubble micronuclei discussed earlier may expand with altitude exposure, with a resultant return of symptoms. Because many diving destinations are in remote tropical areas, divers with DCS are usually very reluctant and financially inconvenienced if they cannot return home for 4 to 6 weeks, so this is a very real practical problem.
It is the policy of the authors of this text to recommend to these divers that they delay flying or ascending to altitude for 2 weeks if possible, with a preferred minimum of 1 week. These times should be extended for divers with continuing symptoms after recompression.
In rare situations one may attempt to remove asymptomatic bubbles and micronuclei by exposing the symptom-free diver to a few 2-hour sessions of breathing 100 per cent oxygen, before flying, and a further possibility is to charter an aircraft whose cabin pressures are kept at 1 ATA (not within many people’s capability!).