Recompression treatment and hyperbaric oxygen (HBOT) are standard treatment for decompression illness. While it is generally accepted that sooner recompression is associated with better outcomes, the urgency of treatment may not be same for all cases. Looking for practical guidelines we regularly consult published case series. Three case series presented at EUBS 2017 may be used to illustrate problems with such approach.
In the first paper1, authors compare outcomes in 24 mild cases of DCS treated in an on-site facility with an average delay to treatment 7.8 hours, to outcomes of 29 mild cases treated at an off-site facility with an averaged delay of 42 hours. Cases treated on-site almost all resolved completely after a single recompression (US Navy Table 6 or US Navy Table 5) and only one case needed an additional treatment. Of 29 cases treated off-site, only 17 resolved after first recompression, eight resolved after additional 1 to 5 tailing treatments, and four were left with some residual symptoms after tailing treatments. The authors suggest that this data supports rapid on-site treatment for all cases. In my opinion, there are two issues with this data.
First, the two datasets may not be comparable. Diagnostic criteria and outcome evaluation methods were not explicitly reported and may have been different in two facilities. Cases treated off-site may have left the site before symptom onset and travel may have contributed to the DCS. Second, the sample size is small enough that apparent differences may have been effected by chance.
The second reported case series2 includes 31 divers treated for DCS or AGE. Patients were thoroughly evaluated after the treatment and two to three months later. The evaluation included explicit inquiry about 20 separate symptoms and overall quality of life (VAS scale 1 – 100). At discharge and follow up 45% and 46% of patients respectively were free of symptoms. The most frequent persisting symptoms were tiredness, tingling, difficulty concentrating, and ear ringing.
The third presented series included 12 cases of inner ear DCS3. All patient were harvester divers and most dives included some omitted decompression time. The average time to treatment was 11 hours (5 – 72). Some cases received an on-site in-water recompression but still needed repeated HBOT. Patients received between 1 and 25 HBOT sessions. Eight cases recovered completely, three had residual symptoms and one was lost to follow up. Interestingly, the outcome was not apparently affected by the time to treatment.
These three case series with different case mixes could not be compared directly to each other, but they are a good reminder that the ability to generalize findings from small case series is questionable, particularly when it comes to the question of how the delay to treatment affects the outcome. This research also supports the call for a more standard and thorough description of case series, so we can better compare case studies, and evaluate the data.
Wang Z. Efficacy of early treatment of decompression sickness in an on-site facility vs. delayed treatment of decompression sickness in an off-site facility. P 49.
Johnsson J, et al. Recompression treated decompression illness signs and symptoms – initial findings and 2-3 months follow-up. P 72.
Calderon J. et all. 12 cases of vestibular decompression sickness with clinical monitoring and recording of video. Hospital Ancud, Chile.