The fact that some authority has promulgated a therapeutic table does not make it effective, and there have been many modifications and deletions made to these tables during the professional lives of these authors.
As a good general rule, if symptoms recur during treatment, both the recompression schedule and the clinical management should be questioned. The physician should ensure that there has been adequate recompression and supportive therapy, including correct positioning, rehydration and so forth. The diagnosis should be reassessed, considering the following:
- Pulmonary barotrauma and each of its clinical manifestations (see Chapter 6).
- Complications of DCS, affecting target organs.
- Non-diving general medical diseases.
Nevertheless, patients with DCS do sometimes deteriorate during recompression therapy. The composition of the breathing mixture should be confirmed, as should the efficiency of the mask seal.
One air table (USN 4, RN 54) frequently caused DCS in attendants who did not even have a nitrogen load to start with. It is difficult to understand how it could then improve patients at the shallow stops. Oxygen is now used by both patient and attendant from 18 metres to prevent this problem. The short air embolism Table 5A, which many of us believed to be a contributor to deaths during treatment, has been removed from the US Navy Manual.
If similar and significant symptoms recur, they must be presumed to represent a reexpansion of a bubble, which was not completely removed, and treated accordingly.
Occasionally, there may be other explanations, such as:
- The inflammatory tissue reaction to the bubble.
- Lipid, platelet or fibrin deposits or emboli.
- Re-perfusion injury.
- Redistribution of gas emboli.
Although redistribution could be expected to respond to recompression therapy, it would be a great coincidence if it were to reproduce the same symptoms as the original lesion.
Recurrences of the original symptoms or the development of other serious symptoms should be seen as resulting from inadequate treatment or caused by aggravation of the problem by re-exposure to nitrogen at depth or on the surface. Recurrence of symptoms requires surface oxygen (if mild), hyperbaric oxygenation or a conventional therapy table.
Paraesthesia and other symptoms developing while undergoing recompression therapy may reflect the development of oxygen toxicity (see Chapter 17) and therefore are not necessarily an indication to extend the therapy.
It is not necessary to recompress repeatedly for minor and fluctuating symptoms, unless these symptoms have some ominous clinical significance. Minor residual musculoskeletal or peripheral nerve disease is very common, and chasing these symptoms to obtain a complete ‘cure’ becomes demoralizing and exhausting for both patient and attendants. It has become common practice to follow a formal recompression table with an ‘oxygen soak’ (typically a 9- to 14-metre oxygen table for 1 to 2 hours) on the following day, to reduce the incidence of minor persistent symptoms. It is probable that most of these symptoms are transient and more anxiety provoking than functionally important.
With spinal cord or cerebral damage, it is common practice to continue with intermittent hyperbaric oxygen therapy until all subjective and objective improvement has ceased. These authors use standard oxygen tables, as described earlier, on a daily schedule. Other regimens may be applied, but the use of repeated diving therapeutic tables, such as extended Table 6 (USN) with its hyperbaric ‘air breaks’, is illogical and has increased complications to both attendant and patient. It is very unusual for even a patient with serious case to receive more than five or six treatment tables.
Both recompression and altitude exposure alter blood gases (oxygen, carbon dioxide and pH) and may affect these minor symptoms, presumably by affecting marginal ischaemia or nerve irritability from myelin sheath damage. Patients should be reassured that such minor symptoms – often persisting for weeks to months after DCS – are not uncommon and do not require intervention.