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Evolution and Performance of The Comex Tables Author: Jean Pierre Imbert
Note: This document was first printed in the Divers Alert Network (DAN) recompression chamber network newsletter in February 2023. As a reminder, DAN is an organization committed to the health and well-being of divers, with research, medical services, and global- response programs that create an extensive network that supports divers with vital services such as injury prevention, safety and educational programs, and lifesaving evacuations. Introduction France has a long tradition in diving, and as a consequence, in treating bent divers. The first account of recompression treatments was published in 1854 by Pol and Wattelle who reported 16 cases of caisson workers experiencing CS. Pol and Wattelle worked in coal mining in the north of France. Pol was the engineer and Wattelle, his friend, a medical doctor. Pol ran pressurized work to around 3 atm to prevent water ingress in the mine shafts and of course witnessed many cases of DCS. Dr. Wattelle described how he and Pol tried to understand the causes and attempted to cure the unfortunate workers. They finally used recompression to ease the symptoms. Pol was involved in the treatment of his workers and eventually died from consequences of severe decompression sickness after he had attended several recompressions with his workers. In the paper, written 10 years later, Dr. Wattelle recalled the dedication of Pol and concluded by the sentence: “you only pay when you leave”. In 1878, Paul Bert published his famous book, “La Pression Barométrique”, where he demonstrated with dog experiments the benefit of oxygen in reducing bubbles produced by a decompression. By the turn of last century, the development of caisson works permitted the edition of early treatment protocols. However, it was not until 1933 that Dr. Benkhe structured and edited the first US Navy treatment tables. In 1965, Dr. Workmann conducted the necessary revision work to give the treatment pro- tocols their final form. Meanwhile, Dr. Val Hempleman designed the Royal Navy Treatment Procedures. The US Navy treatment tables, and in particular the Table 6, have since remained the most used protocols, and the development of commercial diving has permitted the publication of alternative procedures. At the time, Dr. Xavier Fructus was the medical advisor of Comex, a leading commercial diving company located in Marseille. He spent many nights on the phone, assisting work sites involved in divers’ treatment because at the time, the DCS incidence rate was around 10-15%. Based on his operational experience, Dr. Fructus developed in 1974 the first version of the Comex Medical book, which significantly differed from the Navy’s practice. It was designed for a diving supervisor or a caisson master, lost on rig on the other side of the world with a small chamber, a few gas quads, and a fellow diver to treat, trying to establish a phone communication with Marseille. The 1974 Comex Medical Book The early 70’s offered the diving companies the North Sea market for which they were not really prepared. This was an exciting period for the development of diving procedures, but also a time where a lot of divers suffered decompression sickness. Facing this situation, the medical doctors in charge started challenging the idea that prevailed at the time: first recompress the patient to the depth of relief. This concept was behind some deep British treatment tables and has remained underlying the US Navy table 6A, 1A, and 4 with their recompression on air to 50 msw (165 fsw.) However, it was known that in many cases, after the symptoms were relieved, the patient would be too deep, and his return to surface became a second problem. The alternative was to restrict the recompression depth and wait until the symptoms gradually resolved. In 1974, Dr. Fructus edited the Comex Medical Book as a blend of the US Navy and French Navy tables. He introduced the revolutionary Table Cx30 that included a 30 msw maximum recompression. His idea was to avoid deeper recompression, which he formulated as “give time to time”. For surface supplied operations, this first Comex medical book included a long series of treatment tables ranging from 12 msw to 30 msw: The Cx12 table, with two hours oxygen breathing at 12 msw, was the starting point of all the treatments for pain-only symptoms. The Cx18C, with 40 minutes oxygen breathing and the Cx18 L, with 60 minutes oxygen breathing at 18 msw (a short and standard version of the USN Table 6) was designed as a fallback for the Cx12. The Cx30 table, which included 40 minutes at 30 msw on 50/50 gas, was the ultimate table for the recompression of severe DCS cases. The Cx30 was derived from a 30 msw recompression table initially designed by Prof. Bathélémy at the French Navy Diving Department. In the 1974 edition of the Comex medical book, the Cx30 existed in several versions, Cx30, Cx30 A, and Cx30 AL (60 minutes on mix, or 90 minutes on air after an oxygen convulsion). The instructions associated with the Cx30 tables only specified the oxygen percentage without indicating the nature of the treatment mix. Dr. Fructus kept the option for operational flexibility so that people on board could use whatever 50/50 nitrox or heliox they had available. However, he admitted that he already suspected that heliox was particularly efficient in the treatment of air DCS. The 1986 Comex Medical Book In the 80’s, operations changed in the North Sea from platform installation, which requires bottom work performed in saturation, to inspection and maintenance jobs, which mostly concern shallow structures and air diving. Dr. Philip James joined the Comex company when air diving suddenly increased and recruited many severe neurological DCS cases. Dr. James was on the front line and directed a lot of Cx30 tables, which he systematically performed using 50/50 heliox. In 1986, there was a drastic revision of all the Comex diving manuals, associated to the introduction of new air tables, new saturation procedures, and of course, a revised set of treatment tables. Dr. Philip James was instrumental in this revision and wanted to simplify the Comex treatment procedures. He first reduced the DCS type identification table to only two options, simple and serious, as for Type I/Type II in the US Navy manual. Then, Dr. James reduced the number of treatment tables by combining the Cx18C and Cx18L tables into a new Cx1886 table similar to an extended USN Table 6 with 90 minutes oxygen breathing at 18 msw. This way, three tables only could cover DCS occurrence after surface-supplied diving.
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The first comex medical book
The Comex 1974 Medical Book and its table for identification of DCS
The second comex medical book
Comex 1986 Medical Book: Table for DCS Type
Comex 1986 Medical Book: Treatment chart for symptoms after surface-supplied diving
Finally, Dr. James relooked the Cx30 table and gave it the format that it has kept since. 50/50 heliox was specified, regardless of the diving mix. The problem with heliox was associated to isobaric counter diffusion. The effects are sometimes beneficial, sometimes detrimental, and they depend on: The counter diffusing gases, in this case nitrogen and helium. The direction of the exchanges. If the two gases changed sides, the end result may change from super-saturation to under- saturation. The ambient pressure and thus the depth. In Russia, at the time, Dr. Sokolov had developed a systematic approach for the treatment of severe cases of DCS using heliox saturation. In Denmark, Dr. Hyldegaard conducted a series of animal experiments and demonstrated the capacity of helium breathing to reduce the size of nitrogen bubbles. He explained that the diffusion of helium into the bubble combined with the diffusion of nitrogen out of the bubble creates a situation of counter-diffusion. The result is the shrinking of the bubble when the tissue is fatty, as can be assumed for a neurological tissue (Hyldegaard O, Madsen J. Influence of heliox, oxygen and N2O-O2 breathing on N2 bubbles in adipose tissue. Undersea Biomed. Research (1989) 16: 185-193.). He concluded the higher efficiency of 50/50 heliox breathing in the treatment of severe DCS after an air dive. The principle was later endorsed by DMAC (DMAC. Note 23. The Use of Heliox in Treating Decompression Illness. 1993 – now replaced by DMAC C 23 Rev.1 – 2014). Secondly, Dr. James modified the breathing protocol of the attendant after one case of DCS had been recorded. In the new 1986 version, the attendant started taking oxygen at the 12 msw stop and kept it during the ascent to surface. This version of the Cx30 table later became a standard in the offshore industry through Comex and its further avatars (Stolt, Nilson, Acergy, Subsea 7, etc.). The Cx30 was also adopted by Dr. Yehuda Melamed for the Israeli Navy and soon appeared in many other navy manuals (for instance, the Norwegian Navy). It finally reached recreational diving, and DAN centers refer to the Cx30 in several places around the world (for instance Malta Mater Dei hospital on Malta). The Cx30 became a classic.
The 1986 “Classic” Comex Cx30 Table
Offshore performances of the Comex 1986 treatment tables were published using the Comex database containing at the time around 500 treatments of DCS (Imbert, JP. Evolution and offshore performances of the Comex Treatment Tables. Workshop on Decompression Illness Treatment; 18-19 June 1995; Palm Beach, Florida: Undersea Biomedical Hyperbaric Society; 1995).
The 1990 Comex Medical Book In the 90’s, the offshore diving industry became a mature industry, and better controlled its operating procedures. DCS became limited to predictable cases: articular pain in the last 10 msw of saturation decompression or neurological symptoms after a surface decompression. In 1990, there was a new revision of the Comex diving manual and its medical procedures. Dr. Philip James, still in charge of the North Sea, but also Dr. JY Massimelli in Marseille, further reduce the number of treatment tables by eliminating the Cx18 (tables Cx12 and Cx30 were kept unchanged). The rationale was that if the symptoms were pain only, a Cx12 would do the job. If the symptoms were serious, compressing to 18 msw would be a waste of time since a Cx30 would be much more efficient. It was also explained that a compression at 18 msw provides too high a PO2 that should be optimized to around 2 bar, which is the case in the tables Cx12 and Cx30. The decision flow chart after a surface-supplied dive only considered two treatment tables.
Comex 1994 Medical Treatment Chart for Symptoms after Surface-Supplied Diving
Current Commercial Diving Practice Today, Comex has disappeared into the history files, but its contributions still remain. The industry has further improved and DCS has become a rare event. Companies operating in the North Sea report around one case of DCS every 10 years. The culture has changed too, and the emergency medical coverage is ubcontracted to external companies. Therefore, the trend is towards standardization and simplification because the hyperbaric doctor in charge will have to deal with many clients and varied treatment procedures. A typical decision flow chart is presented below. There is no need anymore to make a diagnostic. The recompression starts with a systematic Table 6 and is oriented for the rest of the treatment, depending on the response of the patient at 18 msw. The Cx30 is only there for the serious cases, but most of the time, the patient benefits from successive extensions to the Table 6.
A typical offshore commercial diving medical book in 2022
Conclusion The Comex medical book was typical of a commercial diving company. It came after the Navies had published their treatment procedures and used a different experience. The treatments and the tables were not the same. They were also unique in a sense that Comex was very involved in hyperbaric research. In particular, the table Cx30 has been very successful and deep recompression treatment tables have progressively disappeared from the diving manuals. These original procedures also evolved with time and adapted to the concerns raised by specific worksites. If initially the treatment procedures were a matter of company culture, the international dimension of the offshore industry now requires standardization, and as a consequence, simplification. The Comex Cx30 tables have survived this evolution and have become an international standard, mainly prescribed as a fallback to the Table 6 for severe cases. It still appears in many large commercial diving manuals.