REVIEW ARTICLE Resolution and Severity in Decompression Illness Richard D. Vann , Petar J. Denoble , Laurens E. Howle , Paul W. Weber , John J. Freiberger , and Carl F. Pieper V ANN RD, D ENOBLE PJ, H OWLE LE, W EBER PW, F REIBERGER JJ, P IEPER The Golding Classifi cation for Compressed Air Work: Type 1 CF. Resolution and severity in decompression illness. Aviat Space and Type 2 DCS Environ Med 2009; 80: 466 – 71 . We review the terminology of decompression illness (DCI), investiga- Golding et al. described Type 1 DCS as “ simple bends ” tions of residual symptoms of decompression sickness (DCS), and ap- and Type 2 DCS as serious ( 11 ). They reported 650 Type plication of survival analysis for investigating DCI severity and resolution. The Type 1 and Type 2 DCS classifi cations were introduced in 1960 for 1 cases and 35 Type 2 cases, both requiring recompres- compressed air workers and adapted for diving and altitude exposure sion therapy. In addition, many other cases, described as with modifi cations based on clinical judgment concerning severity and “ niggles, ” involved minor untreated pain considered therapy. In practice, these proved ambiguous, leading to recommenda- too nonspecifi c for study. tions that manifestations, not cases, be classifi ed. A subsequent approach assigned individual scores to manifestations and correlated total case Type 1 DCS was defi ned as pain, usually in or around scores with the presence of residual symptoms after therapy. The next a joint, with a mean onset of 3 h (0 – 12 h range) after step used logistic regression to fi nd the statistical association of manifes- reaching atmospheric pressure. Half the Type 1 cases re- tations to residual symptoms at a single point in time. Survival analysis, sponded to recompression quickly at 2 – 3 psi (0.14 – 0.2 a common statistical method in clinical trials and longitudinal epidemi- ological studies, is a logical extension of logistic regression. The method atm) above the working pressure, and half had to be applies to a continuum of resolution times, allows for time varying infor- kept at therapeutic pressure for up to 1 h before pain mation, can manage cases lost to follow-up (censored), and has poten- was relieved. About 25% had residual soreness after tial for investigating questions such as optimal therapy and DCI severity. treatment — a soreness that was reported as markedly There are operational implications as well. Appropriate defi nitions of mild and serious manifestations are essential for computing probabilistic different from bends pain. Men with Type 1 DCS went decompression procedures where severity determines the DCS probabil- back to work the next day unless, as in a few cases, treat- ity that is acceptable. Application of survival analysis to DCI data would ment had been unusually long. require more specifi c case information than is commonly recorded. Type 2 DCS was defi ned as symptoms other than pain, Keywords: decompression illness , DCI , decompression sickness , DCS , arterial gas embolism , AGE , survival analysis . or physical signs that included vertigo, shock, visual ab- normalities, paralysis, speech defects, seizures, or un- consciousness. The onset of Type 2 cases was rapid, with HERAPY FOR DECOMPRESSION illness is judged a mean of 50 min after reaching atmospheric pressure T successful if the manifestations resolve or if particu- and time of symptom onset ranging from during de- larly serious manifestations improve substantially. Time compression to 6 h after decompression. Type 2 cases to resolution is a measure of this success, but manifesta- were treated by immediate recompression followed by tions do not always resolve simultaneously, and the rela- slower decompression to surface pressure than for Type tionship of resolution time to severity has been diffi cult to 1 cases. Workers with Type 2 DCS were forbidden future investigate. Modern history of the fi eld dates from Gold- compressed air work or were allowed only limited ex- ing, who introduced the diagnostic classifi cations Type 1 posures thereafter. Upon radiological examination, two (mild) and Type 2 (serious) decompression sickness (DCS) Type 2 cases were found to have pulmonary cysts that for treating compressed air workers ( 11 ). The Golding ter- were the suspected cause of injury as a result of arterial minology was adopted for both diving ( 3,14,25 ) and aero- gas embolism (AGE). space ( 21,33,34 ). As discussed in detail below, more quantitative methods measured severity by manifesta- tion scores and associated these scores with residual symptoms at a point in time after therapy ( 1,5,7,12,19,24 ). From the Divers Alert Network, Center for Hyperbaric Medicine and Environmental Physiology, Department of Anesthesiology, Duke Logistic regression attempted to fi nd statistical associa- University Medical Center; the Department of Mechanical Engineer- tions between manifestations and residual symptoms at a ing and Materials Science; and the Center for Aging Division of Biosta- particular time ( 2,13 ). Our review is similar to that of tistics and Bioinformatics, Duke University, Durham, NC. This manuscript was received for review in November 2008 . It was Mitchell et al. ( 17 ), but designed to show a progression of accepted for publication in February 2009 . the fi eld toward survival analysis. Survival analysis is a Address reprint requests to: Richard Vann, Ph.D., Center for Hyper- statistical method that could be used for investigating the baric Medicine and Environmental Physiology, Box 3823 DUMC, Dur- continuum of resolution times, the effects of therapeutic ham, NC 27710; [email protected] . Reprint & Copyright © by Aerospace Medical Association, interventions, the infl uence of demographic factors, and Alexandria, VA. differences between manifestations ( 15 ). DOI: 10.3357/ASEM.2471.2009 466 Aviation, Space, and Environmental Medicine x Vol. 80, No. 5, Section I x May 2009 RESOLUTION & SEVERITY IN DCI — VANN ET AL. Application of the Golding Classifi cation to Diving Type 1 DCS to include “ symptoms involving joint pain, Golding’s classifi cations were widely adopted for de- peripheral nervous system, or simple skin bends. ” Type scribing DCS after diving. In 1969, Kidd and Elliott de- 2 DCS was defi ned as “ symptoms involving the central fi ned Type 1 DCS as joint pain, cutaneous or lymphatic nervous system, cardiovascular system, or pulmonary involvement, and fatigue ( 14 ). Type 2 DCS manifesta- system ” ( 21 ). tions were pulmonary, neurological, or cardiovascular. Decompression Illness and Decompression Injury (DCI) Pulmonary signs included respiratory diffi culty ( “ chokes ” ), substernal burning pain, and coughing. Neurological Discomfort with the Golding classifi cation emerged signs and symptoms included cerebral and the more in 1989 at the Undersea and Hyperbaric Medicine common spinal manifestations. Type 2 symptoms were Society Workshop, Describing Decompression Illness, also defi ned as subjective paresthesias such as “ woolly, ” where the categories AGE, Type 1 DCS, and Type 2 DCS “ cold, ” or “ pins and needles ” sensations. These were of- were declared artifi cial, misleading, and diagnostically ten present in isolated patches on any limb rather than inconsistent ( 10 , pp. 4, 110). Moreover, it was argued, as the more typical segmental distribution of spinal in- clinical symptoms cannot identify the pathological pro- volvement due to trauma. Treatment regimens for Types cesses consistent with AGE, Type 1 DCS, and Type 2 1 and 2 DCS were different, but no difference was indi- DCS, so a pathogenic classifi cation was of little help in cated between AGE and Type 2 therapy. choosing therapy where recompression was the treat- The Type 1/Type 2 terminology began to appear in ment of choice in any event ( 10 , pp. 46, 110). Rather than U.S. Navy literature as early as 1971 in a review of DCS classify cases as AGE, Type 1 DCS, and Type 2 DCS, the cases occurring under pressure ( 25 ), although it appears workshop proposed to classify all manifestations, to have been used informally among submarine medical whether DCS or AGE, under the general designation offi cers as early as 1966. Flynn and Catron included the “ decompression illness ” ( 10 , pg. 110). terminology in lesson plans for a 1975 course on the rec- Dutka participated in the DCI Workshop and agreed ognition and treatment of diving casualties ( 9 ). By 1993 that it was more appropriate to classify manifestations (if not before), it had reached the U.S. Navy Diving rather than to classify cases as AGE, Type 1 DCS, and Manual in the statement: “ Because the treatment of Type Type 2 DCS. However, Dutka preferred the term ‘ de- 1 and Type 2 symptoms is different, it is important to compression injury ’ to ‘ decompression illness ’ and of- distinguish between these two types of decompression fered an alternative classifi cation scheme ( 8 ). (Confusion sicknesses ” ( 27 ). Type 1 was to be treated on Table 5 over the terms seems unlikely since both ‘ decompres- while Type 2 DCS or AGE was to be treated on Table 6 or sion illness ’ and ‘ decompression injury ’ include AGE 6A. Pain-only (Type 1) symptoms were described as and DCS and have the same initials.) Both the Dutka mild to excruciating and typically of a dull, aching qual- and Francis ( 10 ) classifi cations included a time compo- ity that could be diffi cult to differentiate from a muscle nent to facilitate communication about active cases. The sprain or bruise. Type 2 symptoms now included numb- work discussed below usually omitted this time compo- ness, tingling, and decreased sensation to touch or par- nent in favor of post hoc analysis regarding presenting esthesias ( “ tingling, ” “ pins and needles, ” or “ electric manifestations and residual symptoms after therapy sensations ” ) as well as muscle weakness or paralysis, was complete. and abnormalities of mental status or motor perfor- mance. Milder symptoms such as paresthesia were in- DCS Severity Scores cluded as Type 2 out of concern that they would progress In the adaptations of the Golding terminology, Type 1 to serious problems such as paralysis.