Article, Hyperbaric Medicine

Factors associated with residual symptoms after recompression in type I decompression sickness

a b s t r a c t

Purpose: The aim of this study is to investigate factors associated with residual symptoms after Hyperbaric oxygen therapy in type I decompression sickness (DCS).

Basic procedures: An HBOT registry, which includes patients with type I DCS, was analyzed retrospectively. We divided enrolled patients into two groups; complete resolution group and residual symptom (RS) group after a single HBOT session. We investigated factors associated with residual symptoms at discharge with univariable and multivariable analyses. Restrictive cubic spline curve and a test for trend analysis were used to show the trend of therapeutic response after HBOT based on time from symptom onset to HBOT.

Main findings: In a total of 195 patients, 131 (67.2%) patients were included in the RS group after single HBOT. Prolonged time from symptom onset to recompression was independently associated with residual symptoms (P = .004). When patients who underwent recompression within 24 hours from symptom were included in the reference group, the adjusted odds ratios (AOR) (95% confidence interval) of residual symptoms after HBOT were the following: 24 to 96 hours, 2.24 (0.75-6.65); 96 to 240 hours, 3.31 (1.08-10.13); more than 240 hours, 22.83 (2.45-231.43). In terms of sort of diving, commercial and recreational divers had higher probability of residual symptoms than military divers (AOR, 4.78 and 33.36, respectively).

Principal conclusions: Early HBOT is associated with rapid symptom elimination after treatment in type I DCS. Military divers showed a more immediate response after recompression in comparison with commercial and recreational divers.

(C) 2014

Introduction

Decompression sickness (DCS) is caused by inert gas bubbles in tis- sue and blood previously dissolved within tissues during or after inade- quate decompression from hyperbaric exposure. Standard treatment for DCS in divers is hyperbaric oxygen therapy (HBOT), which reduces bub- ble volume and eliminates inert gas [1]. There are two types of DCS I and

II. Type I is the milder type of DCS and manifests as Musculoskeletal pain, cutaneous symptoms, and lymphatic obstruction [2]. With the de- velopment of HBOT, the reported therapeutic success rate for type I DCS is high [3-5]. Although many patients with type I DCS recover complete- ly after a single HBOT session, some patients experience residual pain at discharge that reduces over several days, and some need to undergo surgery because of dysbaric osteonecrosis [6-9]. This study aimed to

? Funding: No.

?? Prior Presentations: no.

* Corresponding author. Department of Emergency Medicine, Seoul National University, Bundang Hospital, 300 Gumi-dong, Bundang-gu, Sungnam-si, Gyeonggi-do, 463-707, Republic of Korea. Tel.: +82 31 787 7572; fax: +82 31 787 4055.

E-mail address: [email protected] (K. Kim).

investigate therapeutic response to HBOT in patients with type I DCS and to identify the clinical factors associated with residual symptoms after a single HBOT session.

Materials and methods

Study hospital and setting

The study hospital is a 200-bed naval hospital with a multiplace hy- perbaric oxygen chamber located in an urban setting. Both military di- vers and civilian divers with DCS are admitted to the emergency department (ED), and only patients who need HBOT are referred to the underwater medical institute of our hospital for HBOT. In the ED, we check the chest radiography and perform a full neurologic examina- tion to identify pneumothorax, type II DCS, and arterial Gas embolism (AGE). We permit patients with type I DCS to sip a small amount water, but not use any analgesics and intravenous fluids. We apply the US Navy treatment Table 5 or 6 to enroll patients according to the US Navy Diving Manual. When patients arrive at 60 f. and symptoms are eliminated within 10 minutes, we progress to Table 5. If patients have residual symptoms at 60 f. after 10 minutes, Table 6 is used [1].

http://dx.doi.org/10.1016/j.ajem.2014.12.011

0735-6757/(C) 2014

364 J. Lee et al. / American Journal of Emergency Medicine 33 (2015) 363366

Data collection

An HBOT registry, which includes patients who undergo HBOT in our hospital, was analyzed retrospectively. The following data were record- ed in the database: age, sex, symptoms, maximal depth of diving, type of diving, repetitive diving, rapid ascent, hard underwater work, time from surfacing to symptoms, time from symptoms onset to HBOT, and resid- ual symptoms after HBOT. Clinical data were obtained from the patient’s statement and recorded by the attending physician. Hard underwater work was recorded according to the patient’s subjective expression. Re- petitive diving was defined as any dive performed while the diver had residual nitrogen gas in his body from a previous dive. We considered patients who did not follow the decompression table as having residual nitrogen gas [1]. Rapid ascent was defined as any dive that violated the diving decompression schedule according to the US Navy Diving Manu- al [1]. Residual symptoms (%) after HBOT were described as a percent- age in comparison with the initial symptoms according to the patient’s statement. We contacted enrolled patients to obtain missed values in the database and investigate the therapeutic results after dis- charge. This study was approved by the institutional review board of the Korean Military Medical Association.

Inclusion and exclusion criteria

Eligible patients were more than 15 years old, diagnosed with type I DCS, and underwent HBOT between August 2004 and December 2013. Patients who were diagnosed with type II DCS or AGE were excluded. Patients whose symptoms were limited to muscles, joints, skin, and lymphatic system were classified as type I DCS. If there were any one of neurologic, respiratory, or circulatory symptoms, the patients were classified as type II DCS. Arterial gas embolism was defined when pa- tients had neurologic symptoms and a history of rapid ascent, breath holding, or the presence of lung injury such as pneumothorax [1].

Statistics

We described the baseline demographic data, information on diving, and the overall treatment result of enrolled patients. Continuous vari- ables were presented as the mean with standard deviation and were compared with Student t test. Binominal variables were presented as the frequency of occurrence and were compared with the ?2 test. We divided enrolled patients into two groups: complete resolution (CR) group and residual symptom (RS) group after a single HBOT session, and investigated the different variables in both groups with univariable analysis. Subsequently, a multivariable analysis was performed to find independent factors using significant variables (P b .05) identified through the univariable analysis. Before performing multivariable anal- ysis, we divided the time from symptom onset to recompression using the interquartile range (median, 96 hours; interquartile range, 24-240 hours). We assumed that significant variables in the multivariable anal- ysis could be factors that influence immediate symptom elimination after HBOT in type I DCS. Restricted cubic spline curve and a test for trend analysis were used to show the trend of early therapeutic re- sponse based on time from symptom onset to recompression [10]. C- statistics was used to evaluate the predictive function of our model and area under the receiving operating curve (AUC), and 95% confi- dence intervals (CIs) were calculated. In addition to multivariable logis- tic regression, we performed a modified Poisson regression to estimate the risk ratio of the risk factors [11]. A two-sided test was used with a 5% level of significance. All calculations were performed using STATA ver- sion 13.0 (StataCorp, College Station, Texas, USA).

Results

A total of 271 patients were admitted to our hospital for HBOT dur- ing the study period. Of these patients, 67 were diagnosed with type II DCS and 2 were diagnosed with AGE. Two hundred two patients were diagnosed with type I DCS, and 195 patients were analyzed in our

Fig. 1. Study population.

J. Lee et al. / American Journal of Emergency Medicine 33 (2015) 363366 365

Table 1

Clinical presentation of enrolled patients

Table 3

Multivariable logistic regression of predictive factors for residual symptoms after a single HBOT session

Total N = 195 (%)

Musculoskelectal pain

186 (95.4)

OR 95% CI

Shoulder

119 (61.0)

Time from symptom to recompression, h

Knee

35 (17.9)

<=24

Reference

Elbow

25 (12.8)

24-96

2.24

0.75-6.65

Neck

19 (9.7)

96-240

3.31

1.08-10.13

Lower back

9 (4.6)

>=240

23.84

2.45-231.43

Ankle

7 (3.6)

Type of diving

Pelvis

7 (3.6)

Military divers

Reference

Hand

7 (3.6)

Commercial divers

4.78

1.43-15.92

Foot

4 (2.1)

Recreational divers

33.36

3.43-323.71

Thigh

3 (1.5)

Repetitive diving

1.04

0.39-2.77

Cutis marmorata 2 (1.0) Abbreviation: OR, odds ratio.

Data are presented as number (percentage) of patients.

study after excluding 7 patients with missing values. After the first HBOT session, symptoms were relieved in all enrolled patients. Sixty- four patients (32.8%) recovered completely after a single HBOT session and classified into the CR group. Patients who discharged with residual pain (131. 67.2%) were classified into the RS group. Average residual pain (%) of the RS group at discharge was 35.5 % in comparison with ini- tial symptoms. When we followed up enrolled patients through phone counseling, 121 (92.3%) of 131 patients had recovered from symptoms within 1 month. Eight patients had residual pain over 1 month after recompression, and 2 patients underwent surgery for shoulder osteonecrosis (Fig. 1). When patients who had residual pain over 1 month or needed surgery were classified as therapeutic failure, the treatment success rate was 94.9%. Among enrolled patients, 186 (95.4%) patients accompanied at least one of muscle or joint pain. Shoulder pain was the most common symptom followed by knee, elbow, and neck pain. None of the enrolled patients had lymphatic obstruction (Table 1).

Table 2

Univariable analysis of baseline characteristics, clinical presentation and time factors

Using univariable analysis, the time delay from symptom onset to recompression was significantly longer in the RS group than in the CR group (P = .045). The military diving group had more patients with early symptom relief than other groups (P = .006) (Table 2). Because recompression time is delayed, more patients would have residual symptoms at discharge in multivariable analysis. However, there was no significant difference in residual symptoms between within the 24-hour group and the 24- to 96-hour group (Table 3). In the restrictive cubic spline curve, the probability of residual symptoms at discharge after recompression was increased with delayed time to recompression (Fig. 2). Patients who underwent delayed treatment tended to have re- sidual symptoms after a single HBOT session in a test for trend analysis (P = .004). With regard to diving type, the military diving group had higher immediate symptom elimination than the commercial diving group, followed by the recreational diving group (Table 3). Although pa- tients without repetitive diving showed a more immediate response after HBOT than patients with repetitive diving in the univariable anal- ysis, this result did not retain significance in the multivariable analysis (Table 3). Predictability of the multivariable logistic regression model was 0.77 (95% CI, 0.68-0.86) as measured by AUC. Estimate risk ratio was calculated with a modified Poisson regression. Significant variables were the same as the multivariable logistic regression, and incidence

Complete recovery

Residual P

symptom

rate ratio was regarded as the risk ratio. The AUC of the modified Poisson regression model was 0.76 (95% CI, 0.67-0.85) (Table 4).

Demographic findings

n = 64 n = 131

Discussion

Age, y

39.5 +- 1.3

40.5 +- 0.76

.498

Male sex, no. (%)

64 (100)

125 (97.4)

.112

BMI, kg/m2

23.9 +- 0.3

24.7 +- 0.3

.087

Type of diving, no. (%)

The purpose of treatment for type I DCS is to eliminate symptoms such as muscle or joint pain and prevent serious complications such as

Military divers

14 (21.8)

12 (9.2)

.006 osteonecrosis. We could not find any clinical factors that influenced

Commercial divers

42 (65.6)

80 (61.5)

the final Treatment outcome because only 5.1% of enrolled patients ex-

Recreational divers

8 (12.5)

38 (29.2)

Information on diving

Diving depth, m

31.2 +- 2.6

28 +- 0.8

.138

Repetitive diving, no. (%)

32 (50)

87 (66.7)

.023

Rapid ascent, no. (%)

25 (39)

37 (28.4)

.137

Hard exercising, no. (%)

12 (18.7)

27 (20.7)

.741

Alcohol before diving, no. (%)

5 (13.8)

4 (17.3)

.715

Symptom, no. (%)

Shoulder pain

37 (57.8)

69 (53.8)

.533

Knee pain

11 (17.1)

21 (16.1)

.855

Elbow pain

8 (12.5)

16 (12.3)

.969

Time

Surfacing to symptom, h

7.3 +- 3.9

6.2 +- 1.7

.766

Symptom to recompression, h

66.4 +- 14.8

342.3 +- 84.2

.045

Patients with delayed treatment

17 (47.2)

73 (77.6)

.001

more than 24 h, no. (%)

Treatment table 5/6 59/5 98/33 .004 Residual symptom/initial symptom, % 0 35.5 +- 1.8 b.001

Patient with residual symptom at 1 mo, no. (%)

0 (0) 10 (7.6) .032

Continuous data are presented as mean +- SD and compared with Student t test. Categorical data are presented as number (percentage) of patients and compared with ?2 test.

Abbreviations: BMI, body mass index; SD, standard deviation.

Fig. 2. Restrictive cubic spline curve.

366 J. Lee et al. / American Journal of Emergency Medicine 33 (2015) 363366

Table 4

Modified Poisson regression of predictive factors for residual symptom after a single HBOT session

IRR 95% CI

Time from symptom to recompression, h

<=24

Reference

24-96

1.35

0.94-1.91

96-240

1.48

1.07-2.05

>=240

1.85

1.37-2.51

Type of diving

Military divers Reference

Commercial divers 1.35 1.23-1.85

Recreational divers 1.58 1.16-2.15

Repetitive diving 1.03 0.83-1.28

Abbreviation: IRR, Incidence rate ratio.

perienced therapeutic failure. Instead of the final treatment outcome, we focused on rapid therapeutic response after recompression because fast symptom relief could increase patient satisfaction and reduce med- ical cost. In our study, fast recompression was the only correctable factor for immediate symptom elimination after HBOT in type I DCS. With re- gard to diving type, military divers had good immediate response after recompression, followed by commercial divers and recreational divers. In case of military diving, diving regulations are strict, and almost all diving is done according to the US diving manual [1]. However, recrea- tional divers may dive without regulation or limitation. A previous study described that civilian divers adhere less to US Navy diving tables than military divers [12]. Patients with type I DCS are likely to ignore their own symptoms and delay treatment because they could have only minor pain or skin lesions. Although type I DCS had minor symp- toms, it can lead to serious complications such as osteonecrosis and progress to type II DCS [13,14]. There is controversy whether early recompression influences cause better outcome in DCS. Previous studies have investigated the delayed time effect in DCS and showed both a negative effect and no-effect on outcome [15-17]. Previous studies mainly focused on type II DCS and described delayed time and final therapeutic outcome. No previous study demonstrated the effect of de- layed recompression on type I DCS in detail. Although delayed recompression did not influence the final therapeutic outcome in type I DCS in our study, more patients with early treatment had symptomatic relief immediately after a single HBOT session. We recommended that patients with type I DCS visit a hospital where HBOT is available as quickly as possible for early symptom relief.

This study has several limitations. First, the percentage of men was

high in the enrolled patients. Therefore, we could not prove whether sex influenced the therapeutic results or not. Second, we did not find

any significant factor that could influence the final therapeutic result be- cause the number of patients with treatment failure was small. Third, the clinical information in the database was obtained through patient statement, and we could not verify the accuracy. Fourth, potential biases might remain because of the retrospective nature of the study.

In conclusion, early HBOT is associated with rapid symptom elimina- tion after treatment in type I DCS. Military divers showed a more imme- diate response after recompression in comparison with commercial and recreational divers.

Acknowledgments

No authors declare a conflict of interest.

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