Decompression illness: a comprehensive overview.

Decompression illness is a collective term for two maladies (decompression sickness [DCS] and arterial gas embolism [AGE]) that may arise during or after surfacing from compressed gas diving. Bubbles are the presumed primary vector of injury in both disorders, but the respective sources of bubbles are distinct. In DCS bubbles form primarily from inert gas that becomes dissolved in tissues over the course of a compressed gas dive. During and after ascent ('decompression'), if the pressure of this dissolved gas exceeds ambient pressure small bubbles may form in the extravascular space or in tissue blood vessels, thereafter passing into the venous circulation. In AGE, if compressed gas is trapped in the lungs during ascent, pulmonary barotrauma may introduce bubbles directly into the pulmonary veins and thence to the systemic arterial circulation. In both settings, bubbles may provoke ischaemic, inflammatory, and mechanical injury to tissues and their associated microcirculation. While AGE typically presents with stroke-like manifestations referrable to cerebral involvement, DCS can affect many organs including the brain, spinal cord, inner ear, musculoskeletal tissue, cardiopulmonary system and skin, and potential symptoms are protean in both nature and severity. This comprehensive overview addresses the pathophysiology, manifestations, prevention and treatment of both disorders.

Chain of events analysis in diving accidents treated by the Royal Netherlands Navy 1966-2023.

Introduction: Diving injuries are influenced by a multitude of factors. Literature analysing the full chain of events in diving accidents influencing the occurrence of diving injuries is limited. A previously published 'chain of events analysis' (CEA) framework consists of five steps that may sequentially lead to a diving fatality. This study applied four of these steps to predominately non-lethal diving injuries and aims to determine the causes of diving injuries sustained by divers treated by the Diving Medical Centre of the Royal Netherlands Navy. Methods: This retrospective cohort study was performed on diving injuries treated by the Diving Medical Centre between 1966 and 2023. Baseline characteristics and information pertinent to all four steps of the reduced CEA model were extracted and recorded in a database. Results: A total of 288 cases met the inclusion criteria. In 111 cases, all four steps of the CEA model could be applied. Predisposing factors were identified in 261 (90%) cases, triggers in 142 (49%), disabling agents in 195 (68%), and 228 (79%) contained a (possible-) disabling condition. The sustained diving injury led to a fatality in seven cases (2%). The most frequent predisposing factor was health conditions (58%). Exertion (19%), primary diver errors (18%), and faulty equipment (17%) were the most frequently identified triggers. The ascent was the most frequent disabling agent (52%). Conclusions: The CEA framework was found to be a valuable tool in this analysis. Health factors present before diving were identified as the most frequent predisposing factors. Arterial gas emboli were the most lethal injury mechanism.

The Influence of Advanced Hyperbaric Medical Training on Arterial Gas Embolism Treatment.

3d Reconnaissance Battalion, a forward-deployed Marine Corps unit in Okinawa, Japan, frequently performs diving operations. Often throughout the year, several reconnaissance teams are diving simultaneously in different locations for training. We present a case of an otherwise healthy 30-year-old-male Reconnaissance Marine who surfaced from a dive with abnormal symptoms and received prompt care from exercise participants who were nonmedical personnel. Studies have demonstrated improved morbidity outcomes in decompression illness patients with shorter times to hyperbaric treatment following the onset of symptoms. High-risk military exercises with diving components have a mandatory safety structure that includes recompression chamber support. All United States Marine Corps Reconnaissance, Marine Corps Special Operations Command, and U.S. Navy dive operations are required to have at least one diving supervisor. To expand the diving capabilities of the unit, Marines are encouraged to attend training and qualify as diving supervisors. This case study demonstrates the efficacy and importance of training Recon Marines to recognize decompression illness as diving supervisors.

Hyperbaric treatment deviations for U.S. Navy divers: Spinal DCS.

Introduction: The United States Navy (USN) developed and refined standardized oxygen treatment tables for diving injuries, but USN tables may not address all situations of spinal decompression sickness (DCS). We describe a detailed recompression treatment regimen that deviated from standard USN protocol for an active-duty USN diver with a severe, delayed presentation of spinal cord DCS. Case Report: A USN diver surfaced from his second of three dives on a standard Navy 'no-Decompression' Air SCUBA dive (Max depth 101 fsw utilizing a Navy Dive Computer) and developed mid-thoracic back pain, intense nausea, paresthesias of bilateral feet, and penile erection. Either not recognizing the con- stellation of symptoms as DCS and after resolution of the aforementioned symptoms, he completed the third planned dive (essentially an in-water recompression). Several hours later, he developed paresthesias and numbness of bilateral feet and legs and bowel incontinence. He presented for hyperbaric treatment twenty hours after surfacing from the final dive and was diagnosed with severe spinal DCS. Based on the severity of clinical presentation and delay to treatment, the initial and follow-on treatments were modified from standard USN protocol. MRI of the spine four days after initial presentation demonstrated a 2.2 cm lesion at the T4 vertebral level extending caudally. Follow-up examinations over two years demonstrated almost complete return of motor and sensory function; however, the patient continued to suffer fecal incontinence and demonstrated an abnormal post-void residual urinary volume. An atypical presenting symptom, a discussion of MRI findings, and clinical correlations to the syndrome of spinal DCS are discussed throughout treatment and long-term recovery of the patient.

A retrospective review of divers treated for inner ear decompression sickness at Fiona Stanley Hospital hyperbaric medicine unit 2014-2020.

Introduction: Inner ear decompression sickness (IEDCS) is increasingly recognised in recreational diving, with the inner ear particularly vulnerable to decompression sickness in divers with a right-to-left shunt, such as is possible through a persistent (patent) foramen ovale (PFO). A review of patients treated for IEDCS at Fiona Stanley Hospital Hyperbaric Medicine Unit (FSH HMU) in Western Australia was performed to examine the epidemiology, risk factors for developing this condition, the treatment administered and the outcomes of this patient population. Methods: A retrospective review of all divers treated for IEDCS from the opening of the FSH HMU on 17 November 2014 to 31 December 2020 was performed. Patients were included if presenting with vestibular or cochlear dysfunction within 24 hours of surfacing from a dive, and excluded if demonstrating features of inner ear barotrauma. Results: There were a total of 23 IEDCS patients and 24 cases of IEDCS included for analysis, with 88% experiencing vestibular manifestations and 38% cochlear. Median dive time was 40 minutes and median maximum depth was 24.5 metres. The median time from surfacing to hyperbaric oxygen treatment (HBOT) was 22 hours. Vestibulocochlear symptoms fully resolved in 67% and complete symptom recovery was achieved in 58%. A PFO was found in 6 of 10 patients who subsequently underwent investigation with bubble contrast echocardiography upon follow-up. Conclusions: IEDCS occurred predominantly after non-technical repetitive air dives and ongoing symptoms and signs were often observed after HBOT. Appropriate follow-up is required given the high prevalence of PFO in these patients.

Atypical distally distributed cutis marmorata decompression sickness associated with unconventional use of thermal protection in a diver with persistent foramen ovale.

Cutis marmorata is a mottled, marbling, livedoid rash caused by vascular inflammation and congestion in cutaneous decompression sickness. It may occur during or after ascent due to the formation of bubbles from dissolved nitrogen accumulated throughout the dive. It is strongly associated with the presence of right to left shunts, particularly persistent (patent) foramen ovale (PFO). We report a case of cutis marmorata decompression sickness of an unusual pattern associated with unconventional use of thermal protection (a 'shorty' wetsuit worn over full suit) by a diver with a PFO. The patient also had neurological manifestations of decompression sickness. The distal lower limb pattern of involvement favours the hypothesis that cutis marmorata in humans is likely to be due to bubbles in the skin itself and/or adjacent tissues rather than cerebrally mediated.

S2k guideline for diving accidents.

For the purposes of this guideline, a diving accident is defined as an event that is either potentially life-threatening or hazardous to health as a result of a reduction in ambient pressure while diving or in other hyperbaric atmospheres with and without diving equipment. This national consensus-based guideline (development grade S2k) presents the current state of knowledge and recommendations on the diagnosis and treatment of diving accident victims. The treatment of a breath-hold diver as well as children and adolescents does not differ in principle. In this regard only unusual tiredness and itching without visible skin changes are mild symptoms. The key action statements: on-site 100% oxygen first aid treatment, immobilization/no unnecessary movement, fluid administration and telephone consultation with a diving medicine specialist are recommended. Hyperbaric oxygen therapy (HBOT) remains unchanged as the established treatment in severe cases, as there are no therapeutic alternatives. The basic treatment scheme recommended for diving accidents is hyperbaric oxygenation at 280 kPa.

Scientific shallow saturation dive expedition using diving rebreathers and a specific dry habitat: medical management of the "Capsule" programme.

BACKGROUND: Scientific underwater exploration could benefit from professional diving facilities. This could allow marine research for durations far exceeding anything currently possible. The closed-circuit rebreather expansion provides new perspectives by unleashing divers and their diving bell. "Under the Pole Expeditions" developed an innovative compact underwater habitat for this purpose. MATERIALS AND METHODS: The habitat's depth was fixed at 20 m. Saturation lasted 3 days and was followed by a 245 min long decompression procedure with mandatory in-water phase. Isolation and environmental constraints will require specific medical and safety procedures. "In situ" medical concerns were considered, and a specific evacuation plan was established. This report describes the medical management of this atypical project and the systematic clinical follow-up mostly targeted on the cardiovascular system, fatigue and psychological tolerance. RESULTS: Seventeen individual saturation exposures were performed. All selected divers were professional. Neither severe illness nor decompression sickness was observed. These short-term saturation exposures appeared to be well tolerated. There was a relatively low bubble grade after decompression. Psychological tolerance appeared good. However, a transient moderate orthostatic hypotension suggested cardiovascular deconditioning after dive. CONCLUSIONS: This first experiment demonstrates the interest and feasibility of a shallow revisited saturation dive with rebreather use. This isolation requires medical accompaniment and rigorous preparation. Medical and physiological risks assessment is essential in this context and must be consolidated by new experiences.

Aviation Decompression Sickness in Aerospace and Hyperbaric Medicine.

INTRODUCTION: The U.S. Navy experienced a series of physiological events in aircrew involving primarily the F/A-18 airframe related to rapid decompression of cabin pressures, of which aviation decompression sickness (DCS) was felt to contribute. The underlying pathophysiology of aviation DCS is the same as that of diving-related. However, based on the innate multifactorial circumstances surrounding hypobaric DCS, in clinical practice it continues to be unpredictable and less familiar as it falls at the intersect of aerospace and hyperbaric medicine. This retrospective study aimed to review the case series diagnosed as aviation DCS in a collaborative effort between aerospace specialists and hyperbaricists to increase appropriate identification and treatment of hypobaric DCS.METHODS: We identified 18 cases involving high-performance aircraft emergently treated as aviation DCS at a civilian hyperbaric chamber. Four reviewers with dual training in aviation and hyperbaric medicine retrospectively reviewed cases and categorized presentations as "DCS" or "Alternative Diagnosis".RESULTS: Reviewers identified over half of presenting cases could be attributed to an alternative diagnosis. In events that occurred at flight altitudes below 17,000 ft (5182 m) or with rapid decompression pressure changes under 0.3 atm, DCS was less likely to be the etiology of the presenting symptoms.CONCLUSIONS: Aviation physiological events continue to be difficult to diagnose. This study aimed to better understand this phenomenon and provide additional insight and key characteristics for both flight physicians and hyperbaric physicians. As human exploration continues to challenge the limits of sustainable physiology, the incidence of aerospace DCS may increase and underscores our need to recognize and appropriately treat it.Kutz CJ, Kirby IJ, Grover IR, Tanaka HL. Aviation decompression sickness in aerospace and hyperbaric medicine. Aerosp Med Hum Perform. 2023; 94(1):11-17.

Cardiac arrest in diving: The key to success.

This case report describes the successful management of an out-of-hospital arrest in a diver following a suspected arterial gas embolism (AGE). It illustrates both the inherent risks of diving and the importance of prompt and effective implementation of the "chain of survival" from bystanders. Rapid on-scene responses from paramedics and helicopter emergency medical services facilitated prompt evacuation to a Category 1 (multiplace) recompression chamber (RCC) where specialists in cardiology and hyperbaric medicine were available. Alternative causes of cardiac arrest were considered, with a presumed AGE successfully treated with multiple rounds of hyperbaric oxygen therapy. The key factors which led to this successful outcome are discussed, including early recognition and call for help, competent cardiopulmonary resuscitation, and direct evacuation to a Category 1 RCC, with additional consideration of the diagnosis leading to cardiac arrest. The case clearly illustrates the need for all those involved in diving regularly to be competent and confident in performing basic life support, as well as the awareness of the emergency services of the need for diving casualties to be treated at appropriate hyperbaric facilities. Were it not for the simple, prompt and effective treatment this diver received, both on scene and in hospital, it is highly unlikely that such a positive outcome would have been achieved.

A review of accelerated decompression from heliox saturation in commercial diving emergencies.

INTRODUCTION: Saturation diving is a specialised method of intervention in offshore commercial diving. Emergencies may require the crew to be evacuated from the diving support vessel. Because saturation divers generally need several days to reach surface, the emergency evacuation of divers is based on dedicated hyperbaric rescue systems. There are still potential situations for which these systems cannot be used or deployed, and where an emergency decompression provides an alternative solution. METHODS: Our objective was to describe historical cases and assess the benefit of emergency decompressions, with the collection of data from the authors' direct experience and networks, providing witness or first-hand information. RESULTS: We documented three cases of emergency decompression following bell evacuations, and six cases of accelerated decompression performed in the chamber or hyperbaric rescue chamber. Review of these cases showed: 1) the complicated nature of such emergencies that make decisions difficult; 2) the variety of solutions implemented; and 3) the surprisingly safe and successful outcomes of several operations. Analysis of the accelerated decompression occurrences allowed derivation of the options used; upward initial excursion, increased chamber partial pressure of oxygen associated to increased ascent rates, and inert gas switching. We identified four published procedures for accelerated decompression. CONCLUSIONS: Despite modern hyperbaric rescue systems, accelerated decompression remains an essential tool in case of emergency. The diving industry needs clear guidance on what can be achieved, depending on the saturation depth and the level of emergency.

Delayed treatment for decompression illness: factors associated with long treatment delays and treatment outcome.

INTRODUCTION: Effectiveness of delayed hyperbaric oxygen treatment (HBOT) for decompression illness (DCI) and factors affecting treatment delays have not been studied in large groups of patients. METHODS: This retrospective study included 546 DCI patients treated in Finland in the years 1999-2018 and investigated factors associated with recompression delay and outcome. Treatment outcome was defined as fully recovered or presence of residual symptoms on completion of HBOT. The symptoms, use of first aid oxygen, number of recompression treatments needed and characteristics of the study cohort were also addressed. RESULTS: Delayed HBOT (> 48 h) remained effective with final outcomes similar to those treated within 48 h. Cardio-pulmonary symptoms were associated with a shorter treatment delay (median 15 h vs 28 h without cardiopulmonary symptoms, P < 0.001), whereas mild sensory symptoms were associated with a longer delay (48 vs 24 h, P < 0.001). A shorter delay was also associated with only one required HBOT treatment (median 24 h vs 34 h for those requiring multiple recompressions) ( P = 0.002). Tinnitus and hearing impairment were associated with a higher proportion of incomplete recoveries (78 and 73% respectively, P < 0.001), whereas a smaller proportion of cases with tingling/itching (15%, P = 0.03), nausea (27%, P = 0.03), motor weakness (33%, P = 0.05) and visual disturbances (36%, P = 0.04) exhibited residual symptoms. Patients with severe symptoms had a significantly shorter delay than those with mild symptoms (median 24 h vs 36 h respectively, P < 0.001), and a lower incidence of complete recovery. CONCLUSIONS: Delayed HBOT remains an effective and useful intervention. A shorter delay to recompression is associated with fewer recompressions required to achieve recovery or recovery plateau.

Descriptive study of decompression illness in a hyperbaric medicine centre in Bangkok, Thailand from 2015 to 2021.

INTRODUCTION: This study aimed to determine the characteristics of decompression illness patients and their treatment outcomes, at the Center of Hyperbaric Medicine, Somdech Phra Pinklao Hospital, one of the largest centres in Thailand. METHODS: Past medical records of patients with decompression illness from 2015 to 2021 were retrieved and analysed. RESULTS: Ninety-eight records of diving-related illness from 97 divers were reviewed. Most of the divers were male (n = 50), Thai (n = 86), and were certified at least open water or equivalent (n = 88). On-site first aid oxygen inhalation was provided to 17 divers. Decompression sickness (DCS) cases were characterised according to organ systems involved. The most prominent organ system involved was neurological (57%), followed by mixed organs (28%), musculoskeletal (13%), and pulmonary (2%). There were three cases of arterial gas embolism (AGE). Median presentation delay was three days. Ninety patients were treated with US Navy Treatment Table 6. At the end of their hyperbaric oxygen treatment, most divers (65%) recovered completely. CONCLUSIONS: Despite oxygen first aid being given infrequently and long delays before definitive treatment, treatment outcome was satisfactory. Basic knowledge and awareness of diving-related illnesses should be promoted among divers and related personnel in Thailand along with further studies.

Efficiency of a 24-hour on-call system for early recompression therapy for acute decompression sickness.

Background: Early recompression therapy is suggested for a better clinical outcome of decompression sickness (DCS) patients. This study analyzed the efficacy of our 24-hour on-call system for early recompression therapy. Methods: We conducted a single-center retrospective cohort study. They were classified into DCS Type I versus Type II, duty time versus non-duty time groups based on the time of emergency department (ED) admission, and hospitalization versus discharge groups according to clinical outcomes. Baseline characteristics, diving variables, and in-hospital course were analyzed. Results: This study investigated 341 acute DCS patients. A total of 81 and 260 patients had Type I and Type II DCS, respectively. While 198 patients accessed the center during duty time, 143 presented during non-duty time. Fifty patients were admitted, and 291 patients were discharged. Total median time from symptom onset to HBO2 therapy was 259 minutes: 240 minutes for the duty group and 292 minutes for the non-duty group (p=0.16); 251 minutes for the discharged group and 291 minutes for the hospitalized group (p<0.001). The median time from ED admission to HBO2 therapy was 65 minutes: 60 minutes for the duty group and 69 minutes for the non-duty group (p=0.23); 63.4 minutes for the discharged group and 92 minutes for the hospitalized group (p=0.05). Conclusion: The 24-hour on-call system was able to provide acute DCS patients with early recompression therapy even during non-duty time. However, in terms of the outcome of treatment of patients, quicker arrival at the hospital and swifter recompression therapy are needed.

Comparison of treatment recompression tables for neurologic decompression illness in swine model.

BACKGROUND: Significant reductions in ambient pressure subject an individual to risk of decompression illness (DCI); with incidence up to 35 per 10,000 dives. In severe cases, the central nervous system is often compromised (>80%), making DCI among the most morbid of diving related injuries. While hyperbaric specialists suggest initiating recompression therapy with either a Treatment Table 6 (TT6) or 6A (TT6A), the optimal initial recompression treatment for severe DCI is unknown. METHODS: Swine were exposed to an insult dive breathing air at 7.06 ATA (715.35 kPa) for 24 min followed by rapid decompression at a rate of 1.82 ATA/min (184.41 kPa/min). Swine that developed neurologic DCI within 1 hour of surfacing were block randomized to one of four United States Navy Treatment Tables (USN TT): TT6, TT6A-air (21% oxygen, 79% nitrogen), TT6A-nitrox (50% oxygen, 50% nitrogen), and TT6A-heliox (50% oxygen, 50% helium). The primary outcome was the mean number of spinal cord lesions, which was analyzed following cord harvest 24 hours after successful recompression treatment. Secondary outcomes included spinal cord lesion incidence and gross neurologic outcomes based on a pre- and post- modified Tarlov assessment. We compared outcomes among these four groups and between the two treatment profiles (i.e. TT6 and TT6A). RESULTS: One-hundred and forty-one swine underwent the insult dive, with 61 swine meeting inclusion criteria (43%). We found no differences in baseline characteristics among the groups. We found no significant differences in functional neurologic outcomes (p = 0.77 and 0.33), spinal cord lesion incidence (p = 0.09 and 0.07), or spinal cord lesion area (p = 0.51 and 0.17) among the four treatment groups or between the two treatment profiles, respectively. While the trends were not statistically significant, animals treated with TT6 had the lowest rates of functional deficits and the fewest spinal cord lesions. Moreover, across all animals, functional neurologic deficit had strong correlation with lesion area pathology (Logistic Regression, p < 0.01, Somers' D = 0.74). CONCLUSIONS: TT6 performed as well as the other treatment tables and is the least resource intensive. TT6 is the most appropriate initial treatment for neurologic DCI in swine, among the tables that we compared.

Hysteria as a Trigger for Epidemic Decompression Sickness Following Hypobaric Hypoxia Training.

INTRODUCTION: Although hypobaric hypoxia training (HHT) is an essential component of aviation physiology training, it poses a risk of decompression sickness (DCS). DCS can sometimes be observed as a cluster of cases, which is referred to as epidemic DCS. In this report, we aim to evaluate an epidemic DCS episode that occurred following two consecutive HHT sessions.METHODS: A total of 16 trainees, all of whom were medical doctors, attended the aviation medicine training course in the aeromedical research and training center. They went through HHT in two sessions, each with eight trainees.RESULTS: Following two HHT sessions, five Type 1 DCS cases occurred among 18 personnel (16 trainees and 2 inside observers). DCS incidence rate was found to be 27.77%. They were successfully treated with hyperbaric oxygen therapy (HBOT).DISCUSSION: Since the DCS incidence rate was found to be higher than the average in such a short period of time, this cluster of cases was labeled as epidemic DCS. We carried out a thorough investigation into all possible causes by following some templates that were developed to conduct comprehensive investigations into epidemic DCS episodes. According to the psychological arguments discussed here, we placed a special emphasis on hysterical and psychosocial components, among other probable factors. In cases where the possibility of hysteria and placebo-nocebo responses exist, it is appropriate to conduct the training and treatment processes with these factors in mind. No matter what the triggering factor is and how the symptoms manifest, HBOT remains crucial in the treatment of DCS.Demir AE, Ata N. Hysteria as a trigger for epidemic decompression sickness following hypobaric hypoxia training. Aerosp Med Hum Perform. 2022; 93(10):712-716.

Recurrent dysbarism presenting with amnesia and hypoaesthesia in a professional breath-hold diver.

Dysbarism is a medical condition arising from change in ambient pressure which outpace the rate at which the body adapts to it. We report a case of recurrent dysbarism consistent with possible decompression illness presenting with amnesia, hypoaesthesia and other neurological manifestations in a professional breath-hold diver treated successfully with hyperbaric oxygen and fluid resuscitation.