Effects of CO2 on the occurrence of decompression sickness: review of the literature.

Introduction: Inhalation of high concentrations of carbon dioxide (CO2) at atmospheric pressure can be toxic with dose-dependent effects on the cardiorespiratory system or the central nervous system. Exposure to both hyperbaric and hypobaric environments can result in decompression sickness (DCS). The effects of CO2 on DCS are not well documented with conflicting results. The objective was to review the literature to clarify the effects of CO2 inhalation on DCS in the context of hypobaric or hyperbaric exposure. Methods: The systematic review included experimental animal and human studies in hyper- and hypobaric conditions evaluating the effects of CO2 on bubble formation, denitrogenation or the occurrence of DCS. The search was based on MEDLINE and PubMed articles with no language or date restrictions and also included articles from the underwater and aviation medicine literature. Results: Out of 43 articles, only 11 articles were retained and classified according to the criteria of hypo- or hyperbaric exposure, taking into account the duration of CO2 inhalation in relation to exposure and distinguishing experimental work from studies conducted in humans. Conclusions: Before or during a stay in hypobaric conditions, exposure to high concentrations of CO2 favors bubble formation and the occurrence of DCS. In hyperbaric conditions, high CO2 concentrations increase the occurrence of DCS when exposure occurs during the bottom phase at maximum pressure, whereas beneficial effects are observed when exposure occurs during decompression. These opposite effects depending on the timing of exposure could be related to 1) the physical properties of CO2, a highly diffusible gas that can influence bubble formation, 2) vasomotor effects (vasodilation), and 3) anti-inflammatory effects (kinase-nuclear factor and heme oxygenase-1 pathways). The use of O2-CO2 breathing mixtures on the surface after diving may be an avenue worth exploring to prevent DCS.

Static Immersion and Negative Static Lung Load-Induced Right Ventricle Systolic Function Adaptation: A Risk Factor for Immersion Pulmonary Edema.

BACKGROUND: Immersion pulmonary edema (IPE) is a form of hemodynamic edema likely involving individual susceptibility. RESEARCH QUESTION: Can assessing right ventricle (RV) systolic adaptation during immersion be a marker for IPE susceptibility? STUDY DESIGN AND METHODS: Twenty-eight divers participated: 15 study participants with a history of IPE (IPE group; mean ± SD age, 40.2 ± 8.2 years; two women) and 13 control participants (no IPE group; mean ± SD age, 43.1 ± 8.5 years; two women) underwent three transthoracic echocardiography studies under three different conditions: dry (participants were in the supine position on an examination table without immersion), surface immersion (participants were floating prone on the water's surface and breathing through a snorkel), and immersion and negative static lung load (divers were submerged 20 cm below the water's surface in the prone position using a specific snorkel connected to the surface for breathing). Echocardiographic measurements included tricuspid annular plane systolic excursion (TAPSE), tissue S' wave, and right ventricle global strain (RVGLS). RESULTS: For all divers, immersion increased RV preload. In the no IPE group, the increase in RV preload induced by immersion was accompanied by an improvement in the contractility of the RV, as evidenced by increases in TAPSE (17.08 ± 1.15 mm vs 20.89 ± 1.32 mm), S' wave (14.58 ± 2.91 cm/s vs. 16.26 ± 2.77 cm/s), and RVGLS (25.37 ± 2.79 % vs. 27.09 ± 2.89 %). Negative SLL amplified these RV adaptations. In contrast, among divers with IPE, the increase in RV preload did not coincide with an improvement in RV contractility, indicating altered adaptive responses. In the IPE group, the TAPSE values changed from 17.19 ± 1.28 mm to 21.69 ± 1.67 mm and then to 23.55 ± 0.78 mm, respectively, in the dry, surface immersion, and immersion and negative SLL conditions. The S' wave values changed from 13.42 ± 2.94 cm/s to 13.26 ± 2.96 cm/s and then to 12.49 ± 0.77 cm/s, respectively, and the RVGLS values changed from -24.09% ± 2.91% to -23.99% ± 3.38% and then to -21.96% ± 0.55%, respectively. INTERPRETATION: Changes in RV systolic function induced by immersion (especially with the addition of negative static lung load) vary among divers based on the history of IPE. Analyzing ventricular contractility during immersion, particularly RVGLS, could help to identify individual susceptibility in divers. These findings provide insights for the development of preventive strategies. TRIAL REGISTRY: Comité de Protection des Personnes; No.: 21.05.05.35821; Recherche Impliquant la Personne Humaine de type 1 (RIPH1) HPS; No.: 2021-A01225-36.

Case report: Reassessing guidelines for safe resumption of diving after spinal decompression sickness: insights from a challenging case.

Background: Recreational divers who have experienced Spinal Decompression Sickness (DCS) often aspire to return to their diving activities. Traditionally, it is recommended to observe a waiting period of several months before contemplating a return to unrestricted diving, particularly when clinical symptoms are absent, spinal cord Magnetic Resonance Imaging shows no anomalies, and the evaluation for Patent Foramen Ovale (PFO) returns negative results. Methods: This article presents a compelling case study involving a 51-year-old recreational scuba diver who encountered two episodes of spinal decompression illness within a two-year timeframe. Notably, the search for a PFO produced negative results. The primary objective of this article is to underscore the critical importance of a meticulously planned approach to resuming diving after DCS incidents, emphasizing the potential for recurrence and the essential preventive measures. Conclusion: We delve into the intricate decision-making process for returning to diving, emphasizing the significance of clinical evaluations, PFO assessments, spinal cord Magnetic Resonance Imaging, and the absence of clinical symptoms. By recognizing the risk of recurrence and the need for proactive prevention measures, we provide recommendations for both medical professionals and divers, with the ultimate goal of enhancing safety and informed decision-making within the diving community.

Hypoxic loss of consciousness in air diving: two cases of mixtures made hypoxic by oxidation of the scuba diving cylinder.

Without an adequate supply of oxygen from the scuba apparatus, humans would not be able to dive. The air normally contained in a scuba tank is dry and free of toxic gases. The presence of liquid in the tank can cause corrosion and change the composition of the gas mixture. Various chemical reactions consume oxygen, making the mixture hypoxic. We report two cases of internal corrosion of a scuba cylinder rendering the respired gas profoundly hypoxic and causing immediate hypoxic loss of consciousness in divers.

Characterizing Immersion Pulmonary Edema (IPE): A Comparative Study of Military and Recreational Divers.

BACKGROUND: Immersion Pulmonary Edema (IPE) is a common and potentially serious diving accident that can have significant respiratory and cardiac consequences and, in some cases, be fatal. Our objective was to characterize cases of IPE among military trainees and recreational divers and to associate their occurrence with exposure and individual background factors such as age and comorbidity. We conducted a retrospective analysis on the medical records and diving parameters of all patients who were treated for IPE at the Hyperbaric Medicine Department of Sainte-Anne Military Hospital in Toulon, France, between January 2017 and August 2019. In total, 57 subjects were included in this study, with ages ranging from 20 to 62 years. These subjects were divided into two distinct groups based on exposure categories: (1) underwater/surface military training and (2) recreational scuba diving. The first group consisted of 14 individuals (25%) with a mean age of 26.5 ± 2.6 years; while, the second group comprised 43 individuals (75%) with a mean age of 51.2 ± 7.5 years. All divers under the age of 40 were military divers. RESULTS: In 40% of cases, IPE occurred following intense physical exercise. However, this association was observed in only 26% of recreational divers, compared to 86% of military divers. Among civilian recreational divers, no cases of IPE were observed in subjects under the age of 40. The intensity of symptoms was similar between the two groups, but the duration of hospitalization was significantly longer for the recreational subjects. CONCLUSION: It seems that the occurrence of IPE in young and healthy individuals requires their engagement in vigorous physical activity. Additionally, exposure to significant ventilatory constraints is a contributing factor, with the intensity of these conditions seemingly exclusive to military diving environments. In contrast, among civilian recreational divers, IPE tends to occur in subjects with an average age twice that of military divers. Moreover, these individuals exhibit more prominent comorbidity factors, and the average level of environmental stressors is comparatively lower.

Therapeutic management of severe spinal cord decompression sickness in a hyperbaric center.

Introduction: Spinal cord decompression sickness (scDCS) unfortunately has a high rate of long-term sequelae. The purpose of this study was to determine the best therapeutic management in a hyperbaric center and, in particular, the influence of hyperbaric treatment performed according to tables at 4 atm (Comex 30) or 2.8 atm abs (USNT5 or T6 equivalent). Methods: This was a retrospective study that included scDCS with objective sensory or motor deficit affecting the limbs and/or sphincter impairment seen at a single hyperbaric center from 2010 to 2020. Information on dive, time to recompression, and in-hospital management (hyperbaric and medical treatments such as lidocaine) were analyzed as predictor variables, as well as initial clinical severity and clinical deterioration in the first 24 h after initial recompression. The primary endpoint was the presence or absence of sequelae at discharge as assessed by the modified Japanese Orthopaedic Association score. Results: 102 divers (52 ± 16 years, 20 female) were included. In multivariate analysis, high initial clinical severity, deterioration in the first 24 h, and recompression tables at 4 atm versus 2.8 atm abs for both initial and additional recompression were associated with incomplete neurological recovery. Analysis of covariance comparing the effect of initial tables at 2.8 versus 4 atm abs as a function of initial clinical severity showed a significantly lower level of sequelae with tables at 2.8 atm. In studying correlations between exposure times to maximum or cumulative O2 dose and the degree of sequelae, the optimal initial treatment appears to be a balance between administration of a high partial pressure of O2 (2.8 atm) and a limited exposure duration that does not result in pulmonary oxygen toxicity. Further analysis suggests that additional tables in the first 24-48 h at 2.8 atm abs with a Heliox mixture may be beneficial, while the use of lidocaine does not appear to be relevant. Conclusion: Our study shows that the risk of sequelae is related not only to initial severity but also to clinical deterioration in the first 24 h, suggesting the activation of biological cascades that can be mitigated by well-adapted initial and complementary hyperbaric treatment.

Individual Changes in Respiratory Compliance Upon Immersion May Predict Susceptibility to Immersion Pulmonary Edema.

BACKGROUND: Immersion pulmonary edema (IPE) is a frequent diving accident, and it is the primary cause of hospitalization for young military divers during training. The objective of this study was to identify immersion-induced parameters predicting individual susceptibility to IPE. METHODS: Eighteen experienced male divers having completed at least 100 dives were recruited. Eight divers had previously been hospitalized for IPE (IPE), and the other ten had never developed IPE (non-IPE). The two groups were matched for age, BMI, and number of dives performed. Ventilatory function and overall compliance of the respiratory system (Crs) were measured on land and during head-out-of-water immersion. Subjects also performed 30 min of fin swimming in a channel at 33 m min-1. Following this exercise, the presence of extravascular lung water, revealed by ultrasound lung comets (ULC), was assessed. RESULTS: In the whole group, the decrease in Crs upon immersion correlated with the immersion-induced alterations to expiratory reserve volume, ERV (r2 = 0.91; p < 0.001), inspiratory reserve volume, IRV (r2 = 0.94; p < 0.001), and tidal volume, Vt, changes (r2 = 0.43; p < 0.003). The number of ULC correlated strongly with immersion-induced changes in ventilatory function (r2 = 0.818; p < 0.001 for ERV, r2 = 0.849; p < 0.001 for IRV, r2 = 0.304; p = 0.0164 for Vt) and reduced Crs (r2 = 0.19; p < 0.001). The variations of ERV, IRV, and Crs at rest induced by head-out-of-water immersion and the number of ULC measured after swimming for 30 min were significantly greater in IPE subjects. CONCLUSION: In the face of similar immersion stresses, the extent of alterations to ventilatory function and the number of ULCs were very different between individuals but remained statistically correlated. These parameters were significantly greater in divers with a history of IPE. Alterations to pulmonary function and, in particular, to pulmonary compliance induced by head-out-of-water immersion, through their effects on work of breathing appear to allow the identification of divers with a greater susceptibility to developing IPE. Measurement of these parameters could therefore be proposed as a predictive test for the risk of developing IPE.

Oxygen uptake ( V ˙ O2) and pulmonary ventilation ( V ˙ E) during military surface fin swimming in a swimming flume: Effects of surface immersion.

Introduction: During military fin swimming, we suspected that oxygen uptake ( V ˙ O2) and pulmonary ventilation ( V ˙ E) might be much higher than expected. In this framework, we compared these variables in the responses of trained military divers during land cycling and snorkeling exercises. Methods: Eighteen male military divers (32.3 ± 4.2 years; 178.0 ± 5.0 cm; 76.4 ± 3.4 kg; 24.1 ± 2.1 kg m-2) participated in this study. They performed two test exercises on two separate days: a maximal incremental cycle test (land condition), and an incremental fin swimming (fin condition) in a motorized swimming flume. Results: The respective fin and land V ˙ O2max were 3,701 ± 39 mL min-1 and 4,029 ± 63 mL min-1 (p = 0.07), these values were strongly correlated (r 2 = 0.78 p < 0.01). Differences in V ˙ O2max between conditions increased relative to l; V ˙ O2max (r 2 = 0.4 p = 0.01). Fin V ˙ E max values were significantly lower than land V ˙ E max values (p = 0.01). This result was related to both the significantly lower fin Vt and f (p < 0.01 and <0.04, respectively). Consequently, the fin V ˙ E max / V ˙ O2max ratios were significantly lower than the corresponding ratios for land values (p < 0.01), and the fin and land V ˙ E max were not correlated. Other parameters measured at exhaustion-PaO2, PaCO2, and SO2 - were similar in fin and land conditions. Furthermore, no significant differences between land and fin conditions were observed for peak values for heart rate, blood lactate concentration, and respiratory exchange ratio R. Conclusion: Surface immersion did not significantly reduce the V ˙ O2max in trained divers relative to land conditions. As long as V ˙ O2 remained below V ˙ O2max , the V ˙ E values were identical in the two conditions. Only at V ˙ O2max was V ˙ E higher on land. Although reduced by immersion, V ˙ E max provided adequate pulmonary gas exchange during maximal fin swimming.

Symptomatic or asymptomatic SAR-CoV-2 positive divers should be medically evaluated before returning to scuba diving.

Introduction: In order to allow the resumption of diving activities after a COVID-19 infection, French military divers are required to undergo a medical fitness to dive (FTD) assessment. We present here the results of this medical evaluation performed 1 month after the infection. Methods: We retrospectively analyzed between April 2020 and February 2021 200 records of divers suspected of COVID-19 contamination. Data collected included physical examination, ECG, blood biochemistry, chest CT scan and spirometry. Results: 145 PCR-positive subjects were included, representing 8.5% of the total population of French military divers. Two divers were hospitalized, one for pericarditis and the other for non-hypoxemic pneumonia. For the other 143 divers, physical examination, electrocardiogram and blood biology showed no abnormalities. However 5 divers (3.4%) had persistent subjective symptoms including fatigability, exertional dyspnea, dysesthesias and anosmia. 41 subjects (29%) had significant decreases in forced expiratory flows at 25-75% and 50% on spirometry (n = 20) or bilateral ground-glass opacities on chest CT scan (n = 24). Only 3 subjects were affected on both spirometry and chest CT. 45% of these abnormalities were found in subjects who were initially asymptomatic or had non-respiratory symptoms. In case of abnormalities, normalization was obtained within 3 months. The median time to return to diving was 45 days (IQR 30, 64). Conclusion: Our study confirms the need for standardized follow-up in all divers after COVID-19 infection and for maintaining a rest period before resuming diving activities.

[Ibrutinib-associated atrial fibrillation : A therapeutic challenge]. / Fibrillation atriale associée à l'ibrutinib : un challenge thérapeutique.

Ibrutinib is a potent Bruton tyrosine kinase inhibitor and is an effective and well-tolerated treatment for a variety of lymphoid diseases. However, its use is associated with an increased incidence of atrial fibrillation ranging from 4% to 16%. New onset atrial fibrillation in cancer patients is associated with a significantly higher risk of heart failure and thromboembolism, even after adjusting for known risk factors. Ibrutinib also inhibits platelet activation and decisions regarding anticoagulation must be carefully weighed against this increased risk of bleeding. It is well-known that the anti-arrhythmic and antithrombotic strategy for atrial fibrillation related to ibrutinib has its own characteristics. Physicians should be familiar with the special management considerations imposed by this drug. Indeed, the co-prescription of therapy in combination with ibrutinib must be carefully weighed in view of its numerous drug interactions. We review the potential mechanisms and incidence of ibrutinib-associated atrial fibrillation.

Influence of prehospital management on the outcome of spinal cord decompression sickness in scuba divers.

BACKGROUND: Decompression sickness (DCS) with spinal cord involvement has an unfortunately high rate of long-term sequelae. The objective of this study was to determine the association of prehospital variables on the outcome of spinal cord DCS, especially the influence of the initial clinical presentation and the time to recompression. METHODS: This was a retrospective study using prospectively collected data which included divers with spinal cord DCS seen at a single hyperbaric centre study from 2010 to 2018. Information regarding dive, latency of onset of symptoms, time to recompression and prehospital management, that is, use of oxygen, treatment and means of evacuation, were analysed as predictor variables. The initial clinical severity was estimated by the score of the French society of diving and hyperbaric medicine (MEDSUBHYP). The primary end point was the presence or absence of sequelae at discharge assessed by the modified score of the Japanese Orthopedic Association. RESULTS: 195 divers (48±12 years, 42 women) were included. 34% had neurological sequelae at discharge. In multivariate analysis, a MEDSUBHYP score ≥6 and a time to recompression >194 min were significantly associated with incomplete neurological recovery (OR 9.5 (95% CI 4.6 to 19.8), p<0.0001 and OR 2.1 (95% CI 1.03 to 4.5), p=0.04, respectively). Time to recompression only appeared to be significant for patients with high initial clinical severity. As time to recompression increased, the level of sequelae also increased (p=0.014). CONCLUSION: Determining the initial clinical severity is critical in identifying patients who need to be evacuated for recompression as quickly as possible.

Epidemiological, clinical, and echocardiographic features of twenty 'Takotsubo-like' reversible myocardial dysfunction cases with normal coronarography following immersion pulmonary oedema.

BACKGROUND: Pulmonary immersion oedema is a frequent diving accident. Although its outcome is generally favourable within 72 h, it can nonetheless lead to heart failure or sudden death. Cases of transient myocardial dysfunction have been reported in the literature. This phenomenon is similar to Takotsubo syndrome in many ways. It is characterised by transient myocardial hypokinesia, without associated coronary lesions. METHODS: We report on 20 cases of patients who showed transient alteration of left ventricular kinetics with normal coronary angiography over the course of an immersion pulmonary oedema. RESULTS: The echocardiographic localisation of the myocardial damage was generally focal and not centred on the apex with an average left ventricular ejection fraction of 45%. The main anomalies in the electrocardiographic repolarisation were T wave inversion with corrected QT interval prolongation. We also observed a moderate increase in troponin levels, with discordance between the enzymatic peak and the severity of the left ventricle segmental dysfunction. CONCLUSION: These cases suggest the incidence of a clinical entity strongly reminiscent of Takotsubo phenomenon of atypical topography as a consequence of diving accidents.

Clinical problem solving: Mental confusion and hypoxaemia after scuba diving.

INTRODUCTION: We report a case of a diving accident associating both cerebral symptoms and signs of respiratory impairment after two dives. The objective is to describe the process for obtaining the diagnosis. CASE REPORT: A 52-year-old man experienced mental confusion associated with hypoxaemia after surfacing. All decompression procedures were fully respected. The diver had a spatio-temporal disorientation accompanied by a marked tendency to fall asleep spontaneously. He had no dyspnoea and no cough, but crepitations at both lung bases were found with oxygen saturation at 80%. CONCLUSIONS: In this clinical case, cerebral magnetic resonance imaging and chest computed tomography scan helped to exclude other pathology that would have necessitated urgent transfer rather than urgent hyperbaric treatment. The imaging is particularly useful in case of cerebral and respiratory symptoms following scuba diving.

[Nursing care of a patient admitted to a hyperbaric chamber for a chronic wound]. / Prise en charge infirmière d'un patient admis au caisson hyperbare pour une plaie chronique.

The hyperbaric chamber is a particularly relevant therapy for the healing of chronic wounds such as radiation-induced wounds, ulcers, diabetic foot or osteomyelitis. This article describes the pathway of a patient with a chronic wound from the perspective of a hyperbaric medicine nurse.

[Is it possible to dive again after decompression sickness?] / Peut-on replonger après un accident de désaturation ?

Decompression sickness in underwater diving exposes the diver to a risk of clinical sequelae which require specific care. In the absence of sequelae or after clinical recovery, the question of diving again may be raised. As part of a secondary prevention approach, the hyperbaric practitioner measures the physical, psychological and social impact of re-exposure to pressure and the immersion of the patient-diver.