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.

Department of Defense positions on alternative uses of hyperbaric oxygen therapy.

Hyperbaric oxygen therapy is an existing and approved treatment to address multiple medical conditions, including decompression sickness, air or gas embolism, carbon monoxide poisoning, and profound blood loss when transfusion cannot be accomplished. However, recent efforts have emerged to promote hyperbaric oxygen therapy for other purposes. The most controversial applications have been utilizing this therapy as a treatment for mild traumatic brain injury and post-traumatic stress disorder. As evidence accumulates and the debate continues about whether published studies have satisfied the threshold of clinical significance, a common issue is raised regarding current clinical practices and health insurance coverage as allowed or recommended by the Department of Defense and other federal agencies. This review describes the current federal policies regarding medical insurance issues for providers and clinical practice guidelines as they pertain to alternative uses of hyperbaric oxygen therapy. First, the current policies are explored for what is reimbursable under federal insurance as approved clinical or research usages. Second, these policies are compared to the clinical practice guidelines to determine what might be clinical best practice versus exploratory research. Third, the evidence from government reports is reviewed as supporting documentation for these positions. As such, the current discussion addresses what can and cannot be covered under health insurance and where various federal health care organizations stand currently on using hyperbaric oxygen therapy as an alternative therapeutic technique. The primary goal is informing military healthcare practitioners and prospective patients about the treatment options available to them under current federal guidelines.

Alternative Uses of Hyperbaric Oxygen Therapy in Military Medicine: Current Positions and Future Directions.

INTRODUCTION: Hyperbaric oxygen therapy (HBOT) is a commonly used treatment for a variety of medical issues, including more than a dozen currently approved uses. However, there are alternative proposed uses that have significant implications among an active duty military or veteran population as treatments for PTSD, mild traumatic brain injury (mTBI), and traumatic brain injury (TBI). These applications have seen a recent groundswell of support from the operator and veteran communities, raising the visibility of using HBOT for alternative applications. The current review will cover the existing evidence regarding alternative uses of HBOT in military medicine and provide several possibilities to explain the potential conflicting evidence from empirical results. MATERIALS AND METHODS: There were no inclusion or exclusion criteria for articles addressing currently approved HBOT uses as covered under the military health system. These references were provided for comparison and illustration as needed. For alternative HBOT uses, the review focuses explicitly upon three alternative uses in PTSD, mTBI, and TBI. The review addresses any piece of case study evidence, observational data, quasi-experimental design, or randomized-controlled trial that explored any or a combination of these issues within an active duty population, a veteran population, or a civilian population. RESULTS: The existing medical evidence does not support a consensus viewpoint for these alternative uses of HBOT. Based on the literature review, there are four competing positions to explain the lack of consistency among the empirical results. These possibilities are described in no particular order. First, an explanation suggests that the results are because of placebo effects. The combination of participant expectations and subjective symptom reporting creates the potential that reported improvements are because of placebo rather than casual mechanisms. Second, another position suggests that experiments have utilized sham conditions which induced therapeutic benefits. If sham conditions have actually been weakened active treatment conditions, rather than placebo controls, it could explain the lack of observed significant differences in randomized clinical trials. Third, there has been a substantial amount of heterogeneity both in the symptoms treated and the treatments applied. This heterogeneity could explain the inconsistency of the data and the difficulty in reaching a consensus viewpoint. Fourth, the HBOT treatments may actively treat some tangential medical issue the patient is having. The treatment would thus promote an environment of healing without directly treating either PTSD, mTBI, or TBI, and the reduction in orthogonal medical issues facilitates a pathway to recovery by reducing tangential medical problems. CONCLUSIONS: The mixed empirical evidence does not support recommending HBOT as a primary treatment for PTSD, mTBI, or TBI. If applied under the supervision of a licensed military medical professional, the consistently safe track record of HBOT should allow it to be considered as an alternative treatment for PTSD, mTBI, or TBI once primary treatment methods have failed to produce a benefit. However, the evidence does warrant further clinical investigation with particular emphasis on randomized clinical trials, better placebo controls, and a need to develop a consistent treatment protocol.

Effect sizes for symptomatic and cognitive improvements in traumatic brain injury following hyperbaric oxygen therapy.

Hyperbaric oxygen therapy has been proposed as a method to treat traumatic brain injuries. The combination of pressure and increased oxygen concentration produces a higher content of dissolved oxygen in the bloodstream, which could generate a therapeutic benefit for brain injuries. This dissolved oxygen penetrates deeper into damaged brain tissue than otherwise possible and promotes healing. The result includes improved cognitive functioning and an alleviation of symptoms. However, randomized controlled trials have failed to produce consistent conclusions across multiple studies. There are numerous explanations that might account for the mixed evidence, although one possibility is that prior evidence focuses primarily on statistical significance. The current analyses explored existing evidence by calculating an effect size from each active treatment group and each control group among previous studies. An effect size measure offers several advantages when comparing across studies, as it can be used to directly contrast evidence from different scales, and it provides a proximal measure of clinical significance. When exploring the therapeutic benefit through effect sizes, there was a robust and consistent benefit to individuals who underwent hyperbaric oxygen therapy. Placebo effects from the control condition could account for approximately one-third of the observed benefits, but there appeared to be a clinically significant benefit to using hyperbaric oxygen therapy as a treatment intervention for traumatic brain injuries. This evidence highlights the need for design improvements when exploring interventions for traumatic brain injury and the importance of focusing on clinical significance in addition to statistical significance.

Case Series of Arterial Gas Embolism Incidents in U.S. Navy Pressurized Submarine Escape Training From 2018 to 2019.

The goal of Pressurized Submarine Escape Training (PSET) is to prepare future submariners for the physical and mental challenges of escaping a disabled submarine and promote proper handling of the Beaufort Ltd Mk 11 Submarine Escape and Immersion Equipment suit. Training participants are only permitted to enter PSET after strict health screening protocols have been met to optimize trainees' safety. Before PSET, trainees are given detailed, one-on-one instruction on proper ascent mechanics by specially trained Navy Dive instructors. Since the reinstatement of PSET by the U.S. Navy, four incidents of arterial gas embolism (AGE) have occurred in submarine trainees with a 10-year period (2009-2019). Of these four incidents, three were observed within a couple months of each other from 2018 to 2019. A comprehensive review of AGE history, epidemiology, dive physiology, pathophysiology, and management was completed. Prompted by the recent incidents relative to the low reported incidence rate of AGE in historical PSET training, reported potential risk factors were compared with better understand potential etiologies of AGE in already medically screened individuals. Risks and benefits of PSET were listed, compared, and analyzed. The relative safety and cost effectiveness of this rigorous form of training was reconfirmed.

Gallbladder Carcinoma, the Difficulty of Early Detection: A Case Report.

Gallbladder carcinoma (GBC) is an uncommon malignancy with a high mortality rate. Detecting gallbladder carcinoma in its early stages can be difficult, despite improvements in ultrasound and computed tomography (CT) imaging. Most diagnoses of GBC are made at advanced stages, with the majority being found incidentally during surgery for cholelithiasis. The presented case demonstrates the difficulty of diagnosing GBC preoperatively in its early stages.

Oxygen breathing accelerates decompression from saturation at 40 msw in 70-kg swine.

INTRODUCTION: Submarine disaster survivors can be transferred from a disabled submarine at a pressure of 40 meters of seawater (msw) to a new rescue vehicle; however, they face an inherently risky surface interval before recompression and an enormous decompression obligation due to a high likelihood of saturation. The goal was to design a safe decompression protocol using oxygen breathing and a trial-and-error methodology. We hypothesized that depth, timing, and duration of oxygen breathing during decompression from saturation play a role to mitigate decompression outcomes. METHODS: Yorkshire swine (67-75 kg), compressed to 40 msw for 22 h, underwent one of three accelerated decompression profiles: (1) 13.3 h staged air decompression to 18 msw, followed by 1 h oxygen breathing, then dropout; (2) direct decompression to 18 msw followed by 1 h oxygen breathing then dropout; and (3) 1 h oxygen prebreathe at 40 msw followed by 1 h mixed gas breathing at 26 msw, 1 h oxygen breathing at 18 msw, and 1 h ascent breathing oxygen. Animals underwent 2-h observation for signs of DCS. RESULTS: Profile 1 (14.3 h total) resulted in no deaths, no Type II DCS, and 20% Type I DCS. Profile 2 (2.1 h total) resulted in 13% death, 50% Type II DCS, and 75% Type I DCS. Profile 3 (4.5 h total) resulted in 14% death, 21% Type II DCS, and 57% Type I DCS. No oxygen associated seizures occurred. DISCUSSION: Profile 1 performed best, shortening decompression with no death or severe DCS, yet it may still exceed emergency operational utility in an actual submarine rescue.

Neuroimaging of hemorrhage and vascular malformations.

Nontraumatic spontaneous intracranial hemorrhage occurs most commonly into the subarachnoid space and brain parenchyma, in contrast to subdural and epidural hematomas that are usually traumatic. The differential diagnosis of nontraumatic subarachnoid hemorrhage includes intracranial aneurysm rupture and vascular malformations, both of which may be investigated noninvasively with computed tomography and magnetic resonance imaging. An isolated intraparenchymal hematoma may be caused by hypertensive vasculopathy, amyloid angiopathy, vascular malformations, or by primary or secondary neoplasms. Knowledge of the appearance of intracerebral vascular malformations will help clinicians request appropriate further imaging and direct treatment.

Decompression sickness in a swine model: isobaric denitrogenation and perfluorocarbon at depth.

INTRODUCTION: Disabled submarine survivors could achieve inert gas tissue saturation likely to cause severe decompression sickness (DCS) on surfacing. This risk increases with time and depth of exposure. Methods to reduce DCS risk and severity are needed specifically for such an operational scenario. METHODS: Yorkshire swine (16.2-26.6 kg) fitted with an external jugular catheter were compressed to 5 ATA for 22 h. They then received an enriched breathing mix of 44% N2 and 56% O2, and an infusion of either saline or a perfluorocarbon (PFC) emulsion, and were observed for 2 h before surfacing without decompression stops. Controls were surfaced after 22 h saturation at 5 ATA. Surface observations continued for another 2 h on all animals and signs of DCS were recorded to the nearest minute. RESULTS: Seizure activity at depth was noted in 0/26 controls, 1/16 in the saline group, and 7/16 in the PFC group. DCS in < 2 h occurred in 25/26 air controls, 2/15 in the enriched mix/saline group, and 4/9 not suffering seizure in the enriched mix/PFC group. Death in < 2 h occurred in 23/26 controls, 1/15 in the saline group, and 1/9 in the PFC group. DISCUSSION/CONCLUSION: This study demonstrates the benefits of breathing increased O2 at depth prior to rapid decompression and the deleterious effects of PFC administration at depth in a swine saturation model with rapid decompression. Future studies should examine a minimal O2 pre-breathe period to offer protection against DCS as well as the role of PFC use after surfacing.