Point-of-care ultrasound in a multiplace hyperbaric chamber

Historically, electronic devices have been generally prohibited during hyperbaric oxygen (HBO2) therapy due to risk of fire in a pressurized, oxygen-rich environment. Point-of-care ultrasound (POCUS), however, has emerged as a useful imaging modality in diverse clinical settings. Hyperbaric chambers treating critically ill patients would benefit from the application of POCUS at pressure to make real-time patient assessments. Thus far, POCUS during HBO2 therapy has been limited due to required equipment modifications to meet safety standards. Here we demonstrate proof of concept, safety, and successful performance of an off-the-shelf handheld POCUS system (SonoSite iViz) in a clinical hyperbaric environment without need for modification.

Brain stem and spinal cord demyelination due to acute carbon monoxide poisoning

Demyelination throughout the brain stem and spinal cord caused by acute carbon monoxide (CO) poisoning has not been previously reported. Magnetic resonance imaging (MRI) has revealed that acute CO poisoning primarily affects the subcortical white matter of the bilateral cerebral hemispheres and basal ganglia. Here we report the case of a patient with delayed neuropsychological sequelae (DNS) due to acute CO poisoning. A 28-year-old man was admitted to our department following a suicide attempt by acute CO poisoning. After a six-month pseudo-recovery period, he was diagnosed with DNS, with MRI evidence of demyelinating change of the bilateral cerebral peduncles. Demyelination was identified throughout the brain stem, expanding from the bilateral cerebral peduncles to the medulla oblongata, occurring approximately six months after poisoning. One and a half years after acute CO poisoning, demyelination of the cervical and thoracic spine was observed, most notable in the lateral and posterior cords. It is evident that previously published research on this topic is extremely limited. Perhaps in severe cases of acute CO poisoning the fatality rate is higher, leading to fewer surviving cases for possible study. This may be because a more severe case of acute CO poisoning would result in the higher likelihood of secondary demyelination. This research indicates that clinicians should be aware of the risk of secondary demyelination and take increased precautions such as vitamin B supplementation and administration of low-dose corticosteroids for an extended period of time in order to reduce the extent and severity of demyelination.

Submarine medicine: An overview of the unique challenges, medical concerns, and gaps

Submariners face many challenges. For example, they “live where they work” and can be called to duty anytime. They have limited access to open space, natural settings, fresh air, fresh food, sunlight, privacy, exercise, and outside communication. They support a wider range of missions than occur aboard most other Navy vessels. At sea or on shore, submariners work long hours under conditions with little margin for error. They may traverse remote or disputed areas of the ocean far from rescue assets, and must remain vigilant for potential encounters with hostile forces, onboard fires, anomalies in the breathing atmosphere, leaks, undersea collisions, or radiation exposures. If any of these factors cause casualties, the Independent Duty Corpsman (with intermittent advice from shore-based medical personnel), must be ready to provide aid as long as necessary. The challenges of submarine service led to the growth of the unique field of submarine medicine, which has maintained an excellent record of health and safety. This review introduces the field of submarine medicine as practiced in the U.S. Navy, describing its major concerns, giving an overview of the operation of a submarine medical department, and identifying several medical gaps that researchers are working to fill. Submarine medicine already has a stellar record in terms of radiation and atmospheric safety and has made strides in fatigue management. Ongoing work will deliver improved psychological screening and support tools. This report summarizes developments in these and other areas of submarine medicine.

Effects of hyperbaric oxygen pretreatment on brain antioxidant capacity in rats with decompression sickness

Objective: Decompression sickness (DCS) causes serious brain hypoxic-ischemic injury. This experiment was designed to observe whether hyperbaric oxygen (HBO2) pretreatment played a neuroprotective effect in decompression sickness rat models and to explore the mechanism of protective effects. Methods: Sprague-Dawley (SD) male rats were pretreated with HBO2 and then underwent decompression to establish the DCS rat model. Antioxidant capacities were evaluated by detecting peroxides (GPx), superoxide dismutase (SOD), catalase (CAT) activity and malondialdehyde (MDA) content in brains. The levels of metal elements manganese (Mn), zinc (Zn), iron (Fe) and magnesium (Mg) in brain tissues were assessed by flame atomic absorption spectrometry. Necrosis and apoptosis of neurons were assessed by H-E staining and immunohistochemical staining. Results: HBO2 pretreatment reduced the degree of necrosis and apoptosis in brain tissues of decompression sickness rat models. In addition, HBO2 pretreatment increased GPx, SOD and CAT activities and reduced MDA accumulation. It also increased the content of Mn, Zn, Fe and Mg in brain tissue, which are all related to free radical metabolism. Conclusion: These results suggested that HBO2 pretreatment has protective effects on brain injury of rats with decompression sickness. The mechanism of the protective effects may be related to reducing oxidative damage by affecting metal elements in vivo.

Multiple and early hyperbaric oxygen treatments enhance muscle healing after muscle contusion injury: a pilot study

Background: The optimal timing of hyperbaric oxygen (HBO2) treatments for the best recovery following muscle injury has yet to be determined. Thus, the optimal number and timing of HBO2 treatments for maximal muscle regeneration were explored. Methods: The HBO2 treatment protocol consisted of 2.5 ATA 100% oxygen for 120 minutes. Muscle-injured rats were randomized to one of 10 groups: single HBO2 treatment immediately after injury (HBO 1T day 0), one day (HBO 1T day 1), three days (HBO 1T day 3) and five days (HBO 1T day 5) after injury; three HBO2 treatments from immediately after injury to two days after injury (HBO 3T day 0-2), from one to three days after injury (HBO 3T day 1-3), from three to five days after injury (HBO 3T day 3-5), from five to seven days after injury (HBO 3T day 5-7); five daily HBO2 treatments (HBO 5T); and no treatment (NT). Results: HBO 5T and HBO 3T day 0-2, days 1-3 and days 3-5 significantly promoted CD206-positive cell infiltration, satellite cell differentiation and muscle regeneration compared to the NT group. Conclusion: Five HBO2 treatments and three HBO2 treatments within three days of injury promote muscle regeneration.

Decrease in dysbaric osteonecrosis severity as a result of 45-minute oxygen pre-breathe

Sudden decompression can result in bubble formation as the result of nitrogen gas (N2) dissolved in tissue during disabled submarine escape (DISSUB). This may cause dysbaric osteonecrosis (DON), a condition in long bones where bubbles in fatty marrow result in ischemia and necrosis. Previous research has shown that oxygen (O2) pre-breathe of two hours resulted in a reduction of DON; however, effects of shorter O2 pre-breathe remain uncertain. This study’s aim was to understand the effect of shorter lengths of O2 pre-breathe. Eight adult Suffolk ewes (89.5± 11.5 kg) were exposed to 33 feet of seawater (fsw) for 24 hours. They were placed randomly into four groups and exposed to either 45, 30 or 15 minutes of O2 (91-88%) pre-breathe; the controls received none. They were then rapidly decompressed. Alizarin complexone was later injected intravenously to visualize the extent of DON in the right and left long bones (radii, tibiae, femur and humeri). The 30- and 15-minute pre-breathe groups saw the greatest deposition. There was significant decrease of variance in the 45-minute group when compared with all other treatments, suggesting that 45 minutes of O2 pre-breathe is required to effectively increase confidence in the reduction of DON. Similar confidence was not reflected in the 30-minute and 15-minute groups: 45 minutes of pre-breathe was the minimum amount needed to effectively prevent against DON in DISSUB escape at 33 fsw. However, future research is needed to determine how to calculate effective dosages of O2 pre-breathe to prevent DON in any given scenario.

Hyperbaric oxygen therapy and fluorescence angiography in arterial insufficiency secondary to injection of crushed hydromorphone

Introduction: Foreign body emboli can lead to acute arterial insufficiency. We present a case report of upper extremity arterial insufficiency in an intravenous (IV) drug user secondary to intra-arterial injection of crushed tablet particles successfully treated with hyperbaric oxygen (HBO2) therapy. Case: A 37-year-old right-hand-dominant male developed pain and swelling of the left hand after attempting to inject crushed hydromorphone tablets into his venous circulation. Angiography revealed incomplete distal filling of the proper digital arteries, princeps pollicis, and radialis indicis branches of the left hand. The patient was treated with HBO2 for acute arterial insufficiency, secondary to these findings. Fluorescence angiography was performed prior to, during and after completion of HBO2, which showed improved perfusion of the hand upon completion of serial imaging. The patient underwent subsequent partial amputation of the left second digit and removal of the thenar and third finger pads. Discussion: Much of the literature on treatment of arterial insufficiency with HBO2 are in relation to chronic problem wounds. However, there is limited data on adjunctive treatment with HBO2 for foreign body embolism. Fluorescence angiography and clinical exam were used to track tissue perfusion and progression throughout course of therapy with HBO2. Conclusion: Acute arterial insufficiency induced by foreign body embolism was successfully treated with HBO2 and provided increased tissue salvage of the patient’s hand. The use of fluorescence angiography as a secondary measure of perfusion can provide additional insight regarding qualitative tissue oxygenation and may be a viable tool to track patient progress during HBO2 treatment.

Hyperbaric oxygen for refractory osteomyelitis

Refractory osteomyelitis is defined as a chronic osteomyelitis that persists or recurs after appropriate interventions have been performed or where acute osteomyelitis has not responded to accepted management techniques [1]. To date, no randomized clinical trials examining the effects of hyperbaric oxygen (HBO2) therapy on refractory osteomyelitis exist, and the number of new osteomyelitis clinical trials conducted over the past decade has been limited. However, based on a comprehensive review of the scientific literature, the addition of HBO2 therapy to routine surgical and antibiotic treatment of previously refractory osteomyelitis appears to be both safe and ultimately improves infection resolution rates. In most cases, the best clinical results are obtained when HBO2 treatment is administered in conjunction with culture-directed antibiotics and initiated soon after clinically indicated surgical debridement. Where extensive surgical debridement or removal of fixation hardware is relatively contraindicated (e.g., cranial, spinal, sternal, or pediatric osteomyelitis), a trial of culture-directed antibiotics and HBO2 therapy prior to undertaking more than limited surgical interventions provides a reasonable prospect for osteomyelitis cure. HBO2 therapy is ordinarily delivered on a once daily basis, five-seven days per week, for 90–120 minutes using 2.0–3.0 atmospheres absolute (ATA) pressure. Where prompt clinical improvement is seen, the existing regimen of antibiotics and HBO2 therapy should be continued for approximately four to six weeks. Typically, 20–40 HBO2 sessions are required to achieve sustained therapeutic benefit. In contrast, if prompt clinical response is not noted or osteomyelitis recurs after this initial treatment period, then continuation of the current antibiotic and HBO2 treatment regimen is unlikely to be effective. Instead, clinical management strategies should be reassessed and additional surgical debridement and/or modification of antibiotic therapy considered. Subsequent reinstitution of HBO2 therapy will again help maximize the overall chances for treatment success in these persistently refractory patients.

The effect of total compression time and rate (slope) of compression on the incidence of symptomatic Eustachian tube dysfunction and middle ear barotrauma: a Phase II prospective study

Eustachian tube dysfunction (ETD) and middle ear barotrauma (MEB) are common reported complications during hyperbaric oxygen treatment. Our Phase I study data was the first to demonstrate a statistically significant decrease in the occurrence of symptomatic ETD and MEB. The Phase I Trial suggested the total time interval and rate (slope) of compression (ROC) may be a determining factor in ETD and MEB. This Phase II study investigates an optimal rate of compression to reduce ETD and MEB when considering each multiplace treatment (with multiple patients) as the unit of observation as a group, rather than for each individual patient. Data were collected prospectively on 1,244 group patient-treatment exposures, collectively including 5,072 individual patient-treatment/exposures. We randomly assigned patient-treatment group exposures to four different time interval and rate (slope) of compression. These compression rates and slopes were identical to those used in the Phase I trial. All patients experiencing symptoms of MEB requiring compression stops were evaluated post treatment for the presence of ETD and MEB using the O’Neill Grading System (OGS) for ETD. Data were analyzed using the IBM-SPSS statistical software program. A statistically significant decrease in the number of compression holds was observed in the 15-minute compression schedule, correlating to the results observed in the Phase I trial. The 15-minute linear compression profile continues to demonstrate the decreased need for patient symptomatic compression stops (as in the Phase I trial) using a USN TT9 during elective hyperbaric oxygen treatments in a Class A multiplace hyperbaric chamber. Trial Registration: ClinicalTrials.gov Identifier: NCT04776967

Changes in acid-base status in oxygen toxicity at 230 kPa oxygen as a function of exposure time

Breathing less than 50 kPa of oxygen over time can lead to pulmonary oxygen toxicity (POT). Vital capacity (VC) as the sole parameter for POT has its limitations. In this study we try to find out the changes of acid-base status in a POT rat model. Fifty male rats were randomly divided into five groups, exposed to 230 kPa oxygen for three, six, nine and 12 hours, respectively. Rats exposed to air were used as controls. After exposure the mortality and behavior of rats were observed. Arterial blood samples were collected for acid-base status detection and wet-dry (W/D) ratios of lung tissues were tested. Results showed that the acid-base status in rats exposed to 230 kPa oxygen presented a dynamic change. The primary status was in the compensatory period when primary respiratory acidosis was mixed with compensated metabolic alkalosis. Then the status changed to decompensated alkalosis and developed to decompensated acidosis in the end. pH, PCO2, HCO3-, TCO2, and BE values had two phases: an increase and a later decrease with increasing oxygen exposure time, while PaO2 and lung W/D ratio showed continuously increasing trends with the extension of oxygen exposure time. Lung W/D ratio was significantly associated with PaO2 (r = 0.6385, p = 0.002), while other parameters did not show a significant correlation. It is concluded that acid-base status in POT rats presents a dynamic change: in the compensatory period first, then turns to decompensated alkalosis and ends up with decompensated acidosis status. Blood gas analysis is a useful method to monitor the development of POT.