Hyperbaric oxygen does not improve cerebral function when started 2 or 4 hours after cerebral arterial gas embolism in swine

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.

Does hyperbaric oxygen cause narcosis or hyperexcitability? A quantitative EEG analysis

Divers breathe higher partial pressures of oxygen at depth than at the surface. The literature and diving community are divided on whether or not oxygen is narcotic. Conversely, hyperbaric oxygen may induce dose-dependent cerebral hyperexcitability. This study evaluated whether hyperbaric oxygen causes similar narcotic effects to nitrogen, and investigated oxygen's hyperexcitability effect. Twelve human participants breathed "normobaric" air and 100% oxygen, and "hyperbaric" 100% oxygen at 142 and 284 kPa, while psychometric performance, electroencephalography (EEG), and task load perception were measured. EEG was analyzed with functional connectivity and temporal complexity algorithms. The spatial functional connectivity, estimated using mutual information, was summarized with the global efficiency network measure. Temporal complexity was calculated with a "default-mode-network (DMN) complexity" algorithm. Hyperbaric oxygen-breathing caused no change in EEG global efficiency or in the psychometric test. However, oxygen caused a significant reduction of DMN complexity and a reduction in task load perception. Hyperbaric oxygen did not cause the same changes in EEG global efficiency seen with hyperbaric air, which likely related to a narcotic effect of nitrogen. Hyperbaric oxygen seemed to disturb the time evolution of EEG patterns that could be taken as evidence of early oxygen-induced cortical hyperexcitability. These findings suggest that hyperbaric oxygen is not narcotic and will help inform divers' decisions on suitable gas mixtures.

Investigating critical flicker fusion frequency for monitoring gas narcosis in divers

INTRODUCTION

Critical flicker fusion frequency (CFFF) has been used in various studies to measure the cognitive effects of gas mixtures at depth, sometimes with conflicting or apparently paradoxical results. This study aimed to evaluate a novel automatic CFFF method and investigate whether CFFF can be used to monitor gas-induced narcosis in divers.

METHODS

Three hyperbaric chamber experiments were performed: 1) Automated and manual CFFF measurements during air breathing at 608 kPa (n = 16 subjects); 2) Manual CFFF measurements during air and heliox breathing at sea level (101.3 kPa) and 608 kPa (n = 12); 3) Manual CFFF measurements during oxygen breathing at sea level, 142 and 284 kPa (n = 10). All results were compared to breathing air at sea level.

RESULTS

Only breathing oxygen at sea level, and at 284 kPa, caused a significant decrease in CFFF (2.5% and 2.6% respectively compared to breathing air at sea level. None of the other conditions showed a difference with sea level air breathing.

CONCLUSIONS

CFFF did not significantly change in our experiments when breathing air at 608 kPa compared to air breathing at sea level pressure using both devices. Based on our results CFFF does not seem to be a sensitive tool for measuring gas narcosis in divers in our laboratory setting.

Perioperative Hyperoxyphobia: Justified or Not? Benefits and Harms of Hyperoxia during Surgery

The use of an inspiratory oxygen fraction of 0.80 during surgery is a topic of ongoing debate. Opponents claim that increased oxidative stress, atelectasis, and impaired oxygen delivery due to hyperoxic vasoconstriction are detrimental. Proponents point to the beneficial effects on the incidence of surgical site infections and postoperative nausea and vomiting. Also, hyperoxygenation is thought to extend the safety margin in case of acute intraoperative emergencies. This review provides a comprehensive risk-benefit analysis for the use of perioperative hyperoxia in noncritically ill adults based on clinical evidence and supported by physiological deduction where needed. Data from the field of hyperbaric medicine, as a model of extreme hyperoxygenation, are extrapolated to the perioperative setting. We ultimately conclude that current evidence is in favour of hyperoxia in noncritically ill intubated adult surgical patients.

Massive cerebral air embolism after blunt chest trauma with full neurological recovery

Cerebral air embolism (CAE) is a common, often lethal, complication in blunt and penetrating chest trauma. The factors affecting the outcome of CAE patients are poorly understood, and there is no generally accepted treatment algorithm. In this report, we present the case of a 28-year-old male motorcyclist with a massive CAE, including bilateral internal carotid artery air on computed tomographic examination following blunt chest trauma. With prehospital intubation, oxygen, transfusion, and open laparotomy but without any specific treatment regarding the CAE, a follow-up computed tomography (CT) scan approximately 6 hours later showed resolution of the cerebrovascular air. Recovery was unremarkable, and the patient was discharged neurologically intact after 22 days.