Physical Aspects of Undersea and Hyperbaric Medicine

The clinical utilization of alterations in atmospheric pressure dictate that the practitioner comprehends both the beneficial and potentially hazardous aspects of this esoteric environment. Key gas laws and their role in hyperbaric medicine will be reviewed, as will pressure measurement conversions related to different hyperbaric chamber types.

 

Mechanisms of Action

Under increased atmosphere pressure, oxygen becomes a potent and dose dependent drug, one that generates several primary and secondary therapeutic effects. They include hyperoxygenation of critically ischemic tissues, bubble volume reduction, vasoconstriction without component hypoxia, neovascularization, fibroplasia, toxin inhibition/inactivation, leukocyte oxidative killing and antagonism of leukocyte induced reperfusion injury. The scientific elucidation of these mechanisms and their clinical relevance are discussed.

 

Patient Care

Emphasis will be placed on the informed consent process, medical history/daily medical status as it relates to hyperbaric-hyperoxic risks, preparation, and education of patients in order to safety and effectively undergo hyperbaric oxygen therapy, related documentation and record keeping.

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Oxygen Toxicity

As a gaseous drug, large doses of oxygen can produce undesirable side effects and drug interactions. The central nervous system and lungs are two most effected organs and their response to hyperbaric oxygen will be reviewed in depth. Special emphasis will be placed on recognition of and management of CNS oxygen toxicity.

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Monoplace Chamber Operations

Through didactic and clinical training sessions (presently limited to video demonstrations as a function of virtual training), prospective hyperbaric team members will appreciate all aspects of the monoplace hyperbaric chamber delivery system.  Standard operational protocols will be augmented with ancillary equipment demonstrations and a detailed review of emergency procedures.

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Contraindications and Risk Factors

Pre-exposure evaluation of risk factors primarily centers on pulmonary barotrauma of ascent and central nervous system oxygen intolerance. The risk-benefit ratio for the range of clinical indications and additional risks associated with the clinical practice of hyperbaric medicine will be comprehensively addressed.

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Non-pulmonary Barotrauma

Boyle’s law dictates that gas volume is inversely proportional to alterations in ambient pressure.  The clinical ramifications of this simple principle as they relate to gas containing and potential gas bearing anatomy will be discussed. The effects of pressure changes and injury mitigation strategies within the middle ear will be examined in detail. Indications for ENT referral for ventilation tubes will be discussed as will the indications, technique and risks associated with emergent needle myringotomy.

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Carbon Monoxide Poisoning/Smoke Inhalation - Cyanide Poisoning

Carbon monoxide is the most common cause of accidental and intentional poisoning. In its subtle form the diagnosis is easily missed. A new appreciation for the phenomenon of clinical relapse following conventional oxygen therapy and the potential for long-term sequelae has reshaped our understanding of this toxic gas and its injurious management. Current concepts of its pathophysiology are explored and include guidance for the pregnant patients.

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Decompression Sickness

This occupational disease of divers, aviators and tunnel workers is no longer limited in presentation to coastal regions and military institutions. Decompression sickness can result from exposure to any body of water deeper than approximately 33 FSW/2.0 ATA. With more divers flying to and from their dive sites, the potential for illness must be considered, regardless of geographic location. Differential diagnosis, on-site management, evacuation protocols and definitive therapy will be discussed, as will the capabilities of the monoplace chamber.

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Cerebral Arterial Gas Embolism

A major life-threatening event, cerebral arterial gas embolization can occur during decompression (in divers and aviators), traumatically in penetrating chest injuries and, most commonly, in the clinical setting secondary to invasive diagnostic, monitoring, or therapeutic procedures. Presentation, differential diagnosis, and management guidelines will be summarized.

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Crush Injuries/Compartment Syndrome — Other Acute Ischemias

In an earlier report, it was found that when hyperbaric oxygen therapy was used to arrest the progression of a skeletal compartment syndrome, the cost of management was one-fourth that of surgically treated compartment syndromes. While not proposed in severe cases, the use of HBO in compartment syndrome in selected cases is based on its ability to down-regulate leukocyte receptor sites, decrease tissue edema, hyper-oxygenate ischemic tissues and overcome diffusion barriers. Evidence for its role in the management of these acute ischemic injuries is reviewed and a management plan proposed.

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Gas Gangrene (Clostridial and Non-Clostridial) — Necrotizing Soft Tissue Infections

Anaerobic infections are among the most challenging infectious disease problems. Optimum management in many instances mandates a combined therapeutic regimen using antibiotics and surgery in combination with adjunctive hyperbaric oxygen when available.There is a growing body of evidence to indicate that HBO provides a number of benefits, which include detoxification of the patient, enhanced white cell activity, synergistic enhancement of selected antibiotics, and improved wound healing.

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Mandibular Osteoradionecrosis

Upon identification of a hypo-vascular, hypo-cellular, hypoxic pathophysiologic underpinning in the early 1980’s, a management scheme that employed hyperbaric oxygen as either primary therapy for early-stage disease or as peri-operative support of advanced cases was introduced. It was called the Marx Protocol. By the turn of the century, advances in microsurgery and free tissue transfer resulted in “single stage” mandibular resection and reconstruction widely considered as standard of care. This modern approach obviated the need for peri-operative hyperbaric oxygenation in advanced stages, and new surgical techniques are also in use to avoid progression to full resection and reconstruction. Antioxidant medical therapy was also introduced at the same time for management of osteoradionecrosis in its early stages. This presentation will address in detail the evolution of ORN management, supportive medical science into the current era, and identify the current role of HBO therapy.  

 

Radiation-Induced Soft Tissue Injuries

The evolution of high-quality laboratory and clinical efficacy evidence has elevated this indication to essential hyperbaric standard of care. Anatomic-specific practice guidelines increasingly incorporate HBO therapy into their management algorithms. This presentation will summarize this evidence evolution, reconcile conflicting data in one clinical trial and provide dosing guidelines that optimize cost-effective outcomes.

 

Selected Problem Wounds; Diabetic Wound Healing; Compromised Skin Flaps

While not indicated for the support of adequately perfused tissue, hyperbaric oxygen can play an important adjunctive role where hypoxia or decreased microcirculatory flow complicates wound healing. In the compromised host setting, HBO can restore a favorable cellular milieu in which the wound repair process and host antibiotic mechanisms are enhanced. Several presentations will address these related indications and provide a detailed reconciliation of conflicting diabetic foot trials.

 

Sudden Sensorineural Hearing Loss

This represents one of the more recent additions to the USA Federal Drug Administration listing of approved hyperbaric uses and now included within authoritative clinical practice guidelines. Given the unique nature of the inner ear’s blood supply it is particularly vulnerable to ischemia/hypoxia. A considerable body of laboratory and clinical data provides a solid foundation for HBO therapy, as both primary therapy in conjunction with steroids and as “salvage” therapy. All of this will be summarized, and a highly regarded management algorithm described. 

 

Central Retinal Artery Occlusion

This is another example of a newly approved FDA indication and increasingly recognized as inherently valuable within the ophthalmology discipline. Supportive literature, hyperbaric medicine’s  rationale, patient selection criteria and clinical management guidelines will be reviewed in detail.

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Transcutaneous Oximetry

Drawing upon the orthopedic and vascular and plastic surgery literature, several indicators have served to both predict outcome from various procedures and determine the degree of severity in vascular disease. One key assessment is tissue oxygen tension, as measured in a transcutaneous manner. It has been introduced into the practice of hyperbaric oxygen as an evidence-based technology. It serves to identity the potential value/indication of oxygen supplementation, confirm a patient’s physiologic capacity to respond at the lesion site to inhaled hyperoxia, guide hyperbaric dosing and help identify the point of maximum benefit. An algorithmic screening and case-management protocol will be presented.

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Case Presentations

Interesting clinical problems and case illustrations will be presented. Cases have been selected which will emphasize key management principles.

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Hyperbaric Emergency Procedures

Effective operational practice mandates the ability to recognize potential and actual threats to patient and staff member safety.  Examples include sudden deterioration in patient status, equipment malfunction, and hazards within or near the hyperbaric facility. Protocols to address each emergency will be described, and complemented by several drills, including emergency evacuation of the facility during simulated patient treatments.

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The Multiplace Chamber

A presentation will describe the design, installation, and operational characteristics of the multiplace hyperbaric delivery system. Chamber nomenclature, air compression options, gas filtration, oxygen delivery systems, fire suppression options, and inside attendance safety will be summarized.  Special attention will be focused on related National Fire Protection Association Standards for safe practice.