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Hyperbaric oxygen in critical care


Hyperbaric oxygen (HBO 2 ) treatment involves intermittent breathing of pure oxygen at greater than ambient pressure (>1.4 atmospheres absolute [ATA]). Over the past 20 years, HBO 2 has undergone refinement, with an increased understanding of the mechanisms of action and clinical applications.

Applications

HBO 2 treatment is carried out in either a monoplace (single person) or multiplace (typically two or more) chamber. Pressures applied while in the chamber are usually 2–3 ATA, representing the sum of the atmospheric pressure plus additional hydrostatic pressure equivalent to 1 or 2 atmospheres. Treatments are usually for 2–8 hours, depending on the indication, and may be performed between 1 and 3 times daily. Monoplace chambers are usually compressed with pure oxygen. Multiplace chambers are pressurized with air, and patients breathe pure oxygen through a tight-fitting face mask, hood, or endotracheal tube. Multiplace chambers require an inside tender to manage the starting and stopping of supplemental oxygen. Patient selection is important when choosing a monoplace vs. multiplace chamber for treatment. During treatment, arterial oxygenation as indexed by the PaO 2 , typically exceeds 2000 mm Hg and levels of 200–400 mm Hg occur in tissues.

HBO 2 should be viewed as a drug and the hyperbaric chamber as a dosing device. Elevating tissue oxygen tension is a primary effect. Although this may alleviate physiologic stress in hypoxic tissues, lasting benefits of HBO 2 must relate to an abatement of the underlying pathophysiologic processes. As knowledge surrounding the biochemical effects of HBO 2 grows, there may be an increase in the list of indications for it. The current accepted indications comprise a heterogeneous group of disorders ( Box 10.1 ), thus implying that there are several mechanisms of action for HBO 2 ( Box 10.2 ).

BOX 10.1
Data from Weaver, LK, ed. Hyperbaric Oxygen Therapy Indications , 13th ed. Durham, NC: Undersea and Hyperbaric Medical Society; 2014.
Accepted Indications for Hyperbaric Oxygen Therapy

  • Air or gas embolism

  • Carbon monoxide poisoning

  • Clostridial myositis and myonecrosis

  • Crush injury, compartment syndrome, acute traumatic ischemia

  • Decompression sickness

  • Enhancement of healing in selected problem wounds

  • Severe anemia

  • Intracranial abscess

  • Necrotizing fasciitis

  • Refractory osteomyelitis

  • Radiation necrosis

    • Delayed radiation injury

  • Compromised skin grafts and flaps

  • Thermal burns

  • Central retinal artery occlusion

  • Idiopathic sudden sensorineural hearing loss

BOX 10.2
Mechanisms of Action of Hyperbaric Oxygen

Related to hyperoxygenation of tissues

  • Angiogenesis/neovascularization/osteogenesis/epithelization in ischemic tissues (mechanisms likely include O 2 behaving as an intracellular signal transducer, leading to augmentation of one or more growth factors and mobilization of vasculogenic stem cells)

  • Bacteriostatic/bactericidal actions

  • Carboxyhemoglobin dissociation hastened

  • Inhibition of Clostridium perfringens alpha toxin synthesis

  • Improved phagocytic bacterial killing

  • Temporary inhibition of neutrophil beta-2-integrin adhesion

  • Vasoconstriction

    • Induction of growth factors and growth factor receptors

    • Inhibition of neutrophil adhesion

    • Reduction of ischemia reperfusion injury

    • Reduction in inflammation and edema

Related to pressurization

  • Reduction of gas bubble volume (Boyle’s law)

In this chapter, we discuss the most common emergent indications for HBO 2.

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