Hyperbaric Oxygen Therapy Indications Simplified

Indication #1: Air Embolism

Hyperbaric oxygen therapy (HBOT) is an effective, accessible, and safe therapeutic modality in the treatment of an extensive variety of clinical conditions. While HBOT is largely used in the treatment of chronic, non-healing wounds, its application extends to both acute hypoxic diseases and many other chronic diseases that present with tissue hypoxia and even intractable infection.¹

While HBO centers have recently gained momentum and experienced growth within the US, they are not a new modality. The first hyperbaric chamber is reported to have been developed 300 years ago and the first HBO chamber in North America was constructed in 1860.² In 1967, the Undersea and Hyperbaric Medical Society (UHMS), previously the “Undersea Medical Society,” was formed to address additional indications.³ In fact, the UHMS has approved indications prior to Food and Drug Administration (FDA) approval, leading the way in terms of best practices and safety.

The FDA has approved 14 indications for HBOT as of 2021. Most of these indications are emergent in nature. A full list can be found in a previous installment of one of our article series “Top Ten Things You Need to Know About HBOT.”

This new series aims to describe and simplify each of these HBOT indications. Join us as we simplify HBOT indications with a brief overview of each of the medical conditions followed by a rationale for the use of HBOT.

What You Should Know About Air Embolism

Air or gas embolism is one of the emergent indications of HBOT. An air embolism occurs when air enters the vascular system and blocks circulation.⁴

There are two types of air emboli, arterial and venous. They can have many different etiologies, with iatrogenic air embolism being the most common. Surgical procedures, particularly those involving the vasculature, certainly place the patient at risk and are a known source of air embolism. These surgical procedures range from neurosurgical interventions to orthopedic and urologic/gynecologic procedures.⁵ Central venous catheter and arterial line placements are major sources of this condition. Hemodialysis has also been associated with air embolism incidence, along with procedures such as endoscopies and tissue biopsies. The surgeries that carry the greatest risk of air embolism are craniotomies performed with the patient in a sitting position, hip replacements, and cardiac surgeries that involve cardiopulmonary bypass.⁶

Other etiologies include penetrating trauma, blunt abdominal trauma, mechanical ventilation, and pulmonary barotrauma during ascent from a dive. Concerning diving, arterial gas embolism is not always related to an abnormal ascent. In fact, air emboli have been reported after a normal ascent and in those instances, emboli have been associated with divers who have an underlying medical history of asthma and bullous disease.⁷ Regardless of the etiology, this condition can arise in virtually all clinical specialties, which makes it of utmost importance that all clinicians can identify and manage air emboli promptly and efficiently.

Typical Case History

A 60-year-old female with no significant medical history s/q to elective right total hip replacement for osteoarthritis. The patient had uneventful surgery but during recovery post-surgery, she suddenly exhibits right sided weakness, slurred speech and confusion with low blood pressure.

Symptoms and Complications of Air Embolism

Symptoms are highly dependent on the location of the embolism and can range from no symptoms to cardiac arrest. Some of the symptoms experienced most by patients include pain, dyspnea, syncope, loss of consciousness, confusion, neurological deficits, and tachypnea.⁸

In the same vein, complications of emboli are also dependent on the site of the embolism. Certainly, some of the sites that would yield the most detrimental effects are the cardiac and cerebral circulations. Symptoms related to right heart failure from pulmonary artery obstruction, such as jugular venous distention and pulmonary edema would accompany the abnormalities seen in the electrocardiogram. Air embolism of the cardiac circulation can result in shock and hypotension, and ultimately lead to cardiac arrest.⁴ The presence of air in the cerebral arterial circulation can lead to transient ischemia or permanent ischemic stroke with irreversible damage.⁹

Venous gas emboli occurring after diving can often be asymptomatic if small enough. This is due to the trapping of the venous gas embolism bubbles within pulmonary capillaries. However, if the gas bubble is large enough, the patient will present with dyspnea, cough, and even pulmonary edema. As the capacity of the capillaries is superseded, bubbles enter the arterial circulation.¹⁰ The mortality rate of air emboli has been reported to be 21%.¹¹

Diagnostic Findings in a Patient With Air Embolism

The true incidence of vascular air embolism is not well established but has been reported to range from 1 in 772 patients to 2.65 per 100,000 hospitalizations.^11,12 These rates are thought to be inaccurate due to a combination of underreporting and asymptomatic cases of air embolism going undiagnosed.¹¹ Additionally, incidence rates will also vary across specific interventions causing the embolism. Specific to arterial gas embolism arising from a diving injury, the evidence suggests an incidence of less than 1 out of 100,000 dives.¹²

Early detection is key to a positive patient outcome. Initial recognition of an acute event is largely achieved through a clinical diagnosis. Thus, further diagnostic approaches are also based on a high level of suspicion. An air embolism should be suspected if there is an acute change in neurological status combined with bradycardia, hypoxia, or hypotension. This is particularly true if this presentation appears during or immediately after the removal of a central venous catheter or surgery with a higher incidence of air embolism such as neurological procedures.¹³ Arterial blood gases will typically show hypoxia and hypercapnia.

No imaging technique has by itself shown to be sufficiently reliable in the diagnosis of a cerebral air embolism. However, computed tomography (CT) of the brain can detect air embolism in the cerebral circulation and is typically the imaging of choice.¹⁴ CT of the chest may also be helpful in the identification of venous gas emboli, particularly in the subclavian and axillary veins, as well as those located in the right ventricle and pulmonary artery.⁵ Magnetic resonance imaging (MRI) also possesses the capability of visualizing gas within cerebral vasculature but has a markedly reduced susceptibility compared to CT. MRI can be useful in the evaluation of ischemia secondary to the embolism rather than the localization of the embolism itself.¹⁵ A precordial ultrasound or transesophageal echocardiography (TEE) can also be used to diagnose a cardiac gas embolus. TEE is very sensitive and can detect as little as 0.02 mL/kg of air.¹⁶

When dealing with air emboli in the cardiac circulation, evidence can be seen during electrocardiography in the form of arrhythmias, ST-segment depressions, and other nonspecific ST-T wave changes reflecting ischemic changes and right ventricular strain.⁹

Treatment for the Patient With Air Embolism

Immediate intervention is necessary for the treatment of an acute air embolism. In the case of an unresponsive patient, it is critical that airway, breathing, and circulation are addressed via cardiopulmonary resuscitation. Identification and removal of the conduit permitting air into the vascular system should be pursued aggressively.¹¹ Oxygen administration via a non-rebreather mask is recommended. If the patient is intubated, the recommendation is to set the FiO₂ at 100%.¹⁷

Positioning becomes important in the treatment of air embolism. Recommended positioning for rendering first aid for arterial gas embolism includes placing the patient in the supine position. Positioning the patient in a lateral decubitus position is recommended if the patient is or becomes unconscious.¹⁸ Removal of an air embolism via the placement of a right atrial catheter is a viable option for those patients who present with an air embolism in this location.¹³

HBOT as an Indication for Air Embolism

Definitive therapy for an air embolus is hyperbaric oxygen therapy, which will ultimately decrease the volume of the air bubbles found intravascularly and thus the magnitude of the obstruction, improving perfusion to the area.¹⁹ This is done by increasing both oxygen tension and ambient pressure within the blood. The hyperoxia experienced by the patient will produce large diffusion gradients that will allow for oxygen to enter the bubble and nitrogen to escape the bubble. The oxygen carrying capacity of plasma increases as a result and will aid in the damage to the microvasculature and the downstream effects.⁶ This includes mitigation of cerebral edema in the case of air emboli causing cerebral damage. Additionally, HBOT is known to decrease the adherence of leukocytes to damage endothelium, which can aid largely with containing inflammatory processes.²⁰

HBOT should be administered as quickly as possible and best results occur within six hours of onset.²¹ If possible initial compression to 2.82 ATA (60 fsw or 18 msw equivalent depth) breathing 100% oxygen is recommended, using U.S. Navy treatment table 6 or equivalent.⁸ Shorter tables designed for use in monoplace chambers have been used with success.²² If clinical response is suboptimal, deeper recompression or extension of tables can be instituted depending on the facility expertise.

A Word to the Wise

·      Maintain a high level of suspicion for air embolism in the setting of new onset neurological or cardiovascular symptoms, immediately or shortly after a procedure.
·      Prompt identification and intervention is key to a good outcome. This should include but not be limited to treatment with HBOT as described above.

Denise Nemeth is a second-year medical student at the University of the Incarnate Word School of Osteopathic Medicine in San Antonio, TX. Formerly a general and vascular surgery PA in a rural community, Ms. Nemeth aspires to become a general surgeon. She is certified wound specialist with the American Board of Wound Management. Her interests include rural health, wound healing, colorectal surgery, and minimally invasive surgery.  

Jayesh B. Shah is Immediate Past President of the American College of Hyperbaric Medicine and serves as medical director for two wound centers based in San Antonio, TX. In addition, he is president of South Texas Wound Associates, San Antonio. He is also the past president of both the American Association of Physicians of Indian Origin and the Bexar County Medical Society and Current of Board of Trustees of Texas Medical Association.   

Join us for the next installment of this series, coming soon.

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