HBOT has been an established treatment for both diving-related and iatrogenic arterial gas embolism (AGE) for many years. It can be secondary to entry of air during vascular surgery, IV therapy, lung biopsy, pulmonary over-inflation during mechanical ventilation, renal dialysis, angiography, etc. Intravascular gas embolism (IGE) and its subset, arterial gas embolism (AGE) may also be caused by penetrating injury to the heart or major vessels, blunt injury to the chest, and by other medical procedures such as insufflation* by gas of a body or organ cavity, and gaseous emission from laser vapor.
*when an inert gas such as carbon dioxide is “blown into” a body cavity to increase space and/or reduce obstruction as in laparoscopic surgery.
All tissues are susceptible to IGE/AGE, and may involve the spinal cord or the brain. Injuries range from a transient ischemic attack-like event (TIA) to a major stroke. When involvement includes the nervous system or heart symptomatology, impact ranges from simple malaise to full neurologic and cardiovascular collapse.
Gas emboli may impede blood and lymphatic flow by blocking the vessel. This results in damage to the vascular lining and causes an immune reaction. The decreased blood supply triggers an ischemic response.
Recovery from CNS IGE/AGE involves the umbra, the region of ischemically destroyed or infracted tissue, and the surrounding penumbra region of viable but functionally impaired tissue. The goal of HBOT is to minimize conversion of penumbral to umbral tissue in regions of marginal brain or spinal cord oxygenation. HBOT may also help prevent leukocyte adherence and mitigate lipid peroxidation in the injured region and slow the progression of ischemic injury.
There are no controlled trials demonstrating the positive effect of HBOT; however, there are numerous case reports and sound mechanistic principles that support its use in AGE. The high oxygen tension promotes the reabsorption of nitrogen from the bubble in accordance with Boyle’s law. Using a standard HBOT treatment protocol for AGE, a gas bubble will be reduced to 82% with a 45% decrease in volume. At this size the bubble can pass through the circulation and embolism may be resolved.
Moon and Gorman report substantial improvement in patients with AGE treated with HBOT. Three hundred forty-six (78%) of the 441 patients who received HBOT fully recovered and 20 (4%) died. Of the 288 with no HBOT, 74 (26%) recovered and 151 (52%) died. Anaesthetizing patients at risk of AGE (such as those undergoing neurosurgery in the sitting position, need to be aware of what HBOT services are available.45
So far, the use of drugs to treat IGE/AGE has not been useful; recompression is the only successful therapy. Promising clinical results in patients with residual neurologic damage with a series of “tailing” HBOT treatments have been seen with low-dose pressures (1.5-2.5).
45R. Moon and D. Gorman. Treatment of the decompression disorders. In: Brubank A, Neuman T. eds. Physiology and Medicine of Diving (5th edition). London: Saunders, 2003; 600-650.