Air embolism
An air embolism, also known as a gas embolism, is a blood vessel blockage caused by one or more bubbles of air or other gas in the circulatory system.[1] Air can be introduced into the circulation during surgical procedures, lung over-expansion injury, decompression, and a few other causes. In flora, air embolisms may also occur in the xylem of vascular plants, especially when suffering from water stress.[2]
Air embolism
Divers can develop arterial gas embolisms as a consequence of lung over-expansion injuries. Breathing gas introduced into the venous system of the lungs due to pulmonary barotrauma will not be trapped in the alveolar capillaries, and will consequently be circulated to the rest of the body through the systemic arteries, with a high risk of embolism. Inert gas bubbles arising from decompression are generally formed in the venous side of the systemic circulation, where inert gas concentrations are highest, these bubbles are generally trapped in the capillaries of the lungs where they will usually be eliminated without causing symptoms. If they are shunted to the systemic circulation through a patent foramen ovale they can travel to and lodge in the brain where they can cause stroke, the coronary capillaries where they can cause myocardial ischaemia or other tissues, where the consequences are usually less critical. The first aid treatment is to administer oxygen at the highest practicable concentration, treat for shock and transport to a hospital where therapeutic recompression and hyperbaric oxygen therapy are the definitive treatment.
Causes[edit]
Decompression illness[edit]
Gas embolism is a diving disorder experienced by underwater divers who breathe gases at ambient pressure, and can happen in two distinct ways:
Diagnosis[edit]
As a general rule, any diver who has breathed gas under pressure at any depth who surfaces unconscious, loses consciousness soon after surfacing, or displays neurological symptoms within about 10 minutes of surfacing should be assumed to be experiencing arterial gas embolism.[5]
Symptoms of arterial gas embolism may be present but masked by environmental effects such as hypothermia, or pain from other obvious causes. Neurological examination is recommended when there is suspicion of lung overexpansion injury. Symptoms of decompression sickness may be very similar to, and confused with, symptoms of arterial gas embolism, however, treatment is basically the same. Discrimination between gas embolism and decompression sickness may be difficult for injured divers, and both may occur simultaneously. Dive history may eliminate decompression sickness in many cases, and the presence of symptoms of other lung overexpansion injury would raise the probability of gas embolism.[5]
Epidemiology[edit]
In terms of the epidemiology of air embolisms one finds that the intraoperative period to have the highest incidence. For example, VAE (vascular air embolism) in neurological cases ranges up to 80%, and OBGYN surgeries incidence can climb to 97% for VAE. In divers the incidence rate is 7/100,000 per dive.[27]
In society and culture[edit]
Direct injection air embolism was one of the methods used by Belgian murderer Ivo Poppe to kill some of his victims (the other method being valium).[28]
William Davis, formerly a nurse in Texas, was convicted in October 2021 of murdering four and injuring two patients by injecting air into their arterial lines following heart surgery.[29] During opening arguments for sentencing, prosecutors told the court that they would present evidence of an additional three murders and three attempted murders.[30]
Dorothy L. Sayers made use of direct injection air embolism as a murder method in her 1927 Lord Peter Wimsey mystery novel Unnatural Death (published in the US in 1928 as The Dawson Pedigree), although her description was subsequently criticised as implausible on account of the injection site and volume.[31]
Air embolism was the method used by an insane nurse to euthanize seven terminally ill patients in the episode "Amazing Grace" of the TV series Shadow Chasers.[32]
Near the end of young adult novel Catching Fire, as well as its film adaptation, protagonist Katniss Everdeen grabs a syringe and fills it with air, with the intention of killing Peeta Mellark quickly via air embolism.[33]
In plants[edit]
Air embolisms generally occur in the xylem of vascular plants because a fall in hydraulic pressure results in cavitation. Falling hydraulic pressure occurs as a result of water stress or physical damage.
A number of physiological adaptations serve to prevent cavitation and to recover from it. The cavitation may be prevented from spreading by the narrow pores in the walls between vessel elements. The plant xylem sap may be able to detour around the cavitation through interconnections. Water loss may be reduced by closing off leaf stomata to reduce transpiration, or some plants produce positive xylem pressure from the roots. When xylem pressure increases, the cavitation gases may redissolve.