Air embolism

Last updated
Air embolism
Other namesGas embolism
Drawing-syringes-with-needle.jpg
Drug injection can potentially be a cause for air embolisms.
Specialty Critical care medicine
Symptoms Hypotension, headaches, vertigo, dizziness
Complications Coma
DurationRapid
Risk factors Divers, substance abuse, improper needle usage, decompression sickness

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]

Contents

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.

Signs and symptoms

Air embolism after transgastral paracentesis of pancreatic pseudocyst after pancreatitis; Echocardiography (parasternal long axis)
Air embolism in the descending thoracic aorta after CT guided percutaneous lung biopsy of a suspected lung tumour. Air embolism in the descending thoracic aorta after CT guided lung biopsy.jpg
Air embolism in the descending thoracic aorta after CT guided percutaneous lung biopsy of a suspected lung tumour.

In surgery

Symptoms include: [3]

In divers

Symptoms of arterial gas embolism include: [4] [5]

Causes

Interventional procedures

Interventional radiology procedures, cardiac, and neurosurgical procedures can predispose to air embolism. [1] Besides, increasing use of pump injectors for contrast delivery, and percutaneous intervention to the lungs also increases the risk of air embolism. [6]

Decompression illness

Gas embolism is a diving disorder experienced by underwater divers who breathe gases at ambient pressure, and can happen in two distinct ways:

Ventilator induced pulmonary barotrauma

Trauma to the lung can also cause an air embolism. This may happen after a patient is placed on a ventilator and air is forced into an injured vein or artery, causing sudden death. [ citation needed ] Breath-holding while ascending from scuba diving may also force lung air into pulmonary arteries or veins in a similar manner, due to the pressure difference. [8]

Direct injection

Air can be injected directly into a vein or artery accidentally during clinical procedures. [9] [10] Misuse of a syringe to meticulously remove air from the vascular tubing of a hemodialysis circuit can allow air into the vascular system. [11] Venous air embolism is a rare complication of diagnostic and therapeutic procedures requiring catheterization of a vein or artery. [12] If a significant embolism occurs, the cardiovascular, pulmonary, or central nervous system may be affected. [9] [12] Interventions to remove or mitigate the embolism may include procedures to reduce bubble size, or withdrawal of air from the right atrium. [12]

The lethal dose for humans is considered theoretically between 3 and 5 ml per kg. It is estimated that 300-500 ml of gas introduced at a rate of 100 ml per sec would prove fatal. [13]

Mechanism

Air embolism can occur whenever a blood vessel is open and a pressure gradient exists favoring entry of gas. Because the circulatory pressure in most arteries and veins is greater than atmospheric pressure, an air embolus does not often happen when a blood vessel is injured. In the veins above the heart, such as in the head and neck, the venous pressure may be less than atmospheric and an injury may let air in. [14] This is one reason why surgeons must be particularly careful when operating on the brain, and why the head of the bed is tilted down when inserting or removing a central venous catheter from the jugular or subclavian veins. [ citation needed ]

When air enters the veins, it travels to the right side of the heart, and then to the lungs. [15] This can cause the vessels of the lung to constrict, raising the pressure in the right side of the heart[ citation needed ]. If the pressure rises high enough in a patient who is one of the 20% to 30% of the population with a patent foramen ovale, the gas bubble can then travel to the left side of the heart, and on to the brain or coronary arteries. [ citation needed ] Such bubbles are responsible for the most serious of gas embolic symptoms.

Venous or pulmonary air embolism occurs when air enters the systemic veins and is transported to the right side of the heart and from there into the pulmonary arteries, where it may lodge, blocking or reducing blood flow. [16] Gas in the venous circulation can cause cardiac problems by obstructing the pulmonary circulation or forming an air-lock which raises central venous pressure and reduces pulmonary and systemic arterial pressures. [16] [17] Experiments on animals show that the amount of gas necessary for this to happen is quite variable. [10] Human case reports suggest that injecting more than 100 mL of air into the venous system at rates greater than 100 mL/s can be fatal. [18] Very large and symptomatic amounts of venous air emboli may also occur in rapid decompression in severe diving or decompression accidents, where they may interfere with circulation in the lungs and result in respiratory distress and hypoxia. [8]

Gas embolism in a systemic artery, termed arterial gas embolism (AGE), is a more serious matter than in a vein, because a gas bubble in an artery may directly stop blood flow to an area fed by the artery. The symptoms of 'AGE' depend on the area of blood flow, and may be those of stroke for a cerebral arterial gas embolism (CAGE) or heart attack if the heart is affected. [8] The amount of arterial gas embolism that causes symptoms depends on location — 2 mL of air in the cerebral circulation can be fatal, while 0.5 mL of air into a coronary artery can cause cardiac arrest. [19] [20]

Prevention and screening

If a patent foramen ovale (PFO) is suspected, an examination by echocardiography may be performed to diagnose the defect. In this test, very fine bubbles are introduced into a patient's vein by agitating saline in a syringe to produce the bubbles, then injecting them into an arm vein. A few seconds later, these bubbles may be clearly seen in the ultrasound image, as they travel through the patient's right atrium and ventricle. At this time, bubbles may be observed directly crossing a septal defect, or else a patent foramen ovale may be opened temporarily by asking the patient to perform the Valsalva maneuver while the bubbles are crossing through the right heart – an action which will open the foramen flap and show bubbles passing into the left heart. Such bubbles are too small to cause harm in the test, but such a diagnosis may alert the patient to possible problems which may occur from larger bubbles, formed during activities like underwater diving, where bubbles may grow during decompression. [21] [22] A PFO test may be recommended for divers intending to expose themselves to relatively high decompression stress in deep technical diving.

Diagnosis

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]

Treatment

A large bubble of air in the heart (as can follow certain traumas in which air freely gains access to large veins) will present with a constant "machinery" murmur. It is important to promptly place the patient in Trendelenburg position (head down)[ dubious discuss ] and on their left side (left lateral decubitus position). The Trendelendburg position keeps a left-ventricular air bubble away from the coronary artery ostia (which are near the aortic valve) so that air bubbles do not enter and occlude the coronary arteries (which would cause a heart attack). Left lateral decubitus positioning helps to trap air in the non-dependent segment of the right ventricle (where it is more likely to remain instead of progressing into the pulmonary artery and occluding it). The left lateral decubitus position also prevents the air from passing through a potentially patent foramen ovale (present in as many as 30% of adults) and entering the left ventricle, from which it could then embolise to distal arteries (potentially causing occlusive symptoms such as stroke). [16] [23]

Administration of high percentage oxygen is recommended for both venous and arterial air embolism. This is intended to counteract ischaemia and accelerate bubble size reduction. [11]

For venous air embolism the Trendelenburg or left lateral positioning of a patient with an air-lock obstruction of the right ventricle may move the air bubble in the ventricle and allow blood flow under the bubble. [24]

Hyperbaric therapy with 100% oxygen is recommended for patients presenting clinical features of arterial air embolism, as it accelerates removal of nitrogen from the bubbles by solution and improves tissue oxygenation. This is recommended particularly for cases of cardiopulmonary or neurological involvement. Early treatment has greatest benefits, but it can be effective as late as 30 hours after the injury. [11]

Treatment of divers

Oxygen first aid treatment is useful for suspected gas embolism casualties or divers who have made fast ascents or missed decompression stops. [25] Most fully closed-circuit rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as an alternative to pure open-circuit oxygen resuscitators. However pure oxygen from an oxygen cylinder through a Non-rebreather mask is the optimal way to deliver oxygen to a decompression illness patient. [8]

Decompression chamber Nasa decompression chamber.jpg
Decompression chamber

Recompression is the most effective, though slow, treatment of gas embolism in divers. [17] Normally this is carried out in a recompression chamber. As pressure increases, the solubility of a gas increases, which reduces bubble size by accelerating absorption of the gas into the surrounding blood and tissues. Additionally, the volumes of the gas bubbles decrease in inverse proportion to the ambient pressure as described by Boyle's law. In the hyperbaric chamber the patient may breathe 100% oxygen, at ambient pressures up to a depth equivalent of 18 msw. Under hyperbaric conditions, oxygen diffuses into the bubbles, displacing the nitrogen from the bubble and into solution in the blood.[ citation needed ] Oxygen bubbles are more easily tolerated. [16] Diffusion of oxygen into the blood and tissues under hyperbaric conditions supports areas of the body which are deprived of blood flow when arteries are blocked by gas bubbles. This helps to reduce ischemic injury.[ citation needed ] The effects of hyperbaric oxygen also counteract the damage that can occur with reperfusion of previously ischemic areas; this damage is mediated by leukocytes (a type of white blood cell).[ citation needed ]

Complications

High incidence of relapse after hyperbaric oxygen treatment due to delayed cerebral edema. [26]

Epidemiology

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

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

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.

See also

Related Research Articles

<span class="mw-page-title-main">Hypoxia (medicine)</span> Medical condition of lack of oxygen in the tissues

Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise.

<span class="mw-page-title-main">Decompression sickness</span> Disorder caused by dissolved gases forming bubbles in tissues

Decompression sickness is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.

<span class="mw-page-title-main">Embolism</span> Disease of arteries, arterioles and capillaries

An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule, a bubble of air or other gas, amniotic fluid, or foreign material.

<span class="mw-page-title-main">Hyperbaric medicine</span> Medical treatment at raised ambient pressure

Hyperbaric medicine is a medical treatment in which an increase in barometric pressure over ambient pressure is employed increasing the partial pressures of all gases present in the compressed air. The immediate effects include reducing the size of gas embolisms and raising the partial pressures of all gases present according to Henry's law. Currently, there are two types of hyperbaric medicine depending on the gases compressed, hyperbaric air and hyperbaric oxygen.

<span class="mw-page-title-main">Barotrauma</span> Injury caused by pressure

Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in tension or shear, either directly by an expansion of the gas in the closed space or by pressure difference hydrostatically transmitted through the tissue. Tissue rupture may be complicated by the introduction of gas into the local tissue or circulation through the initial trauma site, which can cause blockage of circulation at distant sites or interfere with the normal function of an organ by its presence. The term is usually applied when the gas volume involved already exists prior to decompression. Barotrama can occur during both compression and decompression events.

Decompression Illness (DCI) comprises two different conditions caused by rapid decompression of the body. These conditions present similar symptoms and require the same initial first aid. Scuba divers are trained to ascend slowly from depth to avoid DCI. Although the incidence is relatively rare, the consequences can be serious and potentially fatal, especially if untreated.

dextro-Transposition of the great arteries Medical condition

dextro-Transposition of the great arteries is a potentially life-threatening birth defect in the large arteries of the heart. The primary arteries are transposed.

<span class="mw-page-title-main">Atrial septal defect</span> Human heart defect present at birth

Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). It is common in patients with a congenital atrial septal aneurysm (ASA).

<span class="mw-page-title-main">Diving medicine</span> Diagnosis, treatment and prevention of disorders caused by underwater diving

Diving medicine, also called undersea and hyperbaric medicine (UHB), is the diagnosis, treatment and prevention of conditions caused by humans entering the undersea environment. It includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how relationships of a diver's fitness to dive affect a diver's safety. Diving medical practitioners are also expected to be competent in the examination of divers and potential divers to determine fitness to dive.

Diving disorders, or diving related medical conditions, are conditions associated with underwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divides conditions caused by exposure to ambient pressures significantly different from surface atmospheric pressure, and a range of conditions caused by general environment and equipment associated with diving activities.

<span class="mw-page-title-main">Hypoxemia</span> Abnormally low level of oxygen in the blood

Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body.

<span class="mw-page-title-main">Foramen ovale (heart)</span> Passageway between the atria of the human heart

In the fetal heart, the foramen ovale, also foramen Botalli or the ostium secundum of Born, allows blood to enter the left atrium from the right atrium. It is one of two fetal cardiac shunts, the other being the ductus arteriosus. Another similar adaptation in the fetus is the ductus venosus. In most individuals, the foramen ovale closes at birth. It later forms the fossa ovalis.

An embolus, is described as a free-floating mass, located inside blood vessels that can travel from one site in the blood stream to another. An embolus can be made up of solid, liquid, or gas. Once these masses get "stuck" in a different blood vessel, it is then known as an "embolism." An embolism can cause ischemia—damage to an organ from lack of oxygen. A paradoxical embolism is a specific type of embolism in which the embolus travels from the right side of the heart to the left side of the heart and lodges itself in a blood vessel known as an artery. Thus, it is termed "paradoxical" because the embolus lands in an artery, rather than a vein.

A cardiac shunt is a pattern of blood flow in the heart that deviates from the normal circuit of the circulatory system. It may be described as right-left, left-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The direction may be controlled by left and/or right heart pressure, a biological or artificial heart valve or both. The presence of a shunt may also affect left and/or right heart pressure either beneficially or detrimentally.

<span class="mw-page-title-main">History of decompression research and development</span> Chronological list of notable events in the history of diving decompression.

Decompression in the context of diving derives from the reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during this reduction in pressure.

<span class="mw-page-title-main">Decompression theory</span> Theoretical modelling of decompression physiology

Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to the tissues and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure, but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure, are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms caused by decompression occur during or within a relatively short period of hours, or occasionally days, after a significant pressure reduction.

<span class="mw-page-title-main">Physiology of decompression</span> The physiological basis for decompression theory and practice

The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure. It involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs, or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.

Human physiology of underwater diving is the physiological influences of the underwater environment on the human diver, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes the range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus. Several factors influence the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety.

Inner ear decompression sickness, (IEDCS) or audiovestibular decompression sickness is a medical condition of the inner ear caused by the formation of gas bubbles in the tissues or blood vessels of the inner ear. Generally referred to as a form of decompression sickness, it can also occur at constant pressure due to inert gas counterdiffusion effects.

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