Air embolism
Encyclopedia
An air embolism, or more generally gas embolism, is a pathological condition caused by gas
bubbles in a vascular system. The most common context is a human body, in which case it refers to gas bubbles in the bloodstream (embolism
in a medical context refers to any large moving mass or defect in the blood stream). However air embolisms may also occur in the xylem
of vascular plant
s, especially when suffering from water stress.
s is very rare.
For venous air embolisms, death may occur if a large bubble of gas becomes lodged in the heart, stopping blood from flowing from the right ventricle
to the lungs (this is similar to vapor lock in engine fuel systems). However, experiments in animals show that the amount of gas necessary for this to happen is quite variable, and also depends on several other factors, such as body position. 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
.
Gas embolism into an 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
or heart attack
if the brain or heart, respectively, is affected. The amount of arterial gas embolism that causes symptoms depends on location, but in the brain may be a bubble with a volume only a fraction of a milliliter.
s 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 vein
s.
When air enters the veins, it travels to the right side of the heart, and then to the lungs. This can cause the vessels of the lung to constrict, raising the pressure in the right side of the heart. 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
. Such bubbles are responsible for the most serious of gas embolic symptoms.
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. 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.
Air can be injected directly into the veins either accidentally or as a deliberate act. Examples include misuse of a syringe
, and industrial injury
resulting from use of compressed air
. However, the amount of air that would be administered by a single small syringe is, in most cases, not enough to suddenly stop the heart, nor cause instant death. However, such bubbles may occasionally reach the arterial system through a patent foramen ovale, as noted above, and cause random ischemic damage, depending on their route of arterial travel.
There have been rare cases of air embolism being caused by air entering the bloodstream from the uterus or tears in female genitalia. The risk appears to be greater during pregnancy. Cases have been reported that resulted from attempts to perform an abortion by syringing. These appear to have been due to damage to the placenta allowing air to enter the bloodstream. there has been a reported case of autoerotic equipment causing air embolisms. Outside of pregnancy there is at least one case where an air embolism resulted from the insertion of an object into the vagina during masturbation.
Bubbles in the bloodstream from any source are dangerous as they can form clots and precipitate stroke
or thrombosis
. Pulmonary barotrauma, although more dramatic, is less likely to affect oxygen supply to the brain because bubbles tend to be introduced into the venous system and are trapped and managed at the lung. Gas embolism arising from decompression sickness are potentially more dangerous as they can form in the arterial system, the bubbles are smaller and they can travel to and lodge in the brain where they can cause stroke. The first aid treatment for both is to administer oxygen, treat for shock and get to hospital; at the hospital both may use a hyperbaric chamber but otherwise treatment is different.
may be performed to diagnose the defect. In this test, very fine (microscopic) 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 scuba diving.
, the size of the gas bubble or bubbles decreases in proportion to the increase in atmospheric pressure. In the hyperbaric chamber the patient breathes 100% oxygen. Under hyperbaric conditions, oxygen diffuses into the bubbles, displacing the nitrogen from the bubble and into solution in the blood. Oxygen bubbles are more easily tolerated. Air is composed of 21% oxygen and 78% nitrogen with trace amounts of other gases. Additionally, 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. Finally, the effects of hyperbaric oxygen antagonize leukocyte-mediated ischemic-reperfusion injury.
It is also important to promptly place the patient in Trendelenburg position
(head down) and on their left side (left lateral decubitus position). This positioning helps to trap air in the apex of the ventricle and prevent it from reaching the lung circulation.
Oxygen first aid treatment is useful for suspected gas embolism casualties or divers who have made fast ascents or missed decompression stops. Most fully closed-circuit rebreather
s can deliver sustained high concentrations of oxygen-rich breathing gas
and could be used as an alternative to pure open-circuit oxygen resuscitator
s. However pure oxygen from an oxygen tank through a Non-rebreather mask
is always the most optimal way to deliver needed oxygen to a decompression sickness
patient.
of vascular plants because a fall in hydraulic conductivity
results in cavitation
. Possible causes of falling hydraulic conductivity include water stress and the freeze-thaw cycle.
A number of physiological adaptations serve to prevent embolisms. These include variations in the length and diameter of vessel elements in different parts of the plant; and the ability to reduce transpiration by closing off leaf stoma
ta.
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
bubbles in a vascular system. The most common context is a human body, in which case it refers to gas bubbles in the bloodstream (embolism
Embolism
In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...
in a medical context refers to any large moving mass or defect in the blood stream). However air embolisms may also occur in the xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
of vascular plant
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s, especially when suffering from water stress.
In humans and animals
Small amounts of air often get into the blood circulation accidentally during surgery and other medical procedures (for example a bubble entering an intravenous fluid line), but most of these air emboli enter the veins and are stopped at the lungs, and thus a venous air embolism that shows any symptomSymptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s is very rare.
For venous air embolisms, death may occur if a large bubble of gas becomes lodged in the heart, stopping blood from flowing from the right ventricle
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
to the lungs (this is similar to vapor lock in engine fuel systems). However, experiments in animals show that the amount of gas necessary for this to happen is quite variable, and also depends on several other factors, such as body position. 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
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
.
Gas embolism into an 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
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
or heart attack
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
if the brain or heart, respectively, is affected. The amount of arterial gas embolism that causes symptoms depends on location, but in the brain may be a bubble with a volume only a fraction of a milliliter.
Pathogenesis
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 always happen when a blood vessel is injured. In the veins above the heart, such as in the head and neck, the pressure is less than atmospheric and an injury may let air in. This is one reason why surgeonSurgeon
In medicine, a surgeon is a specialist in surgery. Surgery is a broad category of invasive medical treatment that involves the cutting of a body, whether human or animal, for a specific reason such as the removal of diseased tissue or to repair a tear or breakage...
s must be particularly careful when operating on the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, and why the head of the bed is tilted down when inserting or removing a central venous catheter
Central venous catheter
In medicine, a central venous catheter is a catheter placed into a large vein in the neck , chest or groin...
from the jugular
Jugular vein
The jugular veins are veins that bring deoxygenated blood from the head back to the heart via the superior vena cava.-Internal and external:There are two sets of jugular veins: external and internal....
or subclavian vein
Subclavian vein
The subclavian veins are two large veins, one on either side of the body. Their diameter is approximately that of the smallest finger.-Path:Each subclavian vein is a continuation of the axillary vein and runs from the outer border of the first rib to the medial border of anterior scalene muscle...
s.
When air enters the veins, it travels to the right side of the heart, and then to the lungs. This can cause the vessels of the lung to constrict, raising the pressure in the right side of the heart. 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
Coronary circulation
Coronary circulation is the circulation of blood in the blood vessels of the heart muscle . The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries...
. Such bubbles are responsible for the most serious of gas embolic symptoms.
Trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
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. Breath-holding while ascending from scuba diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
may also force lung air into pulmonary arteries or veins in a similar manner, due to the pressure difference.
Air can be injected directly into the veins either accidentally or as a deliberate act. Examples include misuse of a syringe
Syringe
A syringe is a simple pump consisting of a plunger that fits tightly in a tube. The plunger can be pulled and pushed along inside a cylindrical tube , allowing the syringe to take in and expel a liquid or gas through an orifice at the open end of the tube...
, and industrial injury
Industrial injury
An occupational injury is bodily damage resulting from working.In the United States in 2007, 5,488 workers died from job injuries, 92% of which were men, and 49,000 died from work-related injuries. NIOSH estimates that 4 million workers in the U.S...
resulting from use of compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....
. However, the amount of air that would be administered by a single small syringe is, in most cases, not enough to suddenly stop the heart, nor cause instant death. However, such bubbles may occasionally reach the arterial system through a patent foramen ovale, as noted above, and cause random ischemic damage, depending on their route of arterial travel.
There have been rare cases of air embolism being caused by air entering the bloodstream from the uterus or tears in female genitalia. The risk appears to be greater during pregnancy. Cases have been reported that resulted from attempts to perform an abortion by syringing. These appear to have been due to damage to the placenta allowing air to enter the bloodstream. there has been a reported case of autoerotic equipment causing air embolisms. Outside of pregnancy there is at least one case where an air embolism resulted from the insertion of an object into the vagina during masturbation.
Gas embolism in diving
Gas embolism is a diving disorder suffered by compressed air divers and can happen in two distinct ways:- Pulmonary barotraumaBarotraumaBarotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...
: Air bubbles enter the bloodstream as a result of gross trauma to the lining of the lung following a rapid ascent while holding the breath; the air held within the lung expands to the point where the lungs burst (pulmonary barotrauma). This is easy to do as the lungs give little warning through pain until they do burst. The diver will arrive at the surface in pain and distress and may froth or spit blood. A pulmonary barotrauma is very obvious and presents quite differently from the decompression sickness below. - Decompression sicknessDecompression sicknessDecompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
(DCS): Air bubbles precipitate out into the bloodstream if the gas dissolved in the blood at pressure is not allowed sufficient time to out-gas on ascent. The symptoms may be subtle and not immediately noticeable.
Bubbles in the bloodstream from any source are dangerous as they can form clots and precipitate stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
or thrombosis
Thrombosis
Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...
. Pulmonary barotrauma, although more dramatic, is less likely to affect oxygen supply to the brain because bubbles tend to be introduced into the venous system and are trapped and managed at the lung. Gas embolism arising from decompression sickness are potentially more dangerous as they can form in the arterial system, the bubbles are smaller and they can travel to and lodge in the brain where they can cause stroke. The first aid treatment for both is to administer oxygen, treat for shock and get to hospital; at the hospital both may use a hyperbaric chamber but otherwise treatment is different.
Prevention
If an arterial gas embolism resulting from patent foramen ovale is suspected, an exam by echocardiographyEchocardiography
An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart . Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart...
may be performed to diagnose the defect. In this test, very fine (microscopic) 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
Valsalva maneuver
The Valsalva maneuver or Valsalva manoeuvre is performed by moderately forceful attempted exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut...
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 scuba diving.
Treatment
Recompression is the most effective treatment of an air embolism. Normally this is carried out in a recompression chamber. This is because as pressure increases, the solubility of a gas increases. Additionally, owing to Boyle's lawBoyle's law
Boyle's law is one of many gas laws and a special case of the ideal gas law. Boyle's law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system...
, the size of the gas bubble or bubbles decreases in proportion to the increase in atmospheric pressure. In the hyperbaric chamber the patient breathes 100% oxygen. Under hyperbaric conditions, oxygen diffuses into the bubbles, displacing the nitrogen from the bubble and into solution in the blood. Oxygen bubbles are more easily tolerated. Air is composed of 21% oxygen and 78% nitrogen with trace amounts of other gases. Additionally, 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. Finally, the effects of hyperbaric oxygen antagonize leukocyte-mediated ischemic-reperfusion injury.
It is also important to promptly place the patient in Trendelenburg position
Trendelenburg position
In the Trendelenburg position the body is laid flat on the back with the feet higher than the head by 15-30 degrees, in contrast to the reverse Trendelenburg position, where the body is tilted in the opposite direction. This is a standard position used in abdominal and gynecological surgery...
(head down) and on their left side (left lateral decubitus position). This positioning helps to trap air in the apex of the ventricle and prevent it from reaching the lung circulation.
Oxygen first aid treatment is useful for suspected gas embolism casualties or divers who have made fast ascents or missed decompression stops. Most fully closed-circuit rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
s can deliver sustained high concentrations of oxygen-rich breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
and could be used as an alternative to pure open-circuit oxygen resuscitator
Resuscitator
A resuscitator is a device using positive pressure to inflate the lungs of an unconscious person who is not breathing, in order to keep them oxygenated and alive. There are three basic types: a manual version consisting of a mask and a large hand-squeezed plastic bulb using ambient air, or with...
s. However pure oxygen from an oxygen tank through a Non-rebreather mask
Non-rebreather mask
A non-rebreather mask, or NRB, is a device used in medical emergencies that require oxygen therapy. An NRB requires that the patient can breathe unassisted, but unlike low flow nasal cannula, the NRB allows for the delivery of higher concentrations of oxygen.-Design:The non-rebreather mask covers...
is always the most optimal way to deliver needed oxygen to a decompression sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
patient.
In vascular plants
Air embolisms generally occur in the xylemXylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
of vascular plants because a fall in hydraulic conductivity
Hydraulic conductivity
Hydraulic conductivity, symbolically represented as K, is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. It depends on the intrinsic permeability of the material and on the degree of saturation...
results in cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...
. Possible causes of falling hydraulic conductivity include water stress and the freeze-thaw cycle.
A number of physiological adaptations serve to prevent embolisms. These include variations in the length and diameter of vessel elements in different parts of the plant; and the ability to reduce transpiration by closing off leaf stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...
ta.