Air embolism overview

Air Embolism Microchapters
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Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Air embolism from Other Diseases
Epidemiology and Demographics
Risk Factors
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Natural History, Complications, and Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

An air embolism, or more generally gas embolism, is a medical condition caused by gas bubbles in the bloodstream (embolism in a medical context refers to any large moving mass or defect in the blood stream). Small amounts of air may enter the blood circulation during surgery, other invasive medical procedures, or deep sea diving. There are two types of air embolisms: venous or arterial. venous air embolisms rarely present with symptoms. Symptoms or death mainly occur in the arterial system. Symptoms may occur in the venous system, 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, the amount of gas necessary for this to happen is quite variable, and also depends on a number of other factors, such as body position.

Gas embolism into an artery, termed arterial gas embolism, or AGE, is a more severe diagnosis than venous air embolism, since a gas bubble in an artery may directly cause ischemia to an area fed by the artery. The symptoms of AGE depend on the artery and the organs that it supplies. For example,a stroke or a heart attack may occur if the brain or heart (respectively) are affected.

Decompression sickness (DCS) is a diving disorder that SCUBA divers sometimes suffer when they have pressure damage to their lungs following a rapid ascent where the breath is inappropriately held against a closed glottis, allowing pressure to build up inside the lungs, relative to the blood. It is termed "gas" because the diver may be using a diving breathing gas other than air. The gas bubbles can impede the flow of oxygen-rich blood to the brain and other vital organs. They can also cause clots to form in blood vessels.

Gas embolism and decompression sickness (DCS) have similar symptoms, especially in the central nervous system. The treatment for both is the same, because they are both the result of gas bubbles in the body.

Historical Perspective

Not much is known about the history of air embolim, but it has was discovered and diagnosed in the 19th century.

Classification

• Air embolism may be classified according to location and port of entry into 2 subtypes:

• Venous air embolism
• Arterial air embolism

Pathophysiology

Air embolism can occur whenever a blood vessel is open and a pressure gradient exists favoring entry of gas. Because the 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 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.

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, despite being employed by writers of fiction as a clandestine method of murder, amounts of air such as would be administered by a single small syringe are not likely to suddenly stop the heart, nor cause instant death. Single air bubbles in a vein do not stop the heart, due to being too small. 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.

Causes

• Iatrogenic Causes:
  • Central Venous Catheter/IV catheters
  • Hemodialysis
  • Laparoscopic surgery/Abdominal surgery
  • Contrast Studies
  • ERCP
  • Lung Biopsy
  • High pressure mechanical ventilation
  • Endoscopy
  • Intracranial Surgery
  • Gynecological Surgery

• Deep sea diving (Decompression Sickness/ Caisson's Disease/ "the bends")
• Blunt chest trauma

Differentiating Air Embolism from other Diseases

• Air embolism must be differentiated from other diseases that cause dyspnea, joint and muscle pain, and mental status changes, such as

• Pulmonary emboli
• Myocardial Infarction/Acute coronary syndrome
• Stroke
• Cardiogenic shock

Epidemiology and Demographics

• The prevalence of air embolism is approximately 2.65 per 100,000 hospitalizations.
• The prevalence of air embolism is approximately 7 per 100,000 divers.

Age

• Patients of all age groups may develop Air embolism.

Gender

• Air embolism affects men and women equally.

Race

• There is no racial predilection for Air embolism.

Risk Factors

• Common risk factors in the development of air embolism are:
• Operative site more that 5cm above the right atrium
• Numerous uncompressed venous channels in surgical site
• Pressure gradient during surgery
• Barotrauma to chest
• Insertion or removal of catheter
  • Fracture/de attachment of catheter
  • Failure to occlude needle hub
  • Deep inspiration
  • Hypovolemia
  • Up right position
• Scuba diving
  • Rapid ascent rate
  • Diving too long
  • Diving at great depth

Natural History, Complications and Prognosis

• Early clinical features include chest pain dyspnea, and altered mental status.
• Common complications of air embolism include, stroke, seizures, and infarction of various organs.
• Prognosis is generally variable,it depends on the size and location of the embolism , and the mortality rate of patients with air embolism is approximately 48-80%.
• A 200-300ml bolus or 3-5 ml/kg of air in a human is fatal

Diagnosis

Diagnostic Criteria

• There is no specific diagnostic criteria for air embolism.
• The diagnosis of air embolism is clinical and should be suspected in patients with history of:

• High risk procedures
• Scuba diving
• Trauma to head, neck, thorax or abdomen
• Hemodialysis catheters
• Positive pressure ventilation

Symptoms

• Symptoms of air embolism depend on:
  • the location
  • size of the emboli
  • rate of emboli formation
  • patient spontaneously breathing
  • patient under controlled positive pressure ventilation
• Symptoms include the following:

• Dyspnea
• Cough
• Chest pain
• Mental status changes
• Dizziness/ Vertigo
• Nausea
• Syncope
• Headache
• Anxiety

Physical Examination

• Patients with air embolism usually appear distressed.
• Physical examination may be remarkable for:

• Cardiovascular Findings:
  • Arrythmias
  • Murmmurs
  • Jugular venous distension
  • Hypotension
  • ST and T wave changes
  • Pulmonary arterial hypertension
  • Increased central venous pressure
  • Shock and cardiovascular collapse
• Respiratory Findings:
  • Rales/ wheezing
  • Tachypnea
  • Hemoptysis
  • Cyanosis
  • Decreased End Tidal Co2
  • Hypercapnia
  • Pulmonary edema
  • Apnea
• Central Nervous System Findings:
  • Altered mental status
  • Seizures
  • Focal neurological deficits
  • Loss of conciousness
  • Coma

Laboratory Findings

• There are no one test that is diagnostic for air embolism.

• The diagnosis is clinical but some lab findings can help lead to the diagnosis, and can indicate which organs and systems are affected.
• Other laboratory findings consistent with the diagnosis of air embolism include:
  • Decreased End tidal CO2
  • Increased End tidal Nitrogen
  • Increased pulmonary artery pressure.

Imaging Findings

• Transesophageal Echocardiography (TEE) is the most sensitive imaging modality for air embolism.
  • On TEE, air embolism is characterized by detection of air in circulation.
• Precordial Doppler Ultrasound is the most sensitive noninvasive imaging modality for air embolism.
  • Precordial Doppler Ultrasound may demonstrate air in circulation.
• Transcranial Doppler Ultrasound is also used to detect air embolism.
  • Transcranial Doppler Ultrasound may demonstrate cerebral emboli.

Other Diagnostic Studies.

• Air embolism may also be diagnosed using EKG.
• Findings on EKG include ST segment changes, peaked P waves, and tachyarrthmia.
• Pulse Oximetry showing saturation changes is a late finding.

Treatment

Medical Therapy

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.

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 rebreathers can deliver sustained high concentrations of oxygen-rich breathing gas and could be used as an alternative to pure open-circuit oxygen resuscitators.

Surgery

Primary Prevention

If an arterial gas embolism resulting from patent foramen ovale is suspected, an exam by echocardiography 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.