Air embolism overview

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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 embolism, but it has been diagnosed as early as the 19th century.

Classification

• Air embolism may be classified according to location into 2 subtypes:

• Venous air embolism
• Arterial air embolism

Pathophysiology

Air embolism can occur whenever there is access to an open blood vessel 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 and rapid ascent from scuba diving may also force nitrogen air into pulmonary arteries or veins causing Decompression Sickness During a deep sea dive nitrogen accumulates in the tissues of the body, as the diver ascends, the nitrogen leaves the body through the lungs, if the ascent occurs too rapidly nitrogen bubble can form and diffuse into the circulation causing an air embolism.

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
• 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 established 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 consciousness
  • Coma

Laboratory Findings

• There is 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.
• 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.
• Contrast enhanced CT scan of the chest may be used to help diagnose air embolism.
  • CT chest may show intra-cardial air
  • CT chest may show a filling defect in the lungs
• CT or MRI of the head may be used to diagnose air embolism
  • Contrast enhanced CT may show areas of ischemia or entrapment of air
  • MRI may show areas of ischemia

Other Diagnostic Studies.

• EKG may also be used to help diagnose air embolism.
  • Findings on EKG include ST segment changes, peaked P waves, and tachyarrthmia.
• Pulse Oximetry showing saturation changes is a late finding.
• Chest X-ray may be used to rule out other causes of dyspnea and chest pain.
  • Chest X-ray may show intra-cardiac air.

Treatment

Medical Therapy

Air embolism is a medical emergency.The mainstay of therapy for air embolism is high flow oxygen therapy with 100% oxygen.

During surgery:

• Cover surgical site
  • This prevents further air trapping
• Tilt operating table
  • This lowers the source of air entry and eliminates negative air pressure gradient
• Reverse Trendelenburg in procedures that are lower than the heart
• Jugular venous compression during cranial or facial surgery
  • This decreases distal venous pressure and eliminates further air entry from face and head

Post Surgery:

• High flow oxygen therapy/Hyperbaric oxygen therapy
  • This increases partial pressure of nitrogen and oxygen in blood leading to decrease in size of bubble and acceleration of bubble resorption
• Aspiration of air from right atrium
  • Using the Bunegin Albin catheter
  • Swan Ganz catheter is shown to be ineffective
• Hemodynamic and Cardiopulmonary resuscitation if necessary
  • Some studies have shown cardiac massage may be beneficial
    • This forces air out of pulmonary outflow tract leading to improved lateral blood flow

Surgery

Primary Prevention

During Venous catheter placement:

• Place patient in Trendelenburg position
  • this increases the CVP
• Adequate hydration
• Avoid placement during inspiration
• Flush catheter lumens

During Venous catheter removal:

• Place patient in Trendelenburg position
• Remove Catheter during valsalva or expiration
• Cover site and apply pressure for 5-10 minutes
• Patient should remain supine for 30 minutes post procedure

During other Invasive procedures:

• Use of a flush in a closed system
• Prime tubing with saline
• No air should be present in syringes
• Intra operative use of precordial doppler
• Avoid use of Nitrous oxide during abdominal procedures
• "park bench position" should be used for surgeries performed in the sitting position
• Use of Reverse Trendelenburg position during Cesarian section

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.

Secondary Prevention

If air embolism is suspected during a procedure:

• Flush should be stopped
• Rotating hemostatic valve should be opened