Air Embolism

Epidemiology

  • Incidence: increasing frequency (due to increasing risk factors)

Etiology

Cardiothoracic Surgery/Procedures

  • Cardiopulmonary Bypass (see Cardiopulmonary Bypass, [[Cardiopulmonary Bypass]]): venous air embolism
  • Fine Needle Aspiration (FNA) of Lung
  • Lung Resection: venous air embolism
  • Rigid Bronchoscopic Neodymium-Yttrium-Aluminum-Garnet (Nd:YAG) Laser Resection of Endobronchial Lesion: venous air embolism may occur due to coolant gas from the bronchoscope entering the systemic circulation through pulmonary venules
  • Lung Transplantation

General Surgery/Gastrointestinal Procedures

  • Laparoscopy: venous air embolism
  • Colonoscopy: venous air embolism

Neurosurgery

  • General Comments: common surgical precipitant of venous air embolism (as the surgical incision is usually superior to the heart at a distance that is greater than the central venous pressure)
    • Patients are especially at risk of air embolism in the sitting position (Fowler’s position)
    • Incidence of venous air embolism during neurosurgical procedures in the prone position: 10%
    • Incidence of venous air embolism during neurosurgical repair of cranial synostosis in Fowler’s Position: 80%
  • Craniotomy
  • Shunt Placement

Orthopedic Surgery

  • Arthrography
  • Arthroscopy: venous air embolism
  • Endoprosthesis Placement
  • Total Joint Arthroplasty: venous air embolism

Otolaryngologic Surgery

  • General Comments: common surgical precipitant of venous air embolism (as the surgical incision is usually superior to the heart at a distance that is greater than the central venous pressure)

Gynecologic

  • Abortion (by Suction or D+C)
  • Cesarean Section: venous air embolism
  • Douching
  • Hysteroscopy: venous air embolism
  • Laparoscopy: venous air embolism
  • Normal Labor
  • Oral Sex
  • Placenta Previa
  • Vaginal Insufflation

Intravascular Access-Related

  • General Comments
    • Venous air embolism can occur during catheter placement, during use, or at time of catheter removal
    • Risk Factors for Catheter-Related Air Embolism
      • Fracture or Detachment of Catheter Connections: accounts for 60-90% of episodes
      • Deep Inspiration During Catheter Insertion or Removal: increases the magnitude of negative pressure within the thorax
      • Dysfunction of Self-Sealing Valves in Cordis/Introducer Sheath
      • Failure to Occlude the Needle Nub and/or Catheter During Insertion or Removal
      • Hypovolemia: decreases central venous pressure
      • Presence of Persistent Catheter Tract After Central Venous Catheter Removal
      • Upright Positioning of Patient: decreases central venous pressure to below atmospheric pressure, increasing risk for entraining air rapidly into venous circulation
  • Arterial Line (see Arterial Line, [[Arterial Line]])
  • Central Venous Catheter (CVC) Placement (see Central Venous Catheter, [[Central Venous Catheter]]): especially in internal jugular and subclavian veins
    • Air embolism most often occurs with catheter hub fractures or disconnections rather than during the insertion of the catheter
  • Hemodialysis (see Hemodialysis, [[Hemodialysis]])
  • Intravenous Contrast Injection (see Radiographic Contrast, [[Radiographic Contrast]])
  • Pacemaker/Defibrillator Placement
  • Percutaneous Coronary Angioplasty
  • Radiofrequency Catheter Ablation
  • Ruptured Swan-Ganz Catheter Balloon (see Swan-Ganz Catheter, [[Swan-Ganz Catheter]])

Trauma

  • Blunt Abdominal Trauma: venous or arterial air embolism
  • Head/Neck Injuries: venous or arterial air embolism
  • Penetrating/Blunt Chest Trauma: venous or arterial air embolism

Positive Pressure Ventilation

  • Positive Pressure Ventilation, Especially with High Levels of PEEP (see General Ventilator Management, [[General Ventilator Management]]): gas may enter the circulation if the pulmonary vascular integrity is disrupted concomitantly with alveolar rupture from airspace overdistention
    • Occurs most commonly in adults with acute lung injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]]) or premature neonates with respiratory distress syndrome (hyaline membrane disease)

Decompression Sickness

  • Diving Ascent: breath hold (with closed glottis) with ascent leads to gas expansion within lungs, with rupture of alveoli into capillaries -> if the pulmonary veins tear as the alveoli rupture, air can return to the left heart with the oxygenated blood and then embolize through the arterial system (alternatively, air bubbles may form in the venous system during ascent and embolize to the systemic circulation via a patent foramen ovale)
    • Air embolism occurs in 7 out of every 100k dives

Physiology

Venous Air Embolism to Right Ventricle/Pulmonary Circulation

  • Air Embolism Results in Right Ventricular Obstruction: leading to RV failure and increased central venous pressure and hypotension
  • Air Embolism Results in Obstruction to Pulmonary Artery Outflow: results in “air lock”
  • Air Embolism Results in Abrupt Rise in Pulmonary Pressures: due to air bubble emboli to the pulmonary vasculature
  • Air Bubbles Occlude Pulmonary Capillaries and Induce Vasoconstriction and Formation of Platelet Microthrombi: results in local endothelial damage and accumulation of neutrophils, platelets, fibrin, and lipid droplets at the gas-fluid interface
    • Localized pulmonary hypoperfusion: may result in hypercapnia
    • Noncardiogenic pulmonary edema
    • Bronchoconstriction
    • Hypoxemia: due to alveolar flooding and ventilation-perfusion mismatching
    • Increased physiologic dead space: with a rise in PaCO2 if ventilation is held constant
    • Decreased lung compliance: due to pulmonary edema
    • Increased airway resistance: due to bronchoconstricting mediators (serotonin, histamine) released from damaged endothelium
  • Rate/Volume of Air Introduced into the Venous Circulation Determine the Clinical Effect of Venous Air Embolization: due to the fact that the capacity of the lung to filter microbubbles of air from the venous circulation can be exceeded
    • It is estimated that 300-500 mL of gas introduced at a rate of 100 mL/sec is a fatal dose for humans (his flow rate can be achieved through a 14-gauge catheter with a pressure gradient of only 5 cm H2O)

Arterial Air Embolism to Systemic Circulation

  • Mechanisms of Arterial Air Embolism
    • Direct Introduction of Air into Arterial System
    • Incomplete Filtration of Air by Pulmonary Capillary Bed: the capacity of the lung to filter microbubbles of air from the venous circulation can be exceeded (as noted above)
    • Paradoxical Air Embolization From Right->Left Side of Heart Via Intracardiac Shunt: in patients with a left-to-right shunt, venous air embolization into the pulmonary circulation can raise right heart pressures and reverse the direction of the shunt, allowing paradoxical embolism to occur
    • Air Traversal of Pulmonary Circulation Via Pulmonary Arteriovenous Malformation (AVM)
  • Destination of Arterial Air Emboli
    • Coronary Artery
    • Brain
    • Spinal Cord
    • Skin
  • Occlusion of Systemic Vessels: bubbles occlude systemic vessels and allow formation of associated platelet microthrombi, inducing the release of mediators and oxygen free radicals

Diving Ascent

  • Ascent with closed glottis or obstructive airways disease (like asthma) can cause alveolar rupture -> results in pneumothorax or arterial air embolism
  • Air bubble embolism to pulmonary vasculature (or coronary arteries or CNS vessels in case of patent foramen ovale)
  • Bubbles occlude vessels and allow formation of associated platelet microthrombi
  • Large amounts of air can traverse pulmonary circulation

Diagnosis

  • EKG
    • Sinus Tachycardia (see Sinus Tachycardia, [[Sinus Tachycardia]])
    • Right Heart Strain: peaked p-waves
    • Non-Specific ST-Segment and T-Wave Changes
    • Acute Myocardial Ischemia/Infarction
  • Arterial Blood Gas (ABG)
    • Hypoxemia (see Hypoxemia, [[Hypoxemia]]): may be severe
    • Hypercapnia (see Hypercapnia, [[Hypercapnia]]): due to venous air ambolism, causing localized pulmonary hypoperfusion and increased dead space
  • End-Tidal CO2
    • Marked discrepancy between arterial pCO2 and end-tidal (exhaled) CO2 may occur in the setting of venous air embolism [MEDLINE]
    • Decreased end-tidal CO2 occurs due to increased physiologic dead space and worsening of ventilation-perfusion matching
    • Intraoperative echocardiography and end-tidal CO2 monitoring may increase the sensitivity of detecting early air emboli in high-risk patients during surgery
  • CBC
    • Thrombocytopenia (see Thrombocytopenia, [[Thrombocytopenia]]): due to formation of platelet microthrombi
  • Creatine Kinase (CK): increased in divers with air embolism (unclear if this applies to other populations of patients with air embolism)
  • CXR/Chest CT Patterns
    • Normal: most common pattern
    • Pulmonary Edema: may occurs in cases who develop acute lung injury-ARDS
    • Air in Hepatic Circulation
    • Air in Main Pulmonary Artery
    • Atelectasis (see Atelectasis, [[Atelectasis]])
    • Enlargement of Pulmonary Artery
    • Focal Oligemia: predominantly in the upper lobes
    • Intracardiac Air
  • Hemodynamics
    • Central Venous Pressure (CVP): increased
    • Right Ventricular Pressure: increased
    • Pulmonary Artery (PA) Pressure: increased (sensitivity: 45%)
    • Cardiac Output (CO): decreased
    • Mean Arterial Pressure (MAP): decreased
  • PFT’s
    • DLCO: decreased
  • Trans-Thoracic Echocardiogram
    • Acute Right Ventricular Dilation and Pulmonary Hypertension
    • Air in Right Ventricle
    • Ejection Fraction (EF): XXX
    • Intraoperative echocardiography or transcranial Doppler monitoring may increase the sensitivity of detecting early air emboli in high-risk patients during surgery
  • Chest CT
    • May detect air in the central venous system (especially the axillary and subclavian veins), right ventricle, or pulmonary artery
    • However, this finding is non-specific, as small (<1 mL), asymptomatic air emboli can be detected in 10-25% of contrast-enhanced CT scans if carefully sought: false positive CT studies may be more common when higher resolution or electron beam CT scanners are used
  • Head CT: may detect intraparenchymal gas and diffuse edema
  • V/Q Scan: massive air embolism may result in perfusion defects
    • However, air embolism-related perfusion defects usually are transient and resolve within 24 hrs [MEDLINE]
  • Pulmonary Angiogram: variably positive
    • Negative: in cases where the air emboli are rapidly resorbed
    • Positive: may demonstrate signs of vascular occlusion or vasoconstriction -> corkscrewing, tapering, and/or delayed emptying of vessels [MEDLINE]

Clinical Manifestations

General Comments

  • Minor Cases of Air Embolism: common and may be asymptomatic

Cardiovascular Manifestations

  • Acute Myocardial Infarction (see Coronary Artery Disease, [[Coronary Artery Disease]])
  • Acute Right Ventricular Failure (see Congestive Heart Failure, [[Congestive Heart Failure]]): may occur when large amount of air is present in right ventricle
    • Elevated Central venous Pressure (CVP)
  • Chest Pain (see Chest Pain, [[Chest Pain]]): due to myocardial ischemia
  • Crepitus over Superficial Vessels: observed rarely in setting of massive air embolus
  • Hypotension (see Hypotension, [[Hypotension]])
  • Mill Wheel Murmur: churning sound heard throughout the entire cardiac cycle
  • Pulmonary Hypertension/Cor Pulmonale (see Pulmonary Hypertension, [[Pulmonary Hypertension]])
    • May occur when enough air is introduced to obstruct pulmonary vasculature
  • Sinus Tachycardia (see Sinus Tachycardia, [[Sinus Tachycardia]])

Dermatologic Manifestations

Neurologic Manifestations

  • Altered Mental Status/Delirium (see Delirium, [[Delirium]]): most common sign
  • Dizziness/Lightheadedness (see Dizziness, [[Dizziness]])
  • Focal Neurologic Deficits
  • Headache (see Headache, [[Headache]])
  • Obtundation/Coma (see Obtundation-Coma, [[Obtundation-Coma]])
  • Seizures (see Seizures, [[Seizures]])
  • Vision Loss (see Vision Loss, [[Vision Loss]])

Ophthalmologic Manifestations

  • Bubbles within Retinal Arteries

Pulmonary Manifestations

  • Acute Lung Injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]]): may occur even when small smounts of air are introduced
  • Acute Respiratory Failure (see Respiratory Failure, [[Respiratory Failure]])
  • Cough/Gasp (see Cough, [[Cough]]): may occur when air enters the pulmonary circulation
  • Dyspnea (see Dyspnea, [[Dyspnea]]): common (present in 100% of cases)
  • Pleuritic Chest Pain (see Chest Pain, [[Chest Pain]])
  • Tachypnea (see Tachypnea, [[Tachypnea]])
  • Wheezing (see Obstructive Lung Disease, [[Obstructive Lung Disease]])

Prevention

  • Mechanical Ventilation: efforts should be made to minimize barotrauma
  • Central Venous Catheter Removal: catheters should be removed using a specified protocol to mimize the risk of air embolism
  • Neurosurgery: Doppler ultrasound can detect air embolism during neurosurgical procedures

Treatment

Spontaneous Resolution

  • May occur in some cases, due to reabsorption of air from pulmonary vessels

Supportive Care

  • Intravenous Fluid Resuscitation
  • Mechanical Ventilation (see General Ventilator Management, [[General Ventilator Management]])
  • Vasopressors: as required

Prevention of Further Air Embolization

  • With Venous Air Embolism, Move Patient to Left Lateral Decubitus to Place the Right Ventricular Outflow Tract Inferior to Right Ventricular Cavity: this causes air to migrate superiorly into a position within the right ventricle where air is less likely to embolize (and prevents foramen ovale crossover, with subsequent embolization to the brain)
    • Durant’s Manuever: left lateral decubitus position (proven to decrease mortality in animal studies)
    • Left Lateral Decubitus Head Down Position
    • Trendelenburg Position
  • With Arterial Air Embolism, Move Patient to Flat Supine Position
    • Due to force of arterial blood flow, air bubbles will be propelled forward even if the patient is in head down position: consequently, the above maneuvers are unlikely to trp air within the right ventricle
    • Head down positions have the potential to exacerbate the cerebral edema that is generally induced by cerebral air embolism

Restoration of Circulation

  • Move Patient to Left Lateral Decubitus Position to Place the Right Ventricular Outflow Tract Inferior to Right Ventricular Cavity: these maneuvers (described above) may displace large bubbles from the right ventricular outflow tract, relieving the obstruction to blood flow
  • Chest Compressions: force air out of the pulmonary outflow tract and into smaller pulmonary vessels, improving forward flow

Removal of Air Embolism

  • Percutaneous/Trans-Catheter Removal of Air from Right Ventricle: these have been used in studies, but the amount of air to be removed is usually small (<20 ml) and removal is generally limited
    • Percutaenous Needle Aspiration of Air
    • Removal of Air Via Central Venous Catheter: aspiration may be attempted in cases where a central venous catheter is already in place
  • High-Flow Supplemental Oxygen: supplemental oxygen increases the partial pressure of oxygen and decreases the partial pressure of nitrogen in blood -> results in a positive pressure gradient for the diffusion of nitrogen from the air bubbles into the blood, accelerating resorption of air emboli
    • In contrast, nitrous oxide (sometimes given during general anesthesia) can diffuse from the blood into air emboli, causing the gas bubbles to enlarge and the patient to deteriorate: therefore, nitrous oxide should be discontinued at the first sign of air embolism
  • Hyperbaric Oxygen (see Hyperbaric Oxygen, [[Hyperbaric Oxygen]])
    • Rationale: decreases air bubble size and increases the arterial oxygen tension, potentially decreasing ischemia
      • May improve outcome even if it is delayed up to 30 hrs later
    • Indications
      • Cardiopulmonary Compromise
      • Neurologic Deficits

Other

  • Corticosteroids (see Corticosteroids, [[Corticosteroids]]): no proven role (in decreasing spinal cord or cerebral edema) in the treatment of air embolism or decompression sickness

Specific Treatment of Diving-Related Air Embolism

  • Left Lateral, Trendelenburg Position: this traps air bubbles in RA (by placing RV outflow tract below RV cavity), removing obstruction to flow
    • Prevents foramen ovale crossover (with subsequent brain embolization)
    • Not clear that this is actually effective though, as blood flow (rather than buoyancy) may be the main determinant of whether air embolizes
  • Supplemental Oxygen: 100% FIO2
    • Increases the diffusion gradient for nitrogen out of any air bubbles (causing them to shrink)
  • Hyperbaric Recompression: procedure of choice for both decompression sickness and venous/arterial air embolism -> increases nitrogen diffusion from bubbles (causing them to shrink)
    • No randomized trials to establish efficacy though
    • May be useful even in cases where therapy is delayed for 24 hrs or more
  • Correction of Hypothermia: indicated

Prognosis

  • Mortality
    • Older studies cite a mortality rate of approximately 30%
    • Prognosis of Air Embolism in Patients Treated with Hyperbaric Oxygen (2010 Study) [MEDLINE]
      • ICU Mortality Rate: 12%
      • Hospital Mortality Rate: 16%
      • 6-Month Mortality Rate: 18%
      • 1-Year Mortality Rate: 21%
    • Risk Factors for Death in ICU (2010 Study) [MEDLINE]
      • Cardiac Arrest at Time of Air Embolization
      • Simplified Acute Physiology Score (SAPS II) of At Least 33 on ICU Admission
    • Risk Factors for Death Within 1 Year (2010 Study) [MEDLINE]
      • Increasing Age
      • Presence of Babinski Sign at ICU Admission
      • Acute Kidney Injury
    • Predictors of Long-Term Neurologic Sequelae (2010 Study) [MEDLINE]
      • Focal Motor Deficits or Babinski Sign at ICU Admission
      • Need for >5 Days of Mechanical Ventilation

References

  • Venous air embolism. Arch Intern Med 1982; 142:2173- 2176
  • Influence of hypothermia, barbiturate therapy and intracranial monitoring on morbidity and mortality after near drowning. Crit Care Med 1986; 14:529-534
  • Transient pulmonary perfusion scintigraphic abnormalities in pulmonary air embolism. Chest 1989;95(4):910 [MEDLINE]
  • Medical problems associated with underwater diving. N Engl J Med 1992; 326:30-35
  • Venous air embolism: Clinical and experimental considerations. Crit Care Med 1992; 20:1169-1177
  • Delayed hyperbaric treatment of cerebral air embolism. Is J Med Sci 1993; 29:22-26
  • Pulmonary embolism from amniotic fluid, fat, and air. Prog Cardiovasc Dis. 1994 May-Jun;36(6):447-74 [MEDLINE]
  • Body position does not affect hemodynamic response to venous air embolism in dogs. Anesth Analg 1994; 79:734-739
  • Effects of mechanical ventilation with normobaric oxygen therapy on the rate of air removal from cerebral arteries. Crit Care Med 1994; 22:851-857
  • Gas embolism. N Engl J Med 2000; 342:476-482
  • Pulmonary air embolism. J Clin Monit Comput. 2000;16(5-6):375-83 [MEDLINE]
  • Long-term outcome of iatrogenic gas embolism. Intensive Care Med. 2010 Jul;36(7):1180-7. doi: 10.1007/s00134-010-1821-9. Epub 2010 Mar 11 [MEDLINE]