Nonthrombotic embolism

Last updated: September 19, 2023

Summarytoggle arrow icon

The blockage of blood vessels by fat, air, or amniotic fluid is an uncommon but potentially life-threatening event. Fat emboli mostly originate from the bone marrow in patients with long bone fractures. Air can enter the circulatory system as a result of invasive procedures (e.g., vascular surgery or catheterization, neurological surgery), trauma, or rapid ascent when diving (decompression illness), while amniotic fluid emboli typically occur during labor. The emboli usually lodge within the pulmonary arteries and cause right ventricular outflow obstruction and circulatory collapse. General clinical features of nonthrombotic embolisms include acute onset of hypoxia, hypotension, and neurological symptoms (e.g., altered mental status, seizures). Characteristic clinical findings include a nondependent petechial rash on the upper body in fat embolism, the mill wheel sign in venous air embolism, signs of stroke in arterial air embolism, and disseminated intravascular coagulation in amniotic fluid embolism. Nonthrombotic embolisms are primarily a clinical diagnosis, but results of arterial blood gas analysis, ECG, and chest imaging (e.g., chest x-ray, CT) can support the diagnosis and rule out alternative causes. Management is mainly supportive and includes oxygenation, mechanical ventilation, and, if necessary, administration of vasopressors. Nonthrombotic embolisms have a high mortality rate.

For thromboembolic diseases, see “Pulmonary embolism,” “Thromboembolic stroke,” “Acute mesenteric artery embolism,” “Acute limb ischemia,” and “Retinal vessel occlusion.”

See also “Septic emboli.”

Overviewtoggle arrow icon

Overview of nonthrombotic embolisms
Fat embolism [1][2][3] Venous air embolism [4][5][6] Arterial air embolism [4][5][6] Amniotic fluid embolism [7][8][9]
  • Fat cells in the circulation
  • Air in the venous circulation
  • Air in the arterial circulation
  • Fetal cells and debris from amniotic fluid in the maternal circulation
Classic risk factors
Classic clinical features

Distinguishing diagnostic findings

(if clinical suspicion is high)

  • Fat droplets on blood smear
  • Bilateral patchy infiltrates on chest imaging
  • Starfield pattern on MRI brain

Both arterial air embolism and venous air embolism can be caused by laparoscopic surgery, cardiac and vascular surgery, endoscopic procedures, ECMO, and diving-related injuries.

Fat embolism, air embolism, and AFE are all clinical diagnoses.

Fat embolismtoggle arrow icon

Definition [1]

A potentially life-threatening condition caused by the entry of fat cells, usually from bone marrow, into the circulatory system

Etiology [1]

Early operative fixation is recommended in patients with long bone fractures to reduce the risk of fat embolism syndrome. [10]


Clinical features [1][2][3]

Symptoms develop within 12–72 hours of the inciting event.

Fulminant fat embolism syndrome can manifest with ARDS, shock, signs of acute heart failure, and/or DIC. [1]

Diagnosis [1][2][3]

Fat embolism is a clinical diagnosis; rule out other life-threatening causes of dyspnea and critical causes of altered mental status.

Diagnostic criteria

Gurd's criteria and Schonfeld's criteria are commonly used, however, neither has been prospectively validated.

Gurd's criteria

1 major plus 4 minor criteria are required for the diagnosis. [12]

Schonfeld's criteria

Schonfeld's criteria [3]
Criteria Points
Petechial rash 5
Bilateral infiltrates on chest x-ray 4
Hypoxemia < 70 mm Hg 3
Fever > 38°C (100.4°F) 1
Tachycardia > 120/minute 1
Tachypnea > 30 breaths per minute 1


A score of > 5 points is required to make a diagnosis of fat embolism syndrome.

Laboratory studies [2][3]


Management [1][2][3]

Management is primarily supportive, as there are no specific treatments for fat embolism syndrome.

Prognosis [1][3]

Fat embolism syndrome is usually self-limited.

  • Mortality rates are < 10% with appropriate ICU management.
  • Respiratory, neurological, and dermatologic manifestations are usually fully reversible.

Venous air embolismtoggle arrow icon

Definition [4][5]

A rare and potentially life-threatening condition caused by the entry of gas into the systemic venous circulation

Etiology [4][5]

Pathophysiology [4][6]

  • Air enters the venous system → travels to right ventricle → right ventricular outflow obstruction → circulatory collapse
  • Acute cor pulmonale and circulatory collapse typically only occur with large volume embolisms.
  • Small volume emboli may be asymptomatic or cause transient or minimal symptoms.

Clinical features [4][6]

Diagnostic studies [4][6]

Venous air embolism is a clinical diagnosis. Exclude other immediately life-threatening causes of dyspnea or shock.

Management [4][5][6]

For patients with evidence of arterial ischemia (suggesting paradoxical embolism) also see “Management” in “Arterial air embolism.”


Air embolism has a high mortality rate (∼ 20%). [13]

Arterial air embolismtoggle arrow icon

Definition [4][5]

A rare and potentially life-threatening condition caused by the entry of gas into the pulmonary veins or directly into the systemic arterial circulation

Etiology [4][5]

Pathophysiology [4]

Clinical features [4]

Diagnostic studies [4]

Arterial air embolism is a clinical diagnosis. Exclude other critical causes of altered mental status.

Management [4][5][6]

See also “Diving-related injuries.”

Hyperbaric oxygen therapy is the treatment of choice for all patients with symptomatic arterial air embolism. [5][6]


Air embolism has a high mortality rate (∼ 20%). [13]

Amniotic fluid embolism (AFE)toggle arrow icon

Definition [7][8]

A rare life-threatening condition caused by the entry of fetal cells and debris (from amniotic fluid) into maternal circulation [8]


Risk factors [7][8][9]

Clinical features [7][8]

AFE typically manifests during labor or immediately after delivery but can occur up to 48 hours postpartum.

AFE typically manifests with a classic triad of sudden hypoxia and hypotension followed by coagulopathy. [7][8]

Diagnosis [7][8][9]

General principles

If AFE is suspected clinically, do not delay treatment to obtain diagnostic studies. [7][9]

Laboratory studies


Differential diagnosis [7][9]

Management [7]

AFE is a life-threatening condition and must be treated as an emergency.


Pulmonary cement embolismtoggle arrow icon

  • Definition: respiratory insufficiency because of embolization of bone cement material or indirect systemic effects after bone cement implantation
  • Occurrence: after orthopedic procedures using bone cement material
  • Pathophysiology: direct mechanical embolization and thermal effects or an immunological-mediated release of vasoactive substances; often associated with fat embolism
  • Clinical features
  • Diagnostics: CT pulmonary angiogram for the detection of mechanical embolization
  • Treatment
    • Supportive (intensive care) measures, including mechanical ventilation and catecholamine therapy
    • If necessary, interventional or surgical removal of the embolic cement material

Acute management checklisttoggle arrow icon

Referencestoggle arrow icon

  1. McCarthy C, Behravesh S, Naidu S, Oklu R. Air Embolism: Practical Tips for Prevention and Treatment. Journal of Clinical Medicine. 2016; 5 (11): p.93.doi: 10.3390/jcm5110093 . | Open in Read by QxMD
  2. Muth CM, Shank ES. Gas Embolism. N Engl J Med. 2000; 342 (7): p.476-482.doi: 10.1056/nejm200002173420706 . | Open in Read by QxMD
  3. Jorens PG, Van Marck E, Snoeckx A, Parizel PM. Nonthrombotic pulmonary embolism. Eur Respir J. 2009; 34 (2): p.452-474.doi: 10.1183/09031936.00141708 . | Open in Read by QxMD
  4. Bradley LM, McDonald AG, Lantz PE. Fatal systemic (paradoxical) air embolism diagnosed by postmortem funduscopy. J Forensic Sci. 2021; 66 (5): p.2029-2034.doi: 10.1111/1556-4029.14781 . | Open in Read by QxMD
  5. McCarthy C, Behravesh S, Naidu S, Oklu R. Air Embolism: Diagnosis, Clinical Management and Outcomes. Diagnostics. 2017; 7 (1): p.5.doi: 10.3390/diagnostics7010005 . | Open in Read by QxMD
  6. Kosova E, Bergmark B, Piazza G. Fat embolism syndrome. Circulation. 2015; 131 (3): p.317-320.doi: 10.1161/CIRCULATIONAHA.114.010835 . | Open in Read by QxMD
  7. Rothberg DL, Makarewich CA. Fat Embolism and Fat Embolism Syndrome. J Am Acad Orthop Surg. 2019; 27 (8): p.e346-e355.doi: 10.5435/jaaos-d-17-00571 . | Open in Read by QxMD
  8. Newbigin K, Souza CA, Torres C, et al. Fat embolism syndrome: State-of-the-art review focused on pulmonary imaging findings. Respir Med. 2016; 113: p.93-100.doi: 10.1016/j.rmed.2016.01.018 . | Open in Read by QxMD
  9. Pacheco LD, Saade G, Hankins GDV, Clark SL. Amniotic fluid embolism: diagnosis and management. Am J Obstet Gynecol. 2016; 215 (2): p.B16-B24.doi: 10.1016/j.ajog.2016.03.012 . | Open in Read by QxMD
  10. Clark SL. Amniotic Fluid Embolism. Obstet Gynecol. 2014; 123 (2): p.337-348.doi: 10.1097/aog.0000000000000107 . | Open in Read by QxMD
  11. Conde-Agudelo A, Romero R. Amniotic fluid embolism: an evidence-based review.. Am J Obstet Gynecol. 2009; 201 (5): p.445.e1-13.doi: 10.1016/j.ajog.2009.04.052 . | Open in Read by QxMD
  12. Unapproved Drugs. Updated: February 6, 2021. Accessed: December 21, 2022.
  13. Godoy DA, Di Napoli M, Rabinstein AA. Cerebral Fat Embolism: Recognition, Complications, and Prognosis. Neurocrit Care. 2017; 29 (3): p.358-365.doi: 10.1007/s12028-017-0463-y . | Open in Read by QxMD
  14. Gurd AR. FAT EMBOLISM: AN AID TO DIAGNOSIS. J Bone Joint Surg Br. 1970; 52-B (4): p.732-737.doi: 10.1302/0301-620x.52b4.732 . | Open in Read by QxMD

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