Air embolism and Fat embolism

The four most common embolism seen in the critical care patient population are air embolism, fat embolism, cholesterol embolism, and blood embolism (clots).

Embolism is an uncommon complication of altered mentation after invasive procedures, but it must be placed on the list of differential diagnoses.

Air embolism occurs when air enters the systemic vascular circulation during placement or removal of a central venous catheter or at other times when a central venous catheter is in use.

Air can also be introduced into the systemic circulation during cardiac surgery procedures, neurosurgical procedures, and endoscopic procedures. Air that enters the venous circulation can travel to the right side of the heart and cause cardiopulmonary compromise.

The clinical presentation of a venous air embolism is highly variable and depends on the amount of air entry, the speed of entry, and the patient’s size and premorbid condition. Symptoms may range from mild chest discomfort to altered mentation to complete cardiovascular collapse.

Alternatively, a right-to-left shunt can result in an embolus that enters the arterial circulation and causes cerebral ischemia. If a cerebral air embolism is suspected, then the head should be immediately lowered, a fraction of inspired oxygen of 1.0 should be delivered, and adequate ventilation maintained.

One therapy for air embolus is hyperbaric oxygen therapy, which if desired, should be instituted within 5 h of neurologic or cardiac symptoms.

Fat embolism is most commonly the result of trauma or long-bone fracture. However, they can also present following orthopedic procedures such as spine surgery and knee and hip replacements.

The classic findings of fat embolism include petechiae, dyspnea, and altered mental status.

The symptoms of fat embolism usually occur 1 to 2 days after the precipitating event and are the result of a diffuse vasculitis secondary to free fatty acids. Although this entity has a classic appearance, the diagnosis is one of exclusion.

The treatment of fat embolism is supportive and includes oxygen therapy and mechanical ventilation if needed.

Another uncommon cause of altered mental status, especially following cardiac catheterization or arteriography, is a cholesterol embolus. Stroke may result from the embolization of atherosclerotic material that is disturbed by the catheter during the procedure.

The syndrome may present with live do reticularis, severe limb pain, renal failure, or focal neurologic deficits. The neurologic deficits usually present acutely and are frequently reversible.

If skin changes are present, the diagnosis can be confirmed with skin biopsy demonstrating cholesterol crystals. In addition, emboli to the kidney may cause renal dysfunction and emboli to the viscera may be a cause of ischemic bowel.

The most frequent embolic material after invasive procedures is blood. Clots that subsequently embolize occur secondary to intimal disruption and venous stasis from immobility. The time of onset can be variable, as can the presenting symptoms.

Orthopedic surgery and neurosurgery are associated with the highest risks of venous emboli secondary to the release of tissue factor, which is a powerful trigger of blood clotting. Although deep vein thrombosis and pulmonary emboli are common in the postsurgical population, cerebrovascular accidents due to venous emboli require communication between the left and right heart via a septal defect or patent foramen ovale (the classic paradoxical emboli).

The clinical manifestations of cerebral emboli depend on the specific vessel occluded and the distribution of blood from that vessel. For example, occlusion of the middle cerebral artery results in contralateral hemiparesis and sensory loss with more severe symptoms in the arms and face.

Treatment of a thrombotic stroke includes thrombolytic therapy, blood pressure regulation, supportive care, and aggressive physical therapy. Multiple studies have demonstrated the effectiveness of thrombolytic therapy if instituted within the first 3 hours of symptom onset and after a noncontrast computed tomography scan excludes an intracranial hemorrhage.

Suggested Readings

Blacker DJ. In-hospital stroke. Lancet Neurol 2003;2(12):741,746.

Cramer SC. Patent foramen ovale and its relationship to stroke. Cardiol Clin 2005;23(1):7,11.

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