Arterial air embolism

Neurological symptoms and signs occurring within 10 min of surfacing from a scuba dive are usually due to arterial gas embolism— 'the ten minute rule' ( Kizer.1987).

The clinical features of arterial gas embolism are specific to the body region embolized and the cause of the embolus (e.g. thoracic trauma). The most common sites of emboli are the cerebral and coronary circulations.

The symptoms relate to the artery embolized, for example chest pain and dyspnea (coronary artery) and alterations in consciousness and subtle mental changes (cerebral artery). Alveolar rupture, which is often associated with arterial gas embolism, manifests as hemoptysis and pleuritic chest pain.

The signs are primarily of major organ dysfunction. Associated clinical findings include livedo reticularis, Liebermeister's sign (a well-defined area of glossal pallor), and air in the retinal vessels.

Air in the systemic circulation may be difficult to detect. Its absence does not exclude clinically significant arterial gas embolism, as minute amounts of gas can cause significant symptoms. Diagnostic investigations are aimed at either directly demonstrating air in the arterial system or locating the possible source of arterial gas emboli. Transesophageal echocardiography can be used as a sensitive non-invasive procedure to diagnose intrathoracic air embolism on both sides of the circulation (Sajada. etai 1995). Cerebral air embolism seen on CT scanning is diagnostic.

Transcranial Doppler ultrasonography is a non-invasive tool used to monitor middle cerebral artery blood flow during carotid endarterectomy. Air emboli of diameter as small as 30 pm are detected as short-duration high-intensity 'chirps' on the ultrasound flow waveform.

Biochemical and hematological evidence of arterial gas embolism is non-specific. It includes a rise in creatinine kinase and a fall in hematocrit.

Standard radiographs often provide an accessible method of supporting a diagnosis of arterial air embolus, such as looking for barotrauma. Subtle findings of extrathoracic ectopic air on skull and abdominal radiographs can help to confirm the clinical diagnosis.

It should be emphasized that the diagnosis of arterial air embolus is often clinically based. A high index of suspicion is vital for the successful resuscitation of patients with a paucity of abnormal diagnostic investigations.

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