Special Investigations

Once GE has developed, specialized testing is of limited use. However, the following are justified:

-Chest X-ray, not so much to get a picture of the embolus in the heart chambers (i.e., rare) but to check for associated pathologies (lung oedema, aspiration pneumonia; barotrauma),

-Arterial blood gases - directs resuscitative efforts (e.g., metabolic acidosis secondary to the initial cardiovascular collapse and hypoxemia in 50% of cases),

-ECG - indicates cardiac involvement and risk for decompensation (arrythmias are observed in 33% of case).

Some tests have been suggested to support the diagnosis but these are mostly useful for detecting the embolus itself:

- EEG44, when performed at an early stage, show three different phases: (1) depression at the same time as the embolus; (2) transient recovery, and (3) subsequent deterioration with irritatable asymmetrical elements of varying locations; and(4) recovery - gradual and always delayed relative to the clinical picture.

- Catheterisation of the right atrium using an ordinary80 or a Swan Ganz catheter81 is useful for diagnosis and treatment as it may allow aspiration of the air in the right cavities.

- Capnography shows an obvious and fast drop in the peak value of the expired fraction of CO2, indicating haemodynamic disorders in the lungs52,82.

- Doppler ultrasonography either of the precordial area5183, or by a trans-oesophageal probe84, is a sensitive method for detecting even small bubbles in circulation; it is of little use when GE has occurred.

- CT scan of the brain can provide direct images of bubbles obstructing the brain vessels and indirect images of oedema or ischemia85. However it rarely makes a contribution to diagnosis (under 5% of images of intravascular bubbles) and a normal picture does not mean GE can be excluded.

- Echocardiography can also show up bubbles in the heart cavities.

Although various tests have been proposed, GE diagnosis remains mainly clinical, and is based on a combination of a situation of GE risk and the appearance of compatible signs. In no way must a quest for special examinations delay HBO treatment.

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