Cerebral arterial air embolism: III. Cerebral blood flow after decompression from various pressure treatments.

The effect of various combinations of time between 2 and 20 min and between pressures of 2.8 and 10 bar (60 and 300 ft) breathing air or oxygen at 2.8 bar (60 ft), on the continued recovery of cortical evoked potentials (CEP), cerebral blood flow (CBF), and water content of the brain were studied in the dog cerebral arterial air embolism model. It was found that the compression-decompression cycle alone resulted in a rise in cerebrospinal fluid pressure sustained for at least 20 min. The CBF study at 30 min showed an increased flow in dived, nonembolized animals. Water content of the brain was also significantly increased in these animals. The data suggest that the clearance of air is probably independent of pressure once past a threshold of 2.8 bar and is certainly hastened by oxygen. A time of around 8 min is probably required to clear the embolism. The evidence of gas bubble redistribution with recurrence and development of new sites of vascular obstruction in dogs exposed to significant inert gas uptake, however, suggests that a second problem of the clearance of recirculating gas exists. An incidental observation suggests that recently dived dogs may have been more prone to secondary deterioration. The results of these studies again suggest that there may be advantages to confining the treatment of arterial gas embolism to 2.8 bar breathing oxygen.