Effects of mechanical ventilation with normobaric oxygen therapy on the rate of air removal from cerebral arteries

Abstract

Objective: We conducted the current study to evaluate the removal rate of air embolism from cerebral arteries after spontaneous breathing at a low FIO2 in comparison with mechanical ventilation at an FIO2 of 1.0.

Design: Randomized, experimental trial.

Setting: Neuroimaging department at a veterinary school hospital laboratory.

Subjects: Nine anesthetized beagles undergoing mechanical ventilation with previous normal cranial computed tomography (CT) scan.

Interventions: In each dog, after a control scan, air was infused at a constant flow rate, via a catheter inserted into the internal carotid artery. CT scan was repeated until typical bubbles appeared. Immediately after, the animals were randomly assigned to breathe room air (group A), or to be mechanically ventilated at an FIO2 of 1.0 (group B). CT scan was again repeated every minute until the removal of all bubbles. We compared the volume of air infused per kg of body and brain weights, the lowest density among bubbles (Hounsfield units), the duration of radiologic findings, and the ratio of volume/duration (mL/kg/min) between the two groups, using the Mann-Whitney test.

Results: The volume of air infused per kg of body and brain weights and density were not significantly different between the two groups. The duration of radiologic findings was shorter (p < .02) in group B (7.0 +/- 4.7) than in group A (20.4 +/- 3.8), and the air removal rate from cerebral arteries (expressed as volume/duration of radiologic findings) was dramatically improved (p < .02) in group B (0.159 +/- 0.042) in comparison with group A (0.046 +/- 0.016).

Conclusions: These results suggest that the removal rate of air from cerebral arteries is dramatically increased by mechanical ventilation at an FIO2 of 1.0. Consequently, the time of cerebral ischemia may be decreased, but the result does not account for the effects of each factor separately. Further studies are required to evaluate the clinical benefits of high FIO2 administration and of mechanical ventilation separately. However, the prompt application of mechanical ventilation with an FIO2 of 1.0 may be recommended when air embolism is suspected.