EFFECTS OF MECHANICAL VENTILATION WITH NORMOBARIC OXYGEN-THERAPY ON THE RATE OF AIR REMOVAL FROM CEREBRAL-ARTERIES

Objective: We conducted the current study to evaluate the removal rate of air embolism from cerebral arteries after spontaneous breathing at a low FIo(2) in comparison with mechanical ventilation at an FIO2 of 1.0. Design: Randomized, experimental trial. Setting: Neuroimaging dep artment at a veterinary school hospital laboratory. Subjects: Nine ane sthetized beagles undergoing mechanical ventilation with previous norm al cranial computed tomography (CT) scan. Interventions: in each dog, after a control scan, air was infused at a constant flow rate, via a c atheter inserted into the internal carotid artery. CT scan was repeate d until typical bubbles appeared. immediately after, the animals were randomly assigned to breathe room air (group A), or to be mechanically ventilated at an FIo(2) 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 am ong bubbles (Hounsfield units), the duration of radiologic findings, a nd the ratio of volume/duration (mL/kg/min) between the two groups, us ing the Mann-Whitney test. Results: The volume of air infused per kg o f body and brain weights and density were not significantly different between the two groups. The duration of radiologic findings was shorte r (p < .02) in group B (7.0 +/- 4.7) than in group A (20.4 +/- 3.8), a nd the air removal rate from cerebral arteries (expressed as volume/du ration 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 FIo(2) 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 clinic al benefits of high FIo(2), administration and of mechanical ventilati on separately. However, the prompt application of mechanical ventilati on with an FIo(2) of 1.0 may be recommended when air embolism is suspe cted.