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Theoretical assessment of normobaric oxygen therapy to treat pneumocephalus
1Department of Anesthesia, University of Iowa, Iowa City, 52242, USA.
Background:
Pneumocephalus has been linked to several clinical conditions, including headache, lethargy, and even brain herniation or death. The effects of different normobaric oxygen concentrations and durations of therapy on the rate of air absorption were examined.
Methods:
An existing mathematical model of inert gas absorption was used. The model accounts for the major phenomena that determine absorption of bubbles, including surface tension, pressure dependence of bubble size, and removal of gases to the surrounding tissue. Sensitivity analysis tested reliability of our results.
Results:
Times for a 50-ml air collection to have been absorbed were 5.8, 1.9, and 0.6 weeks at an FIO2 of 0.21, 0.4, and 1.0 respectively. Thirty percent and 72% of the air was absorbed in 2 days at an FIO2 of 0.4 and 1.0, respectively. The percent decrease in time for absorption achieved by increasing the FIO2 from 0.21 was nearly identical for different volumes of air. The benefit of increasing the FIO2 decreased with progressive increases in the FIO2. Increasing the FIO2 from 0.21 to 0.4 caused the time to total air absorption to decrease by 67%. In contrast, increasing the FIO2 from 0.8 to 1.0 caused the time to total air absorption to decrease by an additional 3%.
Conclusions:
Based on mathematical model predictions, an FIO2 of 0.4 or 1.0 for at least 1 week or 2 days, respectively, will significantly decrease the time for absorption of a pneumocephalus.