Pneumocephalus

Introduction
Pneumocephalus is defined as the presence of air or gas within the intracranial compartment.

Oxygen supplementation
The theoretical rational for oxygen supplementation is as follows: Intracranial air should be composed of the same gases as atmospheric air (79% nitrogen, 21% oxygen). Supplementing oxygen with replace dissolved nitrogen in the blood, speeding absorption of intracranial air by increasing the diffusion concentration gradient from the intracranial air into the surrounding cerebral tissue and blood. Early mathematical modelling suggested that 100% FiO2 is needed for several days to improve pneumocephalus. However small clinical trial in 2008 of only 13 patients but with blinded outcome suggested benefit of oxygen supplementation with 100% supplemental O2 via nonrebreather for 24 hours (equivalent to FiO2 of ~68%), with mean reduction in pneumocephalus of 65% in the treatment group compared with 31% in the control group at 24 hours, for a rate of decrease of 1.26 mL/hr. Another trial of 44 patients found a significant decrease with 100% FiO2 via entotracheal tube after only 3 hours when measured at 24 hours. This difference at 24 hours was small (21 mL, only approximately 15% more than standard care), but at a faster rate than in the 2008 trial, a rate of 3.57 mL/hr, with higher FiO2 administration. Thus some improvements may be seen fairly quickly.

There are concerns of causing pulmonary toxicity with high oxygen. The measure Unit Pulmonary Toxicity Dose (UPTD) was introduced to quantify relative doses, with one UPTD meaning 1 minute exposure of 100% oxygen at normal atmospheric pressure. The recommended O2 exposure in a single treatment is 615 UPTD, with an upper limit of 1425 UPTD. At 100% FiO2 via endotracheal tube, this upper limit is at approximately 24 hours of treatment.

For nonintubated patients, high-flow nasal cannula is a viable option for delivery of oxygen.