Direct noninvasive assessment of brain metabolism during increased intracranial pressure: potential therapeutic vistas.

Intracranial pressure was increased in cats by infusing 'mock' CSF intracranially, thus decreasing cerebral perfusion and oxygenation. The cats then randomly received either 50% O2 or 50% O2-5% CO2 by inhalation. As monitored by in vivo near-infrared spectroscopy (NIR), no improvement was noted after 50% O2 whereas 50% O2-5% CO2 resulted in increased perfusion, an oxidation of cytochrome a,a3, an increase in oxyhemoglobin, and reduced quantities of de-oxyhemoglobin (p less than 0.01) despite a further increase in intracranial pressure. The authors conclude that: NIR is a useful means of noninvasively and directly assessing brain metabolism and has advantages over simple ICP monitoring; and continued investigations of CO2 as a possible therapeutic modality after head injury appear warranted.