Direct Noninvasive Assessment of Brain Metabolism during Increased Intracranial Pressure: Potential Therapeutic Vistas

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Abstract
Intracranial pressure was increased in cats by infusing ‘mock’ CSF intracranially, thus decreasing cerebral perfusion and oxygenation. The cats then randomly received either 50% 02 or 50% 02—5% CO2 by inhalation. As monitored by in vivo near-infrared spectroscopy (NIR), no improvement was noted after 50% O2 whereas 50% O2-5% C02 resulted in increased perfusion, an oxidation of cytochrome a,a3, an increase in oxyhemoglobin, and reduced quantities of de-oxyhemoglobin (p < 0.01) despite a further increase in intracranial pressure. The authors conclude that: a) NIK is a useful means of noninvasively and directly assessing brain metabolism and has advantages over simple ICP monitoring; and b) continued investigations of C02 as a possible therapeutic modality after head injury appear warranted.