The reversal of the oxygen difference between arterial blood and cerebrospinal fluid in chronic, exacerbated respiratory insufficiency.

The relationship between PaO2 and PCSFO2 (along with other acid-base parameters) was studied in patients with long-lasting respiratory failure. These patients exhibited a highly significant reversal of the normal relationship, i.e. their PCSF O2 was invariably higher, than PaO2. It is suggested that this reflects a mechanism protecting the brain against hypoxia.