[Changes in cerebral oxygen metabolism and significance in patients with severe head injury]

To investigate the changes in cerebral oxygen metabolism following head injury and their relationship with intracranial pressure (ICP), cerebral perfusion pressure (CPP), and Glasgow coma scale (GCS).

Forty-five patients after surgery for serious head injury were studied and divided into different groups according to ICP, CPP and GCS, 10 patients without head injury were enrolled as controls. GCS, ICP, CPP, blood gas analysis, jugular bulb for gas analysis, jugular bulb blood oxygen saturation (SjvO(2)), cerebral arterial venous oxygen content difference (AVDO(2)) were accessed and scored, and cerebral extraction of oxygen (CEO(2)) were calculated in all the patients. The relationships of these parameters with ICP, CPP and GCS score were analysed.

On the 1 st postinjury day SjvO(2) decreased whereas CEO(2) and AVDO(2) increased in all patients, with significant differences compared with the controls (all P<0.05). During the 2nd-4th postoperative days, SjvO(2) gradually increased with CEO(2) and AVDO(2) decreased in patients with mild or moderate head injury of increased in ICP or lowered in CPP group, the changes in the above parameters were slower, with significant difference compared with patients with increase in ICP, and mild or moderate lowering of CPP (all P<0.05). There were significant differences in SjvO(2), CEO(2), and AVDO(2) between the group of GCS<5 and GCS>6-8 during the 2nd-5th days (all P<0.05). ICP was negatively correlated with SjvO(2) (r=-0.8652, P<0.01) and positively correlated with CEO(2) (r=0.4172, P<0.05) and AVDO(2) (r=0.4771, P<0.05). CPP was positively correlated with SjvO(2) (r=0.8830, P<0.01) and negatively correlated with CEO(2) (r=-0.6724, P<0.05) and AVDO(2) (r=-0.8350, P<0.01). GCS score was positively correlated with SjvO(2) (r=0.8230, P<0.01) and CEO(2) (r=0.8010, P<0.001), but there was no correlation between GCS score and AVDO(2) (r=2.6310, P=0.677).

In patients with serious head injury, if the increase in ICP is mild or moderate, there are cerebral hypoxia and ischemia during the first 24 hours after injury. During the 2 nd-4 th postinjury days, the brain becomes hyperemic and hyperoxygenated. Marked increase in ICP results in persistent cerebral hypoxia and ischemia. ICP, CPP and GCS score are main factors affecting cerebral oxygen metabolism.