Effects of changes in mean arterial pressure on SjO2 during cerebral aneurysm surgery.

Twenty-six patients requiring clipping of cerebral aneurysms were anaesthetized with propofol, alfentanil and atracurium infusions and their lungs ventilated mechanically to hypocapnia (3.4-4.5 kPa). SjO2 was measured continuously with an Oximetrix fibreoptic oximetry catheter. Normovolaemia was maintained by observing the response of mean arterial pressure (MAP) and central venous pressure (CVP) to fluid administration. The response of SjO2 to increased MAP was noted and the lactate oxygen index (LOI) calculated at regular intervals. SjO2 measurements indicated a critical MAP of between 80 and 110 mm Hg in nine patients, and one patient had a persistently low SjO2 value despite an MAP of 110 mm Hg. An increase in MAP was associated with an increase in SjO2 in 19 patients (P < 0.001). When the effects of changes in PaCO2 were eliminated, this change was still significant (P = 0.004) (n = 9). Patients with an LOI > 0.08 at any time during the procedure had a worse initial outcome (within the first day) (P < 0.02) than patients who had a normal LOI throughout. Long-term outcome was similar to those with a normal LOI. Increasing MAP did not have a consistent effect on LOI. Jugular bulb cannulation to assess hypoperfusion in conjunction with lactate measurements and calculation of LOI provide useful information on which to base the intra- and postoperative management of patients with subarachnoid haemorrhage.