EFFECTS OF CHANGES IN MEAN ARTERIAL-PRESSURE ON SJ(O2) 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). Sj(O2) 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 Sj(O2) to increased MAP was noted and the lactate oxygen index (LOI) calculated at regular intervals. Sj(O2) measurements indicated a critical MAP of between 80 and 110 mm Hg in nine patients, and one patient had a persistently low Sj(O2), value despite an MAP of 110 mm Hg. An increase in MAP was associated with an increase in Sj(O2) in 19 patients (P < 0.001). When the effects of changes in Pa-CO2 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.