Monitoring regional brain oxygen saturation in patients with clipped aneurysms of the anterior circle of Willis

Introduction

The objective of this work was to assess the usefulness of monitoring regional brain oxygen saturation (rSO₂) in the identification of intraoperative episodes of cerebral ischemia during the surgical clipping of brain aneurysms. Moreover it aimed to verify whether this kind of monitoring affects the incidence of postoperative neurological deficits.

Methods

We monitored 50 patients undergoing cerebral aneurysm clipping with the use of Somanetics INVOS Cerebral Oximeter 4100. The alarm threshold of rSO₂ was defined as a minimum of 20% drop from baseline, triggering intervention aimed at increasing rSO₂ values.

Results

Eleven cases of postoperative deterioration of neurological status were noted, of which six were reversible. Additional intraoperative events, such as numerous surgical clip displacements, temporary clipping, aneurysm ruptures, and trapping occurred in 16 cases. On the operated side, a rapid, lasting increase of rSO₂ values was noted in nearly one-half of the cases; implying an artifact caused by the neurosurgical procedure. On the nonoperated side, seven cases of rSO₂ values dipping below the alarm threshold were noted. In all cases intervention led to an increase and normalization of rSO₂ values in a relatively short time. Since the values registered in the frontal lobe on the nonoperated side were considered representative of the entire brain, the balance of cerebral oxygen supply and consumption was seen as intraoperatively preserved. The comparison between two groups of patients, with and without neurological deficits developed in the postoperative period, revealed no disparities in cerebral oximetry values on the nonoperated side, nor in the range of other monitored physiological parameters. In 10 out of 16 cases involving additional intraoperative events, deterioration of neurological status was noted (62.5%), while in the remaining cases only one such occurrence was registered (2.95%).

Conclusions

Monitoring regional brain oxygen saturation on the operated side is a method hampered by a large percentage of false results, and thus is a monitoring tool of little prognostic value. Assuming that the frontal lobe on the nonoperated side is representative of the entire brain with regard to rSO₂ measures, the maintenance of oxygen supply and demand balance does not safeguard the brain against ischemic lesions in the supply area of the operated artery.