Comparison of cerebral oximeter and evoked potential monitoring in carotid endarterectomy

Purpose

To assess the cerebral oximeter, which measures regional oxygen saturation (rSO₂) continuously and noninvasively, as a cerebral monitor during carotid endarterectomy (CEA). The rSO₂ was compared with Somatosensory Evoked Potentials (SSEPs) as an indicator for shunting and as a predictor of postoperative neurological deficits.

Methods

Seventy-two consenting patients undergoing CEA with general anaesthesia were studied. Normocarbia, normothermia and normotension were maintained. Cerebral monitoring consisted of bilateral median nerve SSEPs and the INVOS 3100 cerebral oximeter with the sensor pad placed on the ipsilateral forehead. Decreases in SSEP amplitude of 50% and in rSO₂ of 10% were considered clinically significant. Neurological assessment was performed at emergence from anaesthesia, 24 hr postoperatively and at discharge. The rSO₂ changes were compared with SSEP changes and with neurological deficits. Statistical analysis was with chi square and analysis of variance. P < 0.05 was considered significant.

Results

During carotid artery clamping, rSO₂ decreased from 72 ±8% to 68 ±9% and mean arterial blood pressure increased from 92 ±14 mmHg to 98 ±14 mmHg. In four patients, the carotid artery was shunted because of SSEP changes after cross-clamping. Five patients had ≥10% decreases in rSO₂ following clamp application. Changes in both SSEP and rSO₂ occurred in two patients. Three of the four shunted patients had transient postoperative neurological deficits. One patient had a transient deficit without changes in either monitor. There were no persistent postoperative deficits. Compared with SSEPs, rSO₂ had a sensitivity of 50% and a specificity of 96%.

Conclusion

Clinical experience with this evolving technology is ongoing. Its role in neurovascular procedures has yet to be established.