Monitoring of intra-operative visual evoked potentials during functional endoscopic sinus surgery (FESS) under general anaesthesia.

Functional endoscopic sinus surgery (FESS) is an effective treatment for inflammatory sinus disease. The potential for major complications during FESS is high particularly under general anaesthesia. The most serious of these is injury to the eye leading to blindness. We looked at the feasibility of monitoring flash visual evoked potentials (VEP) simultaneously from both eyes during FESS. Five patients were included in this preliminary study. A haptic contact lens connected by fibreoptic cable to a photostimulator was placed on the eyes and stimulus of comparable intensity to a conventional strobe was delivered. We found that an increase in P100 latency to be an indicator of optic nerve compression. However, for this to be useful the diastolic blood pressure should not fall below 50 mmHg, the oxygen saturation should be maintained at 98 per cent and bleeding should be minimized during surgery. The changes in the amplitude of P100 was not found to be useful. While there is no substitute for learning endoscopic surgery by cadaveric dissection and supervised training we believe that in selected cases VEP monitoring can be employed with profit.