Does central nervous system monitoring improve outcome?

Work during the past year on monitoring of the nervous system is reviewed, with specific focus on advances in sensory- and motor-evoked potentials, near-infrared spectroscopy, transcranial Doppler, and electroencephalographic techniques to detect awareness under anesthesia. For techniques where a proven relationship to outcome exists (somatosensory-evoked potentials in scoliosis surgery and facial nerve monitoring during vestibular schwannoma resection), recent advances have revolved around enhancements of the technique to improve its usefulness. For transcranial Doppler sonography and near-infrared spectroscopy, recent work has attempted to demonstrate the relationship of the monitoring to changes in the physiological variable of greater interest which cannot in themselves be directly measured (blood flow and cerebral oxygenation, respectively). Finally, studies with the bispectral index, derived from the electroencephalogram, continue to make slow progress in finding the elusive measure of awareness under anesthesia. This review clearly defines the clinical utility of some of these techniques, giving impetus to further studies in their application.