Central nervous system monitoring during open heart surgery: an update.

Electroencephalography (EEG) is used to monitor the function of the central nervous system in a variety of surgical procedures. During cardiac surgery with cardiopulmonary bypass, ischemic changes on the EEG as a result of impaired central nervous system blood supply can be noted. The EEG also may be used to monitor the functional state of the brain during and after profound hypothermic circulatory arrest. If a desired goal is to reduce cerebral metabolism using a barbiturate or other such agent, the EEG can be monitored to provide a measurable pharmacodynamic end point (burst suppression). Techniques have been developed to process the EEG signal using a computer and to improve on-line interpretation. These include fast Fourier transformation to develop a three-dimensional plot or compressed spectral array, evoked-potential monitoring, and bispectral analysis to derive a univariate descriptor of the EEG. These techniques have been used to detect awareness and indirect memory function, as well as to assess the adequacy of anesthesia. There is a good correlation between implicit memory and alterations in midlatency auditory-evoked responses. The bispectral index has been used to assess the adequacy of anesthesia as well as to detect awareness. Preliminary studies suggest that titrating the anesthetic to bispectral index levels may be useful during cardiac surgery.