In addition to looking at the raw EEG data, the EEG recordings can be subjected to quantitative analysis. A number of different quantification methods are available with most commercially available EEG software. Quantification techniques include the calculation of power spectra by means of fast Fourier transform (FFT), which then can be used to calculate ratios of fast over slow activity or other parameters. These can be displayed as numbers or graphically as compressed spectral arrays (CSAs), histograms, or as staggered arrays, which have the potential to unmask subtle background changes when trended over time. The qEEG parameters may include total power, frequency activity totals (eg, total or percentage alpha power), spectral edge frequencies (eg, frequency below which 50% of the EEG resides), amplitude-integrated interval, frequency ratios (eg, alpha-to-delta ratio), and brain symmetry index.6 Other more automated EEG data reduction display formats include the cerebral function monitor (CFAM), EEG density modulation, automated analysis of segmented EEG (AAS-EEG), and bispectral index (BIS) monitor.7-11 However, qEEG should always be interpreted in the context of the raw EEG since artifacts, medications, and other clinical events may cause very similar findings to epileptiform findings (Figure 13-5). This is particularly true for software packages that display “user-friendly” composite scores, and any outputs that are based on unpublished algorithms (“proprietary information”) should be viewed with great caution. The qEEG parameters are particularly useful for seizure quantification and to estimate effects of seizure treatment once the qEEG “footprint” of a seizure has been identified.
For continued NCSE in this patient, a midazolam drip was rapidly titrated up until seizures were controlled. The next morning he underwent tumor resection while on midazolam with no complications. Postoperatively, midazolam was weaned, and on postoperative day 2, he was transferred to the floor with signs of a mild residual neglect. Biopsy revealed glioblastoma multiforme.