Introduction
Contemporary brain monitoring in clinical practice includes multiple global and local modalities such as ABP, ICP, Transcranial Doppler, Laser Doppler Flowmetry, brain tissue oxygenation, jugular bulb oxygen saturation, Near Infrared Spectroscopy, etc. Measured variables require time- and/or frequency-domain on-line analysis to derive further information from spontaneous waves present in those signals (e.g. cardiac related, respiratory and slow waves). Analysis of cross-correlation between signals such as blood flow velocity, laser Doppler-flux or tissue oxygenation helps in the assessment of mechanisms related to cerebral blood flow regulation.
Methods
ICM+ software has been developed in house, borrowing from our 10 years experience in data monitoring and analysis in the neuro critical care unit in Addenbrookes Hospital, Cambridge. Previous versions of the software have allowed us to collect multimodal data from nearly 600 severely head injured patients, along with secondary indices calculated online describing cerebral autoregulation and pressure-volume compensation. ICM+ includes a calculation engine that allows easy configuration and real-time trending of complex parameters. The program records raw signals, and calculates time trends of summary parameters. Configuration of analyses utilises arithmetic expressions of statistical and signal processing functions (moving average, correlation, power spectrum, coherence etc). The software allows configuration of several levels of analysis with the output of each one providing input to the next. The final data are displayed in a variety of ways including simple time trends, as well as time window based histograms, cross histograms, correlations etc, to facilitate data browsing and mining. The post-processing tools also support the calculation of indices of cerebrovascular reactivity from recordings made during interventions like transient hyperaemic response, rapid leg-cuff deflation and CO2 reactivity tests. The ICM+ package facilitates the modification of existing methods of analysis of cerebral haemodynamics and the development of new algorithms. In addition to on-line trends of calculated values and indices, the software also saves raw data from bed side monitors, which enables building up a library of signals for post-processing. These saved raw signals can subsequently be processed using the on-line analysis engine, thus providing a means of testing novel indices and methods of on-line data processing. Tools for manual marking of, and automatic detection of artefacts in the input signals and resulting time trends are provided to ensure high quality of the analysis results.
Results
To verify the usefulness of ICM+ for assessment of cerebrovascular dynamics 187 patients with severe head injury were analysed. In total, 563 recordings of ICP, ABP and TCD FV from 187 patients were processed using a variety of different analysis configurations. Results showed strong correlations between autoregulation indices Mx, Prx and Outcome, and allowed detailed investigation of these relationships. Detailed discussion of those results is presented elsewhere.
Conclusion
ICM+ is a universal tool for clinical and academic purposes. Its flexibility and advanced signal processing features are specialized for the needs of multidisciplinary brain monitoring, and it is particularly well suited for investigations into cerebral haemodynamics.