Spectral analysis of the EEG during halothane anaesthesia: Input-output relations

Abstract

This study was performed to extract parameters from the EEG which would give quantitative information about brain function during Halothane anaesthesia. Most studies concerning EEG changes during Halothane anaesthesia have been restricted to qualitative descriptions, for example those of Backman et al. (1964) and Barry Prynn and Redding (1968). Findeiss et al. (1969) suggested that frequency analysis was a useful method to establish quantitative relations between Halothane concentration and the EEG. However, in their studies the relationship between Halothane concentration and EEG spectrum was investigated in a static way, i.e., the EEG spectrum was determined at steady concentrations of Halothane. In this study our aim was to determine the dynamics of the "Halothane-brain compartment" system, i.e., to measure the response of the system to changes of its input as a function of time. As output we used the EEG spectrum. The Halothane input was changed by step and sinusoidal functions. Determining the dynamics of the system has a practical interest because the feasibility of using the EEG in a monitoring system for Halothane anaesthesia depends to a large extent on knowledge of the system's time constants. The system was also investigated at steady concentrations of Halothane. The results obtained in this study are also being used to improve a model of the distribution of Halothane in the body, which was reported by Zwart et al. (1972).

EEG spectral power during halothane anaesthesia. A comparison of spectral bands in the monitoring of anaesthesia level

“…1, Tables 1, 2). The initial increase and subsequent decrease in the 18-32 Hz frequency band power is in accordance with the results of earlier investigators (6,7). The dependence of 10-14 Hz band power on halothane concentration accords well with the results of Stockard & Bickford (4).…”

“…Some years later it was shown that increased halothane concentrations decrease the fast rhythm of the EEG (3,4). In dogs, halothane produces a typical halothane band in the compressed spectral array (CSA) of the EEG; this band occurs in the beta range of the EEG, and its frequency varies along with rapid changes in halothane concentrations (5,6). A close correlation between spectral power in the beta range and halothane concentration has also been shown by Wark et al who studied patients using the CFAM (cerebral function analysing monitor) (7).…”

Functional connectivity within the visual cortex of the rat shows state changes

“…The ‘slow‐wave’ state and the ‘thin‐peak’ state. It is well established that the depth of anaesthesia can be related to the frequency content of the surface EEG (Lopez da Silva et al 1972). Moderate concentrations of anaesthetics and deep sleep are associated with an increase in the spectral power of frequencies below 10 Hz and a decrease of spectral power for frequencies above 20 Hz and vice versa during the recovery from anaesthetics.…”

Multiple model approach to uptake and distribution of halothane: The use of an analog computer

“…(7). Alveolar concentration can be measured as end tidal concentration so that these variables are clinically easily obtainable.…”