Veränderung des Narkose-EEG mit dem Lebensalter

Zusammenfassung

In routinemäßigen intraoperativen EEG-Registrierungen von älteren Patienten wurden in tiefer Narkose häufig niedrigere Amplituden beobachtet als bei jüngeren Personen. Daher sollte das Narkose-EEG mit Hilfe mehrerer Meßreihen gezielt auf Alterseffekte untersucht werden. Ausgewertet wurden EEG-Registrierungen aus Einleitungsphasen mit 7 mg/kg KG Thiopental bzw. 2 mg/kg KG Propofol sowie aus barbituratinduzierten Enflurannarkosen. Bewertungen des Original-EEG erfolgten in Anlehnung an die Kriterien von Kugler [12]. In den Narkoseeinleitungen mit Thiopental und Propofol traten EEG-Stadien vom Wachzustand bis zu Burst-Suppression-Aktivität auf. In beiden Gruppen erreichten alte Patienten besonders häufig Burst-Suppression-Phasen. In D- und E-Stadien der tiefen Narkose fand sich bei älteren Patienten eine geringere Leistung im Deltaband sowie eine niedrigere Gesamtleistung. Die Ergebnisse zeigen, daß es für den Einsatz einer automatischen EEG-Interpretation erforderlich ist, altersabhängige Veränderungen des Narkose-EEG zu berücksichtigen. Gerade für ältere Patienten, bei denen häufig Vorerkrankungen und eingeschränkte physiologische Leistungsreserven vorhanden sind, ist ein intraoperatives EEG-Monitoring von besonderem Wert, denn das Elektroenzephalogramm erleichtert die Beurteilung der Wirkung zentral wirksamer Medikamente und trägt so zu einer differenzierten Narkoseführung bei.

Abstract

The number of older persons who have to undergo surgical procedures is steadily growing. For these patients the risks of anaesthesia are often increased because of their past medical history and their restricted physiological resources. Apart from parameters of the cardiovascular system, the electroencephalogram (EEG) represents a supplementary method for intraoperative monitoring, because cerebral alterations caused by anaesthetics or narcotics are directly reflected in the EEG. In routinely conducted registrations of the EEG in the operating theatre it appeared that the EEG of older persons differed from the EEG of younger patients. The aim of the present study was to further investigate the effect of patients' age on the EEG during anaesthesia.

Methods. Three data sets from different EEG registrations were analysed. The first data set consisted of inductions of anaesthesia with 7 mg/kg body weight thiopental in 43 patients from 17 to 80 years of age (mean 53.6±16.7 years) using derivations C₃-P₃ and C_z-A₁. The second data set included 69 EEG registrations of general anaesthesia induced with barbiturates and maintained with enflurane in patients from 16 to 83 years (mean 51.4±17.7 years). The third data set comprised inductions of anaesthesia with 2 mg/kg body weight propofol. EEGs of the second and third data set were recorded with the EEG monitor `Narkograph' using derivation C₃-P₃ and derivations C₃-P₃/C₄-P₄, respectively. Classification of the EEGs was performed according to the proposals of Kugler [12]. The basis for the statistical analysis of all data sets was formed by parameters from the power spectra of the EEG recordings.

Results. The data from inductions of anaesthesia with thiopental and propofol showed EEG patterns from alpha-EEG to burst suppression activity, whereby periods with burst suppressions could more often be observed in the EEG of older people. Under thiopental burst suppression activity occured in 20% of patients up to 50 years, in 47% of those between 50 and 70 years and in 89% over 70 years. The corresponding figures for propofol were 0%, 5% and 54%, respectively. Figure 2 depicts the correlation between age and power for the thiopental data. The power decreases with increasing age of the patients. This result led to further investigations of the effect of patients' age on the power in different EEG stages. Of special interest were deep stages of anaesthesia, because especially in these stages visual inspections revealed smaller amplitudes of the EEG signal for older patients than for younger persons. Figure 3 shows the power in the delta frequency band in deep stages of barbiturate-induced enflurane anaesthesia for patients of different age groups. The power in the delta frequency band distinctly decreases for geriatric patients. The same effect could be observed for the propofol data (Fig. 4).

Conclusions. The EEG represents an important method for effective intraoperative monitoring and contributes to an individually adjusted couse of anaesthesia, especially for geriatric patients. In these patients, clinical signs such as parameters of the cardiovascular system, which are usually used to judge the depth of anaethesia, are often altered by the patient's past medical history or by drugs. Furthermore, geriatric patients show a reduced need for narcotic agents. However, the variation of the required dosage is greater in older than in younger persons. The results of the present study show that with regard to an automatic classification of the EEG during anaesthesia, alterations of the EEG with age have to be taken into account.