Abstract
Purpose: To describe the relative effects of graded central nervous system (CNS) depression, using increasing propofol infusion rates, on neurovegetative brainstem-mediated circulatory control mechanisms and higher cortical activity in healthy humans.
Methods: Propofol was administered using an infusion scheme designed to achieve three target blood concentrations in ten healthy volunteers. Blood propofol concentrations and sedation scores were determined at baseline, during the three propofol infusion levels, and 30 min into the recovery period. Electroencephalographic (EEG) power was measured in three frequency bands to quantify cortical activity, and autonomic heart rate control was quantified using spontaneous baroreflex assessment and power spectral analysis of pulse interval.
Results: Sedation scores dosely paralleled propofol blood concentrations (0, 0.53±0.34, 1.24±0.21, 3.11±0.80, and 0.96±0.42 µg·mL−1 at baseline, three infusion levels and recovery respectively), and all subjects were unconscious at the deepest level. Indices of autonomic heart rate control were decreased only at the deepest levels of CNS depression, while EEG effects were apparent at all propofol infusion rates. These EEG effects were frequency specific, with power in the beta band being affected at light levels of sedation, and alpha and delta power altered at deeper levels.
Conclusions: The results of this study support a relative preservation of neurovegetative circulatory control mechanisms during the early stages of CNS depression using gradually increasing rates of infusion of propofol. Indices of arculatory control did not reliably reflect depth of sedation.
Résumé
Objectif: Décrire les effets relatifs d’une dépression graduée du système nerveux central (SNC) sur les mécanismes d’origine centrale du contrôle neurovégétatif de la circulation, et l’activité corticale supérieure chez des humains sains, en utilisant des perfusions de propofol à vitesses croissantes.
Méthode: Le propofol a été administré, chez dix volontaires en santé, selon un schéma de perfusion conçu pour atteindre trois concentrations sanguines cibles. Les concentrations sanguines de propofol et les scores de sédation ont été déterminés au départ, pendant les trois régimes de perfusion de propofol et à 30 min pendant la récupération. La puissance électroencéphalographique (EEG) a été mesurée selon trois bandes fréquentielles pour quantifier l’activité corticale, et le contrôle autonome de la fréquence cardiaque a été mesuré à l’aide d’une évaluation bar oréflexe spontanée et de l’analyse spectrale de la puissance de l’intervalle pulsé.
Résultats: Les scores de sédation ont présenté un étroit parallélisme avec les concentrations sanguines de propofol (0; 0,53±0,34, 1,24±0,21; 3,11±0,80, et 0,96±0,42 µg·mL−1 au début, pendant les trois perfusions et la récupération, respectivement), et tous les sujets ont connu un profond sommeil. Les indices de contrôle autonome de la fréquence cardiaque ont diminué seulement au moment de la plus profonde dépression du SNC, tandis que les effets EEG ont été apparents pour toutes les vitesses de perfusion du propofol. Ces effets EEG différaient selon les fréquences, la puissance de la bande bêta étant affectée à de bas niveaux de sédation et les bandes alpha et delta étant modifiées à des niveaux plus profonds.
Conclusion: Les résultats de l’étude entretiennent une relative préservation des mécanismes de contrôle neurovégétatif de la circulation pendant les premiers stades de la dépression du SNC quand on utilise des vitesses de perfusion de propofol qui augmentent graduellement. Les indices de contrôle circulatoire ne reflètent pas fidèlement la profondeur de la sédation.
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Financial support: Propofol blood concentrations funded by Zeneca Pharma Ltd.
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Lafreniere, G., Milne, B., Brunet, D.G. et al. Autonomic circulatory and cerebrocortical responses during increasing depth of propofol sedation/hypnosis in humans. Can J Anaesth 47, 441–448 (2000). https://doi.org/10.1007/BF03018974
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DOI: https://doi.org/10.1007/BF03018974