Abstract
Transcranial Doppler sonography (TCD) constitutes an advance in noninvasive monitoring of the cerebral circulation. However, as long as the diameter and cross-sectional area of the insonated middle cerebral artery (MCA) remain unknown, the derived flow velocities (v) are not informative. It is not known how the human MCA is influenced by anaesthetic agents. However, a TCD-modification allows noninvasive determination of “vessel area” (VA) and “volume flow” (VF) in MCA by analysing the backscattered Doppler power. This investigation evaluates the effects of isoflurane (in combination with N2O and surgery) on v, VA and VF. In 14 patients (ASA I) scheduled for minor surgical or gynaecological operations, anaesthesia was induced with droperidol, alfentanil, thiopentone and vecuronium. After intubation ventilation with N2O:O2 = 3:2 was adjusted, to maintain endexpiratory carbon dioxide (FECO2) constant between 4 and 5%. Baseline values of heart rate (HR), oscillometric mean arterial pressure (MAP), and TCD variables (v, VA VF) were measured before adding 2.4% isoflurane to the inspiratory mixture. Further measurementswere made 3, 6,10, and 20 min after starting isoflurane. Surgery commenced between the sixth and tenth minute after isoflurane application. The MAP,FeCO2, and v showed only minor alterations; HR increased after 6, 10 and 20 min. Transcranial “vessel area” and “volume flow” showed increases after isoflurane inhalation. The increase of “vessel area” supports the assumption that isoflurane greater than 1 MAC dilates large human cerebral arteries, so that if flow velocities are considered alone, alterations of cerebral blood flow may easily be underestimated.
Résumé
La sonographie par Doppler transcrânien (TCD) constitue un progrès dans le monitorage non invasif de la circulation cérébrale. Cependant, tant que le diamètre et la surface de la région de l’artère cérébrale moyenne (MCA) soumise aux ultrasons restent inconnus, les vélocités (v) enregistrées restent inutilisables. On ne sait pas comment la MCA humaine est influencée par les agents anesthésiques. Néanmoins, une modification de TCD procure une détermination non invasive de la « surface du vaisseau » (VA) et du « débit » (VF) dans la MCA en analysant l’importance du retour d’écho (« backscattered Doppler-power »). Cette investigation évalue les effets de l’isoflurane (en combinaison avec N2O et la chirurgie) sur v, VA et VF. Quatorze patients (ASA 1) programmés pour des opération mineures, générales ou gynécologiques ont eu une anesthésie au dropéridol, alfentanil, thiopentone, et vécuronium. Après l’intubation, une ventilation au N2O/ O2 = 3:2 est ajustée pour maintenir un CO2 respiratoire (FeCO2) constant entre 4 et 5%. Les valeurs de base de fréquence cardiaque (HR), pression artérielle moyenne par oscillométrie (PAM), et des variables TCD (v, VA, VF) sont mesurées avant d’ajouter 2,4% d’isoflurane aux gaz inspirés. Les mesures ultérieures sont réalisées 3, 6, 10 et 20 min après le début d’administration d’isoflurane. La chirurgie a commencé entre la sixième et la dixième minute après l’administration d’isoflurane. MAP,FeCO2 et v montrent que des altérations mineures; HR augmente après 6, 10 et 20 min. La « surface du vaisseau » et le « débit », s’accroissent après l’inhalation d’isoflurane. L’augmentation de la « surface du vaisseau » soutient l’affirmation qu’une administration d’isoflurane supérieure à 1 MAC dilate les grosses artères cérébrales chez l’homme, de telle sorte que si la vélocité est considérée seule, les variations du débit sanguin cérébral peuvent être facilement sous-estimées.
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Schregel, W., Schaefermeyer, H., Sihle-Wissel, M. et al. Transcranial doppler sonography during isoflurane/N2O anaesthesia and surgery: flow velocity, “vessel area” and “volume flow”. Can J Anaesth 41, 607–612 (1994). https://doi.org/10.1007/BF03010001
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DOI: https://doi.org/10.1007/BF03010001