Desfluran und Isofluran

Zusammenfassung

Das neue Inhalationsanästhetikum Desfluran besitzt sehr niedrige Blut-Gas- und Gewebe-Blut-Verteilungskoeffizienten und läßt so raschere Ein- und Ausleitungszeiten erwarten. In der vorliegenden Phase-III-Studie wurden Aufwachverhalten und Hämodynamik unter Desfluran und Isofluran prospektiv randomisiert verglichen. Untersucht wurden 49 chirurgische Patienten (Desfluran n=24, Isofluran n=25) in balancierter Anästhesietechnik: orale Prämedikation mit 7,5 mg Midazolam; Einleitung mit 0,1 mg Fentanyl und 5 mg/kg Thiopental; Narkosebeatmung mit Desfluran 0,5–18 bzw. Isofluran 0,2–3,0 Vol%, jeweils in 50% N ₂ O. Bei den hämodynamischen Parametern ergaben sich keine wesentlichen Unterschiede. Zwei Patienten reagierten nach rascher Erhöhung der Desfluran-Vapor-Einstellung mit Blutdruck- und Herzfrequenzanstieg. Diese Reaktion ließ sich bei allen weiteren Patienten durch langsame Dosissteigerung vermeiden. Nach Anästhesie-Ende flutete Desfluran signifikant schneller ab als Isofluran (F _A /F _A0 ). Trotzdem zeigten die Aufwachzeiten keinen signifikanten Unterschied (Augenöffnen jeweils nach 12 min), vermutlich bedingt durch die angewandte balancierte Anästhesietechnik, die durch gleichzeitigen Einsatz mehrerer Anästhetika zum Profilverlust der Einzelsubstanz führen kann. Zusammengefaßt ergibt sich, daß Desfluran als Hauptkomponente einer balancierten Anästhesie unter den Gesichtspunkten Steuerbarkeit und hämodynamische Stabilität für chirurgische Eingriffe ebenso geeignet erscheint wie Isofluran. Mit einem rascheren Erwachen ist aber bei der balancierten Anästhesietechnik nicht zwangsläufig zu rechnen.

Abstract

Objectives. The new volatile anaesthetic desflurane is characterized by very low blood-gas and tissue-blood partition coefficients, so that rapid induction of anaesthesia and shorter recovery times can be expected. The aim of this investigation was to compare the effects of desflurane and isoflurane on haemodynamics and recovery time when used as part of a balanced anaesthesia technique for elective surgery.

Methods. Fifty patients (18 years and older, ASA status I-III) scheduled for elective surgery (no laparoscopies) of at least 60 min duration were included in this open, randomised, phase-III clinical trial. After oral premedication with midazolam 7.5 mg 45 min before transfer to theatre, anaesthesia was induced with fentanyl 0.1 mg and thiopental 5 mg/kg; succinylcholine or vecuronium facilitated intubation. Desflurane and isoflurane, respectively, were used for maintenance of anaesthesia, both in 50% N₂O, with the inspired concentration adapted to the degree of stimulation. All patients were ventilated in a semi-closed system; muscle relaxation was achieved with vecuronium. The electrocardiogram, heart rate (HR), and direct arterial blood pressure (BP) were recorded continuously and anaesthetic gas detection was performed by an infrared absorption technique. With termination of surgery the volatile anaesthetic was discontinued and the following emergence times recorded: spontaneous ventilation (V_T>300 ml), extubation, eye opening, correctly answering the date of birth, arrival in and possible discharge from the post-anaesthesia care unit (PACU).

Results. In all, 49 patients were studied at random (desflurane n=24, isoflurane n=25). Data of demographics and anaesthetic technique were comparable in both groups (Tables 2 and 3). Anaesthetic elimination (expressed as F_A/F_AO) was significantly more rapid in the desflurane group 3 min after termination of anaesthesia (Fig. 1). Comparing the emergence times, there was no significant difference between desflurane and isoflurane: in both groups patients opened their eyes 12 min (median time) after termination of the operation (Table 4). Haemodynamics (HR, systolic and diastolic BP) were comparable at intubation, skin incision, end of surgery, extubation, and in the PACU (Fig. 2a, b). In 2 patients a rapid increase in the inspired concentration of desflurane during induction of anaesthesia produced a profound sympathoadrenergic reaction with an excessive increase in BP and HR. Similar reactions in other patients did not occur when the inspired concentration of desflurance was slowly increased.

Conclusions. Despite the physicochemical properties of the new agent, emergence times were similar for desflurane and isoflurane in our study. These results, which are in contrast to those of some other authors, are most probably due to the study design, which included the use of premedicants (midazolam) and a low dose of fentanyl. The reported sympatho-adrenergic reactions after rapid changes in the inspired concentration of desflurane during induction of anaesthesia have been observed by others as well. It seems that this initial cardiovascular stimulation can be avoided by slow increases in desflurane concentration. In summary, desflurane compares to isoflurane in balanced anaesthesia for general surgical procedures with regard to haemodynamics, while the time to awakening is not necessarely reduced.