In vivo effects of halothane, enflurane, and isoflurane on hepatic sinusoidal microcirculation

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Abstract
Background: It has been proposed that halogenated anaesthetics interfere with the endothelium‐dependent circulatory control by attenuating the effects of endothelium‐derived relaxing factor (EDRF/NO). This study was designed to determine whether or not volatile anaesthetics in vivo influence the microvascular tone in hepatic sinusoids. Methods: Using epifluorescence videomicroscopy, we compared the effects of the volatile anaesthetics halothane, enflurane, and isoflurane on hepatic microcirculation in ventilated Lewis rats. Animals were initially anaesthetized with pentobarbitone (50 mg‐kg‐1 i.p.) to allow instrumentation and laparotomy and were randomly allocated to one of 4 groups (n=5–6 each) to receive either a supplementary dose of i.v. pentobarbitone (25 mg kg‐1; control group) or 0.75 MAC halothane, enflurane or isoflurane (1.5 MAC h). Results: Halothane decreased significantly the volumetric blood flow as compared with isoflurane (P < 0.05) or pentobarbitone controls (P < 0.05). The decrease in sinusoidal blood flow caused by halothane was largely attributable to a decrease in sinusoidal diameter (P < 0.05), while red blood cell velocity remained unchanged. Isoflurane led to a significant decrease in sinusoidal width compared with controls (P < 0.05) but an increase in red cell velocity offset the effect of sinusoidal narrowing on volumetric blood flow, while enflurane had no significant effect on any of the measured parameters. Conclusion:This study provides the first direct evidence that the volatile anaesthetics halothane and isoflurane in vivo shift the hepatic microvascular tone toward a more constricted state; however, flow velocity is enhanced with isoflurane, offsetting this effect. As a result the volumetric flow is at least affected by isoflurane, then enflurane and most significantly by halothane. Furthermore, our data are consistent with the concept that volatile anaesthetics in clinically relevant concentrations may influence the balance between endothelium‐derived vasoactive factors which control microvascular tone.