The effect of clonidine infusion on distribution of regional cerebral blood flow in volunteers

University Department of Anesthesia and Intensive Care Medicine, CHU de Liege and CHR de la Citadelle, 4000 Liege, Belgium.
Anesthesia and analgesia (Impact Factor: 3.42). 04/2008; 106(3):899-909, table of contents. DOI: 10.1213/ane.0b013e3181619685
Source: PubMed

ABSTRACT Through their action on the locus coeruleus, alpha2-adrenoceptor agonists induce rapidly reversible sedation while partially preserving cognitive brain functions. Our goal in this observational study was to map brain regions whose activity is modified by clonidine infusion so as to better understand its loci of action, especially in relation to sedation.
Six ASA I-II right-handed volunteers were recruited. Electroencephalogram (EEG) was monitored continuously. After a baseline H2(15)O activation scan, clonidine infusion was started at a rate ranging from 6 to 10 microg x kg(-1) x h(-1). A sequence of 11 similar scans was then performed at 8 min intervals. Plasma clonidine concentration was measured. Using statistical parametric mapping, we sought linear correlations between normalized regional cerebral blood flow (rCBF), an indicator of regional brain activity, and plasma clonidine concentration or spindle EEG activity.
Clonidine induced clinical sedation and EEG patterns (spindles) comparable to early stage nonrapid eye movement sleep. A significant negative linear correlation between clonidine concentration and rCBF or spindle activity was observed in the thalamus, prefrontal, orbital and parietal association cortex, posterior cingulate cortex, and precuneus.
The EEG patterns and decreases in rCBF of specific brain regions observed during clonidine-induced sedation are similar to those of early stage nonrapid eye movement sleep. Patterns of deactivated brain regions are also comparable to those observed during general anesthesia or vegetative state, reinforcing the hypothesis that alterations in the activity of a common network occur during these modified conscious states.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Major clinical endpoints of general anesthesia, such as the alteration of consciousness, are achieved through effects of anesthetic agents on the central nervous system, and, more precisely, on the brain. Historically, clinicians and researchers have always been interested in quantifying and characterizing those effects through recordings of surface brain electrical activity, namely electroencephalography (EEG). Over decades of research, the complex signal has been dissected to extract its core substance, with significant advances in the interpretation of the information it may contain. Methodological, engineering, statistical, mathematical, and computer progress now furnishes advanced tools that not only allow quantification of the effects of anesthesia, but also shed light on some aspects of anesthetic mechanisms. In this article, we will review how advanced EEG serves the anesthesiologist in that respect, but will not review other intraoperative utilities that have no direct relationship with consciousness, such as monitoring of brain and spinal cord integrity. We will start with a reminder of anesthestic effects on raw EEG and its time and frequency domain components, as well as a summary of the EEG analysis techniques of use for the anesthesiologist. This will introduce the description of the use of EEG to assess the depth of the hypnotic and anti-nociceptive components of anesthesia, and its clinical utility. The last part will describe the use of EEG for the understanding of mechanisms of anesthesia-induced alteration of consciousness. We will see how, eventually in association with transcranial magnetic stimulation, it allows exploring functional cerebral networks during anesthesia. We will also see how EEG recordings during anesthesia, and their sophisticated analysis, may help corroborate current theories of mental content generation.
    Clinical EEG and neuroscience: official journal of the EEG and Clinical Neuroscience Society (ENCS) 01/2014; DOI:10.1177/1550059413509801 · 3.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The main target site of action for the sedative clonidine (CLO), an α2 adrenoceptor agonist, has been considered to be the locus coeruleus (LC). However, previous reports suggest other sites of action of CLO than the LC. Our previous studies suggested that the neuronal activities in the perifornical area (Pef) could influence the sedative or the anesthetic level induced by anesthetics. Therefore, we examined whether microinjection of CLO into the Pef might induce sedation in rats. Fifty-five Wistar rats were used. The cortical norepinephrine (NE) and acetylcholine (ACh) effluxes were detected using microdialysis and measured by high-performance liquid chromatography in samples collected every 20 minutes. First, we injected CLO (100, 300, and 1000 μg/kg cumulative doses) intraperitoneally (IP) and observed the changes in NE or ACh efflux. Second, we injected CLO (4.8 μg in 0.2 μL) or saline (0.2 μL) into the LC or the Pef and observed the changes in NE or ACh efflux for 2 hours. Finally, a sedative/anesthetic score was obtained after IP, LC or Pef microinjection of CLO. IP injection of CLO induced sedation and resulted in a dose-dependent attenuation of the cortical effluxes of both NE and ACh (P<0.001). Microinjection of CLO either into the LC or the Pef induced sedation and significantly decreased the cortical NE efflux (P<0.001). Cortical ACh efflux was significantly reduced by microinjection of CLO into the Pef but not by microinjection into the LC (P<0.05). The Pef and the LC are responsible for the sedative action of CLO in rats.
    Journal of neurosurgical anesthesiology 10/2013; 25(4):399-407. DOI:10.1097/ANA.0b013e3182978ff0 · 2.41 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: How does general anesthesia (GA) work? Anesthetics are pharmacological agents that target specific central nervous system receptors. Once they bind to their brain receptors, anesthetics modulate remote brain areas and end up interfering with global neuronal networks, leading to a controlled and reversible loss of consciousness. This remarkable manipulation of consciousness allows millions of people every year to undergo surgery safely most of the time. However, despite all the progress that has been made, we still lack a clear and comprehensive insight into the specific neurophysiological mechanisms of GA, from the molecular level to the global brain propagation. During the last decade, the exponential progress in neuroscience and neuro-imaging led to a significant step in the understanding of the neural correlates of consciousness, with direct consequences for clinical anesthesia. Far from shutting down all brain activity, anesthetics lead to a shift in the brain state to a distinct, highly specific and complex state, which is being increasingly characterized by modern neuro-imaging techniques. There are several clinical consequences and challenges that are arising from the current efforts to dissect GA mechanisms: the improvement of anesthetic depth monitoring, the characterization and avoidance of intra-operative awareness and post-anesthesia cognitive disorders, and the development of future generations of anesthetics.
    Annales francaises d'anesthesie et de reanimation 12/2013; 33(2). DOI:10.1016/j.annfar.2013.11.005 · 0.77 Impact Factor

Full-text (2 Sources)

Available from
May 23, 2014