The influence of the alpha2-adrenoceptor agonist, clonidine, on the EEG and on the MAC of isoflurane.
We investigated the influence of intravenous clonidine 2, 4 and 6 microg kg-1 on the electroencephalogram and on the minimal alveolar concentration of isoflurane in 40 patients aged 20-60 years undergoing elective surgery. Minimal alveolar concentration was determined using the Dixon 'up-and-down' method. Thirty min after the clonidine infusion anaesthesia was induced with etomidate, 0.25 mg kg-1. Skin incision was made after stable end-tidal isoflurane concentrations had been maintained for at least 15 min. Clonidine caused significant decreases in the spectral edge (95%) and median power frequency of the electroencephalogram and in the bispectral index. The minimal alveolar concentration of isoflurane decreased in a dose-dependent manner from 1.32% (95% CI, 1.28%-1.36%) in the control group to 1.03% (0.9%-1.18%) in patients given clonidine 6 microg kg-1. Clonidine 4 and 6 microg kg-1 was associated with a moderate reduction in heart rate and arterial systolic blood pressure. We recommend the use of clonidine intravenously as an adjunct to general anaesthesia in a dose of 4 microg kg-1 given 15 min before induction of anaesthesia.
El-Kerdawy
H M
HM
Department of Anaesthesiology, Leiden University Medical Centre, Leiden, The Netherlands.
Zalingen
E E
EE
Bovill
J G
JG
D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000627:therapeutic use*; D000328:Adult; D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000008:administration & dosage* / Q000493:pharmacokinetics; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000032:analysis; D016009:Chi-Square Distribution; D003000:Clonidine / Q000008:administration & dosage / Q000627:therapeutic use; D016001:Confidence Intervals; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D005045:Etomidate / Q000008:administration & dosage; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007262:Infusions, Intravenous; D007530:Isoflurane / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D010919:Placebos; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000378:metabolism; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012815:Signal Processing, Computer-Assisted; D016037:Single-Blind Method; D013990:Tidal Volume / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D010919:Placebos; D002245:Carbon Dioxide; D007530:Isoflurane; D003000:Clonidine; D005045:Etomidate