title: The relationship between expired concentration of sevoflurane and sympathovagal tone in children.
abstract: In children, sevoflurane depresses parasympathetic tone during induction more than halothane. The effects of sevoflurane on parasympathetic activity could explain the difference in heart rate (HR) changes described between infants and children. In this study, we sought to determine the relationship between the end-tidal concentration of sevoflurane and sympathetic and parasympathetic tone in children by spectral analysis of RR intervals. Thirty-three children, ASA physical status I, who required elective surgery were studied. In 10 children (Group A), recordings were performed while gradually decreasing the inspired sevoflurane concentration from 8% to the beginning of clinical awakening. In 23 other children (Group B), recordings were performed while children were awake and at a steady-state of 1 and 2 minimum alveolar anesthetic concentration of sevoflurane. A time-varying autoregressive modeling of the interpolated RR sequences was performed, and spectral density in low-frequency (LF; 0.04-0.15 Hz) and high-frequency (HF; 0.15-0.55 Hz) bands was calculated. In Group A, HR slowing paralleled the decrease in expired sevoflurane concentration. Conversely, the decrease in expired concentration of sevoflurane led to an increase in systolic blood pressure (SBP), HF, LF, and LF/HF. The increase in LF/HF preceded the increase in HF. In Group B, the baseline HF power spectrum and normalized values HFnu (HFnu = HF/LF + HF) were significantly increased in children older than 3 yr. Changes in HR induced by sevoflurane were negatively correlated with baseline HF and HFnu (R(2) = 0.6; P < 0.001). These results demonstrate that withdrawal of parasympathetic tone is the main determinant for the change in HR induced by sevoflurane.
  
  
  CONCLUSIONS
  The effects of sevoflurane on parasympathetic activity could explain the difference in heart-rate changes described between infants and children during induction. This study describes the changes in heart rate and its variability induced by sevoflurane in children and shows that these changes are related to parasympathetic tone before the induction of anesthesia.
authors.affiliation: *Department of Anesthesiology and Surgical Intensive Care, †LTSI, ‡Department of Pediatric and Neonatal Intensive Care, and §Department of Physiology, Université de Rennes 1, Paris, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Wodey
authors.forename: Lotfi
authors.initials: L
authors.lastname: Senhadji
authors.forename: Patrick
authors.initials: P
authors.lastname: Pladys
authors.forename: François
authors.initials: F
authors.lastname: Carre
authors.forename: Claude
authors.initials: C
authors.lastname: Ecoffey
mesh_terms: D000762:Anesthesia Recovery Period; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics* / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D001944:Breath Tests; D002648:Child; D002675:Child, Preschool; D004562:Electrocardiography; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007223:Infant; D008738:Methyl Ethers / Q000493:pharmacokinetics* / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000378:metabolism; D012119:Respiration; D000077149:Sevoflurane; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology*; D014851:Wakefulness
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane