title: The effect of high doses of remifentanil in brain near-infrared spectroscopy and in electroencephalographic parameters in pigs.
abstract: OBJECTIVE
  To study the effects of a high remifentanil bolus dose on pig's electroencephalographic indices and on brain regional and global oxygenation.
  
  
  METHODS
  Prospective experimental study.
  
  
  METHODS
  Twelve healthy Large-White male pigs, age 3 months and weight 26.2 ± 3.6 kg.
  
  
  METHODS
  Anaesthesia was induced with intravenous propofol 4 mg kg⁻¹, then maintained with constant rate infusions of propofol (15 mg kg⁻¹ hour⁻¹) and remifentanil (0.3 μg kg⁻¹ minute⁻¹). Following instrumentation, all pigs received a 5 μg kg⁻¹ remifentanil bolus. The responses of jugular venous oxygen saturation, cardiac output and cerebral oxygen saturation to the remifentanil bolus were studied. The Bispectral index, spectral edge frequency 95%, total power, approximate entropy and permutation entropy were also studied. Repeated measures anova and Pearson correlation were used to analyze the effect of remifentanil bolus on these variables until 5 minutes after the bolus.
  
  
  RESULTS
  Cardiac output and cerebral oxygen saturation decreased significantly after the remifentanil bolus from 4.6 ± 0.9 to 3.8 ± 1.0 L minute⁻¹ and from 65 ± 6 to 62 ± 1% (p < 0.05), respectively. No significant changes were observed in the jugular venous oxygen saturation (p > 0.05) nor in any of the electroencephalogram derived indices (p > 0.05). Correlation analysis revealed strong positive significant correlations between cerebral oxygen saturation and cardiac output (r = 0.82, p < 0.001) and between cerebral oxygen saturation and approximate entropy (r = 0.65, p < 0.001).
  
  
  CONCLUSIONS
  The effect caused by the remifentanil bolus on the brain oxygenation seems to be better reflected by the cerebral oxygen saturation than the jugular venous oxygen saturation. The effect of remifentanil on the electroencephalogram may not be reflected in indices derived from the electroencephalogram, but the potential of the approximate entropy in reflecting changes caused by opioids on the electroencephalogram should be further investigated.
authors.affiliation: Toxicology, REQUIMTE, Faculdade de Farmácia da Universidade do Porto, Porto, Portugal.
authors.forename: Aura
authors.initials: A
authors.lastname: Silva
authors.forename: Carlos
authors.initials: C
authors.lastname: Venâncio
authors.forename: Ana Liza
authors.initials: AL
authors.lastname: Ortiz
authors.forename: Almir P
authors.initials: AP
authors.lastname: Souza
authors.forename: Pedro
authors.initials: P
authors.lastname: Amorim
authors.forename: David A
authors.initials: DA
authors.lastname: Ferreira
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects / Q000662:veterinary*; D006993:Hypnotics and Sedatives / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D000077208:Remifentanil; D013055:Spectrophotometry, Infrared / Q000379:methods / Q000662:veterinary*
chemical_list: D006993:Hypnotics and Sedatives; D010880:Piperidines; D000077208:Remifentanil; D010100:Oxygen
keywords: EEG; anaesthetic techniques - i.v. bolus; cerebral oxygenation; pig; remifentanil