title: On-line monitoring of end-tidal propofol concentration in anesthetized patients.
abstract: BACKGROUND
  Propofol (2,6-diisopropylphenol) has some volatility, so it can be detected in expired breath of individuals receiving intravenous propofol. This study measured volatile propofol exhaled by patients and investigated the relation between exhaled and plasma propofol concentrations.
  
  
  METHODS
  Nineteen patients with American Society of Anesthesiologists physical status I or II who were undergoing elective surgery participated in this two-part study. In study 1 (n = 11), anesthesia was induced with 2 mg/kg propofol, 0.1 mg/kg vecuronium, and 2 microg/kg fentanyl. After intubation, propofol was administered continuously for 60 min at each of three rates: 3, 6, and 9 mg x kg(-1) x h(-1). Blood samples were obtained just before each change in the infusion rate, and the plasma concentrations of propofol were measured. The exhaled propofol concentration was measured continuously by means of proton transfer mass spectrometry. End-tidal propofol concentrations during blood sampling were averaged and compared with plasma propofol concentrations. In study 2 (n = 8), after induction of anesthesia, patients received a bolus injection of 2 mg/kg propofol, and the exhaled propofol concentration was measured.
  
  
  RESULTS
  Volatile propofol was detected in expired gas from all study patients. From study 1, the authors obtained 24 paired data points, i.e., concentrations of end-tidal and plasma propofol. With Bland-Altman analysis, bias +/- precision was 5.2 +/- 10.4 with 95% limits of agreement of -15.1 and 25.6. In study 2, the exhaled propofol concentration curve showed an obvious peak in all patients.
  
  
  CONCLUSIONS
  Agreement between plasma and exhaled propofol concentrations suggests that proton transfer mass spectrometry can be used for real-time propofol monitoring.
authors.affiliation: Graduate Course of Medicine, Department of Anesthesiology, National Defense Medical College, Tokorozawa, Saitama, Japan. a-tacky@bd5.so-net.ne.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Takita
authors.forename: Kenichi
authors.initials: K
authors.lastname: Masui
authors.forename: Tomiei
authors.initials: T
authors.lastname: Kazama
mesh_terms: D000771:Anesthesia, Intravenous; D018686:Anesthetics, Intravenous / Q000032:analysis*; D001944:Breath Tests; D016903:Drug Monitoring / Q000379:methods*; D006801:Humans; D013058:Mass Spectrometry; D015742:Propofol / Q000032:analysis* / Q000097:blood
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol