Fig. 5. The exhaled propofol concentration curve after bolus injection in study 2. After intubation, patients received a bolus injection of 2 mg/kg propofol (time 0). Exhaled propofol was measured with a proton transfer reaction mass spectrometer as described for study 1, and the moving averages of 10 data points are indicated here as solid lines . In all patients, we observed an obvious surge in exhaled propofol after administration of propofol.