Propofol anesthesia and cerebral blood flow changes elicited by vibrotactile stimulation: a positron emission tomography study.

We investigated the effects of the general anesthetic agent propofol on cerebral structures involved in the processing of vibrotactile information. Using positron emission tomography (PET) and the H(2)(15)O bolus technique, we measured regional distribution of cerebral blood flow (CBF) in eight healthy human volunteers. They were scanned under five different levels of propofol anesthesia. Using a computer-controlled infusion, the following plasma levels of propofol were targeted: Level W (Waking, 0 microg/ml), Level 1 (0.5 microg/ml), Level 2 (1.5 microg/ml), Level 3 (3.5 microg/ml), and Level R (Recovery). At each level of anesthesia, two 3-min scans were acquired with vibrotactile stimulation of the right forearm either on or off. The level of consciousness was evaluated before each scan by the response of the subject to a verbal command. At Level W, all volunteers were fully awake. They reported being slightly drowsy at Level 1, they had a slurred speech and slow response at Level 2, and they were not responding at all at Level 3. The following variations in regional CBF (rCBF) were observed. During the waking state (Level W), vibrotactile stimulation induced a significant rCBF increase in the left thalamus and in several cortical regions, including the left primary somatosensory cortex and the left and right secondary somatosensory cortex. During anesthesia, propofol reduced in a dose-dependent manner rCBF in the thalamus as well as in a number of visual, parietal, and prefrontal cortical regions. At Level 1 through 3, propofol also suppressed vibration-induced increases in rCBF in the primary and secondary somatosensory cortex, whereas the thalamic rCBF response was abolished only at Level 3, when volunteers lost consciousness. We conclude that propofol interferes with the processing of vibrotactile information first at the level of the cortex before attenuating its transfer through the thalamus.