Propofol action in both spinal cord and brain blunts electroencephalographic responses to noxious stimulation in goats

Study Objectives: Anesthetics, including propofol, depress the electroencephalogram (EEG) and neuronal activity in the midbrain reticular formation (MRF). Because propofol has anesthetic effects in the spinal cord, we hypothesized that it would indirectly depress EEG and MRF neuronal responses to noxious stimulation in part by a spinal cord action. Design: Six goats were anesthetized with isoflurane and the jugular veins and carotid arteries were isolated to permit cranial bypass and differential propofol delivery. A noxious mechanical stimulus was applied to the distal forelimb while recording bifrontal EEG and MRF single-unit activities. Propofol was separately administered to the cranial (0.08+/-0.06 mg/kg) and torso circulations (4 mg/kg) and the noxious stimulus applied at 1,5, 10, and 15 min after each injection. Setting: N/A Patients or Participants: N/A Interventions: N/A Measurements and Results: Noxious stimulation decreased total power (TP) from 96+/-33 muV(2)/Hz to 38 +/- 20 muV(2)/Hz, (mean+/-SD) and increased spectral edge frequency (SEF) from 10+/-3 Hz to 19+/-5 Hz (p<0.01). Propofol administered to the torso prevented stimulus-evoked changes in TP (121+/- 80<mu>V-2/Hz, 121 +/- 74 muV(2)/Hz, 114+/-74 muV(2)/Hz at 1,5, and 10 min respectively, p<0.01 compared to control evoked response) and SEF (11+/-6Hz, 9+/-2Hz, 10+/-6Hz, and 12+/-5Hz at 1, 5, 10 and 15 min, respectively, p<0.001 compared to control evoked response). Propofol administered to the cranial circulation significantly blunted the EEG and MRF response, while torso-administered propofol had slight effects on MRF responses. Conclusions: Propofol blunted the EEG response to noxious stimulation in part via a subcortical action.