ELECTROENCEPHALOGRAM, CEREBRAL METABOLIC, AND VASCULAR-RESPONSES TO PROPOFOL ANESTHESIA IN DOGS

Previous studies on the cerebral effects of propofol report conflicting results regarding the cerebral metabolic rate for oxygen (CMRO2), cerebral blood flow (CBF), autoregulation of CBF, intracranial pressure, and cerebral perfusion pressure (CPP). The present studies were designed to examine these issues as well as propofol effects on the CBF responses to hypocapnia and on the electroencephalogram (EEG) in a well-known canine model that permits continuous determination of EEG activity, CMRO2, CBF, and cerebrospinal fluid (CSF) pressure. Dogs were studied at normocapnia (n = 6) and at hypocapnia (n = 6) during three doses of propofol (12, 24, and 48 mg kg-1 h-1) and during a combination of propofol and elevated (20-25 mm Hg) CSF pressure. In both groups propofol caused dose-related decreases of EEG power and number of waveforms, CMRO2 (by 25-30%), and CBF (by 73-76%). The cerebral vasoconstrictor response to hypocapnia was preserved at all three doses of propofol. Autoregulation of CBF was preserved at the low and moderate doses of propofol but was impaired at the high dose of propofol (where CPP decreased significantly to approximately 41 +/- 13 mm Hg) and at the high dose of propofol combined with elevated CSF pressure (where CPP decreased significantly to approximately 32 +/- 12 mm Hg). Cerebrospinal fluid pressure decreased (by 33-42%) when the continuous infusion of propofol was begun, but returned to prepropofol values as infusion of propofol continued. The authors conclude that low and moderate doses of propofol decrease EEG activity and CMRO2, causing an associated decrease of CBF and CSF pressure. Autoregulation of CBF and cerebral vascular CO2 reactivity are preserved at these propofol doses. In contrast, high dose propofol significantly decreases CPP, resulting in impaired autoregulation of CBF.