Journal of neurosurgical anesthesiology
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J Neurosurg Anesthesiol · Apr 1992
Autoregulation of cerebral blood flow in response to adenosine-induced hypotension in dogs.
During induced hypotension for surgical procedures, cerebral blood flow (CBF) autoregulation and cerebrovascular responsivity to CO2 may be impaired-changes that appear to be agent-specific. Adenosine is a potent endogenous systemic vasodilator and has been investigated as a hypotensive agent. In this study in dogs we investigated cerebral vascular responses to graded decreases of cerebral perfusion pressure (CPP) (100%, 60%, 45%, and 35% of control CPP) during normocapnia (PaCO2 = 37 mm Hg) and hypocapnia (PaCO2 = 21 mm Hg). ⋯ CBF was significantly greater during normocapnia compared with hypocapnia at all levels of CPP, except at 35% of control when the values were similar. Cerebral metabolic rate was unchanged throughout the study. We conclude that neither CBF nor CO2 responsivity is appreciably altered during adenosine-induced hypotension when GPP remains above the lower limit of autoregulation of CBF.
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J Neurosurg Anesthesiol · Apr 1992
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. ⋯ 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.