Thiopental: CMRO2/CBF relationship

Thiopental (or another barbiturate) administration titrated to EEG suppression causes a decrease in the cerebral metabolic rate of O2 (CMRO2) as well as a decrease in cerebral blood flow (CBF) due to flow-metabolism coupling. At general anesthetic doses, the CBF and CMRO2 are reduced by ~ 30%, whereas with EEG suppression they are maximally reduced by 50%. Note that there is a plateau effect at ~ 50%, after which additional dosing is not efficacious. Also note that tolerance may develop over as few as 24 hours. Cerebral autoregulation is maintained

Thiopental CBF / CMRO2

• General Anesthesia: CBF and CMRO2 are reduced by ~ 30%
• EEG Suppression: CBF and CMRO2 are reduced by ~ 50%
• Other: plateau at ~ 50%; tolerance as soon as 24 hours; cerebral autoregulation maintained