Cbf/CMRO2 drug effects

Cerebral blood flow and cerebral metabolic rate (normally 3.0-3.8 ml O2/ 100gm brain/min) are coupled in the absence of pathology and or various anesthetic drugs. This means when cerebral metabolic rate increases or decreases so does cerebral blood flow. However, some anesthetic drugs are known to alter CBF and CMRO2. Various drug classes and their known effect on CBF and CMRO2 are listed below:

Volatile agents:

• CBF: cause a dose dependent increase in CBF due to vasodilation (Halothane > Desflurane > Isoflurane > Sevoflurane)
• CMRO2: Decrease CMR (luxury perfusion, a state where CBF>CMRO2)
• Exception: nitrous oxide leads to increased CBF and increased CMRO2

IV anesthetics:

• CBF: decrease cerebral blood flow
• CMRO2: decrease cerebral metabolic rate
• Exception: ketamine increases cerebral blood flow and CMRO2

Benzodizapines:

• CBF: minimal change in CBF (unless oversedation -> hypercarbia)
• CMRO2: reduction in CMRO2

Opioids:

• CBF: no affect on CBF (unless rapid infusion leads to decreases in MAP in setting of elevated ICP)
• CMRO2: minimal effects on CMRO2

Non-Depolarizing NMBDs:

• CBF: older agents (tubocuraine -> histamine release and decrease CBF)
• CMRO2: no effect

Succinylcholine:

• CBF/CMRO2: controversial, texts books say that leads to increased CBF and CMRO2 due to increased spindle activity; however, studies have shown this is not clinically significant.