Intravenous Anaesthetic Agents
(excluding ketamine)
- Propofol, thiopentone and etomidate all reduce CMR
- As a result of flow–metabolism coupling they all result in a fall in cerebral blood flow
- Autoregulation is not affected
Ketamine
- Causes increased cerebral blood flow
- Increases cardiac output and MAP
- Increases CMR and dilates cerebral vasculature
- Counteracts mild increase in ICP to maintain perfusion
Volatile Anaesthetic Agents
(excluding N2O)
- Unique in their ability to uncouple CMR and CBF:
- Cause a decrease in CMR
- However, also abolish autoregulation and cause cerebral arteriolar vasodilatation, leading to increased CBF
- The action is dose-dependent:
- Below 1 MAC both effects are approximately equal and CBF is unchanged
- Above 1 MAC the reduction in CMR is already maximal and CBF increases due to cerebral arteriolar vasodilatation
- Sevoflurane has the lowest vasodilatory potential of the volatile agents
- Order of vasodilating potency is halothane > enflurane > desflurane > isoflurane > sevoflurane
N2O
- Both potently dilates cerebral arteries and increases CMR
- As a result CBF significantly increases
Opioids
- No significant effect on either CMR or CBF
- CBF will rise in the setting of opioid induced CO2 retention
NMBA
- No significant effect on either CMR or CBF