inhalational effects on cerebral physiology
INHALATIONAL ANESTHETIC effects on cerebral physiology
volatile anesthetics
-cerebral metabolic rate of oxygen
-cerebral blood flow
-cerebral blood volume
-intracranial pressure
-seizure activity
Nitrous oxide
General: decreased CMR02 increased CBF (increased CBV) increased ICP
-decreased CMR02 and increased CBF creates "luxury perfusion"
-increased CBF occurs generally due to vasodilation of cerebral vessels
-with increased CBF there may be an increased CBV although the relationship is not directly proportional
-with increased CBF and CBV there may be an increased ICP
-patients with decreased intracranial compliance may have marked increase in ICP with inhaltional anesthetics
-greatest reduction of CMR02 occurs with Enflurane and Isoflurane ( approx 50% reduction of CMR02)
-isoflurane reduction of CMR02 is mostly in the neocortex
-least reduction of CMR02 is with halothane (approx 25% reduction of CMR02)
CBV ( at equivalent MAC values and MAP)
- greattest increase in CBF occurs with Halothane ( approx 200% increase of CBF: general increase throughout the brain)
-Enflurane has an increase in CBF (approx. 40%)
-Isoflurane has an increase in CBF (approx 20%) CBF primarily increased in the subcortical and hindbrain portions
-isoflurane is considered the drug of choice for patients with decreased intracranial compliance in prevention of increased ICP
- Enflurane has increased association with seizure activity with MAC values around 1.5-2.0
- Enflurane seizure activity charecterised as spike and wave activity which may be potentiated with auditory stimuli
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