Effect of Anesthesia on the Nervous System

Effect of Anesthesia on the Nervous System

Overall, most general anesthetics have a favorable effect on the CNS by reducing electrical activity. Carbohydrate metabolism decreases, whereas energy stores in the form of ATP, adenosine diphosphate, and phosphocreatine increase. Determination of the effects of the specific agents is complicated by the concomitant administration of other drugs, surgical stimulation, intracranial compliance, blood pressure, and CO2 tension. For example, hypocapnia or prior administration of thiopental blunts the increases in CBF and ICP that usually occur with ketamine and volatile agents

Halothane, desflurane, sevoflurane, and isoflurane produce dose-dependent decreases in CMR. Isoflurane produces the greatest depression (up to 50% reduction), whereas halothane has the least effect (< 25% reduction).

Volatile anesthetics dilate cerebral vessels and impair autoregulation in a dose-dependent manner Halothane has the greatest effect on CBF; at concentrations greater than 1%, it nearly abolishes cerebral autoregulation

The response of the cerebral vasculature to CO2 is generally retained with all volatile agents. Hyperventilation (hypocapnia) can therefore abolish or blunt the initial effects of these agents on CBF

With the exception of ketamine, all intravenous agents either have little effect on or reduce CMR and CBF. Moreover, with some exceptions, changes in blood flow generally parallel those in metabolic rate. Cerebral autoregulation and CO2 responsiveness are preserved with all agents.

Barbiturates have four major actions on the CNS: (1) hypnosis, (2) depression of CMR, (3) reduction of CBF due to increased cerebral vascular resistance, and (4) anticonvulsant activity. These properties make barbiturates, particularly popular.