Central Nervous System

Central Nervous System

During pregnancy the changes in central nervous system physiology include changes in pain threshold, susceptibility to general and local anesthetics (LA), and alterations in mood and cognitive function. The pharmacological response to general and LA are brought about by increased concentrations of progesterone and endogenous opioids (B-endorphins). The minimal alveolar concentration (MAC) for volatile anesthetic agents are decreased and the amount of LA required to block nerve conduction is reduced. During pregnancy a given dose of intrasthetcal epidural LA blocks more dermatomes than in non-pregnant patients. This may be due to increased susceptibility of nerve fibers to local anesthetics, but the anatomical changes in the epidural space that occur during pregnancy also contribute. Engorgement of epidural veins caused by aorto-caval compression leads to a reduction in the volume available for the spread of LA within the vertebral canal. Therefore an identical volume of LA will spread more extensively in the pregnant state.