Responses of the gravid uterine vasculature to arterial levels of local anesthetic agents.

Responses of the uterine vasculature and myometrium to uterine arterial infusions of local anesthetic agents were evaluated in chronically prepared conscious ewes between 86 and 141 days of gestation. Decreases in uterine blood flow (UBF) with increasing levels of anesthetic drugs were similar to those previously observed in nonpregnant ewes. A 25% decrease in UBF occurred at 7 micrograms of bupivacaine, 11.5 micrograms of 2-chloroprocaine, and 19.5 micrograms of lidocaine per milliliter of control UBF. Myometrial tonus did not change significantly except with bupivacaine where an increase occurred (P less than 0.001). These data indicate that local anesthetic agents may lower gravid UBF by a direct vascular effect and by stimulation of myometrial contractility. The possible clinical implications of these observations are discussed.