Ketamine, catecholamines, and uterine tone in pregnant ewes.

Blood levels of ketamine, measured in both mother (1,230 ng/ml at 1 minute) and fetus (470 ng/ml at 1 minute) illustrate not only rapidly decreasing levels of the drug after its intravenous administration but also its transplacental passage. Concentrations of norepinephrine, epinephrine, and dopamine did not change in the mother or fetus after ketamine, with the exception of maternal levels of epinephrine, which were significantly higher at 45 minutes than control values (p less than 0.05). Maternal effects of ketamine consisted of increases in mean arterial pressure (7% p less than 0.05), cardiac output (16% p less than 0.01), and respiratory acidosis, all of which were slight and transitory. Although resting uterine tone increased (39% p less than 0.01), the uterine blood flow remained constant. None of the physiologic alterations could be correlated with changes in catecholamine levels. Therefore, the cardiovascular and uterine stimulating properties of ketamine at a dose of 0.7 mg/kg are small and are not the result of increased catecholamine levels in plasma. Further studies are necessary to elucidate the mechanism.

Nitroglycerin therapy for phenylephrine-induced hypertension in pregnant ewes.

Obstetrical situations in which endogenous or exogenous vasoactive amines precipitously increase maternal blood pressure and decrease uterine blood flow may be associated with increased maternal morbidity and mortality and with development of fetal acidosis and distress. We examined the effectiveness of nitroglycerin in lowering maternal blood pressure and increasing uterine blood flow during the infusion of the alpha-adrenergic agent phenylephrine. During the phenylephrine infusion maternal blood pressure increased 20%, cardiac output decreased 25%, total peripheral vascular resistance increased 60%, pulmonary arterial pressure increased 40%, uterine blood flow decreased 50%, and fetal arterial pH decreased from 7.37 to 7.30 (p less than 0.05). While maintaining the phenylephrine infusion at a constant rate, the infusion of nitroglycerin rapidly returned maternal systemic pressure and pulmonary arterial pressure to control values, decreased total peripheral resistance to 18% above control, increased cardiac output to 12% below control, increased uterine artery blood flow to 30% below control, and increased the fetal arterial pH from 7.30 to 7.35 (p less than 0.05). It is concluded that maternal hypertension resulting from intense alpha-adrenergic stimulation may be treated rapidly and effectively by the intravenous infusion of nitroglycerin with a partial restoration (20%) of uterine artery blood flow toward control.