Effects of phenylephrine and sodium salicylate on maternal and fetal cardiovascular indices and blood oxygenation in sheep

Common problems in critically ill obstetric patients, with an emphasis on pharmacotherapy

Pharmacological treatment of critically ill obstetric patients can be especially challenging due to the complexity of caring for 2 patients, with a paucity of research to support practice. This review will provide practitioners with primary recommendations for management of the critical illnesses most commonly encountered in pregnancy and will discuss the scientific and clinical merit of these recommendations.

Reduction of uterine blood flow by phenylephrine, an alpha-adrenergic agonist, in the day 11 pregnant rat: relationship to potentiation of acetazolamide teratogenesis

We have demonstrated previously that phenylephrine, a selective postsynaptic alpha-1-adrenergic agonist, significantly potentiates the incidence of acetazolamide-induced right forelimb ectrodactyly in a dose-response manner. As reported herein, phenylephrine also decreases maternal uterine blood flow in a dose-response manner as measured by radioactive microsphere methodology. At the potentiative dose of 12.5 mg/kg phenylephrine decreases uterine blood flow by 86.8% when compared to control. In turn, pretreatment with prazosin, a selective postsynaptic alpha-1-adrenergic antagonist, prevents this large decrease in uterine blood flow and abolishes the potentiation of acetazolamide teratogenesis by phenylephrine. Although the effects of acetazolamide or acetazolamide + phenylephrine on uterine blood flow were not measured the data suggest a correlation between decreased uterine blood flow and potentiation of acetazolamide teratogenesis.

Intrauterine growth retardation after long-term maternal salicylate administration in the rabbit

The effects of chronic maternal salicylism on fetal growth were studied in chronically catheterized pregnant rabbits. Graded intravenous infusions of sodium salicylate were given continuously between days 22 and 29 of gestation. Maternal plasma salicylate concentrations (mean +/- SD) of 12.0 +/- 1.6 mg/dl (low-dose group) or 24.1 +/- 5.3 mg/dl (high-dose group) were achieved. Control rabbits were infused with saline solution. Pups were delivered by hysterotomy on day 29. Fetal/maternal salicylate concentration ratios were near unity for both infusion groups. There were significant dose-related reductions (mean +/- SD) in fetal weight (control, 39.7 +/- 6.7 gm; low-dose group, 34.4 +/- 6.4 gm; high-dose group, 22.2 +/- 7.1 gm; p less than 0.001) and in crown-rump length (control, 9.7 +/- 0.45 cm; low-dose group, 9.1 +/- 0.68 cm; high-dose group, 7.7 +/- 0.86 cm; p less than 0.001). There was a significant reduction in fetal brain weight only in the high-dose group, and brain weight/fetal weight ratios were increased, suggesting relative sparing of brain growth. Liver weight was significantly reduced in both low- and high-dose groups. In contrast to results in previous animal studies, standardized intravenous maternal salicylate administration in rabbits induced a reproducible and dose-dependent asymmetrical fetal growth retardation.

Ocular oxygenation: the effect of phenylephrine on anterior chamber oxygen tension

Phenylephrine preparations are widely used in medicine for their vasoconstrictive and mydriatic effects. The effect of phenylephrine, a powerful alpha-receptor stimulant, on anterior chamber oxygen tension (Po2) was studied using a polarographic electrode inserted into the mid anterior chamber of cats. A commercial 10% solution was applied topically. A decrease in anterior chamber Po2 was usually observed in 8-24 minutes and declined steadily thereafter. Prior to treatment, the mean anterior chamber Po2 was 26 +/- 3 torr; 1/2 hour after treatment it decreased to 20 +/- 7 torr. After 1 hour it dropped to 13 +/- 8 torr and was further reduced to 11 +/- 6 torr by 2 hours. By 90 minutes, the drug had caused a 58% reduction in anterior chamber oxygen tension. This drop is similar to that reported for epinephrine. It is suggested that the mechanism for most of this decrease is reduced blood flow, mediated by the direct vasoconstrictive effect of the drug in addition to compression of the iris vasculature induced by dilation. The resulting change (reduction) in caliber of the iris arteries produces a parallel change (reduction) in blood volume and flow resulting in a diminished Po2. The clinical implications of this conclusion in disorders where hypoxia is felt to play a causal role such as neovascular glaucoma, diabetes, pregnancy and hyphema in sickle cell disease are explored.

Maternal and fetal cardiovascular indices during fetal hypoxia due to cord compression in chronically cannulated sheep. II. Responses to promazine

Promazine (Sparine) administered to chronically cannulated pregnant ewes caused significant maternal and fetal tachycardia and hypotension, depressed uterine blood flow and fetal Pao2, and increased fetal Paco2. When the drug was given before brief compression of the umbilical cord, uterine flow was more depressed than by compression alone, the fetal pressor response was attenuated, and fetal posthypoxia tachycardia was augmented. We conclude that promazine taken by a mother could have especially deleterious effects on her fetus when the latter's oxygenation is already depressed (e.g., by cord compression), and suggest that the use of promazine during labor be reevaluated.

Maternal and fetal cardiovascular indices during fetal hypoxia due to cord compression in chronically cannulated sheep. I. Responses to timolol

Timolol, one of the newer beta-adrenergic antagonists, has less depressive effects on the heart than propranolol, so that it has the potential for use by pregnant women. In chronically cannulated ewes, timolol at 0.01 and 0.1 mg/kg of body weight induced maternal and fetal bradycardia; the higher dose also depressed uterine blood flow and fetal PaO2. When this higher dose preceded brief compression of the umbilical cord, uterine flow was further depressed and the usual posthypoxia rebound tachycardia did not develop. Both the blocking of fetal responses to hypoxia (precluding detection of fetal distress) and the reduction in uterine flow led us to conclude that timolol taken by a mother could pose particular hazards for her fetus in hypoxic conditions, such as during cord compression at parturition.