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PubMed2000

Effect of prolonged asphyxia on skin blood flow in fetal lambs.

OBJECTIVE: To determine the effect of a prolonged period of asphyxia on skin blood flow, a potential indicator of fetal cardiovascular responses to asphyxia, in the chronically catheterized fetal lamb. METHODS: Eight chronically instrumented pregnant ewes were studied at 118 +/- 1 days' gestation. After a control period, fetal acid-base status was assessed and regional blood flows were determined with dye-labeled microspheres. Fetal asphyxia was then induced by partial umbilical cord occlusion, decreasing fetal arterial oxygen pressure to 15 torr while maintaining pH above 7.28. Fetal cardiovascular status was monitored continuously. Fetal acid base status was evaluated every 10-15 minutes during cord occlusion. Regional blood flow determinations were repeated after 90 minutes of stable asphyxia. Results are expressed as the mean +/- standard error. Student t test for paired data was used to compare hemodynamic, acid-base, and regional blood flow determinations before cord occlusion and after 90 minutes of asphyxia. RESULTS: There was a significant increase in blood flow to the fetal scalp from a control value of 52 +/- 8 mL per minutes per 100 g to 175 +/- 30 mL per minute per 100 g at 90 minutes of asphyxia (P =.01). Similarly, there was an increase in blood flow to the skin overlying the fetal hindquarter from 39 +/- 12 mL per minute per 100 g during control to 153 +/- 47 mL per minute per 100 g at asphyxia (P =.038). CONCLUSION: In the chronically instrumented fetal lamb, a 90-minute period of asphyxia produced by partial cord occlusion resulted in a significant increase in blood flow to the fetal skin.

Animals↗

PubMed1997

The effects of bupivacaine, L-nitro-L-arginine-methyl ester, and phenylephrine on cardiovascular adaptations to asphyxia in the preterm fetal lamb.

UNLABELLED: The preterm fetal lamb that is exposed to clinically relevant plasma concentrations of lidocaine loses its cardiovascular adaptations to asphyxia, and its condition deteriorates further. Nitric oxide (NO) is an important regulator of vascular tone, and local anesthetics are known to inhibit endothelium-dependent vasodilation. The purpose of the present study was to determine whether the adverse effects of lidocaine noted in the preterm fetal lamb also occur with bupivacaine and whether the inhibition of NO results in effects similar to those of bupivacaine. Thirty-two chronically prepared pregnant sheep were studied at 117-119 days' gestation. Maternal and fetal blood pressure, heart rate, and acid-base state were evaluated. Fetal organ blood flows were determined using 15-microM diameter dye-labeled microspheres. After a control period, mild to moderate asphyxia (fetal PaO2 15 mm Hg) was induced by partial umbilical cord occlusion and maintained throughout the experiment. Ewes in Group I (n = 13) were given a two-step intravenous infusion of bupivacaine for 180 min. Fetuses in Group II (n = 12) received an intravenous injection of L-nitro-L-arginine-methyl ester (L-NAME) (25 mg/kg), and measurements were taken 10 and 30 min after the injection. A third group (Group III) of fetuses (n = 7) were given an intravenous infusion of phenylephrine to mimic the blood pressure increases noted in L-NAME-treated fetuses. At 90 min of stable asphyxia, there was a significant decrease in fetal PaO2 and pHa and an increase in PaCO2 and mean arterial blood pressure. There was also an increase in blood flow to the adrenals, myocardium, and cerebral cortex, whereas blood flow to the placenta decreased. Administration of bupivacaine during asphyxia did not affect the changes in mean arterial blood pressure and acid-base state but did abolish the increases in blood flows to the myocardium and cerebral cortex. Injection of L-NAME to the asphyxiated fetus resulted in an increase in mean arterial blood pressure above the level noted at 90 min of cord occlusion, and an increase in fetal PaO2 toward control levels. This was accompanied by a reduction in organ blood flows to preasphyxia levels. In asphyxiated Group III fetuses, titration of the phenylephrine infusion to achieve blood pressure increases similar to those noted with L-NAME were also associated with an increase in fetal PaO2. These data indicate that bupivacaine abolishes some of the circulatory adaptations to mild to moderate asphyxia induced by partial cord occlusion in the preterm fetal lamb. It is not clear whether these effects of bupivacaine are due to inhibition of NO. IMPLICATIONS: In the preterm fetal lamb, clinically relevant plasma concentrations of bupivacaine achieved by intravenous infusion to the pregnant ewe (80% gestation) abolished some of the fetal cardiovascular adaptations to asphyxia induced by partial umbilical cord occlusion.

Adaptation, Physiological↗

PubMed1997

Fetal testing in postdates.

Postdate pregnancies are at significant risk for perinatal morbidity. Fetal testing may be used to observe the prolonged pregnancy safely while awaiting onset of labor. Pitfalls associated with the use of fetal testing in this situation are discussed. The current literature addressing these problems is reviewed.

Amniotic Fluid↗