Jack N. Blechner

A study of prolongation of obstetric anesthesia.

The clinical and biochemical effects of prolonging obstetric anesthesia were studied at cesarean section, using Pentothal, nitrous oxide, and succinylcholine. Mother, fetus, and newborn infant were evaluated. The average interval between the first injection of Pentothal and delivery was 36 minutes. Maternal respiratory gas and acid-base levels remained stable, as did uterine metabolism. Apgar scores were lower and more vigorous resuscitation was necessary with prolongation of anesthesia. The nitrous oxide concentrations in maternal, fetal, and newborn blood were significantly greater in this series of cases than in those delivered more rapidly. Effects of high nitrous oxide contents on newborn arterial oxygenation are discussed.

Effects of maternal metaboHc acidosis on the human fetus and newborn infant

The effects of maternal metabolic acidosis on fetal acid-base balance have been studied by comparing the P co 2 , pH, and bicarbonate levels in maternal, fetal, and newborn human blood plasma. Observations have been made without superimposed maternal acidosis during and following the slow infusion of ammonium chloride and during and following more rapid infusion. The results demonstrate that maternal metabolic acidosis is not necessarily accompanied by fetal or neonatal metabolic acidosis. Despite significant reductions in the maternal plasma HCO − 3 and pH, the fetal levels remain relatively unchanged. As the maternal pH falls, the usual transplacental pH gradient is virtually eliminated.

Observations on pregnancy at altitude

We have compared the oxygen, carbon dioxide, and hydrogen ion concentrations of pregnant sheep and goats at sea level with those obtained in the same animal in an altitude chamber at 5,000, 10,000, and 15,000 feet. By using indwelling plastic catheters, the changes which occur in the uterine circulation (and in a single instance, in the umbilical circulation) have been observed under conditions shown to be compatible with a live fetus. The effect of altitude upon the transplacental oxygen and carbon dioxide pressure gradients has been estimated and the results discussed in terms of the physiologic adaptations of the pregnant animal to an acute reduction in oxygen tension.

Blood flow and oxygen consumption of pregnant goats

Abstract The antipyrine method was employed for measuring the rate of blood flow per kilogram of tissue in the pregnant uterus of unanesthetized and apparently unstressed goats. The data were known with certainty to be compatible with the continued growth and development of the fetus. Uterine blood flow was high in early gestation but fell to a plateau of 354 ml. per kilogram per minute after the sixtieth day. Rate of O 2 consumption per kilogram was minimal in the first 2 months and then rose to a plateau of 8.1 ml. per kilogram per minute.

Observations on pregnancy at altitude: II. Transplacental pressure differences of oxygen and carbon dioxide☆☆☆

Abstract The oxygen and carbon dioxide contents and tensions have been determined in the maternal arterial, uterine venous, umbilical arterial, and imbilical venous blood in pregnant ungulates bred and pastured at sea level and then exposed to altitudes as high as 15,000 feet. At altitude, the oxygen tension in the umbilical blood vessels decreases less than in the maternal placental vessels. Despite a smaller transplacental difference in oxygen pressure, the carbon dioxide pressure difference remains unchanged from sea level.

Simplified method of estimating the oxygen pressure difference between maternal and fetal blood in the placenta

Abstract The transplacental difference in oxygen pressure can be estimated from the “effective” oxygen tMlsions in the uterine and umbilical circulations. The “effective” oxygen tensions are determined from the mean values of arterial and venous percentage saturations and pHs by extrapolation from the maternal and fetal oxygen dissociation curves. Results with this method have bun compared with 34 published estimations of the oxygen pressure difference in two species, using the Bohr integration procedure. The two estimates agru to within 2 mm. Hg in 29 of the 34 and to within 3.6 mm. Hg in the remaining 5 cases. In an additional comparison of mean gradient values for a single species, the difference between the two estimates is only 1.2 mm. Hg. The simplified method presented appears to be sufficiently accurate for use in the quantitative description of the transplacental diffusion of oxygen.

Blood flow and gaseous metabolism of the rabbit uterus during pregnancy.

Abstract Using indwelling plastic catheters, blood samples were drawn from an artery and a uterine vein of anesthetized and unanesthetized rabbits at selected stages in gestation. Oxygen content and oxygen capacity were determined on the samples. The coefficient of oxygen utilization by the uterus increased from an average value of 15 per cent early in gestation to 63 per cent in the last few days of the gestation period. The antipyrine method was employed for measuring the rate of blood flow per kilogram of tissue. Uterine blood flow was high in early pregnancy and decreased as gestation advanced. The rate of O 2 consumption per kilogram remained unchanged from the eleventh week onward; the average value was 7.42 c.c. per kilogram per minute.

Colloidal osmotic pressures of human maternal and fetal blood plasma

The colloidal osmotic pressure and the concentration of the plasma proteins of human maternal and fetal blood have been measured in term pregnancy. The mean material colloidal osmotic pressure is 356mm. H 2 O and the fetal 305mm. H 2 O. The findings indicate that the movement of water from mother to fetus is not dependent upon the colloidal osmotic pressures of the maternal and fetal plasma proteins.

Oxygenation of the human fetus and newborn infant during maternal metabolic acidosis

Abstract The effects of maternal metabolic acidosis on fetal and newborn oxygenation were studied by comparing the oxygen content, oxygen saturation, and lactic and pyruvic acid contents in maternal, fetal, and newborn human blood. Observations were made without superimposed maternal acidosis, during and following the slow infusion of ammonium chloride, and during the following more rapid infusion. The results demonstrate that maternal metabolic acidosis is not accompanied by changes in concentrations of oxygen in maternal blood. The levels in fetal blood at birth and in newborn blood shortly after delivery, however, are significantly below control values.

Oxygen, carbon dioxide, and hydrogen ion concentration in arterial and uterine venous blood of pregnant goats

Abstract Using indwelling plastic catheters, blood samples were drawn from an artery and a uterine vein of unanesthetized pregnant goats at selected stages in gestation. Oxygen and carbon dioxide contents, pH, and oxygen capacity were determined on the samples. The coefficient of oxygen utilization by the uterus increased from 9 per cent early in gestation to 25 per cent in the last third of the gestation period of 145 to 147 days. The CO 2 tension of the arterial blood ranged between 25.1 and 31.9 mm. Hg (average, 28.6) and the pH was 7.32 to 7.49 (average, 7.41).