L. Stanley James

INFLUENCE OF MATERNAL HYPERVENTILATION ON THE NEWBORN INFANT.

Abstract Moderate controlled hyperventilation during cesarean section can cause the fetus to have slightly less acidosis at birth. However, if maternal P CO 2 is lowered below 17 mm. Hg, the infant is likely to have severe acidosis and delayed onset of respiration. Although hyperventilation was not always accompanied by maternal alkalosis in this study, 1 of the two mothers with the most alkalosis belonged to the group in which the anesthesiologist was attempting to maintain a normal level of ventilation. There is danger not for the conscious patient hyperventilating voluntarily, but for the unconscious patient who undergoes artificial ventilation after receiving muscle relaxants. Considerable caution should be exercised, therefore, in the ventilation of pregnant women who undergo cesarean section when muscle relaxants are being used; willful overventilation should be avoided.

Changing incidence of bronchopulmonary dysplasia

APART FROM RARE AND ISOLATED CASESOfpulmonary fibrosis occurring in very small infants, b ronchopu l monary dysplasia was first noted at the Babies Hospital , New York City, when artificial vent i la t ion for the treatmen t of respiratory distress syndrome was insti tuted. Over the past eight years, the incidence of BPD has fal len as techniques of neona ta l care have been improved and greater experience with artificial vent i la t ion has been gained. The lower incidence occurred despite an increase in survival rate and more frequent use of vent i la tory support on very small infants. We consider that the diagnosis of BPD canno t be m a d e without a history and wi thout a s tudy of sequent ia l films. With the changing techniques of assisted venti lat ion, we now rarely see the typical stages of the disease as described by Northway. In our lnsn tunon , we have seen two types of chronic lung disease in neonates : the first in the smallest in fant with little or no respiratory distress syndrome, and the second in infants surviving severe RD S (Table I). The changing survival rates according to weight group for the period 1972 to 1977 are presented in the Figure. The improved survival rate in very small infants has occurred concurrent ly with changes in bo th obstetr ic pracnce and newborn care. There have been more l iberal indicat ions for cesarean section for p remature b reech deliveries and for the very immatu re infant with fetal distress, as well as an earlier inst i tut ion of CPAP using nasal prongs and an increased use of mechan ica l venti lation for the very immatu re infant with respiratory difficulty. The changing incidence of BPD is presented in Table II. In 1970-1971. the condi t ion was seen in only four of 85 patients with RDS. two of whom were normal at seven months and two years, respectively; two died. A s t h m a and wheezing dur ing the first four years of life were seen in

Transmission of Mepivacaine Hydrochloride (Carbocaine) Across the Human Placenta

Transmission of mepivacaine hydrochloride (Carbocaine) across the placenta was studied in 56 healthy women at term who received epidural analgesia during labor and delivery. All infants were delivered vaginally. Concentrations of mepivacaine were determined in maternal and umbilical cord blood by the methyl orange method. Mepivacaine administered into the maternal epidural space passed rapidly into the blood stream and crossed the placenta. Five mothers who received repeated injections, developed toxic symptoms; concentrations of the drug in blood were significantly higher than those in patients without complications. Twelve infants were depressed at birth; in 5, blood levels of the drug were significantly higher than those found in vigorous babies.

Oligohydramnios-Induced Lung Hypoplasia: The Influence of Timing and Duration in Gestation

Abstract: We drained amniotic fluid for periods of 5 and 10 days at various times in gestation between days 40 and 55 in the guinea pig (term is 67 days). We analyzed the impact of this procedure on fetal lung growth and used untouched littermate fetuses as controls. During the canalicular stage of lung development, total lung DNA per gram of fetal weight was significantly reduced after only 5 days of oligohydramnios and the percent change did not vary between the two consecutive 5-day periods studied (period A, days 40 to 45,δ of −0.047 mg, p = 0.004; period B, days 45 to 50, δ of −0.042 mg, p = 0.002). The impact of the same duration of oligohydramnios on lung growth later in gestation, during the terminal sac stage of lung development, was less (period C, days 50 to 55, δ of —0.027 mg, p = 0.097). This reduction in effect between period A or B and C was significant at the 0.05 level using a one way analysis of variance. Two overlapping 10-day periods were also studied. In both experiments, the percent changes in lung DNA per gram of fetal weight between experimental and littermate controls were significant (period D, days 40 to 50, δ of −0.072 mg, p = 0.001; period E, days 45 to 55, 5 of −0.047 mg, p = 0.001). The inhibitory effect of oligohydramnios on lung growth was more marked in period D than E (significant at the 0.05 level). A two-way analysis of variance indicated that the magnitude of the changes was related to both the time of onset and the duration of oligohydramnios. We conclude that even a short period of oligohydramnios interferes with lung development, and that the extent of this interference depends to a large extent on the time of onset and to a lesser extent on the duration of oligohydramnios. Irrespective of duration, the greatest effects were observed during the canalicular stage of lung development.

Pulmonary follow-up of moderately low birth weight infants with and without respiratory distress syndrome*

Pulmonary function was measured in 18 children aged 6 to 9 years who had been born prematurely (mean birth weight 1760 +/- 555 g) and who had each received greater than 100 hours (mean 177 +/- 74 hours) of mechanical ventilation for respiratory distress syndrome (RDS). We used as controls 26 children aged 6 to 7 years who had been born prematurely (mean birth weight 1636 +/- 554 g) but who had required no treatment for pulmonary disease. Results for total lung capacity, FEV1, ratios of functional residual capacity and residual volume to total lung capacity, specific airway conductance, and alveolar plateau slope did not differ in the RDS and control groups. Eight of the 18 children in the RDS group had had radiologic evidence of bronchopulmonary dysplasia at 30 days and oxygen dependence at 30 days, but did not differ from the control group for any of the indices of pulmonary function. However, FEV1 and specific airway conductance were significantly reduced in the premature control group compared with children born at term. Therefore, factors associated with prematurity rather than combined effects of RDS and its treatment determined pulmonary function at age 6 to 9 years.

Acidosis of the newborn and its relation to birth asphyxia.

Oxygen levels in the newborn infant at delivery have been intensively studied in recent years, blood being obtainedfrom the umbilical cord (4, 9, 15, 17, 30, 32, 35). These studies have revealed a wide range of values. Eastman (9) was responsible for some of the earliest pioneering work. He reported oxygen saturations in the umbilical artery from 6 to 27 per cent, and in the vein 38 to 58 per cent, in 15 babies delivered vaginally. In one elective cesarean section a value of 30 per cent was obtained from the umbilical artery and 63 per cent from the vein. Table 1 demonstrates that the larger the series, the wider has been the range. The present study shows 0-67 in the artery and 9 to 96 in the vein. A few samples from the umbilical vein have been almost identical to maternal arterial blood. It was futher observed that even at elective cesarean section the same wide range was obtained. Some investigators have taken an average of these values to be an indication of

Increased uterine activity and fetal deterioration during maternal hyperthermia

The role of hyperthermia in the absence of infection has been investigated in the pregnant baboon. Twenty-three near term animals were used. Catheters were placed in maternal and fetal arteries and thermocouples implanted in maternal colon and fetal esophagus. Maternal temperature was raised to between 41 and 42 degrees Centigrade (C.), by applying external heat. The temperature gradient between fetus and mother (delta T F-M) was 0.47 degree C. under steady-state conditions with maternal temperature at 38 degrees C. and rose to 0.75 degree C. at 42 degrees C. Hyperthermia caused a twofold increase in uterine activity; a metabolic acidosis developed in the mother and a profound acidosis and hypoxia developed in the fetus. There was also a marked fall in blood pressure and an increase in heart rate in both mother and fetus; late deceleration of the fetal heart rate occurred at a higher oxygen level and pHa than has been observed under normothermic conditions.

Temperature gradient between fetus and mother as an index for assessing intrauterine fetal condition.

Temperature gradient between fetus and mother (deltaTF-M) was measured in 29 pregnant baboons. Thermocouples were implanted in the fetal esophagus and the maternal colon, and, in some instances, thermistor probes were also placed in the fetal esophagus, scalp, and shoulder muscle. Under steady-state conditions, the fetal temperature was found to be higher than that of the mother. Temperatures in the fetal esophagus, scalp, and shoulder were 0.47, 0.28, and 0.19 degrees C. respectively, higher than those in the maternal colon. There was an increase in deltaTF-M during acute fetal stress induced by asphyxia, secondary to occlusion of the umbilical cord, maternal aorta, or inferior vena cava, or to acutely increased uterine activity. This increase in deltaTF-M most likely reflects impairment of heat dissipation from the fetus to the maternal compartment. A decreased deltaTF-M was observed when the stress on the fetus was subacute and prolonged. This is probably the result of a diminution of heat production by the fetus as the metabolic rate is lowered during prolonged hypoxia. Ten to 30 minutes after the cessation of vital signs of the fetus, the deltaTF-M became zero.

Vasopressin secretion induced by hypoxia in sheep: Developmental changes and relationship to β-endorphin release☆☆☆

To investigate the developmental changes in the secretion of vasopressin and the potential role of beta-endorphin as a stimulus to the release of vasopressin, the concentrations of these peptides were measured in fetal, newborn, and adult sheep after episodes of induced hypoxia. The studies confirm that hypoxia is a potent stimulus to the release of both vasopressin and beta-endorphin in the fetal animal. In both the newborn lamb and the ewe, more profound hypoxia is necessary for a similar release. In the fetus, the release of both vasopressin and beta-endorphin after hypoxia increased with gestational maturation. A comparison of control concentrations of both peptides, the discordance of release in the newborn lamb, and the absence of a change in concentrations of vasopressin with infusion of beta-endorphin implies that these hormones are released in parallel but independently during hypoxic stress.

Reduced uterine blood flow and fetal hypoxemia with acute maternal stress: Experimental observation in the pregnant baboon

The effects of maternal hyperexcitability on the fetus were studied in 17 baboons. In the period of agitation, induced by stressful stimulus such as exposure to bright light or by clamping of the toe, the mother exhibited an increase in arterial blood pressure and, in some instances, arrhythmia. These changes were accompanied by an increased uterine activity and reduced uterine blood flow, and resulted in a decrease in heart rate and arterial oxygenation in all fetuses. Fetal recovery was prompt after maternal agitation was terminated, either by removal of the stimulus or by sedation with pentobarbital or nitrous oxide. This sedation also prevented a decrease in uterine blood flow when stress was repeated.