Edward H. Hon

Clinical fetal monitoring

Fetal evaluation during both the antepartum and intrapartum periods is increasing in our quest to improve perinatal morbidity and mortality rates. Currently, continuous electronic fetal heart rate (FHR) monitoring is being used increasingly for fetal surveillance during the intrapartum period. Assessment of the possible benefits of clinical monitoring is pertinent since this technique requires capital expenditure, educational programs, and increased patient surveillance. The absolute proof of perinatal benefit is difficult since there is a lack of clear-cut, measurable end points which denote success or failure. Perinatal death is fortunately infrequent, but its occasional occurrence does provide an acceptable end point which can be evaluated. In order to evaluate the possible effects of clinical monitoring, the perinatal mortality rate in a large monitored group was compared with that in an unmonitored group. The incidence of intrapartum fetal and neonatal death was compared in these two groups. The monitored group was comprised of patients with “high-risk” obstetric problems who should have contributed heavily to over-all perinatal deaths. However, comparison revealed that the perinatal outcome was better in the monitored than in the unmonitored group. Although clinical fetal monitoring seems to provide some immediate perinatal benefit, the over-all impact and potential benefit await critical infant follow-up evaluation.

Clinical fetal monitoring. VII. The evaluation and significance of intrapartum baseline FHR variability.

The clinical usage of intrapartum fetal monitoring has increased dramatically in the past few years. Understanding of the pathophysiologic significance of FHR patterns has been further elucidated, but quantitation and prediction on an individual basis at times present a practical clinical dilemma. Baseline FHR variability was evaluated in order to see if it provided additional commentary on fetal status. The presence of FHR variability appears to be a favorable commentary regarding both fetal and newborn status. A clinical method of apprasing FHR is presented and the significance of FHR variability suggested.

Significance of meconium during labor.

Continuous fetal heart rate (FHR) monitoring and routine fetal scalp blood sampling was utilized in the evaluations of 366 fetuses during labor. One hundred and six patients had meconium in the amniotic fluid at some time during labor. A total of 26,110 uterine contractions were monitored during these 366 labors. The incidence of FHR patterns as a percentage of uterine contractions was calculated for the meconium and nonmeconium groups. Although there was a 3 1/2-fold increase in the incidence of low five-minute Apgar scores (less than 7) in the meconium group, signs of fetal distress were, with rare esception, not significantly different from those in the nonmeconium group. The presence of meconium in the amniotic fluid without signs of fetal asphyxia (late decelerations and acidosis) is not a sign of fetal distress and need not be an indication for active intervention. The combination of fetal asphyxia and meconium staining of the amniotic fluid, however, does enhance the potential for meconium aspiration and a poor neonatal outcome. Universal fetal heart rate monitoring and appropriate fetal acid-base evaluation is recommended for following patients with meconium in the amniotic fluid during labor.

Fetal and neonatal biochemistry and Apgar scores

Abstract Biochemical changes during labor, delivery, and the first hour of life were evaluated in 150 high-risk pregnancies. No differences in the biochemical status of the fetus (pH, Po 2 , Pco 2 , and base deficit) were found during early labor with different groups of patients divided according to low or high Apgar scores at 1 and 5 minutes. During labor and delivery, the fetus gradually becomes acidotic, with the acidosis more marked in fetuses who subsequently had lower Apgar scores; at birth there was a momentary accentuation of the acidosis during the first few minutes of life. It is speculated that the prediction of Apgar scores may be possible by measuring the fetal pH during the course of labor and delivery and that serial biochemical measurements with guide preparation for adequate treatment of a depressed newborn infant.

Quantitation of uterine activity in 100 primiparous patients

An on-line technique for quantitating uterine activity by measuring the total area under the intrauterine pressure curve was utilized during the labor of 100 primiparous patients. Uterine activity was measured in uterine activity units (1 UAU=1 Torr minute). UAUs were calculated for each patient in both cumulative and noncumulative fashions. The rate of uterine activity (UAU per unit of time) increased as labor progressed, yet the total UAUs expended at each centimeter of dilatation progressively decreased with advancing dilatation. Thus, the rate of cervical dilatation increased faster than could be accounted for by the increase in uterine activity. The implication being that the efficiency of uterine contractions increases with advancing labor. It no longer appears reasonable to refer to labor in terms of elapsed time. Information regarding the pattern of cervical dilatation and uterine activity appears to be much more meaningful to the evaluation of progress in labor. Quantitation of uterine activity may provide useful information for the ongoing management of labor. Quantitation of UA does provide a means of evaluating the effects of specific events such as medication, anesthesia, and manipulation on UA.

Hyperventilation during labor.

Abstract The effect of maternal hyperventilation during labor was studied in 20 patients. Fetal scalp blood samples were analyzed for pH, pO 2 , pCO 2 , and base excess and compared with maternal free-flowing venous blood samples taken at the same time. Samples were obtained for baseline values and repeated during and following a period of active hyperventilation. Both maternal and fetal pH rose with hyperventilation. No fetal acidosis was observed even in the 5 cases of severe maternal hypocarbia. Maternal pCO 2 during labor was low even prior to intentional hyperventilation. Both maternal and fetal pCO 2 decreased, the maternal change being greater than the fetal. There was a slight but statistically significant decrease in the fetal pO 2 during hyperventilation. However, fetal oxygen levels remained within physiologic range throughout the study.

Fetal cardiac response to paracervical block anesthesia. Part I

Abstract Fetal bradycardia following mepivacaine (200 mg.) paracervical block anesthesia occurred in 24 of 92 patients who had 100 paracervical blocks. Gestational age, parity, fetal weight, and maternal complications did not influence the incidence of fetal bradycardia following paracervical block. There was a significant fall in pH and rise in base deficit only in those fetuses with bradycardia lasting more than 10 minutes. In all instances, recovery from the transient metabolic acidosis was complete. A transient increase in uterine activity as measured by the area under the uterine pressure curve was noted in the majority of patients with post-paracervical block fetal bradycardia. The majority of patients who had no fetal bradycardia had a decrease in uterine activity.

Cardiac and respiratory activity in relation to gestation and sleep states in newborn infants.

Summary: In order to provide normative values of heart and respiratory rate and variability in relation to gestation and sleep states, 32 neonates who were free from cardiopulmonary disease were studied during the 1st-6 day of life. The infants were grouped as follows: group A, 9 infants with gestational ages of 27-33 wk; group B, 14 infants with gestational ages of 34-36 wk; and group C, 9 infants with gestational ages of 37-40 wk. Recordings and observations were made during a 1-hr postprandial nap. During active sleep (AS) and quiet sleep (QS), heart rate, short-term and long-term variability of the heart rate, respiratory rate, variability of the respiratory rate and apnea density were measured. Both the long- and short-term heart rate variability was less in preterm infants (group A) than the less immature or full term infants (groups B and C, P <0.01). Breath-to-breath respiratory variability was not significantly affected by gestational age, whereas percent duration of apnea was less in full term (group C) than the preterm groups of infants during quiet sleep (groups A and B, P < 0.05). There was no significant difference between baseline heart rate, short-term heart rate variability, and respiratory rate during AS and QS states at any given gestational age. Long-term variations in heart rate, breath-to-breath respiratory variability, and percent duration of apnea were significantly less in QS in comparison to AS at each gestational age group (P < 0.01).Speculation: Systematic monitoring of newborn infants by the techniques presented in this report would further define normal cardiorespiratory functions in relation to maturity and sleep states. Application of these techniques to the study of the distressed newborn should provide an early indication of morbidity and recovery from disease.

The neonatal value of fetal monitoring

In general the use of fetal monitoring has been felt to be of benefit in the prevention of fetal death. The type of recording obtained during labor may also be of significant value to the pediatrician in permitting him to anticipate respiratory distress. In this article an attempt is made to point out the various areas of the fetal heart rate tracing that can be used in such prognostic attempts.

The effects of ritodrine hydrochloride on uterine activity and the cardiovascular system.

The effects of ritodrine hydrochloride were evaluated in 10 patients in active labor with continuous electronic monitoring of fetal and maternal cardiovascular systems and uterine activity. Ritodrine infused at 150 μg per minute significantly decreased uterine activity and increased maternal heart rate with only minimal blood pressure changes. During the period of increased maternal heart rate, nonspecific changes in the maternal electrocardiogram were noted and thought to be rate related. The drug has no demonstrable effect on the fetal heart rate, fetal electrocardiogram, or acid-base status.