Magnesium sulfate in the management of acute intrapartum fetal distress

Acute tocolysis for suspected intrapartum fetal distress: maternal effects of terbutaline versus magnesium sulfate

This study was undertaken to determine the maternal hemodynamic impact of terbutaline versus magnesium sulfate in the acute treatment of fetal distress prior to cesarean delivery. Forty-six women were prospectively randomized to receive 0.25 mg subcutaneous terbutaline or 4.0 g intravenous magnesium sulfate for in utero fetal resuscitation before cesarean delivery. There were no significant differences between groups in baseline mean arterial pressure, arterial pressure before and after induction of anesthesia, maternal heart rate, maternal oxygen saturation, estimated blood loss, and pre- and postoperative hematocrits. Magnesium sulfate-treated women received significantly more intraoperative intravenous fluids (2365 +/- 877 ml) than the terbutaline group (1624 +/- 564 ml; P < 0.001). However, mean urine output was significantly greater in the terbutaline group (88 +/- 42 ml/h) than in those treated with magnesium sulfate (61 +/- 26 ml/h; P < 0.03). Terbutaline, the superior agent for acute tocolysis, is not associated with an increase in maternal cardiovascular side effects during anesthesia.

Intrapartum fetal distress and magnesium sulfate

OBJECTIVE

Intrapartum fetal distress is an obstetric emergency traditionally managed by immediate delivery by either the vaginal route or cesarean section. However, there is usually time to attempt intrauterine resuscitation. The purpose of this study was to report the utilization of magnesium sulfate for intrauterine resuscitation.

METHOD

Twenty-one fetuses received magnesium sulfate 4-g intravenous bolus in mothers awaiting cesarean section for fetal distress in the labor room of the Complejo Hospitalario Metropolitano de la Caja de Seguro Social de Panamá, from March through August 1997. Fetal distress in labor was defined as the presence of repetitive late decelerations, persistent loss of baseline variability, severe variable decelerations, or bradycardia.

RESULTS

Twenty-one fetuses received magnesium sulfate 4-g intravenous bolus in mothers awaiting cesarean section for fetal distress. Uterine activity ceased in seven patients, diminished in 13 patients and did not change in one. In all cases, but one, there was recovery of the FHR within 4 min; furthermore there was rose reactive of FHR in nine patients. The 1-min Apgar scores were 7 or above in 18 cases and the 5-min Apgar scores were 7 or above in 20 patients.

CONCLUSIONS

In summary, magnesium sulfate may be useful in the management of acute intrapartum fetal distress when there is evidence of increased uterine activity.

Management of fetal distress

Since its introduction more than 20 years ago, continuous electronic FHR monitoring has become the standard in most modern obstetric units. Practitioners well versed in FHR pattern interpretation do not question the value of fetal monitoring. Not only does this modality detect hypoxia early in its evolution, but also it allows the opportunity to understand the physiology of the hypoxia and to intervene if necessary. Although nonrandomized studies demonstrate an improvement in the perinatal death rate with continuous monitoring, most randomized studies have failed to confirm this observation. Continuous fetal monitoring has been associated in several studies with an increase in the CS rate; however, concomitant changes in obstetric practice have also raised the incidence of CS, making the interpretation of to what degree fetal monitoring is responsible for this increase difficult. Other than this association with an increased CS rate, fetal monitoring seems to present few risks. A thorough understanding of basic fetal heart abnormalities is crucial to prevent unnecessary intervention; however, although quite sensitive, FHR monitoring remains nonspecific in predicting fetal metabolic acidosis. Fetal pulse oximetry is a recent development still undergoing investigation. The ability to measure fetal oxygen saturation during labor adds critical information about fetal status and refines the interpretation of abnormal FHR patterns. If approved by the US Food and Drug Administration, it has the potential to affect dramatically the practice of obstetrics.

Intrapartal tocolysis: an option for acute intrapartal fetal crisis

Tocolytic drugs are commonly used by the obstetric community to produce uterine quiescence in premature labor. The use of tocolytic agents has been expanded to intrapartal emergencies. Intrapartal tocolysis has implications for obstetric nurses, which include possession of knowledge of the pharmacologic and physiologic effects of these drugs. Intrapartal tocolysis offers a beneficial management strategy that can be used in an acute intrapartal fetal crisis. The use of tocolytics provides valuable time for the health care team to assess the etiology of a nonreassuring fetal heart rate pattern, increase options for the birth, and mobilize resources for delivery.

Acute tocolysis for fetal distress: terbutaline versus magnesium sulphate

Forty-six women in active labour who developed fetal distress requiring abdominal delivery were randomized to receive 0.25 mg of terbutaline (subcutaneously) or magnesium sulphate as a 4-g bolus (intravenously) to decrease uterine activity. The terbutaline-treated group in contrast to the magnesium sulphate-treated group had reduced uterine activity as measured by Montevideo units (p < 0.002). This decrease in uterine activity was noted more rapidly in all 23 patients who received terbutaline, 1.8 +/- 0.74 minutes compared to 7.5 +/- 2.1 minutes in the 16 of 23 patients (magnesium sulphate-treated women) in whom a decrease in uterine activity occurred (p < 0.001). Umbilical cord arterial blood pH at delivery was less than 7.20 in only 2 of the 23 patients treated with terbutaline versus 7 of the 23 in the magnesium sulphate-treated group. We conclude that terbutaline is an effective and more rapid-acting tocolytic agent to arrest uterine activity prior to delivery for fetal distress.

Single injection of terbutaline in term labor. I. Effect on fetal pH in cases with prolonged bradycardia

Thirty-three patients with prolonged fetal bradycardia (fetal heart rate baseline less than 100 bpm for a minimum of 3 minutes or less than 80 bpm for at least 2 minutes) in labor were studied. They were treated with a bolus injection of terbutaline if the bradycardia persisted at less than 80 bpm for 2 minutes and other efforts to improve the fetal heart rate (oxygen, positional changes) had failed. After the bolus injection a scalp blood pH (or a cord arterial pH in abdominal deliveries) was obtained within 30 minutes. Fetal acidosis was common if the bradycardia lasted 10 minutes or more, particularly if the rate was less than 80 bpm with a flat baseline for 4 minutes or more. The fetal heart rate improved after injection in 30 cases; 23 patients had vaginal delivery of infants in good condition. Ten underwent cesarean section: three for no improvement in fetal heart rate, two for cord prolapse, four for later ominous fetal heart rate, and one for failure to progress. These results suggest that tocolysis in selected cases can be of benefit for the fetus with prolonged bradycardia. In cases with an ominous fetal heart rate pattern preceding the bradycardia and in abruptio placentae immediate operative intervention without delay is probably better. Administration of terbutaline should be regarded as a temporary measure until it is apparent that the fetal heart rate has recovered. Preparation for emergency delivery should be made while a recovery is awaited.

Evaluation of the pharmacodynamics and pharmacokinetics of ritodrine when administered as a loading dose. On establishing a potentially useful drug administration regimen in cases of fetal distress

Inhibition of labor during the intrapartum period has been suggested as a method of managing acute fetal distress. In such cases, rapid tocolysis is desirable but, in high doses, beta-adrenergic-receptor agonists, such as ritodrine, may cause severe maternal hypotension that could aggravate the existing fetal distress. We undertook the present study to establish a safe infusion protocol for ritodrine that achieves high plasma concentration rapidly. Twelve nonpregnant female volunteers received, on separate days, three infusions of ritodrine, that is, 1, 2, and 3 mg, during a 2-minute period. The peak plasma concentration measured by high-performance liquid chromatography with electrochemical detection averaged 37, 74, and 100 ng/ml after the 1, 2, and 3 mg doses, respectively. Ritodrine concentrations decreased rapidly and with the 3 mg dose the ritodrine concentration was only 14 ng/ml after 15 minutes. The elimination phase half-life of ritodrine averaged 6.11 hours. None of the doses significantly affected systolic blood pressure but ritodrine increased heart rate and the plasma glucose level and decreased diastolic blood pressure and the plasma potassium concentration. Even at the highest infusion rate, the maximal changes in cardiovascular and metabolic variables were short-lived and clinically modest; heart rate increased 29 bpm, diastolic blood pressure decreased 8 mm Hg, glucose level increased 26 mg/dl, and potassium concentration decreased 0.6 mEq/L. These data indicate that high plasma concentrations of ritodrine can be achieved rapidly without serious side effects.