The effect of amnioinfusion on uterine pressure and activity: A preliminary report

The effect of amnioinfusion on uterine pressure and activity: A preliminary report Marvin D. Posner, MD, Susan A. Ballagh, MD, and Richard H. Paul, MD Los Angeles, California Transcervical intrapartum amnioinfusion of normal saline solution is being used in a number of centers. Over the past few years indications for the procedure have included prophylaxis and treatment of intrapartum decelerations in both term and preterm gestations, dilution and lavage of meconium-stained amniotic fluid, and for direct administration of antibiotics within the amniotic cavity in cases of chorioamnionitis. Little is reported about the real or potential risks of this procedure to both the mother and fetus. Over the past 2 years we observed several isolated cases of increased uterine activity by palpation coupled with fetal distress during amnioinfusion. These instances prompted us to study in a systematic fashion the relationships between uterine tone and activity during intrapartum amnioinfusion. We measured uterine tone and quantitated uterine activity in 10 patients undergoing intrapartum amnioinfusion and compared values 20 minutes before, during, and 20 minutes after amnioinfusion. A significant increase in uterine tone (p < 0.05) was noted during and after the infuSion. No difference in uterine activity was observed in any of the study periods. A case of uterine hypertonus and fetal bradycardia and a suggested procedure scheme for intrapartum amnioinfusion are presented. (AM J OSSTET GVNECOl 1990;163:813-8.)

Key words: Amnioinfusion, uterine tone, uterine activity Amnioinfusion has been used with increasing frequency during the intrapartum period over the past few years. The technique has been primarily used to decrease or relieve variable decelerations during labor. I .' Additional studies have addressed the use of this technique in pre term premature rupture of membranes,4 meconium-stained amniotic fluid,5.6 and intrauterine infection therapy with direct antibiotic instillation. 7 In the first prospective randomized clinical trial with amnioinfusion Miyazaki et al. 2 described a significant decrease in variable decelerations in the amnioinfused group (51 %) versus the noninfused group (4.2%). This was most significant in the nulliparous patients with relief noted in 66.7% of the amnioinfusion group versus 0% in the noninfusion group. There was also a significant decrease in the rate of cesarean section in these patients for fetal distress, 14.8% in the infusion group versus 47.8% in the noninfusion group. In a randomized trial of amnioinfusion versus controls in preterm premature rupture of the membranes, Nageotte et a1. 4 showed both a statistically significant difference in the incidence of all variable decelerations during the first stage of labor (2.4% versus 7.9%) and From the Department of Obstetrics and Gynecology, University of Southern California School of Medicine, Los Angeles CountyUniversity of Southern California Medical Center. Presented at the Tenth Annual Meeting of the Society of Perinatal Obstetricians, Houston, Texas, January 23-27, 1990. Reprint requests: Marvin D. Posner, MD, Department of MaternalFetal Medicine, Santa Barbara Cottage Hospital, P.O. Box 689, Pueblo at Bath Street, Santa Barbara, CA 93102. 6/6/22584

a significant decrease in severe variable decelerations during the second stage of labor in the amnioinfusion group as compared with controls (2.9% versus lO.1 %). They also showed a significant difference in pH values between the treated and control groups. A recent publication by Wenstrom et a1. 5 described a successful decrease in the incidence of low I-minute Apgar scores, meconium noted below the cords, and of operative deliveries with saline solution amnioinfusion in the presence of meconium-stained amniotic fluid. Similarly, Sadovosky et al. 6reported an incidence of thick meconium noted at delivery of 5% in amnioinfused patients versus 62% of controls. In patients who had intrapartum amnioinfusion their fetuses also had a decreased incidence of acidosis (16% versus 38%) and meconium noted below the cords (29% versus 0%) as compared with controls. Although the procedure of amnioinfusion with normal saline solution is generally believed safe, potential complications must be considered. Gimbel" posed the question of an increased incidence of umbilical cord prolapse after amnioinfusion; however, no substantiative reports have emerged. An additional consideration relates to the potential occurrence of uterine hypertonus as a result of stretching of the myometrial muscle fibrils, which in turn causes increased passive tension. This theoretical effect coupled with clinical observations that suggest increased uterine tonus is most pertinent given a potentially compromised fetus or a patient with a prior uterine scar. Miyazaki 2 noted an "artificial increase" in the 813

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Fig. 1. Study device consisted of conventional fluid-filled intrauterine pressure catheter attached with heat-shrinkable tape to commercially available pressure-tipped intrauterine sensing device (Liurel Medical, Northfield, Minnesota).

resting tone of the uterus and attributes this "artificial increase" to resistance to outflow of the infusate through the holes of the catheter. Evaluation of the technique and existent data preclude a clear answer with regard to uterine tone. The purpose of this study was to evaluate the effects, if any, on the uterine tone and activity associated with intrapartum transcervical amnioinfusion.

Material and methods Patients were selected for amnioinfusion on the basis of anyone or combination of the following criteria. Decreased amniotic fluid volume on the basis of amniotic fluid index of <5.0 em, the presence of moderate to severe variable decelerations refractory to position changes, or the presence of meconium-stained amniotic fluid. Ten intrapartum patients with ruptured membranes, undergoing continuous direct fetal heart rate (FHR) monitoring, and deemed suitable for the insertion of an intrauterine pressure catheter were studied. All patients had amniotic fluid volume assessed by the four-quadrant technique described by Rutherford et al.,9 both before and immediately after the amnioinfusion. The infusion-study device consisted of a standard intrauterine pressure catheter attached with heatshrinkable tape to a pressure-tipped sensor transducer,

both of which are commercially available (Fig. 1). Normal saline solution, 250 ml warmed to 37° C was infused through the intrauterine pressure catheter by gravity flow. The patient was prepared and draped for vaginal examination and the pressure-tipped device was zeroed to atmospheric pressure before insertion. After insertion of the study device the resting tone of the uterus was measured. The basal tone of the uterus as measured by the fluid-filled catheter was matched to that of the pressure-tipped catheter. For a period of 20 minutes before the infusion, the uterine activity from both systems was recorded on both a paper strip chart and on a multichannel tape recorder. After the 20-minute observation period the intrauterine pressure catheter was disconnected and the infusion of 250 ml warmed normal saline solution was begun. During the amnioinfusion, uterine tone and activity was continuously monitored with the pressure-tipped sensing device. After the infusion, the intrauterine pressure catheter was reconnected and the uterine activity was recorded for 20 minutes. The uterine tone was measured in millimeters of mercury (mm Hg) and overall uterine activity was measured and expressed in Alexandria units'O for the three study periods. Alexandria units are the average intensity of contractions, multiplied by the frequency of con-

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tractions in a 10-minute period, multiplied by the average duration of the contractions (Fig. 2). Analysis of variance with subsequent Tukey-A and Tukey-B post hoc comparison was used for evaluation of both the uterine tone and uterine activity expressed in Alexandria units for the 20-minute preinfusion, during the infusion, and the 20-minute postinfusion time periods. Significance was reached with a value of p < 0.05.

Results A statistically significant increase (p < 0.05) was noted comparing the preinfusion period uterine tone with that observed during the infusion period. Significance (p < 0.05) was also found in comparing preinfusion period uterine tone with that of the postinfusion period. The comparison of uterine tone during the infusion period with that of the postinfusion period showed no difference (Fig. 3). The comparison of uterine activity, expressed in Alexandria units for all study periods failed to show significance at the p < 0.05 level (Fig. 4). Additional observations noted from review of the data showed an average increase in the amniotic fluid infusion of 4.6 ± 1.8 cm for each 250 ml of sterile saline solution infused. The average time required for infusion of 250 ml was 24.6 ± 10.4 minutes. The range of time was 16.2 to 50.7 minutes. There was a single notable complication observed during this limited evaluation in 10 study subjects. One patient had an episode of uterine hyperactivity soon

after the amnioinfusion was begun. This was associated with a prolonged FHR deceleration. Both abnormalities seemingly responsed to intravenous administration of magnesium sulfate. The patient was taken to the operating room for emergency cesarean delivery but on reevaluation the uterus relaxed and the FHR had become normal. Fifteen hours later a 3540 gm male infant was delivered by vacuum extraction with Apgar scores of 9 at both 1 and 5 minutes (Fig. 5).

Comment In recent years there has been an increasing interest in transcervical intrapartum amnioinfusion. Present indications include prophylaxis and treatment of intrapartum decelerations in both term and preterm gestations,'-4 dilution and lavage of meconim-stained amniotic fluid," 6 and for direct administration of antibiotics within the amniotic cavity in cases of chorioamnionitis. 7 In the limited number of current reports that describe amnioinfusion, little has been reported with regard to potential morbidity to either the mother or fetus. Clinicians performing amnioinfusion must be aware of the theoretical and potential risks associated with this procedure. When asked by Gimbel 8 about the possibility of cord prolapse, Miyazaki responded that the incidence of this potentially devastating complication was actually one half that seen in vertex presentations during normal labor. We were unable to document other reports of this complication. In our institution over the past year we have noted several instances of fetal dis-

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tress during amnioinfusion. These were associated with a picture that suggests increased uterine activity with clinical palpation. These findings prompted us to better document such occurrences and perhaps define their cause.

Previously Tabor and Maier ll reported a case of polyhydramnios and elevated uterine pressure during amnioinfusion. According to their report, 4300 ml of normal saline solution was transcervically amnioinfused over a 21-hour period. Some of the fluid leaked out of

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Fig. 5. FHR tracing for patient who experienced uterine hypertonus soon after amnioinfusion was begun. Uterine activity was recorded from external tocodynamometer, pressure-tipped catheter, and open-ended fluid-filled catheter. Patient history and outcome are reported.

the uterus but the majority remained. No estimation of the fluid volume was performed until fetal bradycardia was present. At that time the intrauterine resting pressure had increased to 50 mm Hg from 10 mm Hg before infusion. The FHR returned to normai only after subcutaneous terbutaline administration and removal of 900 ml of fluid. It was speculated that the increased intrauterine pressure had decreased uteroplacental perfusion that resulted in the fetal bradycardia. Even with a small 250 ml volume of infusate our results show a statistically significant difference in the basal uterine tone when comparing preinfusion with infusion and postinfusion periods. We observed one case in which the uterine tone became excessive. This occurrence in one of 10 patients with the associated abnormal FHR findings is reason for concern and requires further investigative study. To that end an optimal approach to intrapartum amnioinfusion appears to be one in which either two intrauterine pressure catheters or a dual lumen catheter is used. Intrauterine pressure can thus be monitored at all times during the infusion. In addition some objective assessment of amniotic fluid volume should be performed before and at regular intervals after the infusion. In those facilities where such an approach is impractical, amnioinfusion may also be considered beneficial. The minimally acceptable approach in such instances would seemingly demand palpation of the uterus during infusion and close scrutiny of fetal well-being as judged by FHR. In our institution we currently perform concomitant direct intrauterine pressure monitoring during the am-

nioinfusion. In addition we measure the amniotic fluid infusion of each patient before and immediately after the amnioinfusion. We attempt to achieve an amniotic fluid infusion of ~8.0 cm and our infusion volumes are limited. An amniotic fluid infusion ~8.0 cm was chosen as an objective postinfusion value because it is above our 5.0 cm "at risk" value and it also is well above the range of interobserver error of ± 2.0 cm as reported by Rutherford et al. 12 Estimated infusion volume is calculated according to the observations of Strong et aI.," substantiated in this limited study, in that 250 ml of infusate will increase the amniotic fluid index by approximately 4 cm. With this method we should minimize the risk of polyhydramnios and overdistention of the uterus. Further investigation will more accurately define the frequency of complications and probable major benefits for both the fetus and mother of this emerging intrapartum therapy.

REFERENCES 1. Miyazaki FS, Taylor NA. Saline amnioinfusion for relief of variable or prolonged decelerations. AM] OBSTET GyNECOL 1983; 146:670. 2. Miyazaki FS, Nevarez F. Saline amnioinfusion for relief of repetitive variable decelerations: a prospective randomized study. AM] OBSTET GYNECOL 1985;153:301. 3. Strong TS, Hetzler G, Sarno AP, Paul RH. Prophylactic intrapartum amnioinfusion: a randomized clinical trial. AM] OBSTET GYNECOL 1990;162:1370-5. 4. Nageotte MP, Freeman RK, Garite T], Dorchester W. Prophylactic intrapartum amnioinfusion in patients with preterm premature rupture of membranes. AM ] OBSTET GYNECOL 1985;153:557.

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5. Wenstrom KD, Parsons MT. The prevention of meconium aspiration in labor using amnioinfusion. Obstet Gynecol 1989;73:647. 6. Sadovsky Y, Amon E, Blade ME, Petrie RH. Prophylactic amnioinfusion during labor complicated by meconium: preliminary report. AM j OBSTET GYNECOL 1989; 161 :613. 7. Haesslein HC, Goodlin RC. Delivery of the tiny newborn. AM j OBSTET GYNECOL 1979; 134: 192. 8. Gimbel GG. Concern about amnioinfusion [Letter). AMj OBSTET GYNECOL 1986;155:227. 9. Rutherford SE, PhelanjP, Smith CV,jacobs N. The fourquadrant assessment of amniotic fluid volume: an adjunct to antepartum fetal heart rate testing. Obstet Gynecol 1987;70:353.

September 1990 Am J Obstet Gynecol

10. EI-Sahwi S, Gaafar AA, Toppozada HK. A new unit for evaluation of uterine activity. AM j OBSTET GYNECOL 1967 ;98:900. 11. Tabor BL, Maier jA. Polyhydramnios and elevated intrauterine pressure during amnioinfusion. AMj OBSTET GyNECOL 1987;156:130. 12. Rutherford SE, Smith CV, Phelan jP, Kawakami K, Ahn MO. Four-quadrant assessment of amniotic fluid volume. interobserver and intraobserver variation. j Reprod Med 1987;32:587. 13. Strong TS, Hetzler G, Paul RH. Amniotic fluid volume increase after amnioinfusion of a fixed volume. AM j OBSTET GYNECOL 1990;162:746-8.

Comparison of umbilical artery pH and 5-minute Apgar score in the low-birth-weight and very-Iow-birth-weight infant Craig F. Stark, MD, Ronald S. Gibbs, MD, and Walter L. Freedman, MD Denver, Colorado The division between "normal" and low Apgar scores is based largely on data obtained from term newborns and may not apply to the premature infant. Umbilical artery pH has been suggested as a better indicator of intrapartum asphyxia. We examined the charts of 558 infants with birth weights :s25oo gm with respect to umbilical artery pH, 5-minute Apgar scores, and birth weight percentiles. A positive correlation between birth weight and 5-minute Apgar score was noted. No such relationship existed between birth weight and umbilical artery pH. Within birth weight groups, small-for-gestational-age infants have higher Apgar scores and lower umbilical artery pH values than their appropriate-for-gestational age counterparts. (AM J OBSTET GVNECOL 1990;163:818-23.)

Key words: Low birth weight, very low birth weight, acid-base status, Apgar scores The Apgar score was introduced in the early 1950s to assess, compare, and discuss the results of obstetric practices, types of maternal pain relief, and the effects of resuscitation on the newborn. 1 Although Apgar scores <7 at 5 minutes may implicate the presence of intrapartum asphyxia, most of these infants are vigorous and exhibit no other evidence of an asphyxial insult. 2 • s Umbilical arterial pH may be a more reliable indicator of perinatal asphyxia, but no agreement exists on a value to distinguish normal from abnormal. Most published data on Apgar scores and pH have studied term newborns. Extrapolation of these data to low birth weight (:52500 gm) and very low birth weight (:51500 gm) may not be appropriate. We surveyed the charts of all infants delivered at our institution over a 25-month period with birth weights between 500 and 2500 gm to evaluate the relationships From the Departments of Obstetrics and Gynecology, Denver General Hospital, University of Colorado Health Sciences Center. Presented at the Tenth Annual Meeting of the Society of Perinatal Obstetricians, Houston, Texas, January 23-27, 1990. Reprints not available.

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between birth weight, 5-minute Apgar scores, and umbilical pH. We subsequently divided the study population into small-for-gestational-age and appropriatefor-gestational-age groups to determine if differences existed between them when either umbilical artery pH or 5-minute Apgar scores were considered. Methods and material On Oct. 1, 1987, it became standard policy at Denver General Hospital to obtain umbilical cord blood samples on all newborns for blood gas analysis. The samples were obtained by double clamping a section of umbilical cord immediately after delivery of the infant. Blood was drawn into a pre heparinized syringe and analyzed within 30 minutes on a Corning 178 blood gas analyzer. Gestational age was calculated with one of the following: (1) last mentrual period if the patient reported regular menses, had a pelvic examination in the first trimester, and had not used oral contraceptives within 2 months before conception, (2) obstetric ultrasonography if performed before 24 weeks or, if neither of these are available, (3) neonatal assessment of gestational age was determined with the Lubchenco method