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Fetal Heart Rate Changes After Intrathecal Sufentanil or Epidural Bupivicaine for Labor Analgesia: Incidence and Clinical Significance

Nielsen, Peter E. MD; Erickson, J. Randall MD; Abouleish, Ezzat I. MD; Perriatt, Sheryl RN; Sheppard, Celeste MD

Obstetric Anesthesia

The objective of this study was to compare the incidence of intrapartum fetal heart tracing (FHT) abnormalities and the obstetric outcome after intrathecal sufentanil (ITS) versus epidural bupivacaine (EB).During the period from April to September 1994, 129 patients who met inclusion criteria were prospectively identified during labor at a single university-affiliated hospital. Inclusion criteria included: singleton, gestational age >or=to36 wk, and cephalic presentation. In the ITS group, epidural anesthesia was not administered before 60 min after ITS. Sixty-five consecutive ITS patients were compared to 64 consecutive EB patients. Each FHT was reviewed independently by two obstetricians blinded to the type of analgesia. The FHT characteristics evaluated included baseline rate, variability, and periodic changes. No differences in the incidence of clinically significant FHT abnormalities (recurrent late decelerations and/or bradycardia) were observed between the two groups (ITS 21.5% versus EB 23.4%). The rates of clinically significant FHT abnormalities in both groups was not different when patients with hypotension and medical complications were excluded (16.9% vs 17.1%). In addition, equal rates of hypotension (18.5% vs 17.2%) were noted between the groups. In both groups there was a significantly higher risk of cesarean section in patients whose previously normal FHT became abnormal postanalgesia when compared to patients without a new onset FHT abnormality (ITS 28.6% [4/14] versus 2.0% [1/51], P < 0.01; EB 33.3% [5/15] versus 8.2% [4/49], P < 0.05). This increased risk was associated with an increase in cesarean section for nonreassuring FHT in both groups (ITS 14.3% [2/14] versus 0% [0/51], P = 0.04; EB 13.3% [2/15] versus 0% [0/49], P = 0.05). These results support the conclusion that the incidence of clinically significant FHT abnormalities and hypotension is equivalent in patients receiving ITS when compared to EB within the first hour of administration. During this period, patients should have continuous FHT monitoring since a new onset FHT abnormality unveils and alerts the physicians to a possible compromised fetal condition and a corresponding increased risk of cesarean section.

(Anesth Analg 1996;83:742-6)

Departments of Obstetrics, Gynecology and Reproductive Sciences (Division of Maternal Fetal Medicine) (Nielsen, Erickson, Perriatt, Sheppard) and Anesthesiology, The University of Texas Health Science Center, Houston, Texas (Abouleish).

Accepted for publication June 6, 1996.

Address correspondence and reprint requests to Ezzat Abouleish, MD, Department of Anesthesiology, University of Texas Houston Health Science Center, 6431 Fannin, Suite 5.020, Houston, TX 77030.

The use of intrathecal narcotics for obstetric analgesia has become increasingly popular, especially in community hospitals where anesthesia coverage may be limited [1-4]. Sufentanil in particular is favored because of its rapid onset of action, longer duration, lack of motor blockade, allowance of ambulation, and absence of associated hypotension compared to epidural analgesia [5-7]. However, other studies have suggested that the use of intrathecal sufentanil (ITS) during labor may be associated with an increased frequency of fetal heart rate abnormalities as well as maternal hypotension [4,8,9]. Prospective data evaluating the effect of epidural analgesia on fetal heart rate characteristics have suggested that variability as well as periodic heart rate changes may be affected [10,11]. Considering the controversies regarding the influence of ITS and that of epidural bupivacaine (EB) on the fetal heart rate, this study was conducted to compare the effects of ITS versus EB on fetal heart tracing (FHT) characteristics during labor, and the obstetrical outcome.

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After approval by the Committee for the Protection of Human Subjects at the University of Texas Health Science Center and over the 5-mo interval from April to September 1994, a total of 129 patients meeting inclusion criteria and delivered at Hermann Hospital in Houston, Texas, were prospectively identified. Inclusion criteria were singleton, term (gestational age >or=to36 wk), and cephalic presentation. Informed consent was obtained from all patients prior to entry into the study. The study population was made up of 65 consecutive patients receiving ITS and 64 consecutive patients receiving EB. A chart review was performed by reviewing the notes of the anesthesiologist, obstetrician, and nurse. The demographic data shown in Table 1 were collected. Data were also recorded regarding the type of anesthesia, amount and types of drugs used, and the cervical examination prior to initiation of induction of analgesia. Intrapartum and delivery variables evaluated are included in Table 2.

All patients received an intravenous infusion of 1000 mL lactated Ringer's solution during the 30-min interval prior to the administration of the anesthetic. The type of anesthetic technique used was based on patient's request, anesthesiologist's preference, and obstetrician's choice. In the ITS group, all patients received a single intrathecal dose of sufentanil (10 micro gram in 2 mL normal saline) via a combined spinal epidural technique previously described [12]. These patients then received epidural analgesia at least 1 h after ITS, and the epidural technique was the same as performed on the EB group. Patients in the EB group had an 18-gauge Touhy needle inserted at the L2-3 or L3-4 interspace and the epidural space was reached with loss of resistance technique. The epidural catheter was then inserted. After a test dose of 2 mL of 0.25% bupivacaine, a therapeutic dose of the same anesthetic was administered through the catheter in a divided fashion to provide adequate analgesia (T8-10 sensory level). Maintenance of analgesia was achieved with a continuous infusion of 0.125% bupivacaine at 10-12 mL/h. During the study period, neither epinephrine nor opioids were added to bupivacaine for epidural analgesia.

FHTs were reviewed independently by two obstetricians blinded to the type of anesthesia used. When differences in interpretation between the obstetricians were noted, the tracings were independently reviewed by a third obstetrician, and the two opinions in agreement were used. FHTs were evaluated in 20-min intervals for 1 h prior to and for 1 h after administration of the anesthetic. Each interval was evaluated for baseline rate, long-term variability, presence of periodic heart rate changes (decelerations) and uterine activity (number of contraction per 10 min recorded by external tocodynamometer). Standard definitions were used to identify normal and abnormal FHTs [13,14]. Normal FHT baseline included a rate between 120 and 160 bpm that persisted for at least 15 min. Bradycardia was defined as a fetal heart rate <120 bpm for >2 min. Normal long-term variability was defined as 3-5 cycles/min of at least 5 bpm amplitude. Decelerations were recorded as early, late, or variable. Early decelerations were defined as uniform in shape, 20-30 bpm below the baseline rate with the nadir at the peak of the uterine contraction. Those decelerations uniform in shape, 10-40 bpm below the baseline rate, and with the nadir following the peak of the uterine contraction were considered late decelerations. Severe variable decelerations included those of >60-s duration, >60 bpm below the baseline rate, and/or a nadir <60 bpm. All other variable decelerations were classified as mild.

Bradycardia and/or repetitive late decelerations (more than three consecutive decelerations) were considered significant (pathologic) changes of the fetal heart rate, since most obstetricians would consider intervention necessary in light of these findings. Although repetitive variable decelerations may also be classified as significant, they were not considered so in this study, since this heart rate abnormality is generally the result of cord compression and would not be anesthesia related. All actions taken to correct the FHT abnormalities were noted and included maternal position change, supplemental oxygen therapy, discontinuation of oxytocin, intravenous hydration, and/or the use of other medications (e.g., ephedrine, terbutaline). All patients were placed in the left lateral decubitus position after analgesia. Maternal blood pressure was measured twice during the hour prior to analgesia and every 3 min during the 1-h postanalgesia evaluation period. Blood pressure was evaluated more frequently in patients who experienced hypotension and during its treatment. The definition of hypotension used was an absolute systolic blood pressure of <100 mm Hg or >or=to20% decrease in systolic blood pressure from baseline preanalgesia value.

Means +/- SD of data were computed. Continuous data were compared using the two-tailed Student's t-test and nominal data using chi squared analysis or Fisher's exact test where appropriate. A P value of <0.05 was considered significant. This study had a power of 0.8 to detect an 18% difference between the groups (assuming an abnormal FHT rate associated with analgesia of 18% in the EB group and 0% in the ITS group).

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Maternal age was the only variable that demonstrated a statistically significant difference between the groups Table 1. There were no observed differences in intrapartum events between the groups including cervical dilation at initiation of analgesic technique, duration of the first and second stages of labor, oxytocin use, its duration or maximum dose required Table 2. The incidence of meconium and chorioamnionitis was the same for each group. No significant differences between the groups were noted with respect to malposition, defined as cephalic presentation other than occiput anterior, or mode of delivery Table 2. Neonates in the ITS population had a significantly higher birth weight than those in the EB group (3463 +/- 479 g vs 3276 +/- 507 g; P = 0.03). However, there were no observed differences between the groups with respect to arterial or venous cord pH data or 5-min Apgar scores <7 (0% in each group).

Hypotension occurred with similar frequency after the administration of both ITS and EB (18.5% [12/65] vs 17.2% [11/64], P = NS) Table 3. However, hypotension after ITS occurred more frequently in the first 20-min interval compared to the second 20-min interval (9/12 vs 3/12; P = 0.04). Epidural-related hypotension was evenly distributed between the first and second 20-min intervals after bupivacaine injection (6/11 vs 5/11; P = NS). No patient had hypotension in the final 20-min interval evaluated. Hypotensive episodes were transient and promptly corrected by uterine displacement, infusion of intravenous fluids, and/or the use of ephedrine in 10-mg increments.

No differences in the incidence of clinically significant FHT abnormalities, increased or decreased LTV, or increased baseline heart rate (>20 bpm) were observed between the two groups Table 4. Approximately one third of the pathologic FHTs in each group were associated with hypotension. Chronic medical conditions were present in five (7.7%) ITS patients and eight (12.5%) EB patients (P = NS). Identified medical conditions complicating these pregnancies were chronic hypertension, mild and severe preeclampsia, systemic lupus erythematosus, insulin-requiring diabetes mellitus, and intrauterine growth retardation. In reviewing the rates of pathologic FHTs, there was no difference between the groups after exclusion of patients with hypotension or a medical condition (16.9% vs 17.1%). Sixty percent (three of five) of the ITS patients with medical conditions had a significant FHT abnormality, and all of these tracings were associated with hypotension. Fifty percent (four of eight) of the EB patients with a chronic medical condition had a significant FHT abnormality and two of them were associated with hypotension.

None of the patients had episodes of recurrent late decelerations in the 40- to 60-min interval after administration of either ITS or EB. In addition, no significant difference in the incidence of repetitive late decelerations was found between the 0- to 20-min interval and the 20- to 40-min interval in either group. No episodes of uterine hyperstimulation (>six contractions/10 min) were noted.

In either regional analgesia technique, a new onset of a pathologic FHT was associated with a significantly greater risk of cesarean section compared to the subgroup that did not develop this change (ITS 28.6% [4/14] vs 2.0% [1/51], P < 0.01; EB 33.3% [5/15] vs 8.2% [4/49], P < 0.05, respectively) Table 5. This increased risk was associated with an increase in cesarean section rate for nonreassuring FHT in both groups (ITS 14.3% [2/14] vs 0% [0/51], P = 0.04; EB 13.3% [2/15] vs 0% [0/49], P = 0.05). Two of the four patients who required cesarean section for nonreassuring FHT (one from each group) delivered within the 1-h interval after analgesia. The other two patients who had cesarean section for nonreassuring FHR had surgery performed remote from the study period, and both of them had maternal medical complications (severe preeclampsia and chronic hypertension). In cases where maternal hypotension was noted, surgery was indicated despite correction of hypotension.

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The use of intrathecal opioids for labor analgesia is attractive to obstetricians and anesthesiologists searching for a simple technique to provide adequate maternal pain relief with few adverse maternal or fetal effects. Interaction of these drugs at opioid receptors in the spinal cord should theoretically produce pain relief without proprioceptive or motor blockade, hypotension, or subsequent changes in the FHTs [6,7]. In contrast, epidural analgesia has been associated with varying degrees of motor block and maternal hypotension ranging from 7% to 17% [10]. FHT abnormalities ranging from 7% to 25% have also been seen with epidural analgesia and have been reported to be related to either maternal hypotension or uterine hyperstimulation [11,15,16].

In a recent study by Cohen et al. [8]. ITS (10 micro gram) was evaluated to determine effects on several variables. Patients with significant medical problems (preeclampsia, diabetes, chronic hypertension), prematurity, multiple gestations, or "fetal complications" were excluded. Hypotension occurred in 14% of patients (all within 10 minutes of ITS administration). When FHTs were evaluated, 15% of patients were noted to have significant FHT changes (variables, late decelerations, or bradycardia). However, no FHT change was considered clinically significant and none required intervention for fetal compromise [8]. The absence of maternal medical problems possibly allowed the rapid recovery of the fetus. No comparison group was provided, therefore controls with other types of analgesia were absent.

Our study is the first direct comparison of the effect of ITS and EB on the FHT. Randomization of the two groups would have been preferable; however, the two groups were comparable Table 1 and Table 2. Furthermore, the obstetricians who reviewed the fetal heart rate tracings were blinded to the type of analgesia technique used. Moreover, we attempted to conduct the study in such a way as not to interfere with routine patient care. Therefore, the method of analgesia was based on patient's desire, anesthesiologist's preference, and obstetrician's agreement. The purpose of our study was to compare two analgesic groups; one was a well established technique (the EB group) which could be considered the Control group, compared with a relatively new technique (the ITS group) which can be considered the Study group. To have a third group not requiring pain relief was considered not comparable as the course of labor and the obstetric outcome could be different [17].

No significant differences were found between these groups with respect to their effect on long-term variability, baseline rate, or the incidence of repetitive late decelerations or bradycardia during the one-hour interval after analgesia. Despite the ease and promptness in the correction of hypotension, its occurrence was associated with a higher incidence of new onset FHT abnormalities, especially in patients with medical complications. These changes in the FHT may be due to a precarious uteroplacental blood flow, especially in patients with chronic hypertension and preeclampsia. When patients with hypotension or a medical condition of pregnancy were excluded, the rates of significant FHT abnormalities remained equivalent (about 17%). The significant FHT abnormalities noted might have been related to effects on uteroplacental blood flow, a redistribution of cardiac output, rapid fetal descent caused by relaxation of the perineal muscles, increased baseline uterine tone, or a direct effect on the fetus via an unknown mechanism. These observations make it clear that even patients without clinically significant hypotension or a medical condition complicating pregnancy should have continuous fetal monitoring during the 40-minute or preferably the one-hour interval after administration of either analgesic. This is important, since many institutions allow laboring women to ambulate after the intrathecal injection of sufentanil. Under these circumstances discontinuation of FHT monitoring is not recommended, and the use of a remote electronic monitoring system is advised.

It should be noted that despite these significant FHTs, no difference in neonatal outcome was observed (using either five-minute Apgar scores or umbilical cord pH data). However, immediate intervention was required in some patients and ranged from changes in maternal position, supplemental oxygen, intravenous hydration, ephedrine use, or operative delivery.

As previously mentioned, two patients (one in each group) required cesarean section for a diagnosis of fetal distress within the one-hour interval after analgesia. Since a sham control group was not included in the study design, conclusions regarding a cause and effect relationship of using either analgesic technique on the incidence of cesarean section for fetal distress cannot be made with certainty. However, in both groups a new onset FHT abnormality unveils and alerts the physician to a possible compromised fetal condition, and increases the risk of cesarean section for fetal compromise throughout the remainder of the patient's labor course compared to those patients in whom no new onset abnormal FHT was detected. Therefore, care should be taken to monitor the FHT carefully after the induction of either type of analgesia, especially in patients who have a concurrent medical problem or who develop hypotension.

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© 1996 International Anesthesia Research Society