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OBSTETRIC ANESTHESIOLOGY

A Randomized Trial of Dural Puncture Epidural Technique Compared with the Standard Epidural Technique for Labor Analgesia

From the Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.

Address correspondence and reprint requests to Lawrence C. Tsen, MD, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, 75, Francis St., CWN-L1 Harvard Medical School, Boston, MA 02115. Address e-mail to ltsen{at}zeus.bwh.harvard.edu.

Abstract

BACKGROUND: We designed this prospective, double-blind, randomized study to examine whether a dural puncture without intrathecal drug administration immediately before epidural drug administration would improve labor analgesia when compared to a traditional epidural technique without prior dural puncture.

METHODS: Eighty nulliparous parturients with cervical dilation less than 5 cm were randomly assigned to receive a standardized epidural technique, with or without a single dural puncture with a 25-gauge (G) Whitacre spinal needle. After successful placement of the needle(s) and the epidural catheter, 12 mL of bupivacaine 2.5 mg/mL was administered through the epidural catheter and a patient-controlled epidural infusion of bupivacaine 1.25 mg/mL + fentanyl 2 µg/mL was initiated. The presence of sacral analgesia (S1) and pain scores were compared between groups.

RESULTS: In demographically similar groups, parturients with prior dural puncture had more frequent blockade of the S1 dermatome (absolute risk difference [95% confidence interval] 22% [6–39]), more frequent visual analog scale scores <10/100 at 20 min (absolute risk difference 20% [1–38]), and reduced one-sided analgesia (absolute risk difference [95% CI] 17% [2–330]). The highest median sensory level (T10) was no different between groups.

CONCLUSIONS: Dural puncture with a 25-G spinal needle immediately before the initiation of epidural analgesia improves the sacral spread, onset, and bilateral pain relief produced by analgesic concentrations of bupivacaine with fentanyl in laboring nulliparous patients.

The combined spinal epidural technique (CSE) has become an increasingly popular method for delivering labor pain relief because of its rapid onset of profound analgesia, minimal motor blockade, augmentation of labor progress, and high patient satisfaction.1–3 In addition to providing verification of epidural space proximity through the definitive return of cerebrospinal fluid (CSF) via the spinal needle, the CSE technique has also been associated with a reduction in epidural catheter failures.4,5 In the parturient in active labor, where the intensity of pain can be severe and the delivery outcome uncertain, the ability to provide rapid and continuous analgesia, as well as the ability to rapidly convert to epidural anesthesia, represent a distinct advantage of the technique. These advantages, however, must be balanced against the potential for hemodynamic instability, fetal bradycardia, side effects and complications associated with the dural puncture and the intrathecal administration of local anesthetics and opioids, and the inability to quickly confirm the functional status of the epidural catheter.1,6

A novel method to potentially minimize the risks of CSE analgesia, with the exception of those associated with the actual dural puncture per se, is to perform a dural puncture without the injection of intrathecal drugs; local anesthetics and opioids are administered only into the epidural space. This "dural puncture epidural" (DPE) technique potentially allows verification of epidural space proximity, improved hemodynamic stability, assessment of epidural catheter function, and enhanced labor analgesia (more rapid onset, reduced unblocked segments) compared with the standard epidural technique.7 Using the DPE method in orthopedic patients undergoing knee surgery, Suzuki et al. demonstrated more rapid onset and improved sacral distribution of surgical anesthesia after dural puncture with a 26-gauge (G) Whitacre spinal needle and an initial epidural dose of 18 mL of mepivacaine 20 mg/mL.7 In contrast, in laboring parturients with a DPE technique using a 27-G Whitacre spinal needle, Thomas et al. did not find any benefit compared with traditional epidural analgesia.8 Acknowledging that the flux between the epidural and dural spaces is dependent on the size of the needle,9 we hypothesized that the DPE technique with a larger 25-G Whitacre spinal needle would allow increased subarachnoid transfer of analgesic doses of epidurally administered drugs, and ultimately improve the onset, sacral spread, and overall quality of labor analgesia compared to a conventional epidural analgesia technique.

METHODS

After IRB approval and informed consent, 80 nulliparous parturients with singleton, vertex presentation fetuses at 38–42 wk gestation in active labor with cervical dilation <5 cm, were randomized via a computer-generated random number sequence to receive a standardized epidural technique with (DPE) or without (E) a dural puncture. Patients were recruited from August 2006 until August 2007. Group assignments were concealed in opaque numbered envelopes and were opened by the anesthesiologist performing the block immediately before initiation of analgesia. Both the parturient and study personnel assessing outcome were blinded to group assignment. Exclusion criteria included clinically significant diseases of pregnancy (i.e., preeclampsia, gestational diabetes), contraindications to neuraxial analgesia, conditions associated with an increased risk of a cesarean delivery (i.e., history of uterine anomaly or surgery, morbid obesity), and known fetal anomalies.

All patients were premedicated orally with sodium citrate, an IV catheter was placed, and standard monitors, including automated noninvasive arterial blood pressure, pulse oximetry, and fetal tocodynometry, were applied. One liter of lactated Ringer's solution was infused IV over 15 min immediately before the neuraxial procedure. The procedure was performed in the seated position. The epidural space was identified with a 17-G, 8.5 cm Weiss epidural needle using a loss of resistance to air (<2 mL) technique and a 25-G, 12 cm Whitacre spinal needle was placed into the shaft of the epidural needle (when fully inserted, the spinal needle protruded 15 mm beyond the epidural needle tip). In patients randomized to receive a dural puncture (DPE), a single puncture with confirmation of free flow CSF was performed. In the standard epidural group (E) the spinal needle was removed without performing a dural puncture. A 20-G multi-port polyamide catheter (Portex, Kent, UK) was placed 5 cm into the epidural space. After a negative aspiration for blood and CSF, 12 mL of bupivacaine 2.5 mg/mL was administered over 5 min through the catheter, followed by the immediate initiation of patient-controlled epidural analgesia: bupivacaine 1.25 mg/mL with fentanyl 0.2 µg/mL, background infusion at 6 mL/h, demand dose of 6 mL, lockout interval of 15 min, and no hourly limits. IV or intrathecal epidural needle or catheter insertion and the presence of CSF with the dural puncture were recorded on the anesthetic record by the unblinded operator performing the procedure; these elements were added to the study data sheet after the delivery of the infant.

Analgesia was evaluated by a blinded observer assessing visual analog scale (VAS) pain scores, sensory level, and motor blockade, immediately after the complete administration of the initial 12 mL dose of bupivacaine and 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, and 30 min later. Assessments continued at regular 90-minute intervals; with any anesthetic interventions, including requests to evaluate analgesia or side effects (hypotension, pruritus, nausea, and fetal bradycardia); and immediately after delivery. Hypotension was defined as a 20% reduction in the systolic blood pressure from the admission blood pressure in the absence of uterine contraction. Fetal bradycardia was defined as a heart rate of <110 bpm for more than or equal to 10 min. VAS scores were performed with an unmarked 100 mm sliding scale indicator (Astra Laboratories, Worchester, MA). Sensory levels were assessed using a nontraumatic pinprick stimulus starting caudad at the S2 dermatome and moving cephalad. In the lower extremity, dermatomal levels were assessed by stimulating the inguinal crease (L1), anterior thigh (L2), medial knee (L3), medial malleolus (L4), dorsum web between great and second toe (L5), the lateral heel (S1), and the medial popliteal fossa (S2). On the torso, dermatomal levels were assessed in the midclavicular line. Motor strength was assessed with a modified Bromage score (0 = full flexion of knees and ankles, 1 = partial flexion of knees, full flexion of ankles, 2 = inability to flex knees, partial flexion of ankles; 3 = inability to flex knees and ankles). Pruritus and nausea were evaluated on a scale ranging from 0 = none, 1 = mild, 2 = moderate, and 3 = severe.

In the event of inadequate analgesia, defined as patient request for a supplemental analgesia beyond boluses self-administered by patient-controlled epidural analgesia, an assessment was made by an anesthesiologist blinded to group assignment. Supplemental analgesia was provided by 6 mL of bupivacaine 2.5 mg/mL administered in 3 mL increments over a period of 5 min. In the event of inadequate analgesia and a unilateral block (defined as a sensory blockade with a difference of more than three dermatomal levels between the left and right side of the patient anytime during labor after the initial dose), the patient was placed on the less blocked side and a supplemental epidural dose was administered. If the unilateral block persisted, the catheter was withdrawn 1 cm and an additional supplemental dose was given. In the event of inadequate analgesia and the presence of no sensory level or a bilateral, but low, sensory level, a supplemental epidural dose was administered. If subsequent improvement of the analgesia was not observed, the epidural catheter was replaced.

IV ephedrine 10 mg was used to treat hypotension. Subsequent doses were titrated to effect to maintain arterial blood pressure within 20% of the resting admission systolic blood pressure.

Maternal demographic and fetal characteristics (gender, birthweight, Apgar scores) were recorded by the blinded observer, as was the presence of a postdural puncture headache (PDPH) at a postprocedure visit between 36 and 48 h after delivery. Patients were instructed to contact the anesthesia service after discharge if they experienced symptoms suggestive of a PDPH, or had any other concerns or questions about their care.

The primary outcomes in this trial were the presence of sacral dermatome (S1) blockade (either unilateral or bilateral) and a VAS analgesia score of <10 within 20 min of initiation of epidural analgesia. Based on pilot data with a baseline incidence of S1 blockade of 25% for epidural labor analgesia using the study drug solution, and the outcomes reported by Suzuki et al.,7 the expected sample size requirement to detect a doubling of sacral block to 50% in the DPE group, at 80% power and = 0.05 was 29 per group. However, to account for the potential reduction in effect size with the use of labor analgesic concentrations of local anesthetics in the present study (compared with surgical anesthetic concentrations in the Suzuki et al. study), the sample size was arbitrarily increased to 40 per group; this is also in keeping with the total number of subjects evaluated in a CSE versus epidural analysis by Roux et al.10 VAS scores (at 20 min) were analyzed by ANOVA for repeated measures. Maternal and fetal demographics were tested by ANOVA (continuous data) or ² (categorical data) as appropriate. Apgar scores and times to achieve various block and VAS end-points were tested by Wilcoxon's ranked sum test. Adverse events were tabulated according to treatment group, severity, and resultant treatment and compared using Fisher's exact test. Statistical significance was assumed when P < 0.05.

RESULTS

Eighty nulliparous parturients were enrolled (group DPE: n = 40) (group E, n = 40). One patient in the DPE group was excluded from analysis due to failure of CSF return from the spinal needle. Demographic characteristics and initial VAS pain scores were similar in both groups (Table 1). The likelihood of achieving either a unilateral or bilateral S1 sensory block at 20 min after block initiation was not different between the DPE and E groups (Table 2). The likelihood of achieving a unilateral or bilateral S1 sensory block at any time during the study, however, was significantly higher in the DPE group (absolute risk difference [95% confidence interval] 22% [6–39]) (Table 2). In addition, more women had a VAS score <10/100 at 20 min in the DPE group (absolute risk difference 20% [1–38]). This finding corresponded with a reduced incidence of unilateral block at any time during labor (absolute risk difference [95% CI] 17% [2–33]). The median highest dermatome blocked was T10 in both groups, and the time to achieving this level did not differ between groups (mean [95% CI] difference DPE vs E, –13 [–32–6] min). The incidence of S2 block at any time during labor did not differ between groups. Of those who ultimately achieved a sacral sensory level, the incidence of bilateral involvement and the time to obtain this level did not differ between the groups (Table 2). There were no differences in the degree of motor blockade; all patients experienced a Bromage score of 0 throughout the study, with the exception of a single patient in the DPE group who had a Bromage score of 1–2 for the first hour of analgesia, which resolved to a Bromage score of 0. In those patients in the DPE group who received additional analgesia or anesthesia for an instrumented delivery (range 189–740 min after initiation of analgesia), no episodes of high or total spinal blockade occurred.

There were no episodes of inadvertent epidural needle dural puncture or IV catheter placement in either group. The overall catheter manipulation and replacement rates and the need for additional boluses in the first, second, and third hour after the initial technique placement did not differ (Table 2). The incidence of hypotension, pruritus, nausea, and fetal bradycardia was low and did not differ between the groups. In the E group, two patients experienced mild nausea not requiring treatment. In the DPE group, 1 patient experienced mild pruritus and 1 patient experienced hypotension that resolved with a single 10 mg dose of ephedrine. There were no episodes of fetal bradycardia after the initiation of analgesia in either group at any of the time points evaluated. Instrumental delivery for nonreassuring fetal status occurred in 4 and 2 DPE and E group patients, respectively, but no earlier than 228 min after the initiation of labor analgesia. No differences in the incidence of cesarean delivery were observed between the groups; however, there was a lower incidence of spontaneous vaginal delivery in the DPE group versus the E group (P = 0.04) (Table 3). There were no PDPHs in either group.

DISCUSSION

This investigation suggests that dural puncture with a 25-G pencil-point spinal needle immediately before initiation of epidural analgesia improves the sacral spread, onset, and bilateral pain relief produced by analgesic concentrations of bupivacaine in laboring nulliparous patients.

The translocation of epidural medications through a dural puncture into the subarachnoid space has been postulated as a possible mechanism by which the CSE technique improves analgesia or anesthesia.11 Indeed, Bernards et al.12 observed, in an in vitro dural puncture study, that subarachnoid flux of local anesthetics is dependent on the size (18–24 G) and distance of the dural puncture from the site of epidural drug administration; moreover, the investigators noted that subarachnoid flux can be proportional to the intact meningeal surface area exposed to the drug. Clinically, three studies, including the current study, have investigated the sensory and motor blockade produced in the setting of dural puncture without intrathecal drug injection followed immediately by epidural drug administration (DPE technique). The two prior studies used anesthetic concentrations of local anesthetics as the initial epidural drug bolus, but different sized needles. Suzuki et al.7 observed that a dural puncture with a 26-G Whitacre spinal needle resulted in faster onset and improved sacral spread after 18 mL of 2% mepivacaine for knee arthroscopy. No alterations in cephalad level of anesthesia were observed. Thomas et al.,8 in a group of parturients of mixed parity, found no significant differences in the quality of labor epidural analgesia (inadequate, unilateral, sacral sparing, or number of top-up doses required) or catheter manipulation or replacement rates when dural puncture with a 27-G Whitacre needle preceded an epidural dose of 10 mL of lidocaine 2% and an infusion of bupivacaine 0.11% + fentanyl 2 µg/mL. The cephalad level of labor analgesia was not different and the caudad level was not recorded. The current study used a 25-G needle. An in vitro study of cadaver dura found that lidocaine flux through dura punctured with a 27-G Whitacre spinal needle was not significantly greater than through intact dural tissue, but dural puncture with a 24-G Sprotte spinal needle was associated with increased flux.12 Although the results of these studies suggest that smaller dural punctures limit the in vivo transfer of local anesthetic from epidural to intrathecal spaces, and may explain the conflicting nature of the results of the clinical trials, firm conclusions cannot be made from the available evidence, because of the different doses of local anesthetics used for initiation of epidural blockade among the three studies and the absence of early analgesia data in the Thomas et al. study.

The higher concentration, moderate volume (12 mL of bupivacaine 2.5 mg/mL) dose used for the initiation of epidural labor analgesia in the current investigation was selected in lieu of the more dilute, higher volume doses often used in current clinical practice, including our own, for several reasons. First, the concentration and volume combination has more than a decade of safe and effective clinical use for initiation and supplementation of epidural labor analgesia. Second, the Suzuki et al. study appears to indicate that even with anesthetic concentrations of epidural mepivacaine, only a small amount traversed through the 26-G dural hole; greater local anesthetic passage would have been expected to create an even more rapid sacral, and a potentially higher cephalad, sensory blockade. The in vitro characteristics of local anesthetic flux through a dural hole from epidural to intrathecal spaces has not been well described. Epidural pressure increases during epidural drug administration; however, this is a time-limited phenomenon, and flux secondary to the epidural-intrathecal space pressure differential should occur only until pressure equalization.13 The kinetics of local anesthetic passage through a dural hole, as well as the necessary hole proximity and drug dose, concentration and volume, required to make a meaningful clinical difference requires further investigation.

In the present investigation, we observed an improvement in the onset of labor analgesia, a higher incidence of an S1 sensory block (the majority bilateral), and a greater likelihood of an overall bilateral sensory block after initiation of epidural analgesia after a dural puncture with a 25-G spinal needle followed by the initiation of epidural analgesia with analgesic concentrations of bupivacaine and maintenance with a continuous low-concentration bupivacaine-fentanyl epidural infusion typical of modern labor epidural analgesia. These qualities, particularly the relatively rapid (within an average of 25 min) onset of sacral analgesia, with no changes in the cephalad level, are potentially beneficial effects of the DPE technique, particularly in the second stage of labor. A DPE compared to CSE technique may minimize the intrathecal exposure to intrathecal opioids, which are frequently used as sole or adjuvant drugs in the initiation of CSE analgesia and may be associated with fetal heart rate abnormalities in a dose-related manner.14,15

Although improved bilateral spread of analgesia was observed in the DPE group, the effect of the dural flux appears limited to the analgesia resulting from the initial bolus dose. Continuing labor analgesia requirements (number of boluses per hour for the first 3 h) and the catheter manipulation or replacement rates did not differ between groups, despite a significant difference in the bilateral nature of the sensory analgesia produced. Flux through a 25 G dural puncture may therefore be limited to a certain amount of time after the puncture or dependent on the volume or epidural pressure generated with epidural medication boluses.16 The low incidence of PDPH after a 25 G Whitacre needle dural puncture would suggest that CSF flux is a time-limited phenomenon.9 It is also possible that any additional contribution from flux through the dural hole during continuous epidural infusion is obscured by the analgesia produced via the epidural infusion. As the resting CSF pressure is typically higher than epidural space pressure, it is possible that a net efflux rather than influx limited further drug transfer from the epidural into the intrathecal space.

The incidence of potential complications associated with a dural puncture, including PDPH, hemodynamic alterations, nausea, pruritus, and high sensory or greater motor blockade, were no different between the groups.

Although the rate of cesarean delivery was not altered by group allocation, we observed more instrumental vaginal deliveries in the DPE group. Because our study was not specifically designed or powered to evaluate this outcome, it can only be speculated that this may have related to differences in obstetric practice17 or longer labor in the DPE group, as suggested by a trend towards longer epidural duration. The total dose of bupivacaine received in either group was not collected in our study; however, it is possible that greater neuraxial exposure to local anesthetics, either through total dose or the combination of intrathecal and epidural exposure, could play a role in such deliveries. A higher incidence of instrumental deliveries was observed in the "COMET" trial in patients managed with "traditional" epidural boluses of bupivacaine 2.5 mg/mL versus CSE or low dose bupivacaine-fentanyl epidural analgesia.18 The association of the DPE technique with instrumental delivery, as well as benefits of the technique compared to a conventional CSE technique, should be confirmed in further studies.

In summary, our findings suggest that a 25-G Whitacre dural puncture without intrathecal drug administration followed by the epidural administration of local anesthetic-opioid solution (DPE technique) may benefit the nulliparous parturient by improving the sacral spread, onset, and bilateral nature of epidural labor analgesia compared to standard epidural analgesia. Whether the technique adversely affects the instrumental vaginal delivery rate, or whether there is value to this technique compared with a conventional CSE technique should be confirmed by further investigation.

Footnotes

Accepted for publication June 9, 2008.

Supported by the Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital.

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