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OBSTETRIC ANESTHESIA

The Effects of Needle Bevel Orientation During Epidural Catheter Insertion in Laboring Parturients

Michael G. Richardson, MD^*, and Richard N. Wissler, MD, PhD^*,

Departments of *Anesthesiology and Obstetrics & Gynecology, University of Rochester School of Medicine and Dentistry, Strong Memorial Hospital, Rochester, New York

Address correspondence to Michael G. Richardson, MD, Department of Anesthesiology, University of Rochester School of Medicine and Dentistry, Box 604, Strong Memorial Hospital, 601 Elmwood Ave., Rochester, NY 14642. Address e-mail to MRichardson{at}Anes .Rochester.edu.

	Abstract

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Lateral needle bevel orientation during identification of the epidural space has been recommended to reduce the risk of postdural puncture headache (PDPH). Rotation to cephalad or caudad orientation before catheter insertion is assumed necessary for analgesic success. We prospectively compared the effects of catheter insertion through lateral- and cephalad-oriented Tuohy needle bevels in laboring parturients. Anesthesiology residents were randomized to identify the epidural space with bevels oriented cephalad or lateral. Catheters were inserted without needle rotation. Outcomes compared included ease of insertion, analgesic effectiveness, and complications. We evaluated 534 catheter insertions in 500 parturients. Initial catheter insertion produced satisfactory analgesia in 80.2% of the lateral group versus 91.1% of the cephalad group (P < 0.001). Resistance preventing catheter insertion accounted for the difference. There were no differences in IV cannulation (5.8% vs 5.1%), dural puncture (3.8% vs 2.0%), PDPH (0.4% vs 0.7%), or asymmetric block (31% vs 27%). There was a slightly higher rate of paresthesias in the lateral group (31% vs 23%; P = 0.048). In 78% of parturients experiencing both paresthesias and asymmetric block, the side of the paresthesia and greater extent of block were the same. Analgesic effectiveness, as measured by using a visual analog scale, was not different between the groups.

Implications: Two methods of epidural catheter insertion were compared in laboring parturients. Catheter insertion with the needle orifice oriented cephalad was associated with the greatest initial success and the fewest complications.

	Introduction

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Postdural puncture headache (PDPH) is a complication of epidural anesthesia. It may be mild and self-limited or severely debilitating, requiring time-consuming and invasive therapy. Techniques that reduce the incidence of PDPH without compromising analgesic efficacy are desirable. In laboring parturients, inadvertent dural puncture with an epidural needle bevel orifice oriented laterally (parallel to the longitudinal axis of the spine) may result in reduced incidence of PDPH compared with cephalad (perpendicular) orientation (1). Some authors recommend that the epidural needle be routinely inserted with the bevel oriented laterally, followed by 90° rotation to cephalad after obtaining loss of resistance and before catheter insertion (1–4). Such recommendations have prompted much debate regarding the safety of needle rotation within the epidural space, with concern about potential "coring" of the dura mater during needle rotation (2,5–8). Although 90° rotation of a laterally oriented bevel to cephalad or caudad has been assumed to be necessary before epidural catheter insertion (1–3,9–11), there are no supporting data. Radiographic studies of lumbar epidural catheters inserted through needle bevels oriented cephalad and caudad suggest that the path and ultimate location of the catheter tip in the epidural space are unpredictable (9,11–14). We postulated that catheters inserted through lateral-oriented needle bevels would result in equally satisfactory placement and analgesic block as those inserted through cephalad-oriented bevels. We prospectively compared the analgesic success, side effects, and complications associated with catheter insertion through lateral- and cephalad-oriented Tuohy needle bevels in laboring parturients.

	Methods

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This prospective study received human subjects review board approval. Informed consent for epidural analgesia was obtained. Verbal consent was obtained from all patients for data collection. Anesthesiology residents assigned to the obstetric anesthesia service were randomly assigned to identify the epidural space with the needle bevel oriented either cephalad or lateral for the first half of the month-long rotation, and vice versa during the second half. The epidural space was identified using the midline approach with an 18-gauge Tuohy needle and loss of resistance to either saline or air. After loss of resistance, a 20-gauge open-ended, nonstyletted, single-orifice polyamide catheter (B. Braun Medical, Inc., Bethlehem, PA) was inserted without needle rotation. Inadvertent dural punctures and IV catheters were managed at the discretion of the anesthetist. After ruling out IV and intrathecal catheter position using 3 mL of lidocaine 1.5% with epinephrine 1:200,000, the therapeutic dose (fentanyl 50–100 µg in bupivacaine 0.25%) was administered. No further anesthetic was administered for 20 min. Details of catheter insertion and anesthetic management were recorded, including ease of catheter insertion, presence and location of paresthesias, bilateral upper and lower extent of sensory block (to pinprick) at 20 min, need for further anesthetic administration because of inadequate analgesia at 20 min, need for catheter replacement because of failed block, and occurrence of IV cannulation or dural puncture. Parturients rated labor pain before catheter insertion and 20 min after administration of the therapeutic dose, using a nongraduated 100-mm visual analog scale (VAS). The ends of the VAS were labeled "no pain" and "worst pain imaginable." Parturients placed a single line on the VAS to describe the severity of their contraction pain. Asymmetric sensory block was defined as a two or more segment greater extent of block on either side. All parturients were evaluated 24–48 h after delivery for PDPH and postpartum neurologic complications. The outcomes of catheter insertion compared were successful insertion and analgesia, successful insertion but replaced because of IV cannulation or inadequate analgesia, and insertion impossible. The outcome "successful catheter insertion and analgesia" included parturients who obtained satisfactory analgesia after the initial dose, partial analgesia made complete after a single additional epidural dose of bupivacaine at 20 min, and initial IV cannulation followed by satisfactory analgesia after partial withdrawal and testing of the catheter. Demographic data recorded included age, weight, height, parity, and gravidity.

Outcomes were compared using 2 analysis with or without Yates correction for continuity, as appropriate. Outcomes compared between groups included major outcomes of catheter insertion, incidence of dural puncture, paresthesias, and asymmetric block. 2 was used to analyze paresthesias and asymmetric block, side of lateral bevel orientation and side of paresthesia, and side of paresthesia and side of greater extent of asymmetric block. Pain VAS scores were compared between the lateral and cephalad groups by performing inference hypothesis testing from 95% confidence intervals for the means. Pain VAS scores were also analyzed separately for parturients who did and did not require further analgesia at 20 min. Demographic characteristics were compared using Student's t-test or the Mann-Whitney rank sum test, as appropriate. Statistical significance was determined by P < 0.05.

	Results

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We evaluated 534 attempted catheter insertions in 500 parturients: 240 insertions in the lateral group (L) and 294 in the cephalad group (C). A single catheter was placed in 467 patients, two catheters were placed in 32, and three catheters were placed in 1. There were no differences in baseline demographic variables (Table 1). The use of air as the fluid for loss of resistance during epidural needle placement was similar between groups (68% L, 59% C). There were 15 dural punctures (9 L, 6 C) in 534 attempts (2.8%), and the incidence was not different between groups (3.8% L vs 2.0% C; P = 0.35). Dural puncture was recognized by cerebrospinal fluid flow through the needle in all but one case, in which an intrathecal catheter was detected only after the administration of a test dose. Three parturients (one L, two C) experienced PDPH (incidence 0.6%). The two parturients in the cephalad group required a single autologous epidural blood patch each for PDPH. Deviations from the protocol with regard to epidural medication administration occurred in 44 parturients. These data and those from the parturients experiencing dural puncture (n = 15) were eliminated from further analysis. Outcomes of the remaining 475 catheter insertions in 445 parturients are presented in Table 2. Mean volumes of bupivacaine 0.25% used for initiation of analgesia were 7.4 ± 2.1 mL in the L group and 7.5 ± 1.8 mL in the C group (P = 0.85). Mean fentanyl doses used for induction were 64 ± 25 µg in L versus 71 ± 25 µg in C (P = 0.024). Initial catheter insertion provided satisfactory analgesia in 80.2% of the L group compared with 91.1% in the C group (P < 0.001). These included 48 parturients who had partial analgesia requiring further epidural administration of bupivacaine at 20 min (18 L versus 30 C; P = 0.29). Each of these had adequate analgesia thereafter. Catheter insertion beyond the needle orifice after obtaining loss of resistance was more often impossible in the lateral group (12.4% L versus 1.9% C; P < 0.001), accounting for the difference in outcomes between the groups. However, subsequent successful catheter insertion and adequate analgesia was achieved in each of these patients by needle withdrawal and reestablishment of loss of resistance (Table 3). Epidural catheters were replaced in 33 of the patients: 24 (12 L versus 12 C; P = 0.9) because of IV cannulation, and 10 (4 L versus 6 C) because of no detectable block or inadequate sensory analgesia. Of the 29 parturients experiencing IV cannulation (14 L versus 15 C, P = 0.86), the catheters were withdrawn partially, tested, and provided satisfactory epidural analgesia in 5.

Pain VAS scores (mean [95% confidence interval]) at 20 min (15 mm [12–17] in the L group, 13 mm [11–16] in the C group) were significantly lower than baseline scores (80 mm [78–82] in the L group, 81 mm [78–84] in the C group) for both groups, and there were no significant differences between groups. When those who required further analgesia at 20 min (n = 48) were analyzed separately, pain VAS scores at 20 min were 39 mm (29–49) in the L group and 42 mm (33–50) in the C group. At 20 min, pain scores in those who did not require further analgesia (n = 398) were significantly lower (9 mm [7–10] in the L group, 9 mm [7–11] in the C group). There were still no differences in pain VAS scores between the groups.

Eight parturients had transient postpartum neurologic sensory symptoms (three L versus five C; P = 0.95). Seven women had paresthesias or numbness, and three experienced motor weakness. All symptoms resolved by the second postpartum day. Five deficits occurred in parturients who did not experience paresthesias during catheter insertion, whereas paresthesias occurred on the same side as the deficit in three. In seven parturients, catheter insertion was easy, whereas in one, right lateral insertion was impossible, the needle was redirected to left lateral, and insertion was easy.

	Discussion

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The major difference between groups was a sevenfold greater incidence of resistance preventing catheter insertion in the L group (12.4% vs 1.9%), which accounted for the reduced success of initial catheter placement compared with the C group. Other investigators have reported incidences of catheter insertion difficulty ranging from 1% to 14% (2,3,10,15). All parturients in whom catheter insertion was initially impossible (33 of 534) had successful insertion and effective analgesia after immediate needle withdrawal and reidentification of the epidural space. Deflection of the Tuohy needle away from midline during advancement through subcutaneous tissue and interspinous ligament may account for the increased difficulty in passing the catheter through the lateral-oriented bevel. Several investigators have demonstrated significant deviation of spinal and epidural needles during advancement through styrofoam models (4,16) and animal tissue (16–18). As a Tuohy needle is advanced, there is deviation toward the side of the needle tip orifice. The ligamentum flavum (LF) of the lumbar spine lies most superficially in the midline, with sharp, deep angulation away laterally on both sides of the midline (19,20). Using the midline approach, if the laterally oriented Tuohy needle punctures the LF lateral to midline and at an angle, the orifice may be obstructed by the lateral wall of the epidural space or by a flap of LF, thereby preventing catheter passage. Alternatively, lateral needle deviation may be so extreme that loss of resistance occurs in the most lateral aspect of the epidural space (16), lateral to the thecal sac where the anteroposterior dimension of the epidural space is very small.

Orientation of the epidural needle orifice in a cephalad or caudad direction before catheter insertion has been assumed necessary to provide effective analgesia (1–3,9–11). We did observe increased difficulty threading the catheter in the lateral group compared with the cephalad group. However, catheter insertion through the lateral-oriented Tuohy bevel was easily achieved and resulted in satisfactory analgesia with the initial attempt in most parturients (80.2%). Pain VAS scores provided objective evidence of comparable analgesic efficacy between the groups, although the analgesia assessment method did not account for increased time spent dealing with insertion difficulties in the lateral group. Our definition of asymmetry was highly sensitive to small differences in extent of block (two or more segment difference). Despite this, there was no difference in the incidence of asymmetric block between the groups. Several investigators have demonstrated radiographically that the path and ultimate position of the epidural catheter tip within the lumbar epidural space is unpredictable regardless of cephalad or caudad bevel orientation (9,11–14). Although we did not perform radiologic evaluations, our results suggest that the same may be true with the lateral technique. We observed no differences in incidences of inadequate or failed blocks, dural puncture, PDPH, or IV cannulation between the groups. IV cannulation (5.4%) occurred with an incidence similar to that reported by others with (3,7,21) and without (10,15,22,23) rotation of the needle within the epidural space. The incidence of inadequate or failed block requiring catheter replacement (2.1%) was comparable to the experience of other authors (2,10), as was the incidence of PDPH (1,2).

We did observe a small but statistically significant increase in the incidence of paresthesias during catheter insertion with the lateral technique. The same mechanism described above may account for this difference. If the needle enters the epidural space lateral to midline, the catheter may be more likely to come into contact with a spinal nerve to produce a paresthesia. Although contact between a catheter and spinal nerve has not been proven to be the cause of paresthesias during epidural catheter insertion, the following results from our study support this mechanism. First, paresthesias experienced in the lateral group occurred more often on the same side as the bevel orifice. Second, asymmetric block occurred more often when paresthesias were present than when they were absent. Third, those experiencing both paresthesias and asymmetric blocks had a greater extent of block on the same side as the paresthesia 78% of the time. Our results are consistent with the assumption that asymmetric block is due to location of the catheter tip in the lateral portion of the epidural space. The overall incidence of paresthesias (26.6%) was similar to that reported by others (20%–56%) (3,10,15,23–25). Some authors have voiced concern that paresthesias during epidural catheter insertion may increase the risk of neural trauma and postanesthetic neurologic complications (10,15,23). Although no studies have substantiated this concern, when catheter insertion produces painful paresthesias, we do not attempt further advancement. We did not observe any adverse neurologic sequelae other than transient deficits in eight parturients (1.5%), with no difference between the groups.

Radiographic evaluation of the catheter location would have enhanced this study and facilitated elucidation of the mechanisms discussed. However, such a study would be costly and difficult to perform. Instead, we studied a large number of catheter insertions and focused on the most important clinical outcomes. Similar to the design of Norris et al. (1), residents were randomized to the two different techniques to facilitate rapid acquisition of a large sample. Trainees served as their own controls, by cross-over to the other technique midway through their rotation. Unlike the design of Norris et al. (1), our analysis included analgesic effectiveness and extent of sensory block in addition to adverse effects and complications. Although the study was not blinded, outcomes and details of catheter insertion were objective in nature and unlikely to be affected by observer bias. The inclusion of pain VAS scores enhanced the results by providing an unbiased measure of analgesic effectiveness.

Lateral bevel orientation of the epidural needle at the time of dural puncture was shown in a single study to reduce the incidence and severity of PDPH in parturients compared with cephalad orientation (1). Some authors have recommended identification of the epidural space with needle bevels oriented parallel to the long axis of the spine (bevel lateral) (1–4). Many of the same authors recommend subsequent 90° rotation of needle to cephalad orientation before insertion of the epidural catheter (1–3). These recommendations have drawn strong criticism from others on the grounds of safety of the rotation maneuver (5,6,8). Although the lateral approach with rotation may reduce the risk of PDPH in parturients sustaining inadvertent dural puncture (1), rotation of the epidural needle within the epidural space may cause dural puncture (2,7). There are little objective data to solve the rotation controversy, which is largely based on theoretical concerns and speculation. Although catheter insertion through the laterally oriented orifice eliminates concern regarding needle rotation, the technique is associated with greater difficulty passing the catheter beyond the needle orifice, as well as a greater incidence of paresthesias. These drawbacks must be weighed against any potential benefit in prevention of PDPH associated with this technique.

	Acknowledgments

 
The authors thank Nancy K. Richardson and Malini Singh for their assistance in the preparation of this manuscript.

	Footnotes

 
Presented in part at the annual meeting of the American Society of Anesthesiologists, New Orleans, LA, October 23, 1996.

	References

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This Article Abstract Full Text (PDF) En Espanol Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Richardson, M. G. Articles by Wissler, R. N. Search for Related Content PubMed PubMed Citation Articles by Richardson, M. G. Articles by Wissler, R. N.