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Departments of Anesthesiology, University of Miami School of Medicine, Miami, Florida; and St. Luke's-Roosevelt Hospital Center, College of Physicians and Surgeons of Columbia University, New York, New York
Address correspondence to David J. Birnbach, MD, Department of Anesthesiology, University of Miami School of Medicine, 1611 NW 12th Ave., Miami, FL 33136. Address e-mail to dbirnbach{at}med.miami.edu.
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Abstract |
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Introduction |
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There are several techniques currently used for performing CSE; the needle-through-needle technique is the most common. Compared with the double interspace approach, the needle-through-needle technique seems to improve patient satisfaction and to cause less patient discomfort, trauma, and morbidity from inter-spinous space penetration including backache, epidural venous puncture, hematoma, infection, and technical difficulties (2,3). Cadaver studies and isolated case reports of intrathecal catheter migration, failure to obtain CSF, and paresthesia have appeared in the literature (4,5) and have caused concern among some anesthesiologists (6). Recently, epidural needles with a separate spinal aperture have been introduced as a means to decrease some of these risks. When these needles became available at our institution, we noted a decrease in the rate of paresthesias and hypothesized that the needle design was responsible for this decrease.
The aims of this study were to compare the efficacy and incidence of complications associated with a newly introduced modified epidural needle (Espocan® needle; B. Braun, Bethlehem, PA) with a conventional Tuohy epidural needle using a needle-through-needle CSE technique in parturients receiving labor analgesia.
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Methods |
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60 mm on 2 consecutive contractions. Patients with a contraindication to neuraxial analgesia, history of neurological, neuromuscular, or psychiatric disorders, history of drug or alcohol abuse, weight >120 kg, or height <150 cm were excluded. After requesting analgesia, the patients were randomized by computer-generated code to receive CSE analgesia using an Espocan® (ES) needle (18-gauge Tuohy epidural needle with an extra lumen in the needle heel) (B. Braun Medical) or a conventional 18-gauge Tuohy needle (B. Braun Medical) (Fig. 1). Blocks were performed by postgraduate year-3 or -4 residents, fellows, or attending anesthesiologists. If a block was performed by a resident or fellow, an attending anesthesiologist was present for the procedure. Monitors included maternal noninvasive arterial blood pressure, pulse oximetry, as well as cardiotocograph.
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All patients were placed in the sitting position and the epidural space was identified at the L3–4 ±1 interspace using a midline approach and loss of resistance-to-air technique, with the bevel of the epidural needle facing cephalad at all times.
In the ES group, a 27-gauge 12.75-cm spinal Pencan® needle with centering sleeve (Fig. 3) was inserted through the back hole of the epidural needle. With this technique, the Pencan® needle protrudes 15 mm beyond the epidural needle tip when inserted to the hub of the epidural needle. The centering sleeve is designed to force the spinal needle through the back hole, rather than to allow it to bend and pass through the main lumen of the epidural needle. Its design, however, would not be conducive to placement through a standard epidural needle, where it would be required to bend in order to exit. Therefore, a nonsleeved spinal needle was chosen for CSE with the conventional Tuohy epidural needle. A laboratory evaluation of the sleeved spinal needles demonstrated that they went through the correct lumen in 80% of attempts, as compared with 56% with a nonsleeved spinal needle (7). Except for the presence of the sleeve, the shape of the spinal needles and ports was almost indistinguishable, and should not have been responsible for any observed differences in measured outcomes. In the Tuohy group, a standard 12.4-cm 27-gauge Gertie Marx® spinal needle (International Medical Development Inc., UT) was inserted through an unmodified Tuohy needle. The Gertie Marx® needle protrudes 15 mm beyond the tip when inserted to the hub of the epidural needle. When free flow of CSF was noted at the hub of the spinal needle, a standard spinal medication (5 µg of sufentanil plus 2.5 mg of bupivacaine) was injected. If the anesthesiologist failed to confirm free flow of CSF through the spinal needle by observation or aspiration, a second attempt at spinal needle insertion was made, after redirecting the epidural needle. If no CSF was obtained on the second attempt, but the anesthesiologist was confident that the epidural needle was correctly positioned, an epidural catheter was inserted and a standard epidural technique was performed. After removal of the spinal needle, a multi-orifice polyamide 20-gauge epidural catheter was advanced approximately 5 cm into the epidural space. The catheter was aspirated to check for the presence of blood or CSF and was secured with an occlusive dressing and tape. After negative aspiration, an epidural infusion of 0.0625% bupivacaine, 1 in 700,000 epinephrine, and 1 µg/mL fentanyl was initiated at a rate of 10–12 mL/h. If the dura was accidentally punctured by the epidural needle, the epidural catheter was advanced intrathecally 3 cm and a continuous spinal technique performed, according to our standard practice.
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An independent observer, who did not view the epidural or spinal needle and thus could not identify which needle set was used, collected the following data during the procedure: presence of paresthesia on insertion of the spinal needle, unintentional dural puncture with the epidural needle ("wet tap"), intrathecal or intravascular epidural catheter placement. In addition, the anesthesiologist performing the spinal (unblinded) was asked to identify failure to obtain CSF through the spinal needle after placement of the epidural needle. If a patient experienced a paresthesia, they were asked to describe the sensation and if it was "unpleasant."
Maternal and fetal heart rate and maternal oxygen saturation were continuously monitored. Arterial blood pressure was monitored every 2.5 min for the first 20 min and at 15-min intervals after CSE placement. Patients were assessed hourly for the presence of motor block until delivery.
The sample size was estimated on the incidence of paresthesia, an important adverse event occurring with sufficient frequency and reasonable to study. This sample size (50 per group) would be able to detect a difference in paresthesia rates (50% versus 20%) with a power of 89.4% at an 
level of 0.05. The rates were based on past experiences with the frequency of paresthesia in our residency training program and are only slightly more than reported in the literature for attending physicians. Data analyses were performed using the Fisher's exact test with a P < 0.05 considered significant.
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Results |
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Pricing of the two needle combinations was also evaluated. The cost of the standard epidural kit ($22) plus a stand-alone atraumatic spinal needle ($6.25) was associated with a $5.75 savings as compared with the use of the ES kit ($34).
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Discussion |
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The reported incidence in the literature of paresthesia with CSE technique varies from 18% to 37% (8,9). Paresthesias may also be associated with conventional epidurals and threading of epidural catheters, with previously reported rates as frequent as 44% in one series (10). The incidence of paresthesia in our study was 14% in the ES group and 42% in the Tuohy group, which although frequent, is similar to the incidence reported by other investigators. The majority of CSEs in our study were performed by anesthesiology residents, which may, in part, explain our frequent incidence of paresthesias and failure to obtain CSF on first attempt. In addition, our patients were specifically asked about paresthesias, which may have increased the rates as compared with the alternative where, if a patient did not complain, it was assumed that no paresthesia had occurred. Nonetheless, we believe our findings reflect the activity of a busy anesthesiology residency training program and may be a more realistic portrayal of everyday practice on a busy obstetric unit in an academic institution.
Paresthesia occurring during CSE placement is a relatively common event, but uncomfortable for the patient. This is highlighted by the finding that all of our patients who experienced a paresthesia rated it as "unpleasant" or "painful." Its sudden onset may cause the patient to move unexpectedly and may result in further paresthesia or even dural tap. Needle trauma and local anesthetic toxicity are believed to be the primary causes of neurological complications associated with regional anesthesia. Although most cases of paresthesias are benign and associated with no further sequelae, if persistent neurological injury occurs, the deficit is usually in the same dermatomal distribution as the elicited paresthesia (11).
Because different spinal needles were used in the two groups evaluated in this study, it is possible that the difference in incidence of paresthesia was related to the spinal needle design. Dural tenting may also cause tension on nerve roots leading to discomfort or paresthesia (12). The relatively frequent incidence of paresthesia during CSE performed by our residents may be the result of the tendency of those inexperienced with CSE to advance the spinal needle to the hub of the epidural needle too rapidly, thus causing more of the spinal needle to protrude beyond the epidural needle. Furthermore, it is likely that the increase in incidence of paresthesias seen in the conventional epidural needle group was caused by the angulation of the spinal needle when it followed the direction of the main epidural orifice, as compared with the straight angle when exiting the back hole of the ES (Fig. 2). Improvements in teaching residents slow, controlled advancement of the spinal needle may decrease the incidence of paresthesias to the point where choice of needle may not be significant as relates to paresthesias.
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Failure to obtain CSF on the first attempt may be explained by unintentional paramedian placement of the epidural needle or incorrect placement of the epidural needle, which was presumed to be located epidurally but was not. Lateral placement of the epidural needle in the epidural space may result in failure of the spinal component of CSE, as the spinal needle may pass tangentially toward the lateral recess of the intervertebral space, completely bypassing the subarachnoid space as it passes to the side of the dural sac (12).
A further possible explanation for failure to obtain CSF is potential tenting of the dura mater with the spinal needle, which has been observed in epiduroscopic studies (4). In addition, the angle at which the spinal needle encounters the dura on emerging from the epidural needle may impact dural tenting (90° versus 45–60° for ES and conventional Tuohy needles, respectively). The "centering sleeve" (Fig. 3) that forces the spinal needle to exit through the back hole used in the ES epidural set may add further stability to the spinal needle than the conventional spinal and Tuohy needle combination used in this study.
Many practitioners avoid aspiration of CSF through the 27-gauge spinal needle in order to prevent inadvertent displacement of the needle from the subarachnoid space. Avoidance of aspiration, however, may result in a successful dural puncture being missed and thus considered a failure, despite correct placement. In this study, if free flow of CSF was not noted, the needle was gently aspirated and none of the needles that had no flow before aspiration were found to have CSF on aspiration.
More recently, it has been demonstrated that the length of the spinal needle used in CSE is also important (13). The spinal needle should protrude an adequate distance beyond the tip of a particular epidural needle to reliably puncture the dura. It is possible that the change of angle in the back hole of the ES needle allowed greater protrusion of the spinal needle.
Although an overall rate of 18% failure to obtain CSF on first attempt may seem frequent, after needle redirection, many of these spinal needles were successfully placed so that the overall failure after 2 attempts was 6%. By comparison, an overall failure rate of 16% was reported by Lyons et al. (14) and a recent Japanese study reported a failure rate of 25% (15).
Of note, 67% of the catheters that were advanced on the assumption that the epidural needle was in the correct place, despite failure to observe CSF, did not provide satisfactory labor analgesia. This suggests that most of these epidural needles were not located in the epidural space and that the spinal component may in fact be a sensitive verification of appropriate epidural needle placement. Loss of resistance that occurred in these cases may have been caused by a false loss of resistance that may occur when the epidural needle lies superficial to the vertebral lamina. Another potential space that can cause a false loss of resistance is the paraligamentous space associated with the tissues adjacent to the interspinous ligament (16).
Although intrathecal catheter migration after CSE remains a concern to some, in this study, no patient developed symptoms or signs to suggest accidental intrathecal catheter placement or migration. Based on the rarity of catheter migration, combined with the limited sample size, it is difficult to comment about the ability of back-hole epidural needles to prevent this complication. Although partial or complete intrathecal catheter placement may not be immediately detectable at such small concentrations of local anesthetic, the use of a test dose, aspiration of a multi-orificed epidural catheter before bolus administration of medication, and frequent assessment of motor blockade are also very likely to prevent untoward sequelae (17).
The cost of the ES CSE kit is approximately $5.75 more than the cost associated with a standard epidural kit plus an atraumatic spinal needle. The ES kit includes everything that a standard epidural kit contains, plus an atraumatic spinal needle; therefore, no other equipment is necessary. With a 28% difference in incidence of paresthesias, we calculate there is about a $20 cost per paresthesia avoidance (in 100 patients, $575 cost, 28 fewer paresthesias). We are unable to comment on the potential economic benefits of fewer intrathecal or IV insertions because of the rarity of these situations. We are also unable to comment on the value of using the ES kit in avoiding long-term/permanent nerve damage because none were reported in this study. It is not unreasonable, however, to expect a difference because nerve damage is often accompanied by paresthesias. Any reduction in these events, given the potential severity and expensive health care costs associated with a complication, might offset the small extra expenditure per case.
In conclusion, epidural needles with a back hole for CSE during labor may reduce the incidence of failure of the technique and lessen the incidence of paresthesia.
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Footnotes |
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Accepted for publication January 11, 2005.
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