| JOURNAL HOME | CME HOME | THIS MONTH | PAST ISSUES | ETOC | COLLECTIONS |
| AUTHORS | REVIEWERS | EDITORIAL BOARD | FEEDBACK | RSS | HELP |
| ||||||||||||||
| ||||||||||||||
|
|
|
|
||||||||||||
|
||||||||||||||
*Obstetric Anesthesia Unit,
Department of Obstetrics and Gynecology,
Epidemiology Unit, and
||Department of Anesthesia, The Edith Wolfson Medical Center, Holon, affiliated with the Sackler Faculty of Medicine, Tel Aviv University, Israel; and
Outcomes ResearchTM Institute and Departments of Anesthesiology and Pharmacology, University of Louisville, Louisville, Kentucky
Address correspondence and reprint requests to Tiberiu Ezri, MD, Department of Anesthesia, Wolfson Medical Center, Holon, 58100, Israel. Address e-mail to tezri{at}netvision.net.il
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
IMPLICATIONS: In laboring women receiving epidural analgesia, identifying the epidural space by loss-of-resistance with lidocaine was more effective and caused fewer complications than identifying the epidural space by loss of resistance with air.
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
In contrast, the use of saline is reported to slow the onset and reduce the quality of epidural analgesia (12,13). Sarna et al. (14) reported that results were similar when air or liquid was used to identify the epidural space, but others found the use of liquid to be superior (15,16).
There is thus no consensus as to whether air or a liquid should be used for identifying the epidural space when using a loss-of-resistance technique (1,2). It is also possible that sequential use of air and a liquid will provide the advantages of both methods. We therefore compared the ease of performance, quality of analgesia, and complications associated with loss of resistance to air and lidocaine or with their sequential use.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
The parturients were hydrated with lactated Ringer’s solution (10 mL/kg). Epidural analgesia was administered when a patient’s uterine cervical dilation measured 2.5 to 5.5 cm. Epidural catheters were inserted by anesthesiologists with at least 5 yr of experience in obstetric anesthesia and who were familiar with the loss-of-resistance technique with both air and liquid. With patients in the sitting position, an 18-gauge Tuohy needle (Portex Inc., Keene, NH) was inserted at the L2-3 or L3-4 intervertebral space.
The loss-of-resistance method with a plastic syringe was used to localize the epidural space. Patients were randomly allocated to one of the three methods: 1) 3 mL of air (n = 180), 2) 3 mL of lidocaine 2% (n = 185), or 3) sequential use of air and lidocaine (n = 182). In the last group (air plus lidocaine), we first identified the epidural space with 3 mL of air and then reconfirmed correct position of the needle by injecting 3 mL of 2% lidocaine. In each case, all of the air or lidocaine was injected.
Once the needle was appropriately positioned, a multiorifice epidural catheter was threaded 2.5 cm into the epidural space. If after 5 min there was no blood or cerebrospinal fluid (CSF) aspiration, 3 mL of 2% lidocaine was administered through the catheter in all groups. After waiting an additional 5 min with no signs of subarachnoid block or intravascular injection, patients were turned into the left lateral position, and 10 mL of 0.2% ropivacaine was injected epidurally in 5-mL increments over 10 min. All subsequent analgesic management and study measurement (below) were performed by an anesthesiologist blinded to the method used to detect the epidural space.
Analgesia was maintained throughout the labor and delivery with a patient-controlled epidural analgesia device with a PCAM syringe pump (Model P500; IVAC Medical System, NH) with 0.2% ropivacaine administered as a 5 mL/h basal infusion and a patient-controlled bolus of 5 mL with a 20-min lockout interval and a 20 mL/h limit. Patients who requested additional analgesia were given up to an additional 10 mL of the same solution in 5-mL increments with the patient-controlled epidural analgesia device. This bolus was included in the 20 mL/h limit.
Monitoring consisted of noninvasive arterial blood pressure, maternal heart rate, tocodynamometry, and continuous external fetal heart rate measurement. The anesthesiologist performing the epidural block recorded the rate of catheter insertion failure, the occurrence of unintentional subarachnoid puncture, and accidental intravascular catheter insertion. Other variables recorded included cervical dilation at epidural insertion, use of oxytocin, duration of labor, and mode of delivery.
A blinded anesthesiologist assessed the following variables: the onset of sensory block (assessed by pinprick); the existence of unblocked segments; the extent of sensory and motor block (assessed by the modified Bromage score); the ability of the parturient to cooperate (push on demand) during delivery (graded as "yes" or "no"); and side effects or complications caused by the epidural analgesia, including hypotension (systolic blood pressure <100 mm Hg or a decrease of >20% from baseline), postpartum urinary retention, postdural puncture headache (PDPH), and transient neurological deficits.
The patients graded pain on a 100-mm-long visual analog scale (with 0 mm as no pain and 100 mm as the most pain imaginable). The visual analog scale scores, sensory upper limit, and motor blockade were evaluated 1 h after epidural catheter insertion and at the second stage of labor. If unblocked segments were present, the epidural catheter was repositioned, additional local anesthetic was administered, and the patient’s position was changed. Patients were excluded from the study if clinicians suspected accidental dural puncture or catheterization of a blood vessel.
The primary outcome was the inability to insert an epidural catheter. Although the incidence of difficult epidural catheter insertion is reportedly only 2% (16), we observed a 4.5% difficulty rate with fluid or the combination of air and fluid in a preliminary study. We therefore assumed a difficulty rate of 10% in the air group and a 4.5% difficulty rate in each of the other two groups. Using the sample size test for proportions, we calculated that 517 participants would provide an 80% power to detect a relative difference of 55% in the incidence of difficult catheter positioning. Secondary outcomes included accidental intravascular catheter placement, unblocked segments, and inadvertent dural puncture. Statistical data analysis was performed with SPSS 9.0 for Windows (SPSS Inc., Chicago, IL). Data were evaluated for normal distribution by using the Kolmogorov-Smirnov test. Continuous variables with distribution significantly differing from normal were compared by using the Mann-Whitney U- or median tests. Categorical data were described by using frequency counts and percentages and were compared by using 
2 (with the Yates correction) or Fisher’s exact tests, as appropriate. All tests were considered significant at P < 0.05.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
|
|
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Previous studies reported slow onset and reduced quality of epidural analgesia when saline was used instead of air for loss of resistance (12,13). Presumably, saline slows onset and reduces block quality by diluting the local anesthetic that is subsequently injected. We sought to avoid dilution by performing the loss-of-resistance maneuver with lidocaine rather than saline. Consistent with this theory, we observed comparable onset time and improved block quality with lidocaine compared with air. We note, though, that our study did not include a comparison between saline and lidocaine. It thus remains possible that results would have been similar with each liquid.
A drawback of using lidocaine instead of saline for loss of resistance is the possibility of converting an accidental dural puncture into an actual subarachnoid block. This did not occur in our study, presumably because the fluid pushed the needle away from the dura, thereby minimizing the risk of inadvertent puncture.
The idea behind the combined technique (air plus lidocaine) was based on our observation in a pilot study that in some patients, the epidural space was difficult to identify with air but was easier to identify when we switched to lidocaine. The opposite (crossover from fluid to air) may also help, although this hypothesis was not tested in this study. The purpose of this alternative technique was also to identify the epidural space and push the dura anteriorly, thereby widening the epidural space and reducing the risk of accidental puncture of the dura or epidural veins.
Our findings are consistent with those of Beilin et al. (16) and Valentine et al. (15). Both reported that the loss-of-resistance technique with small amounts of saline (2 or 4 mL) was superior to using the same amount of air. The differences in the quality of analgesia and incidence of complications reported in other previous studies (1–16)1 can be explained by the different volumes of air or saline.
Both the air and saline loss-of-resistance techniques have well known advantages and disadvantages. The loss-of-resistance technique with air is associated with several negative side effects. For example, there is a 2% dural puncture rate, compared with only 0.3%–0.4% when saline is used (5–7,17). This may be caused by the difference in compressibility of lidocaine versus air, which may explain the more frequent incidence of epidural catheter insertion failure in the air group. Therefore, we believe that the loss-of-resistance technique with air is less reliable for locating the epidural space. Air in the epidural space appears to increase the occurrence of PDPH. The association between pneumoencephalos and PDPH is clear (6). As reported previously, we found that using air to locate the epidural space increased the incidence of unblocked segments (11). Other reported side effects of the epidural injection of air include emphysema of the neck (18,19), neck and shoulder pain (20), venous air embolism (9), and persistent neurological deficits (10). The epidural air bubbles may be enlarged by the concomitant use of nitrous oxide (21).
However, large volumes (i.e., 10 mL) of normal saline injected epidurally for loss of resistance may produce inadequate analgesia, presumably caused by the dilution of the local anesthetics (13). Large volumes of saline may also modulate the speed of onset of the epidural block (12,13). It was shown (13) that the number of segments with hypoesthesia for cold and pinprick after 8 mL of 1.5% mepivacaine administration was inversely related to the interval between the administration of saline solution during the loss-of-resistance method. When accidental dural puncture occurs with use of saline for locating the epidural space, the CSF can be differentiated from saline by its glucose and protein content (22).
Leaking of edema fluid may also occur (23). Addressing this issue, Russell (2) suggested that it is better to use a technique that reduces the incidence of complications rather than one that facilitates their diagnosis.
Previous studies (14,16) have reported a similar incidence of intravascular cannulation with air and saline loss-of-resistance techniques. In contrast, we found a 17% occurrence of intravascular cannulation in our air group, compared with only 6% in the lidocaine group—a statistically and clinically significant difference.
This difference could be explained by the different compressibility of air versus lidocaine. Therefore, injecting a liquid into the epidural space pushes the blood vessels away from the epidural catheter.
The position of the patient during the performance of epidural block was found to be related to the incidence of intravascular injection, with the head-down lateral recumbent position having a less frequent incidence (2%) than the sitting position (10.7%) (24). The incidence of postpartum urinary retention was comparable among the groups, despite the more frequent incidence of unblocked dermatomal segments in the air group.
The choice of the currently used loss-of-resistance techniques for locating the epidural space with air or saline generally depends on the anesthesiologist’s experience and personal preference. Among 404 surveyed obstetric anesthesiologists (25), 59% started their practice using air for loss of resistance, but only 37% are currently using air. Fifty-three percent use saline, and 6% use both techniques. Twenty-three percent had changed their technique from air to saline, but only 4% had changed from saline to air. A recent review concluded that the literature supports the use of a small volume of saline for loss of resistance not only because of better analgesia, but also for the decreased morbidity (26). Because liquids are incompressible, the transition from complete resistance to loss of resistance is more obvious; therefore, liquids are ideal for performance of needle insertion into the epidural space with the loss-of-resistance technique. The sequential use of air and lidocaine (air-plus-lidocaine group) did not change the quality of analgesia or the incidence of complications compared with the use of lidocaine alone. We believe, however, that the sequential combination of air and lidocaine technique (which was not reported in previous comparative studies) may strengthen the anesthesiologist’s belief that the needle is correctly placed.
In conclusion, this technique may be especially helpful in difficult epidural blocks. Our results demonstrate a reduced incidence of unblocked segments and complications with use of lidocaine rather than air for identifying the epidural space. Sequential use of both techniques in a given patient did not offer advantages over the use of lidocaine alone.
|
Footnotes |
|---|
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  F van Kooten, R Oedit, S L M Bakker, and D W J Dippel Epidural blood patch in post dural puncture headache: a randomised, observer-blind, controlled clinical trial J. Neurol. Neurosurg. Psychiatry, May 1, 2008; 79(5): 553 - 558. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. T. Riley and B. Carvalho The EpisureTM Syringe: A Novel Loss of Resistance Syringe for Locating the Epidural Space Anesth. Analg., October 1, 2007; 105(4): 1164 - 1166. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Evron, V. Gladkov, D. I. Sessler, V. Khazin, O. Sadan, M. Boaz, and T. Ezri Predistention of the Epidural Space Before Catheter Insertion Reduces the Incidence of Intravascular Epidural Catheter Insertion Anesth. Analg., August 1, 2007; 105(2): 460 - 464. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Halpern and P. Angle Identification of the Epidural Space Anesth. Analg., April 1, 2005; 100(4): 1218 - 1218. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
