Combined spinal and epidural anaesthesia (CSE) is widely practised. The two techniques currently used are the needle-through-needle (NTN) technique  and the double-space technique. Compared to the double-space technique the attractions of NTN are single injection site and speed. One of the several new NTN kits available on the market is the Epistar®. The unique advantage with this compared to other NTN kits is that it allows insertion of the epidural catheter prior to the spinal injection, allowing catheter problems to be overcome before rather than after the intrathecal injection of local anaesthetic has begun to work.
Ten years ago we compared the two techniques of NTN and double-space in a randomized-controlled trial and found the NTN technique to be less effective . Since then the appearance of a number of specialized kits has indicated the timeliness to review our original conclusion. We have therefore compared the double-space technique to the Epistar® NTN technique in a prospective study.
This randomized single blind-controlled trial was approved by our hospital Ethics Committee. After written informed consent, 200 pregnant females of ASA I-II, with a healthy singleton term fetus of more than 36 weeks gestation scheduled for elective Caesarean section were recruited and randomized to one of two groups using a computer-generated random sequence. Allocation was determined after recruitment, immediately before surgery.
Group 1 patients received combined spinal epidural anaesthesia using a double-space technique. The epidural catheter was inserted using an 18-G Tuohy needle at the L2-3 interspace, followed by an intrathecal injection using a 27-G Whitacre needle (Portex, Hythe) at the L3-4 interspace.
Group 2 patients received combined spinal epidural anaesthesia with the Epistar® NTN kit in the L3-4 interspace. The Epistar kit consists of a modified double lumen Tuohy needle with the upper lumen used for threading the 18-G epidural catheter and the lower lumen for inserting the 27-G Whitacre spinal needle. Only one skin puncture was required.
In both the groups the epidural space was identified first by loss of resistance to saline before the 18-G catheter was inserted. A test dose of 2% lignocaine calculated at a dose of 1 mg kg−1 was given via the epidural catheter . Accidental intravascular and intrathecal injections were detected by asking the patient for relevant symptoms and from continuous non-invasive blood pressure (BP) measurement. As part of our routine protocol for double-space CSE, at least 5 min was allowed to elapse before the intrathecal injection. The 3 mL intrathecal injection consisted of 13 mg of 0.5% hyperbaric bupivacaine with 400 μg diamorphine. A block height of T5 to touch was required before surgery. To assess possible bias from posture we performed the CSE with 50 females in the left lateral and 50 in the sitting position. Routine electrocardiography, pulse oximetry and non-invasive BP measurement were performed, and intravenous access was secured prior to the procedure. Ephedrine 30 mg was added routinely to the saline infusion and additional boluses were given to maintain a normal BP. Established practice was followed at all times.
Individual and obstetric data were recorded. Outcomes were the number of females who completed the procedure without supplementation and the number requiring epidural augmentations prior to surgery. Intraoperative analgesic requirement, the duration of surgery, the time interval between local infiltration to skin and intrathecal injection, and the number of spinal injections completed with a single skin puncture were also recorded. On the next day patients were questioned about discomfort during insertion and backache. This was recorded on a 0-100 visual analogue scale (VAS), where 0 = no discomfort/no backache and 100 = worst discomfort ever/worst backache ever.
From the findings of our previous study  we calculated that to detect a clinically significant difference of 15% between groups at a power greater than 0.8 for P < 0.05, 100 patients were needed in each group. Statistical analysis used Fishers exact or χ2-test for categorical data and Mann-Whitney U-test for comparison of means as appropriate. Software packages used were Excel 2000 (Microsoft) and SPSS 9.0 (SPSS Inc).
Two hundred females completed the study. The individual and obstetric characteristics of the two groups were similar (Table 1). The double-space technique was completed without supplementation more often than the NTN technique (80 vs. 54, odds ratio 0.29).
There were no significant differences between the groups in the requirement of epidural augmentations before surgery (16 vs. 21, odds ratio 0.4) and in the intraoperative analgesic requirements (8 vs. 13, odds ratio 0.5). The duration of surgery was 60.2 min (95% confidence interval (CI): 40-79) in the double-space group and 61.9 min (95% CI: 53-70.5) in the NTN group. The times from start of skin infiltration to start of intrathecal injection were 15 min (95% CI: 12.7-17.4) for the double-space technique and 12.9 min (95% CI: 11.5-14.3) for the NTN technique and were not significantly different. The number of successful spinal injections from a single puncture was 59 in the double-space group and 55 in the NTN group (odds ratio 0.85).
The median (interquartile range) of the VAS in the double-space group for discomfort at insertion was 30 (12.5-51.5) and for postoperative backache 0 (0-10). In the NTN group the mean score was 32 (12.75-60) and 0 (0-10.75) for discomfort at insertion and backache, respectively.
Performance in the first and second half of the study were compared. In the NTN group 25 were successfully completed at first pass out of the first 50 patients compared to 30 in the second 50 patients (odds ratio 1.5). In the double-space group, 40 out of 50 were successful in both halves of the study (odds ratio 1). The success with relation to posture was compared in both the groups. In the NTN group the successes were 28 and 26 of 50 in the sitting and left lateral position, respectively (odds ratio 1.18). In the double-space group 39 and 41 of 50 were successful in the sitting and left lateral positions, respectively (odds ratio 0.78). These differences did not reach statistical significance.
The aim of this study was to evaluate a new NTN kit by comparing it with a double-space technique. Previous studies have reported up to 24.5% failure rate with the NTN kits . Whilst Lyons and colleagues  reported a failure rate of 16% to establish spinal block with the NTN technique compared to a 4% failure rate with the double-space technique, in patients undergoing orthopaedic and urological surgery, Casati and colleagues  demonstrated a much lower rate of unsuccessful dural puncture of 5% in the NTN group compared with 1.6% of cases in the double-space group.
In our study several criteria were used to define success. The main outcome used was how often the intrathecal component could achieve a T5 block for Caesarean section without the need for epidural augmentation or an alternative technique. On this criterion the double-space technique proved significantly more successful than the NTN technique. In other respects the differences between the two techniques were small and in particular the use of the epidural component was not significantly different between the groups. The limitation of the NTN technique is that when dural puncture fails , realignment of the Tuohy needle is not possible until the epidural catheter has been removed. To achieve this the needle and catheter must be removed completely, whereas the spinal introducer of the separate space technique can readily be redirected with a minimum of fuss.
A need for epidural augmentation in the region of 20% and an intraoperative augmentation rate in the region of 10% requires an explanation. This is a teaching unit and to make the study more robust, trainees were actively involved in the study. Similarly, obstetricians in training were responsible for most of the operations. Operating times varied considerably and frequently exceeded 1 h. Many of the intraoperative supplements were to ensure continued comfort. By defining a successful block in terms of inability to detect light touch to a dermatomal level of T5, we have made the outcome more exact than some might consider necessary . This should also be taken into account when the overall success rate of the blocks is considered.
If success with the double-space technique had been defined as a single pass of the spinal needle introducer, then the difference between the techniques would not have been so apparent (54 in the NTN group vs. 59 in the double-space group). When dural puncture failed through the Tuohy needle, the simpler solution was to complete the intrathecal component in another space. Whilst this underlines the flexibility of the double-space technique, it also highlights the way in which choice of outcome can influence the way in which the performance is perceived.
The NTN approach was the less familiar of the two techniques, and we looked for the evidence of a learning curve. Performance with the double-space technique was static throughout the study, but the second 50 in the NTN group had more successes than the first. The difference did not reach significance, but the study was not powered to detect changes of this nature and a learning curve cannot be dismissed. Had the evaluation continued beyond 200 females, it is possible that the difference in performance of the two techniques might have closed further.
There are small procedural differences between the techniques. When double spaces are used, the epidural component is completed before the intrathecal injection is attempted. With the NTN technique, the intrathecal injection is made using the Tuohy needle as an introducer, with the epidural catheter in situ. When the intrathecal injection is completed, the needle is withdrawn, and then the Tuohy needle is withdrawn, leaving the catheter to be withdrawn to the desired mark. This leads to a fine difference in the two techniques with regard to the time a female is left sitting after the completion of the intrathecal injection. There was a possibility that this might adversely affect block height and density in the NTN group. To try and identify this we conducted 50% of the blocks sitting and 50% in the lateral position. Posture did not appear to influence the performance of the blocks.
In conclusion, the flexibility offered by redirecting the spinal needle introducer is the chief reason that makes the double-space technique perform better than a NTN kit. The double-space technique is also cost-effective and more readily available. It is the preferred technique in our hospital.
We wish to thank Medimex for their support. An abstract of this work was presented at the Eeuroanaesthesia 2002 meeting. The authors would like to acknowledge that they have no conflicts of interest with any aspect of this study.
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