Spinal anesthesia has certain advantages that have made it a worthy alternative to general anesthesia. It is a simple and economical method, and a small dose of local anesthetic produces an effective block with complete muscle relaxation. Compared to general anesthesia, severe respiratory depression is uncommon, and postoperative sedation is avoided. Disadvantages, such as the risk of an extensive block, the fixed duration of anesthesia, hypotension, and the risk of postdural puncture headache, have given rise to the use of epidural anesthesia as an alternative. In this method, an exact block height can be titrated and maintained with supplementary doses, and it is possible to use the catheter for postoperative pain relief. Epidural anesthesia is, however, more time consuming and involves a higher incidence of insufficient or superficial blockade, especially of the motor roots, despite large doses of local anesthesia. Hence a combination of these two methods would be attractive.
In the literature, various methods are described for the practical conduct of combined spinal and epidural anesthesia (CSE), and packaged combination sets are now being produced. In this paper we attempt, through a literature review, to describe these techniques and discuss advantages and disadvantages of the various products available on the market.
CSE was described for the first time in 1937 by Soresi , who used the "episubdural" technique by first injecting a dose of local anesthetic epidurally and, after advancing the needle inside the dural cavity, injecting the spinal dose. The epidural was a "single shot," which rendered exact dosage to the required level and the use in postoperative analgesia impossible. The technique did not arouse any interest and was not developed further.
Curelaru  performed the first combined spinal anesthesia and catheter-based epidural anesthesia in 1979. He introduced an epidural catheter through a Tuohy needle, gave a test dose, then performed a traditional dural puncture 1-2 lumbar segments distally using a 26-gauge spinal needle. This technique is known as the double-segment technique (DST). The report caused little response until Brownridge [3,4] described the successful use of DST for elective cesarean section.
CSE was performed in 1982 on a single spinal segment for lower limb surgery by Coates  and Mumtaz et al. . The epidural anesthesia was performed with a 16-gauge Tuohy needle, after which a 25- to 26-gauge spinal needle, approximately 1 cm longer than the epidural needle, was introduced with the Tuohy needle as introducer. After the injection of local anesthetic, the spinal needle was withdrawn and the epidural catheter inserted. In 1984, Carrie and O'Sullivan  reported the use of this technique for cesarean section. Many reports on the single-space technique (SST) have since been published, all using conventional epidural and spinal needles [8-13].
Nickalls and Dennison  modified the SST in 1984, arguing that varying depths of the epidural cavity made the use of longer spinal needles preferable. To prevent the displacement of the spinal needle in the Tuohy needle after identification of the dural space had been established, they recommended that the spinal needle be fixed with an artery clip at the hub of the Tuohy needle. The weight of the clip may, however, displace the spinal needle or damage the needle and impair liquor flow .
In traditional SST, using a Tuohy epidural needle, the spinal needle is bent approximately 10 degrees when it leaves the Huber eye, causing the dural lesion to appear slightly offset the longitudinal axis of the Tuohy needle. Controversy has surrounded the theoretical possibility of introducing the epidural catheter through this dural lesion [9,16-18]. To overcome this problem, it has been recommended that the epidural space be located with the eye of the Tuohy needle facing caudally, and then that the needle be rotated 180 degrees before introducing the catheter in the usual manner . Ferguson  has added that rotation of the Tuohy needle, in itself, constitutes a risk of dural lesion, and that this may be reduced by rotating the needle 90 degrees only. Nevertheless, spinal catheter placement was observed in two cases. Rawal et al. [9,16] could not pass an epidural catheter through a dural lesion made by a 26-gauge spinal needle. Therefore, rotation of the epidural needle was found to be unnecessary and to constitute an increased risk of dural puncture [9,16].
SST versus DST
The reduced number of skin punctures in SST may theoretically decrease the incidence of pain, infection at puncture sites, and formation of hematomas . The use of a Tuohy needle as an introducer lessens the likelihood of contamination of the spinal needle with skin-borne microorganisms [20,21]. However, no quantitative studies have been performed to confirm these assumptions. In DST, there is a theoretical, but undocumented, possibility of damaging the epidural catheter with the spinal needle .
If one wishes to use spinal anesthesia in younger patients with increased risk of postdural puncture headache, an introducer needle is usually required to allow insertion of a pencil-point needle with an atraumatic, conical tip or a 27- to 29-gauge needle. In SST, the Tuohy needle may function as a more suitable introducer than a normal introducer needle, as the tip of the spinal needle can be directed more accurately [5,15,23]. However, dural identification may be complicated. One cannot be sure of dural penetration after a successful localization of the epidural space, as any deviation of the Tuohy needle from the sagittal plane may cause the spinal needle to enter the epidural space and pass the dural sac laterally . A study including 100 women scheduled for elective cesarean section showed a 16% failure rate of the spinal anesthesia in SST compared to only 4% when using DST . In SST, Kumar  has reported insufficient spinal blocks accompanied by a small amount of clear fluid in the epidural catheter, in which aspiration of spinal fluid was impossible. The explanation may be either a puncture of the dural wall ventrally, or insufficient introduction of the spinal needle into the dural space causing leakage of cerebrospinal fluid into the epidural space. These problems associated with SST may be attributable to the lack of tissue support for the spinal needle. In this technique, the spinal needle is in contact with only dura and the Tuohy needle, which may increase the risk of displacement of the spinal needle . Nevertheless, failure rates of only 4%-10% in SST have been reported , in contrast to the 16% failure rate in the study by Lyons . A device to maintain the position of the spinal needle in the Tuohy needle has been described .
Problems in introducing the epidural catheter after the injection of spinal anesthetic using SST have been described [10,27], but the mechanisms remain uncertain. If a hyperbaric local anesthetic is used, a unilateral block may develop if the patient is in the lateral decubitus position and the introduction of the epidural catheter proves difficult . On the other hand, SST in a sitting patient may cause hypotension . Finally, it is considered difficult to test the position of the epidural catheter in SST . Test procedures will be discussed below.
Conventional Sets. Until the manufacture of specialized kits, the use of conventional Tuohy needles and long spinal needles has been necessary in performing SST [16,28]Figure 1. Introduction of the spinal needle through a traditional Tuohy needle may lead to several complications: rotation of the Tuohy needle to increase the distance between the dural puncture site and the insertion of the epidural catheter may lead to dural tear by the Tuohy needle, while avoiding rotation may cause the catheter to enter the spinal cavity (see above). Friction between two metal needles can damage the point of the spinal needle [20,27] and generate metal fragments, which may be introduced epidurally or spinally . In an in vitro study, however, in which the needles were flushed with saline after friction, no metal particles could be found . However, concern about these potential dangers have nurtured the development of different combination sets specifically designed for SST.
Double-Lumen Needles. In this technique, a Tuohy needle is equipped with a parallel tube that acts as a guide for a thinner spinal needle. There are two types--a bent parallel tube and a straight parallel tube. The bent parallel tube consists of a curved 20- to 22-gauge spinal needle of the same length as the Tuohy needle [20,31]Figure 2. The straight tube is fixed on the side of a Tuohy needle; the point of the guide is situated 1 cm behind the eye of the Tuohy needle. Spinal needles of normal length can be used Figure 3. The double-lumen concept allows insertion of the epidural catheter before positioning the spinal needle. Thus, rotation of the Tuohy needle in situ is unnecessary, and the possibility for a spinal placement of the catheter is diminished. By using these combination sets, one avoids the bending of the spinal needle when it leaves the eye of an ordinary Tuohy needle. However, there is still friction between the two needles, especially when the bent introducer is used .
CSE Tuohy Needles with Additional Aperture. A new concept in SST involves the use of a 17-gauge Tuohy needle with an additional aperture situated at the end of the longitudinal axis. This aperture permits passage of a spinal needle as it is introduced . The available kits feature essentially identical Tuohy needles. In some sets, however, maximal introduction of the spinal needle causes the tip to protrude only 7.5 mm past the tip of the Tuohy needle, which in some patients is insufficient [14,34,35]. The usual technique is used for identification of the epidural space. After dural puncture, the spinal needle is withdrawn and the epidural catheter introduced. The larger diameter of the catheter causes this to pass through the usual Huber opening Figure 4. These modified Tuohy needles function as a suitable introducer for even the thinnest spinal needle, as kinking and friction in the Huber eye of the Tuohy needle is avoided. Advancing the spinal needle through the back hole may offer a more distinct sensation of dural puncture . To accomplish proper passage through the "back eye," however, the Quincke point of the spinal needle must face the same way as the Huber opening of the Tuohy needle; otherwise the spinal needle may pass through the Huber eye (personal observation) . A traditional insertion of the Tuohy needle with the Huber eye facing cephalad will then cause a Quincke point spinal needle to cut the dural fibers horizontally. This has been shown to increase the risk of postdural puncture headache .
In a prospective study by Joshi and McCarroll  including 40 patients, a kit featuring a back hole Tuohy needle was compared prospectively to a conventional needle-through-needle kit. No significant difference in frequency of spinal placement of the catheter was found. Block extension was similar in the two groups .
Dosage in CSE
CSE often produces a more extensive block than expected [9,10]. Perhaps the postulated subatmospheric pressure in the epidural space is alleviated by the Tuohy needle before the injection of the local anesthetic, which may in turn reduce the volume of the dural sac and thereby extend the level of anesthesia .
The necessary epidural dose for extension of a spinal block varies between 1.5 and 3 mL per added segment, less than needed for extending a conventional epidural anesthesia [8,9]. Diffusion of local anesthetic from the epidural cavity to the spinal canal through the puncture site has been stated as a possible, but unconfirmed, mechanism for block extension. A convincing study by Blumgart et al.  has clarified the exact mechanism. After intraspinal injection of 1.6-1.8 mL hyperbaric bupivacaine, patients were allocated to receive either extradural saline 10 mL, bupivacaine 10 mL, or no supplementary injection. In the two first groups, a significant and similar block extension was noted, compared to the group receiving no injection. On this basis the authors concluded that the mechanism of block extension is due to compression of the dural sac by the extradural injection. However, data collection was limited to 30 min after extradural injection. With further supplements, one must expect a difference between saline and bupivacaine to emerge.
Generally, small amounts of spinal anesthetic are used for cesarean section patients, presumably because venous engorgement around the spinal canal causes compression of the dural sac . An increased sensitivity of nerve fibers to local anesthetic in pregnant patients has been postulated as an additional explanation .
The literature presents diverging views of both the dose and the baricity of the local anesthetic used in CSE. In most studies the patients are subjected to elective or emergency cesarean section Table 1. In all but two studies, the patients received a hyperbaric solution for spinal anesthesia. In general, a small spinal dose is accompanied by a correspondingly larger epidural dose to achieve the desired block height. When using an isobaric solution, the block height becomes unpredictable . To avoid an excessive block, a small spinal dose followed by an optional epidural dose has been used .
The Test Dose
The location of the epidural catheter cannot be tested by injecting the usual volume of local anesthetic, as the presence of a high spinal block could cause a total spinal anesthesia if the catheter is placed spinally. A possible procedure might consist of epidural injection of 1.5 mL isobaric lidocaine 2% when, or if, the spinal block extends below T-11. With a correctly inserted epidural catheter, the block height will increase only approximately two segments. If the catheter has entered the spinal canal, the resulting block will not extend to a level causing diaphragmatic paralysis.
As proposed by Blumgart et al. , one may alternatively choose to extend the block with saline perioperatively if the duration of surgery permits. Of course, injection of a local anesthetic is necessary if the block is to be maintained for several hours.
By performing CSE, profound and uniformly distributed analgesia with good muscle relaxation of spinal anesthesia, as well as the possibility for peri- and postoperative epidural supplements, results. An insufficient block may be extended to a satisfactory level and maintained throughout the operation without difficulty. The time from injection to the full effect of the block is short, which makes it a suitable method for emergency cases. CSE makes it possible to combine epidural and spinal doses. By using a small initial dose for the spinal anesthesia and afterward extending the block epidurally to the desired level of anesthesia, excessive sympathetic block and intercostal paralysis can be avoided . Still, a considerably smaller amount of local anesthetic is used compared to an epidural block, which reduces the plasma concentration of local anesthetic . These advantages make CSE especially appropriate for the high-risk patient and for cesarean section [8-10,12,21]. However, as mentioned above, the initial spinal block may be more extensive than one would expect with a simple spinal anesthesia.
CSE performed as SST simplifies the use of thin spinal needles or pencil-point needles, as the Tuohy needle acts as an introducer. Even with the use of Quincke-point needles, the frequency of postdural puncture headache is reduced. Compression of the dural sac by the epidural injection is thought to be responsible [3,5,11,25,30].
A theoretical advantage of CSE is proposed by Dirkes et al. . By examining sensory thresholds to electrical stimulation, a combination of epidural and spinal anesthesia provided an enhanced afferent blockade unobtainable by either spinal or epidural anesthesia used alone.
The use of a catheter for continuous spinal anesthesia is becoming more common and possesses several of the above-mentioned advantages. However, spinal catheters are expensive, and the risk of confusing the spinal catheter with an epidural catheter may restrict their use in postoperative pain management. In CSE, it is possible to administer an intraspinal opioid and take advantage of the long duration of action compared to epidural administration [21,41]. The disadvantages of CSE include the risk of spinal placement of the epidural catheter and the complicated test procedure. Moreover, the procedure may at times be technically difficult , depending, however, on the chosen technique [15,42]. The present range of purpose-designed utensils for CSE is limited, and the available packaged sets make it difficult to select for individual needle type or length.
The kits featuring Tuohy needles with an additional aperture have theoretical advantages: there is no deformation of the spinal needle, rotation of the epidural needle is unnecessary, and the design simplifies the practical use in comparison with other purposedesigned sets . The kits, nevertheless, leave room for improvement, in that it can be difficult to ensure correct passage of the spinal needle through the "back eye" without a specific orientation of the spinal needle.
CSE offers advantages of both spinal and epidural anesthesia: rapid onset and profound level of anesthesia, possibility of supplementary doses and postoperative pain therapy. The technique is useful in many obstetric and orthopedic procedures. There are several specially designed kits for single-space use. Among these, the kits including a Tuohy needle with a back hole may offer practical advantages.
1. Soresi AL. Episubdural anesthesia. Anesth Analg 1937;16:306-10.
2. Curelaru I. Long duration subarachnoid anesthesia with continuous epidural blocks. Praktische Anaesthesie Wiederbelebung und Intensivtherapie 1979;14:71-8.
3. Brownridge P. Epidural and subarachnoidal analgesia for elective caesarean section [letter]. Anaesthesia 1981;36:70.
4. Brownridge P. Central neural blockade and caesarean section. Part I: review and case series. Anaesth Intensive Care 1979;7:33.
5. Coates MB. Combined subarachnoid and epidural techniques [letter]. Anaesthesia 1982;37:89-90.
6. Mumtaz MH, Daz M, Kuz M. Another single space technique for orthopedic surgery [letter]. Anaesthesia 1982;37:90.
7. Carrie LES, O'Sullivan GM. Subarachnoid bupivacain 0.5% for Caesarean section. Eur J Anaesthesiol 1984;1:275-83.
8. Rawal N. Single segment combined subarachnoid and epidural block for caesarean section. Can Anaesth Soc J 1986;33:254-5.
9. Rawal N, Schollin J, Wesstrom G. Epidural versus combined spinal epidural block for cesarean section. Acta Anaesthesiol Scand 1988;32:61-6.
10. Carrie LES. Epidural versus combined spinal epidural block for caesarean section [letter]. Acta Anaesthesiol Scand 1988;32:595-6.
11. Kumar CM. Combined subarachnoid and epidural block for caesarean section [letter]. Can J Anaesth 1987;34:329-30.
12. Dennison B. Combined subarachnoid and epidural block for caesarean section [letter]. Can J Anaesth 1987;34:105.
13. Patel M. Combined spinal and extradural anesthesia [letter]. Anesth Analg 1992;75:640-1.
14. Nickalls RWD, Dennison B. A modification of the combined spinal and epidural technique [letter]. Anaesthesia 1984;39:935-6.
15. Lifschitz R, Jedeikin R. Spinal epidural anaesthesia. Anaesthesia 1992;47:503-5.
16. Rawal N. Combined spinal-epidural needle (CSEN) for the combined spinal-epidural block [reply]. Acta Anaesthesiol Scand 1989;33:618.
17. Eldor J, Chaimsky G, Olshwang D. Combined spinal-epidural needle (CSEN) for the combined spinal-epidural block [letter]. Acta Anaesthesiol Scand 1989;33:617.
18. Kumar CM. More on combined subarachnoid and epidural techniques [letter]. Anaesthesia 1986;41:90-1.
19. Ferguson DJM. Dural puncture and epidural catheters [letter]. Anaesthesia 1992;3:272.
20. Eldor J, Chaimsky G. Combined spinal-epidural needle (CSEN) [letter]. Can J Anaesth 1988;35:537-9.
21. Kestin IG. Spinal anesthesia in obstetrics. Br J Anaesth 1991;66:596-607.
22. Kestin IG. Spinal anesthesia in obstetrics [reply]. Br J Anaesth 1991;67:663.
23. Vandermeersh E, Kick O, Mollmann M, et al. Combined spinal and epidural anesthesia. Reg Anaesth 1991;14:108-12.
24. Lyons G, Macdonald R, Mikl B. Combined epidural/spinal anesthesia for Caesarean section. Through the needle or in separate spaces? Anaesthesia 1992;47:199-201.
25. Patel M, Swami A. Combined epidural/spinal anesthesia for caesarean section [letter]. Anaesthesia 1992;47:1005-6.
26. Simsa J. Use of 29-gauge spinal needles and a fixation device with combined spinal epidural technique. Acta Anaesthesiol Scand 1994;38:439-41.
27. Brownridge P. Spinal anaesthesia in obstetrics [letter]. Br J Anaesth 1991;67:663.
28. Desira WR. A special needle for combined subarachnoid and epidural block [letter]. Anaesthesia 1985;40:308.
29. Eldor J, Brodsky V. Danger of metallic particles in the spinal-epidural spaces using the needle-through-needle approach [letter]. Acta Anaesthesiol Scand 1991;35:461-3.
30. Hargreaves J. Metal particle generation caused by the combined spinal-extradural technique [letter]. Br J Anaesth 1993;70:706.
31. Torrieri A, Aldrete JA. The T-A pair needle [letter]. Acta Anaesth Belg 1988;39:65-6.
32. Eldor J, Guedj P, Gozal Y. Combined spinal-epidural anesthesia using the CSEN [letter]. Anesth Analg 1992;74:169-70.
33. Eldor J. A new needle [reply]. Anesth Analg 1992;75:303-4.
34. Joshi GP. Combined spinal-epidural technique using the needle-through-needle technique [letter]. Anesthesiology 1993;78:406-7.
35. Joshi GP, McCarroll MC. Evaluation of combined spinal-epidural anesthesia using two different techniques. Reg Anesth 1994;19:169-74.
36. Lybecker H, Moller JT, May O, Nielsen HK. Incidence and prediction of postdural puncture headache. A prospective study of 1021 spinal anesthesias. Anesth Analg 1990;70(4):389-94.
37. Blumgart CH, Ryall D, Dennison B, Thompson-Hill LM. Mechanism of extension of spinal anesthesia by extradural injection of local anaesthetic. Br J Anaesth 1992;69:457-60.
38. Diebold M. Combined spinal/epidural anaesthesia for caesarean section [letter]. Anaesthesia 1993;48:535.
39. Turner MA. Combined epidural/spinal anaesthesia for caesarean section--single-space/double-barrel technique [letter]. Anaesthesia 1992;47:814.
40. Dirkes WE, Rosenberg J, Lund C, Kehlet H. The effect of subarachnoid lidocaine and combined subarachnoid lidocaine and epidural bupivacaine on electrical sensory thresholds. Reg Anesth 1991;16:262-4.
41. Campbell C. Epidural opioids--the preferred route of administration. Anesth Analg 1989;68:710-1.
© 1995 International Anesthesia Research Society
42. Forster SJ. Combined subarachnoid and epidural techniques [letter]. Anaesthesia 1983;38:72.