Combined Spinal–Epidural (CSE) Anesthesia

Epidural needle is placed in the epidural space indentically to the technique in epidural anesthesia

In recent years, regional anesthesia techniques for surgery, obstetrics, and postoperative pain management have been used with increasing frequency.[1−3] The combined spinal–epidural (CSE) technique, a comparatively new anesthetic technique, includes an initial subarachnoid injection followed by epidural catheter placement and administration of epidural medications delivered for extended periods. Clinical studies have demonstrated that the CSE technique provides excellent surgical conditions as quickly as the single-shot subarachnoid (SSS) block, and with advantages compared with the epidural block alone.[4−6] The introduction of CSE anesthesia offers benefits of both spinal and epidural anesthesia. Although the CSE technique has become increasingly popular over the past two decades, it is a more complex technique that requires comprehensive understanding of epidural and spinal physiology and pharmacology. This article discusses the technical aspects, advantages, potential complications, and limitations of the CSE technique for surgery and analgesia during labor.

Clinical Use Of CSE Anesthesia

The results of a recent survey demonstrate wide variation in CSE use and practice among experienced anesthesiologists,⁷ reflecting concern over the frequency of CSE-related complications,^8,9 controversy over the technique,^10,11 and the potential for higher failure rates with CSE than with individual spinal or other anesthetic techniques.¹²

General Surgery

In the literature, the technique has been described for use in general, orthopedic, and trauma surgery of lower limb, as well as in urologic and gynecologic surgery. Clinical studies have demonstrated that the CSE technique provides excellent surgical conditions as quickly as with SSS block—conditions that are better than with epidural block alone.^4,13 With the CSE technique, surgical anesthesia is established rapidly, saving 15–20 min compared with epidural anesthesia. Furthermore, epidural catheterization provides the possibility of supplementing subarachnoid anesthesia, which may be insufficient when used alone. In a recent article it was also observed that various needles can be used in different combinations when performing CSE and may have different advantages and disadvantages for different patients and situations.¹⁴ This will be discussed later in the article.

Labor Analgesia

The CSE technique is widely used in obstetric practice to provide optimal analgesia for parturients. It offers effective, rapid-onset analgesia with minimal risk of toxicity or motor block.¹⁵ In addition, this technique provides the ability to prolong the duration of analgesia, as required, through the use of an epidural catheter. Furthermore, should an operative delivery become necessary, that same catheter can be used to provide operative anesthesia. The onset of spinal analgesia is almost immediate, and the duration is between 2 and 3 h, depending on which agent or agents are chosen. The duration of spinal analgesia, however, decreases when administered to a woman in advanced labor versus one in early labor.¹⁶ Patients may have greater satisfaction with CSE than with standard epidurals, perhaps because of a greater feeling of self-control.¹⁷ The original description of spinal labor analgesia involved sufentanil or fentanyl,¹⁸ but the addition of isobaric bupivacaine to the opioid produces a greater density of sensory blockade while still minimizing motor blockade.¹⁹ Originally, 25 mcg of fentanyl or 10 mcg of sufentanil was advocated, but more recent studies have suggested using smaller doses of opioid combined with a local anesthetic.²⁰ For example, many clinicians are now routinely use 5 mcg of sufentanil or 15 mcg of intrathecal fentanyl. Recent studies have suggested that ropivacaine and levobupivacaine can be substituted for intrathecal bupivacaine to provide labor analgesia.^21,22 The CSE technique has also made ambulation possible for many women receiving neuraxial analgesia, although ambulation may be possible with other techniques. In addition to the advantage of rapid onset of pain relief, the CSE technique may reduce the incidence of several potential problems associated with the conventional epidural technique, including incomplete (patchy) blockade, motor block, and poor sacral spread. Another potential advantage of the CSE technique is that, as suggested by preliminary study, it may be associated with a significant reduction in the duration of the first stage of labor in primiparous parturients.^23,24

Cesarean Delivery

The CSE technique, first reported as an option for cesarean section in 1984,²⁵ has recently increased dramatically in popularity. The advantage of this technique is that it provides rapid onset of dense surgical anesthesia while allowing the ability to prolong the block with an epidural catheter. In addition, because the block can be supplemented at any time, the CSE technique allows the use of smaller doses of spinal local anesthetics, which may in turn reduce the incidence of high spinal block or prolonged hypotension.²⁶ Potential problems of the CSE technique for cesarean delivery include an inability to test the catheter, the possibility of a failed epidural catheter after spinal injection, and the risk of enhanced spread of previously injected spinal drug after use of the epidural catheter.²⁷

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Advantages Of CSE

Comparison With Conventional Epidural Or Subarachnoid Anesthesia

When CSE block was compared with either epidural or subarachnoid block for hip or knee arthroplasty, CSE anesthesia was found to be superior to epidural anesthesia. With the CSE technique, surgical anesthesia was rapidly established, saving 15–20 min compared with epidural anesthesia. Furthermore, the epidural catheter provided the possibility of supplementing insufficient subarachnoid anesthesia.⁴ Patients who received the CSE technique had a more rapid onset of anesthesia and more intense motor blockade than those who received epidural anesthesia alone.

CSE has been reported to decrease the failure rate and incidence of adverse events of neuraxial analgesia.²⁸ In a retrospective analysis of 19,259 deliveries (75% neuraxial labor analgesia rate), the overall failure rate with this technique was 12%. The patients had adequate analgesia from initial placement, but 6.8% of patients had subsequent inadequate analgesia during labor and required epidural catheter replacement. Ultimately, 98.8% of all patients received adequate analgesia, even though 1.5% of patients had one or more replacements. However, when compared with epidural analgesia alone for labor, the incidence of overall failure, accidental intravascular placement of epidural catheters, accidental dural punctures, inadequate epidural analgesia, and catheter replacements were shown to be significantly lower in patients receiving CSE analgesia.^15,28,29

Norris and coworkers and Eappen and colleagues reported that CSE has higher success rate than the conventional epidural technique.^15,28 This difference may be due to the option to confirm questionable epidural location by successful spinal injection.

CSE enables low-dose spinal anesthesia for cesarean delivery.³⁰⁻³⁴ When using SSS anesthesia for ambulatory surgery, many anesthesiologists tend to overdose because there is only one chance to ensure an effective spinal block. The presence of an epidural catheter as a “safety net” allows the anesthesiologist to use the lowest effective dose of local anesthetic. Urmey and coworkers used the CSE technique to investigate the appropriate dose of intrathecal isobaric lidocaine 2% for day-case arthroscopy.³⁵ The CSE technique provided excellent anesthesia for all 90 patients in his study. Patients receiving the smallest dose (40 mg) had a significantly shorter duration of anesthesia, which allowed quicker discharge than for the patients receiving 60 or 80 mg of intrathecal lidocaine.

Norris suggested the use of a CSE technique with intrathecal sufentanil alone for outpatient shock-wave lithotripsy, reserving the use of epidural catheter for patients with inadequate analgesia.³⁶

Epidural volume extension (EVE) and enhancement of a small-dose intrathecal block by epidural saline infusion has been demonstrated via a CSE technique.³⁷ The advantage of this EVE technique is that a small-dose spinal block may provide an adequate level of anesthesia while allowing faster motor recovery of the lower limbs. In a prospective, randomized, double-blind study, the EVE technique was compared with SSS anesthesia with respect to its sensory and motor block profile and hemodynamic stability. Sixty-two patients scheduled for elective cesarean delivery were randomized to receive either spinal anesthesia with hyperbaric 0.5% bupivacaine (9 mg) and fentanyl (10 mcg) or CSE with intrathecal hyperbaric 0.5% bupivacaine (5 mg) with fentanyl (10 mcg), followed by 0.9% saline (6.0 mL) through the epidural catheter 5 min later. Both groups were comparable in terms of demographic data and duration of surgery. In the comparison of sensory block, both groups had similar peak sensory block height and VAS pain scores. The hemodynamic profile and ephedrine dose required were comparable between the two groups. Patients in the EVE group, however, demonstrated significantly faster motor recovery to modified Bromage score of 0 (73 ± 33 min versus 136 ± 32 min; p < 0.05). CSE with EVE provided adequate anesthesiawith only 55% of the bupivacaine dose and allowed faster motor recovery of the lower limbs.

In another study, four different intrathecal doses of hyperbaric bupivacaine (2.5, 5, 7.5, and 10 mg) were compared in patients undergoing cesarean section under sequential CSE block, a technique that involves administration of a relatively small subarachnoid block that may be supplemented as needed by epidural local anesthetics. The authors demonstrated that 5 mg of intrathecal bupivacaine combined with an appropriate dose of epidural lidocaine provided adequate surgical analgesia while maintaining hemodynamic stability. Higher doses of intrathecal bupivacaine were associated with typical adverse effects of high subarachnoid block such as nausea, vomiting, and dyspnea.³⁸

CSE For High-Risk Patients

The sequential CSE technique may be particularly advantageous in high-risk patients, such as those with cardiac disease, when slower onset of sympathetic blockade is desirable.³⁹ Most spinal anesthetics are administered as a single-injection procedure and rapid onset of sympathetic blockade may result in abrupt, severe hypotension. Traditionally, high-risk patients are treated with slow epidural anesthesia, which requires much higher total dosages of local anesthetic than is the case with sequential CSE.With careful positioning of the patient prior to induction of subarachnoid anesthetic, and by allowing titration with small incremental epidural doses to the precise level of anesthesia desired, the sequential CSE technique may enhance the safety of the neuraxial block.

In summary, CSE can reduce or eliminate many of the disadvantages of subarachnoid or epidural anesthesia alone while preserving their respective advantages. The CSE block offers the speed of onset, efficacy, and minimal toxicity of a subarachnoid block combined with the potential for improving an inadequate block or prolonging the duration of anesthesia with epidural supplements and extending the analgesia well into the postoperative period. Although the sequential CSE technique will take somewhat longer than the standard CSE technique, the use of minimal doses of local anesthetics has been shown to reduce the frequency and severity of hypotension when compared with epidural or spinal techniques.⁴⁰

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Functional Anatomy Related To CSE

When performing an epidural block, skin to epidural space distance (SED) and the posterior epidural space distance (PED) are measures that can help in reducing the inadvertent penetration of the dura and injury to neural structures.^41,42 The knowledge of these measures is also important in the success rate of epidural anesthesia. The PED, a measure of the epidural space depth, is particularly important with the CSE needle-through-needle (NTN) technique. Underestimation of this distance (short protrusion of the spinal needle through the epidural needle) will result in a higher incidence of spinal block failure. Any non-midline approach also would increase the risk of not reaching the subarachnoid space because the dural sac has a triangular shape with the top pointing dorsally. Overestimation of PED will cause overprotrusion of the spinal needle that may increase the risk of neural damage.⁴³ These distances have been measured using various methods,⁴⁴ including MRI, CT, and measurement of CSE tip-to-tip distance or the amount of protrusion of the spinal needle beyond the Tuohy needle. The SED distance is most commonly 4 cm (50%) and is 4–6 cm in 80% of the population according to detailed records of 3200 cases.⁴⁴ The width of the PED varies with vertebral level, being thewidest in the midlumbar region (5–6 mm) and decreasing toward the cervical vertebral column. In the midthoracic region, it is 3–5 mm in the midline and narrows laterally. In the lower cervical region, it is only 1.5–2 mm in the midline.⁴⁵ These spaces also correlate with the weight-to-height ratio and BMI.⁴⁶ Based on these measures, the present design of spinal needle protrusion varies between 10 and 15 mm beyond the epidural needle.

Epidural Space & Ligament Flavum

The thickness of the ligamentum flavum, distance to dura, and skin-to-dura distance varywith the area of vertebral canal (Table 1).

Table 1. Characteristics of Ligamentum Flavum at Different Vertebral Levels
Site	Skin to Ligament (cm)	Thickness of Ligament (mm)
Cervical	–	1.5–3.0
Thoracic	–	3.0–5.0
Lumbar	3.0–8.0	5.0–6.0
Caudal	Variable	2.0–6.0
Data used, with permission, from Brown DL: Spinal, epidural, caudal anesthesia. In Miller RD (ed): Anesthesia, 6th ed. Churchill Livingstone, 2005, pp 1657.

The two ligamenta flava are variably joined (fused) in the midline, and this fusion or lack of fusion of the ligamenta flavum occurs at different vertebral levels in individual patients. Lirk and coworkers investigated the incidence of midline gaps in the lumbar ligamentum flavum in embalmed cadavers.⁴⁷ Vertebral column specimens were obtained from 45 human cadavers. The gaps in the lumbar ligamentum flavum are most frequent between L1 and L2 (22.2%) but are rare below this level (L2 through L3=11.4%, L3 through L4 = 11.1%, L4 through L5 = 9.3%, L5 through S1 = 0). Therefore, when using midline approach, one cannot rely on the ligamentum flavum to impede entering the epidural space in all patients.

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Technique

A number of recent reviews have discussed the technical factors related to performance and success of CSE.⁴⁸⁻⁵⁰

Although CSE is considered a new technique, Soresi in 1937 described the intentional injection of anesthetic agents outside and within the subarachnoid space.⁵¹ Somewhat different from current practice, Soresi intentionally used a single needle. He first injected some local anesthetic into the epidural space and then advanced the needle and injected the rest of the medication to cause a subarachnoid block. Although this technique included both spinal and epidural anesthesia, no catheter was used. In 1979 Curelaru⁵² reported the first CSE with an introduction of an epidural catheter through a Tuohy needle. Catheter insertion was followed by a test dose and then a traditional dural puncture, which was performed at a different interspace using a 26-gauge spinal needle. That same year, Brownridge suggested the use of CSE for obstetrics. He described successful use of CSE for elective cesarean section in 1981.^53,54 In 1982, the needle-through-needle (NTN) CSE technique was first described independently by Coates⁵⁵ and Mumtaz and colleagues,⁵⁶ and its use in obstetric practice was first published in 1984 by Carrie and O’Sullivan.⁵⁷

Several approaches for initiation of CSE have been described in the recent literature.

Needle-Through-Needle Technique

In contrast to Serosi’s description of CSE, in which a single needle was introduced into the epidural space and then advanced into the subarachnoid space, the needle-through-needle (NTN) technique includes use of separate epidural and spinal needles.

The epidural space is penetrated with a conventional epidural needle and technique, and then a long spinal needle is passed through the epidural needle until CSF appears in the hub of the spinal needle. Drug is administered into the subarachnoid space, the spinal needle is removed, and an epidural catheter is inserted into the epidural space (Figures 1 through 7). Although several different CSE techniques are used in clinical practice (including the two needle, two interspace technique), NTN is the most widely used CSE technique in the US.

Figure 1. Epidural needle is placed in the epidural space indentically to the technique in epidural anesthesia	Figure 2. Entry of the needle into the epidural space is recognized by a sudden loss of resistance to injection of air.	Figure 3. A small-bore spinal needle is placed through the epidural needle until CSF appears at the hub of the needle, indicating successful entrance of the spinal needle into the subarachnoid space. Typically, a loss of resistance is felt as the needle makes a slight bend to exit through the curved tip of the epidural needle and another as the spinal needle pierces the dura and enters the subarachnoid space.
Figure 4. CSF appears in the hub of the spinal needle, indicating the subarachnoid placement of its tip.	Figure 5. A desired dose of local anesthetic with or without additives is injected through the spinal needle.	Figure 6. A flexible catheter is placed through the epidural needle and left about 5 cm in the epidural space.
	Figure 7. Epidural catheter is checked by the aspiration test to rule out its inadvertent intravascular (appearance of blood in the catheter) or intrathecal (appearance of CSF) placement.

Separate Needle Technique

CSE may be performed using two separate needles (separate needle technique; SNT), with spinal block and epidural catheter placement at either a single^58,59 or two different interspaces.⁶⁰⁻⁶² If the epidural catheter is placed first, proper placement can be tested before administration of spinal medications, potentially decreasing the risk of inadvertent intravascular or intrathecal catheter migration. Placing the epidural catheter first may also reduce the risk of neural damage, which may occur when the catheter is inserted after subarachnoid block, since paresthesia and other warning signs of improper needle placement may be absent after administration of spinal medications. However, there is also a risk of striking the epidural catheter with the spinal needle.⁶³⁻⁶⁵ Some authors consider this to be a purely hypothetical risk and have demonstrated that it is not possible to perforate an epidural catheter with commonly used spinal needles.^66,67

Cook⁶⁸ recently reported a series of 201 consecutive CSEs performed with a novel separate-needle technique. The study was designed to avoid potential and actual problems associated with the CSE technique. Cook placed the spinal needle in the subarachnoid space and then replaced the spinal needle stylet to stop the CSF leak. He next placed the epidural catheter through a different interspace and returned to the spinal needle to inject the subarachnoid drug, thus avoiding epidural catheter insertion in an anesthetized patient. This method of CSE anesthesia, though more work, may be associated with high success and low complication rates.

Regardless of which component is performed first, the major disadvantage of the two-needle/two-interspace technique is that it takes longer to perform and requires two separate injections.

Comparison Of Techniques

Comparison of NTN & SNT CSE Techniques

The SNT technique has a few theoretical advantages over the NTN technique. It enables placement of the epidural catheter prior to initiation of the spinal block. The SNT may thus theoretically reduce the risk for neurologic injury, since paresthesia and other symptoms are not masked. Since the epidural catheter is placed early, problems that may occur due to delayed catheter placement (technical problems) after the injection of a hyperbaric spinal solution (such as unilateral, sacral, or low lumbar regional neuraxial block) are avoided.⁶⁹⁻⁷¹

Several studies have compared NTN and SNT techniques.⁷²⁻⁷⁵ Some have reported better success and lower failure rates with the SNT. However, these studies also report greater patient acceptance and less discomfort with the NTN technique. A recent prospective randomized study⁷⁶ compared the outcomes and techniques of NTN and SNT (double space) CSE in 200 patients receiving elective cesarean section. A successful block to the T5 level with the double–space and the NTN techniques were 80 vs 54, with an odds ratio of 0.29. SNT had a greater success rate than the NTN technique; the T5 dermatome was reached with fewer corrective manipulations (epidural augmentation or repeated blocks). Failure to enter the intrathecal space once the epidural space had been located occurred in 29 patients in the NTN group. Time to readiness for surgery was slightly increasedwith SNT (15 min with SNT vs 12.9 min with NTN).

Techniques To Improve Success & Safety Of CSE

The success of CSE block depends heavily on accurate cannulation of the epidural space. The identification of the epidural space is traditionally achieved by a blind loss of resistance. With the blind handling of the needles, in which the feedback to the operator is merely tactile, deviation of the axis of the needle trajectory may occur. Because of the triangular form of the dural sac, deviation from the midline of the spinal needle will cause the operator to miss the dural sac, leading to spinal component failure or unsuccessful dural puncture. Complications such as paresthesia, postdura lpuncture headache (PDPH) are also associated with the puncture technique.

Grau and coworkers performed real-time ultrasonic scanning of the lumbar spine to provide accurate reading of the location of the needle tip and to facilitate the performance of CSE anesthesia.⁷⁷ Their aim was to establish a less-invasive method to monitor the advancement of the needle in real time.

Thirty parturient patients scheduled for cesarean section were randomized to three equal groups. Ten control patients received conventional CSE anesthesia. Ten received ultrasonic scans by an offline technique. The remaining 10 received online imaging of the lumbar region during puncture. The Tuohy needle was inserted using the midline approach in all three groups. In the control group, CSE was performed using the single-space NTN technique with the standard loss of resistance to saline method.

In the offline group, ultrasound images were taken just before the puncture to improve needle trajectory. In the online group, ultrasonic images were taken to monitor and identify needle trajectory in real time.

They reported that in both ultrasound groups, a significant reduction in the number of necessary puncture attempts was found (p < 0.036); the number of interspaces necessary for puncture was reduced (p < 0.036); the number of spinal needle manipulations was significantly reduced (p < 0.036). Dural tenting was observed in 9 out of 10 online group (tenting length 2.4 mm). Asymmetric block was observed in 10% of those in the control group, but not in any of those in the ultrasound groups.

The authors concluded that the use of ultrasound imaging was obviously helpful in finding the ideal needle trajectory and to improve puncture conditions by demonstration of the relevant anatomy.

In the CSE NTN technique, there is no practical test to confirm correct epidural catheter placement. Tsui and colleagues proposed the use of nerve stimulators to confirm the proper placement of epidural catheter.⁷⁸ They studied 39 obstetric patients in labor who received epidural catheters (not CSE) for analgesia. A low-current (1–10 mA) electrical stimulation was used to confirmthe correct placement of epidural catheter (19-gauge Arrow Flextip Plus). A positive motor response (truncal or limb) indicated that the catheter was in the epidural space. They reported that the sensitivity and specificity of this test was 100% and 100%, respectively, with 38 true-positive tests and 1 true-negative test. A case of intravascular epidural catheter migration was detected using this new test and was subsequently confirmed by a positive epinephrine test. If the motor response only occurs with larger currents (> 10 mA) or does not respond at all (before receiving any local anesthetics), the catheter is outside the epidural space. If a positive response occurs at an unusually low milliamperage (< 1 mA), intrathecal placement is likely.

The electrical stimulation test may not be applicable when the CSE technique is used for surgery in which anesthetic doses of local anesthetics are administered intrathecally prior to the placement of the epidural catheter. When using the CSE technique for labor analgesia, this test may be utilized as a simple and practical method for determining the epidural catheter placement. The standard test dose (3 mL of 1.5% lidocaine with 1:200,000 epinephrine) may help to identify vascular and intrathecal placement, but it does not verify appropriate epidural placement or function.

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Pharmacologic Choices For CSE

Sufentanil and fentanyl, with or without local anesthetics, are most often administered intrathecally to provide analgesia for the laboring woman receiving CSE. The usual dosage of sufentanil is 2.5–10 mcg; however, most practitioners are now using 2.5 or 5 mcg. The ED50 and ED95 for laboring patients were found to be 2.6 mcg and 8.9 mcg, respectively.⁷⁹ The doses of fentanyl used are typically 10–25 mcg. The median effective dose (ED50) and the effective dose for 95% of patients (ED95) for laboring patients has been reported to be 5.5 and 17.4 mcg, respectively.⁸⁰ Although the original studies used much higher doses of intrathecal opioids (10 mcg sufentanil and 25–50 mcg of fentanyl), subsequent studies have suggested the use of smaller doses, with reduced side effects and similar analgesic effect.⁸¹

Morphine, a highly ionized, water-soluble opioid, produces analgesia of long duration, but with a slow onset (approximately 60 min between injection and onset). In addition it may be associated with an unacceptably high incidence of side effects such as nausea, vomiting, and pruritus, as well as the potential for delayed respiratory depression. These side effects, coupled with the slow onset of pain relief, limit the usefulness of intrathecal morphine for labor analgesia. Intrathecal meperidine (10 mg) may provide reliable analgesia in advanced labor,⁸² but has been associated with a high incidence of nausea, vomiting, hypotension, and ephedrine requirement. In addition, it is the only opioid that has intrinsic local anesthetic properties at clinically used doses,⁸² by blocking nerve conduction at the proximal end of the dorsal root⁸³ by a mechanism other than sodium channel blockade.⁸⁴ This nerve conduction blockade is not naloxone reversible.⁸³

In many patients, a single intrathecal injection of a lipidsoluble opioid is insufficient to produce analgesia for the entire duration of labor.

When the second stage of labor is imminent, the subarachnoid administration of local anesthetic plus opioid should be considered to achieve a greater depth of pain relief. The combination of 2.5 to 5 mcg sufentanil plus 2.5 mg bupivacaine provides rapid analgesiawithoutmotor block, alleviates the pain of the second stage of labor, and lasts longer than sufentanil alone.⁸⁵ Although the original reports⁸⁶ recommended the use of 10 mcg of sufentanil, Sia and colleagues showed that adequate relief of labor pain could be safely provided by administering half that dose of intrathecal sufentanil plus bupivacaine.⁸⁷

New studies⁸⁸ have attempted to determine the ED50 for intrathecal bupivacaine, defined as the minimum local anesthetic dose (MLAD) and then use this to asses the effect of different doses of fentanyl. The MLAD of intrathecal bupivacaine has been found to be 1.99 mg, and the addition of 5 mcg of intrathecal fentanyl offered a similarly significant sparing effect to 15 or 25 mcg of fentanyl, resulting in less pruritus but with a shortening of duration of action.

Levin and coworkers compared a standard dose of intrathecal bupivacaine with sufentanil for CSE analgesia using two doses of ropivacaine (2 and 4 mg) with sufentanil and concluded that both local anesthetics provided similar duration of labor analgesia with equivalent side effects.⁸⁹ In addition, a recently published pilot study showed that intrathecal ropivacaine with or without sufentanil also provides effective analgesia and does not impair motor strength, which might facilitate ambulation during labor.⁹⁰

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Complications & Concerns Of CSE Technique

Failure Of The Spinal Component

The most common method of performing a CSE is the single-interspace NTN technique. In earlier reports, failure to achieve a spinal block with this technique has been reported in 10 to 15% of cases in the past.^91,92 However, more recent reports have demonstrated failure rates in the range of 2 to 5%.⁹³⁻⁹⁵

Figure 8. Successful entrance into the epidural space may not always guarantee successful subarachnoidal needle placement. This can particularly be the case with an odd angle of needle insertion or the use of excessively long needles that may bend during the advancement. Figure 9. A CSE needle-through-needle design with the spinal needle exiting the epidural needle. The spinal needle is shown exiting at an angle that may cause it to miss the subarachnoid space.

Most current needle designs allow extension of the spinal needle 12–15 mm beyond the tip of the Tuohy needle. Excessively long needles, however, pose problems of handling and depth of placement. Deviation from midline will lengthen the epidural–dural distance and may also cause the spinal needle to miss the spinal space laterally (Figures 8 and 9). Saline used to identify the epidural space may enter the spinal needle and may be misinterpreted as CSF.

Spinal Migration Of The Epidural Catheter & Intrathecal Administration Of Epidural Drugs

Subarachnoid Placement of Intended Epidural Catheter

One of the concerns with the CSE technique is that the epidural catheter may inadvertently pass through the dural puncture hole into the subarachnoid space during CSE technique. This seems more likely with NTN CSE technique than with SNT or with epidural needles with back holes. Although this may seem a rare theoretical problem, several publications have reported its occurrence.^109−112

Angle and coworkers¹¹³ recently studied factors contributing to unintentional subarachnoid catheter passage after epidural placement with an in vitro model using human dural tissue. In that study, the dura was punctured with 25-gauge Whitacre spinal needles. The researchers compared the subarachnoid catheter passage of the intact dura with that of the dura with obvious epidural needle punctures, and single 25-gauge Whitacre spinal needle punctures after a CSE technique. Their conclusion was that the catheter passage intrathecally is unlikely in the presence of an intact dura or after an uncomplicated combined spinal–epidural technique.

Therefore, unintentional subarachnoid passage of the epidural catheter suggests dural damage with the epidural needle.

Holtz and colleagues investigated the possible passage of the epidural catheter into the subarachnoid space in an anatomic preparation.¹¹⁴ In 10 series of experiments, the epidural compartment was entered with an 18-gauge Tuohy needle. The spinal puncture (27- or 29-gauge Quincke needle) was performed with the NTN technique. Subsequently, the internal side of the intrathecal compartment was examined endoscopically for penetration of the epidural catheter. In a similar way, the endoscope was inserted epidurally to visualize the movements of the epidural catheter in the epidural compartment. In this model of simulated physiologic intrathecal conditions, using a one-space NTN technique, they could not detect intrathecal passage of the epidural catheter.

Holmstrom and coworkers also reported, in a percutaneous epiduroscopy study using fresh cadavers that it was impossible to force an epidural catheter into the subarachnoid space after a single perforation of the dura with a small-gauge spinal needle. However, they found that the risk of intrathecal catheter migration increased to approximately 5% after multiple dural punctures with the spinal needle. Dural penetration of the epidural catheter after a dural puncture with a Tuohy needle was clearly demonstrated in the same study.¹¹⁵

Whether the incidence of an unintentional passage of the epidural catheter into the subarachnoid space is greater with CSE than with standard epidural technique alone is controversial. Therefore, regardless of the technique used, all epidural medications should be given in incremental doses.

Subarachnoid Spread of Epidurally Administered Drugs

Leighton and colleagues reported that following a CSE, a dose of epidural local anesthetic will produce a higher dermatomal level than expected, presumably due to subarachnoid flux of the drug. However, when used for labor analgesia, unless the dura is breached with the epidural needle¹¹⁶ or large bolus volumes are administered,¹¹⁷ flux should not be clinically significant. Suzuki and coworkers found that dural puncture using a 26-gauge Whitacre spinal needle before the epidural injection in nonpregnant patients increased caudal spread of analgesia induced by epidural local anesthetics with no change in the cephalad spread.¹¹⁸

Holst and coworkers investigated endoscopically the possible passage of the epidural catheter anesthetic through the dural puncture hole into the CSF compartment in an anatomic preparation.¹¹⁴ Even 1 h after epidural administration of 20 mL of methylene blue-dyed local anesthetic (bupivacaine 0.5%, isobaric), no passage of local anesthetic into the intrathecal compartment could be detected under continuous endoscopic monitoring.

Theoretically, a dural puncture may allow dangerously large quantities of subsequently administered epidural drugs to reach the subarachnoid space. Bernard and colleagues investigated the risk of epidural drug reaching the subarachnoid space through the dural hole left by spinal needles and concluded that the magnitude of flux was a function of the diameter of the spinal needle. The risk may be decreased by using the smallest possible needle to puncture the meninges.¹¹⁹ However, the possibility of this hazard is supported by reports of high or total spinal block during epidural anesthesia administered following unintentional dural perforation with the epidural needle.^120,121 Eldor and coworkers reported a case of delayed respiratory arrest in the CSE anesthesia. They commented: “The event was likely due to morphine injected through the epidural catheter, unintentionally entering into the subarachnoid space through the hole in the dura that was made previously by the spinal needle in the needle-through-needle technique.”¹²¹ However, data from some clinical studies of the CSE technique have not indicated an increase in spread of sensory block due to subarachnoid leakage of epidurally administered medications.^{114,122−124}

The administration of a test dose for spinal placementof an epidural catheter may be problematic and aspiration may fail, but test doses have been found to detect more intrathecal catheters than aspiration alone during labor analgesia.¹²⁵ Despite the studies that have reported that intrathecal migration is very rare and the flux should not produce clinically relevant complications, epidural drugs or catheters may migrate into the spinal space following CSE. Therefore, all epidural doses should be incremental and patients receiving continuous epidural infusions for analgesia should be checked every hour to rule out excessive motor or sensory block that may be indicative of intrathecal administration of drugs.

Hypotension

Does subarachnoid block induced by CSE (using loss of resistance to air) render a higher level of sensory anesthesia than single-shot spinal (SSS) when an identical mass of intrathecal anesthetic was injected?

Goy and Sia performed a prospective randomized study comparing CSE (using loss of resistance to air) vs SSS on 60 patients who were undergoing minor gynecologic procedures and concluded that subarachnoid block induced by CSE produces a greater sensorimotor anesthesia (p < 0.01) and prolonged recovery (p < 0.05) than SSS.¹²⁶ They also found a more frequent incidence of hypotension and vasopressor use in the CSE group (p < 0.05), despite using identical doses of intrathecal medications.¹²⁶

Another study reported similar findings when only 4 mL of air was used as part of the loss-of-resistance technique.¹²⁷ The objective of that study was to determine the ED50 of intrathecal hyperbaric bupivacaine for CSE and SSS by using the up–down sequential allocation technique. Sixty participants were separated into two groups in a doubleblind, randomized, prospective study design. The researchers concluded, under similar clinical conditions, that the ED50 of intrathecal hyperbaric bupivacaine in CSE was 20% less than that in SSS. Although the mechanism that accounts for this finding is undetermined, the loss-of-resistance technique in CSE could introduce air pockets within the epidural space. MRI has demonstrated residual air pockets to extend up to three lumbar vertebral segments and compress the lumbar thecal sac dorsally and laterally.¹²⁸ This could result in a reduction of the lumbosacral CSF volume and enhance the extent of sensory anesthesia.¹²⁹

Epidural administration of drugs seems to affect the thecal contents and therefore influences the spread of earlier induced subarachnoid block.^130,131 The magnitude of this effect depends on the time interval between the injections and the volume of the epidural injectate. Initially, the proposed mechanism for this effect was the subarachnoid leakage of epidurally administered medications.

In a retrospective study Klasen and colleagues examined whether the patients receiving spinal anesthesia as part of CSE experienced amore frequent incidence of relevant hypotension than patients receiving spinal anesthesia alone.¹³² Anesthesia records from 1596 patients who received spinal anesthesia and 1023 patients who received CSE for elective surgery were reviewed. The investigators reported that the patients who had CSE had a significantly more frequent prevalence of arterial hypertension as a major risk factor. The level of sensory block after 10 min was higher with CSE than with spinal anesthesia alone. In this study after the typical loss of resistance, a volume of 5 to 10 mL of saline 0.9% was injected into the epidural space, followed by dural puncture and administration of intrathecal local anesthetic. They suggested that the increased volume in the lumbar epidural space with 5 to 10 mL of saline may lead to an enhanced cephalad spread of the local anesthetic in the subarachnoid space.

Blumgart and colleagues in a prospective, randomized study, demonstrated a similar increase in cephalad spread of subarachnoid block after either 10 mL of saline or 10 mL of local anesthetic solutions when injected epidurally after establishing a subarachnoid block.¹³³ Thus, they concluded that the mechanism of extension of spinal anesthesia by extradural injection of local anesthetics is largely a volume effect.

In a prospective randomized study Takiguchi and coworkers reported similar results.¹³⁴ The purpose of that study was to clarify the volume effect caused by epidural injection of saline after spinal anesthesia.¹³⁴ The participants were 20 patients undergoing cesarean delivery under CSE anesthesia whose analgesic levels did not reach the surgical regions 10 min after spinal medication. These patients were randomly assigned to two groups. The control group (n = 10) received no epidural saline, and the saline group received 10 mL of saline through the epidural catheter 10 min after spinal anesthesia. In the saline group, the levels of analgesia 15 and 20 min after spinal anesthesia were significantly higher than those in the control group (p < 0.05). Next, they examined the volume effect of epidural saline with myelography using two subjects. They reported that the diameter of the subarachnoid space diminished to less than 25% after injection of saline. Concurrently, the contrast medium injected into the lumbar subarachnoid space increased from L3 to L1 and from L2 to T12.

Hypotension can occur following the administration of intrathecal fentanyl or sufentanil, even if sympathetic blockade does not occur. However, the hemodynamic effects of intrathecal fentanyl are usually benign in nature and typically due to a decrease in catecholamines secondary to pain relief. Vasodilation due to sympathectomy, however, causes a decrease in preload, end-diastolic index, and in stroke index, as well as an increase in heart rate. Since the end-diastolic index and stroke index remained relatively stable and the heart rate decreased in a study by Mandell and colleagues, these authors concluded that the observed hypotension was not due to vasodilation.¹³⁵ The hypotensive episodes following administration of neuraxial opioids for labor are transient, easily treated, and not necessarily associated with adverse fetal heart rate changes.

Neurologic Injury

Neurologic complications directly related to spinal anesthesia may be caused by trauma, cord ischemia, infection, and neurotoxicity.

Needle Trauma

Needle- or catheter-induced trauma rarely results in permanent neurologic injury. However, Horlocker and coworkers, in a retrospective review of 4,767 consecutive spinal anesthetics for CNS complications, concluded that the presence of a paresthesia during needle placement significantly increased the risk of persistent paresthesia (p < 0.001). In that review, paresthesia was elicited during needle placement in 298 (6.3%) cases. Six patients reported pain (persistent paresthesia) upon resolution of the spinal anesthetic; four of the cases resolved within 1 week, and the remaining two resolved in 18 to 24 months.¹³⁶ It is not known, however, how the report of the paresthesia by the patient can be used to avoid such complications from occurring.

The increase in the risk of neurologic sequelae following the CSE technique may have the following causes. In the single-space, NTN technique, the insertion of epidural needle and catheter after administration of spinal local anesthetics may prevent identification of paresthesias that may warn the anesthesiologist about needle misplacement. Higher incidence of paresthesia during CSE is a recognized factor. In accordance with literature paresthesia is reported in 0.9 to 11% of patients undergoing CSE.¹³⁷ Browne and colleagues reported a 14% incidence of paresthesias with the Espocan needle (18-gauge Tuohy epidural needle with an extra lumen in the needle bevel) and a 42% incidence with the conventional Tuohy epidural needle.¹⁴

In a randomized prospective study, McAndrew and Harms reported that 37% (17 of 46) of women in the NTN group and only 9% (4 of 43) in the SSS group had paresthesia upon spinal needle insertion (p < 0.05). The equipment used was a 16-gauge/26-gauge CSE kit and a 26-gauge pencil point spinal needle with introducer (both Sims Portex, Australia). They postulated that the higher incidence of paresthesia may be related to deeper penetration of the subarachnoid space with CSE technique. However, in that study, none of the patients had persistent neurologic symptoms on examination at postoperative day 1.¹³⁸

Holloway and coworkers conducted a pilot survey on anesthetists’ experiences of neurologic sequelae following spinal and CSE anesthesia in obstetric units in the UK.¹³⁹ Because of the retrospective nature of the survey, many neurologic problems that were reported lacked detail. However, no obvious differences occurred in the incidence of problems associated with CSE vs the SSS techniques. Turner and Shaw suggested the possibility that painful insertion and subsequent root damage might be increased by the use of atraumatic pencil point spinal needles.¹⁴⁰ In that survey, problems were reported with both Whitacre and Sprotte needles, but none with Quincke needles. However, the numbers using Quincke needles were too small to permit statistical analysis. More dangerous than root damage is damage to the spinal cord, and in that survey¹⁴⁰ two cases of conus damage were reported: one with CSE and one with SSS. This complication is not a fault of atraumatic needles, but rather of the technique itself. In 19% of patients the spinal cord terminated below L1. In more than 50% of cases the chosen space is incorrectly identified.¹⁴¹ Therefore, the L3-4 intervertebral space or below should be selected for CSE or SSS.

Risk of Metal Toxicity in CSE

It has been alleged that during the NTN technique, tiny metal particles abraded by the spinal needle from the inner edge of the Tuohy needle may be introduced into the epidural or spinal compartment.¹⁰⁸ In order to examine this concern, Holst and colleagues simulated the NTN technique in an in vitro model.¹¹⁴ They used atomic absorption spectrography (AAS) to identify abraded metal particles. The needles were then examined under an electron microscope. They reported no increased alloy components detected in the rinse solution after either two-fold or five-fold puncture compared with the control measurements. After five punctures, and handling the needle as in normal practice, no traces of use could be detected by electron microscopy on the inner ground edge of the Tuohy needle.¹¹⁴

Infectious Neurologic Complications

Although overall incidence of infections and their sequelae following placement of CSE is perceived to be extremely low, the relative risk compared with either a spinal or epidural alone is unknown.

In a classic study, Dripps and Vandem prospectively reported no cases of meningitis after 10,098 spinal anesthetics.¹⁴² Phillips and coworkers also reported no cases after a prospective review of 10,440 such cases.¹⁴³ These studies included patients undergoing obstetric and urologic operations, which are known to be associated with perioperative bacteremia. However, case reports of meningitis following CSEs appear in the journals beginning mid-1990s.^144,145 Theoretically, CSE is thought to be associated with an increased risk of meningitis compared with epidural alone because the dura (protective barrier for the CNS) is punctured deliberately during CSE and then a foreign body, an epidural catheter, is placed nearby. The epidural catheter can lie close to the dural hole and is a potential focus of infection, especially following bacteremia.¹⁴⁶ Contamination of the subarachnoid space may occur from bleeding due to needle trauma in a bacteremic patient or from failure of aseptic technique.

Headache and neck pain or neck stiffness in a patient who recently received spinal anesthesia is often attributed to postdural puncture headache (PDPH). One case report highlighted the dangers associated with missed diagnosis of meningitis. The patient was misdiagnosed as having endometritis when she presented with headache, vomiting, and fever 2 days after uncomplicated epidural analgesia for labor. Her condition rapidly deteriorated, and meningitis was not considered as a diagnosis until it was too late. She died in intensive care a few weeks later.¹⁴⁷

Several studies have shown that facemasks prevent forward dispersal of organisms from upper airway and downward dispersal during talking and head turning.^148,149 Despite this, in 1996 a postal survey of members of the Obstetric Anaesthetists Association found that over half those surveyed did not routinely wear facemasks when performing neuraxial anesthesia.¹⁵⁰

Postdural Puncture Headache

The incidence of PDPH after CSE technique is controversial; some authors have reported decreased incidence when compared with epidural alone,¹⁵¹ but others report an increased incidence.¹⁵²

Norris and coworkers¹⁵ reported that the patients who requested only epidural analgesia were more likely to suffer an accidental dural puncture (twofold increase; epidural vs CSE = 4.2%:1.7%). These investigators offered two possible explanations for this result. The first was that they usually choose CSE for women who are most often in early labor and reserved epidural analgesia for patients in the more painful active phase of labor. Therefore, the patients in the epidural group aremore likely to move during the procedure, and thus cause a “wet tap.” Secondly, during CSE if one is uncertain of the location of the epidural needle, the spinal needle can be inserted to look for CSF¹⁵³ or closeness to dura.

Other factors may decrease the incidence of PDPH following the CSE technique. Administration of intrathecal opioids has been shown to decrease the incidence of PDPH.¹⁵⁴ Subsequent infusion of an epidural local anesthetic increases the subarachnoid pressure and also may help to decrease the incidence of PDPH following CSE. Dunn and colleagues argued that the intentional dural puncture involved in the CSE technique would increase the risk of PDPH in obstetric patients compared with those receiving epidural analgesia alone.¹⁵² The use of small-gauge atraumatic pencil point spinal needles (such asWhitacre, Pencan, Sprotte, and Gertie Marx) greatly reduce the incidence of PDPH in patients receiving CSE.^151,155

Chan and Paech reported three cases of persistent CSF leak following uneventful CSE analgesia for labor.¹⁵⁶ Using β₂-transferrin immunofixation assay, they confirmed that the leaking fluid was CSF in two cases.¹⁵⁷ None of the patients developed PDPH or any other complications. Howes and Lenz also reported CSF cutaneous fistula in two patients following epidural anesthesia (not CSE) for postoperative pain relief. Both patients developed PDPH only after removal of the catheters and were treated successfully with an autologous blood patch.¹⁵⁸

Complications Related To Labor Analgesia

Fetal Bradycardia

Reports in the literature suggest an increased frequency of nonreassuring fetal heart rate tracings and fetal bradycardia associated with CSE.^159−161 The cause of the fetal bradycardia after CSE remains elusive, but it may be related to an acute reduction in circulating maternal catecholamine levels after the quick onset of analgesia. In addition, it has been postulated that an imbalance between epinephrine and norepinephrine levels causes unopposed α-adrenoceptor effects on uterine tone and decreases uterine blood flow. However, preliminary reports suggest that there may be no alteration in uteroplacental blood flow.¹⁶²

The resulting fetal bradycardia is usually short-lived and typically resolves within 5 to 8 min.¹⁶³ A retrospective study of 1,240 patients who received regional labor analgesia (mostly CSE) and 1,140 patient who received systemic medication or no analgesia demonstrated no significant difference in the rate of cesarean delivery, with rates of 1.3% and 1.4%, respectively. That study also reported that no emergency cesarean deliveries for acute fetal “distress” were necessary in the absence of obstetric indications up to 90 min after intrathecal sufentanil administration.¹⁶⁴

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Equipment

CSE technique has gained popularity and acceptance, especially in obstetrics. Special kits have been produced for CSE. (Example: B Braun Medical Ltd. comprising the standard 16–gauge, 8-cm Tuohy needle with a 26-gauge Quincke spinal needle). Various concerns of the CSE technique have led to some modification of the needles used.

The potential dangers of the single-level NTN kit include introduction of very fine metal particles abraded by the spinal needle as it is maneuvered through the tip of the Tuohy needle¹⁰⁸ and unintentional passage of epidural catheter through the dural hole caused by the spinal needle.¹⁰⁹ As previously mentioned, Holst and coworkers, using AAS, showed no contamination of the intrathecal space by metal particles after normal clinical use in the NTN technique.¹¹⁴

In order to direct the epidural catheter away from the dural puncture site, Rawal and colleagues recommended rotation of the epidural needle 180 degrees following dural puncture. This maneuver directs the epidural catheter 2–2.5 mm away from the dural puncture site.¹⁶⁵ However, Meikljohn, using postmortem dura mater, demonstrated that rotation of the epidural needle significantly decreases the force required to puncture the dura.⁹⁹

Figure 11. A specialized needle with an orifice in the back curve (back hole) of the epidural needle for separate spinal needle passage has been made available. A: The tip of the epidural needle is shown in the epidural space. A spinal needle is shown passing through the lumen of the epidural needle and entering the subarachnoid space. B: After the spinal anesthesia has been accomplished, the spinal needle is withdrawn and an epidural catheter is advanced into the epidural space.

Figure 10. Epidural needle with a back hole (an exit on the back of the Tuohy tip) for introduction of the spinal needle.

Recently, CSE kits designed with an orifice in the back curve (back hole) of the epidural needle for separate spinal needle passage have been made available¹⁴ (Figure 10).

This needle is expected to reduce the likelihood of dural passage of the epidural catheter by directing the catheter away from the dural puncture site (Figure 11). However, the spinal needle may not always go through the spinal needle orifice and may exit through the Huber tip, thus losing the advantage of the back hole¹⁴ Joshi and McCarroll suggested a technique to enhance the spinal needle exit through the spinal needle orifice.^91,166 The modified technique consisted of first aligning the bevel orifice of the spinal needle in the same direction as the Tuhoy bevel and then bending the spinal needle 10 degrees toward the Tuohy bevel while advancing through the Tuohy needle. This technique guides the spinal needle tip to exit through the back hole. In a prospective randomized study Pan evaluated the success rate of the spinal needle exiting through the spinal needle orifice, in two commonly available single-lumen, dual-orifice CSE needle kits.¹⁶⁷ The CSE kits studies were:

1. Espocan CSE kit (Braun Medical Ltd.), which consists of a standard 18-gauge Tuohy needle with a 26-gauge sleeved Quincke spinal needle that extends 12 mm beyond the tip of the Tuohy needle through the back hole. The sleeve on the spinal needle was designed to guide the spinal needle to exit through the back hole.
2. Espocan CSE kit (BraunMedical Ltd.), which consists of the same epidural needle with a 27-gauge nonsleeved Sprotte spinal needle that extends 13 mm beyond the tip of theTuohy needle throughthe back hole.

This researcher performed 1600 attempts, which included modified technique described by Joshi and McCarroll. The modified technique improved the success rate of spinal needle exiting through the back hole from 67% to 94% for kit 1 and 50% to 81% for kit 2; cephalad orientation of the Tuohy needle bevel further improved the success rate to 96% and 91%, respectively. Overall, the sleeved spinal needle has a better success rate than the unsleeved spinal needle.

The failure of the spinal needle to exit through the back hole may also result in bending of the spinal needle and less protrusion beyond the tip of the Tuohy needle. This may contribute to the increased failure rate of dural puncture. The ideal length of spinal needle protrusion is reported to be at least 12–13 mm. In a prospective randomized study of 40 patients, Joshi andMcCarroll reported a 15% failure rate of CSF return when the spinal needle protruded only 10 mm beyond the tip of the Tuohy needle, and 0% with 13 mm protrusion.⁹¹ Riley and coworkers reported¹⁶⁸ similar results comparing 24-gauge Sorotte (9-mm protrusion past the tip of the Tuhoy and 17% failure to obtain CSF) and Gertie Marx (protrusion 17 mm and 0% failure rate). The number of patients developing PDPH and requiring blood patch was greater with the Gertie Marx than the Sprotte needle. However, this difference was not statistically significant. It is possible that the longer spinal needle also punctures the anterior aspect of the dura and causes a greater CSF leak. Greater paresthesia was also noted (anecdotally) with the 127-mm needle, and the 124-mm Gertie Marx needle was suggested as an excellent compromise.

Herbstman and colleagues compared four pencil point spinal needles commonly used in the CSE technique and reported that longer spinal needles are associated with significantly more transient paresthesias (Gertie Marx 15-mm protrusion with 29% incidence; Whitacre 10-mm protrusion with 17% incidence). Success in obtaining CSF and the incidence of PDPH did not differ among the four needles.¹⁶⁹

Figure 12. A dual-lumen CSE kit. This kit has two separate lumens: one for the catheter and another for the spinal needle. The theoretical advantage of this design is that the possibility of dural puncture with the epidural catheter is avoided.

The conventional spinal needle in the CSE kit, which does not lock within the epidural needle, is difficult to handle and stabilize during injection of spinal medication. The displacement of the spinal needle during aspiration of the CSF and injection may result in failed anesthesia or may push the spinal needle deeper, leading to nerve damage or anterior dural perforation. To overcome this problem, Simsa suggested an external fixation device.¹⁷⁰ This device, however, is somewhat complicated to handle. Recently, spinal needles with an adjustable locking device have been introduced (CSEcure and Adjustable DursafeCSE needle). Studies on the lockable extensions reported that they provide safe and stable conditions during placement of the syringe and injection.^44,171 However, both studies reported frequent inability to feel dural perforation with the locking needles (15.3% with CSEcure and 25% with Adjustable Durasafe), the reason for which is unclear.

In a CSE technique, sometimes the epidural catheter cannot be threaded or threaded intravascularly after the intrathecal drugs has already been injected. To overcome this problem, a dual-lumen, dual-orifice CSE kit was developed, in which an epidural catheter can be inserted in place prior to inserting the spinal needle and mediation.^172,173 This is possible because the catheter and the spinal needle each have a separate lumen (Figure 12).

Recently, a dual-lumen CSE needle lumen has been commercialized in Europe (Epistar; Medimex, Germany).

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Controversial Issues In CSE Technique

Test Dose

The issue of whether a test dose is needed when administering epidural analgesia for labor is controversial.^174,175 Because ultradilute solutions are commonly used and aspiration is often diagnostic, some authors believe that a test dose is unnecessary.¹⁷⁶ However, because catheter aspiration is not always predictive (especially when using a single orifice epidural catheter), others maintain the importance of a test dose to improve detection of intrathecal or intravascular placement of an epidural catheter.¹⁷⁷ Part of the controversy surrounding the testing of epidural catheters involves the use of epinephrine. Epinephrine has been shown to produce a reliable increase in heart rate in volunteers and surgical patients when the epidural has been sited in a blood vessel.¹⁷⁷ However, in a laboring patient, maternal heart rate variability from the pain of uterine contractions may confuse interpretation of the heart rate response, and intravenous epinephrine may have deleterious effects on uterine blood flow.¹⁷⁸ Means to improve the reliability of epinephrine include injecting the dose between uterine contractions and repeating the test dose when the response is equivocal. However, the lack of sensitivity and specificity of the test dose calls into question its usefulness as a diagnostic tool. Leighton and colleagues have described an alternative means of testing an epidural catheter for intravascular placement. They advocate the injection of 1 to 2 mL of air into the epidural catheter while listening over the precordium with the maternal external Doppler monitor for evidence of air.¹⁷⁹ With the recent reports of subarachnoid administration of chloroprocaine,¹⁸⁰ it is possible that in the future this agent will be utilized for testing epidural catheters. Before this happens, more information is essential.

If continuous infusion of dilute local anesthetic is administered and the patient remains comfortable without a motor block, proper epidural catheter placement is likely. That is, if the epidural catheter is intravascular, the patient should have inadequate pain relief, and if the catheter is subarachnoid, a solid motor block would develop. Although infusions of ultradilute local anesthetics do not pose a serious threat, such is not true of concentrated local anesthetics used for operative delivery. Some authors have suggested that a test dose is essential for any parturient receiving epidural anesthesia.¹⁷⁷ Regardless of the technique used, the safe practice of administering labor epidural analgesia dictates initial catheter aspiration, incremental injections, and continuous monitoring for evidence of local anesthetic toxicity.

Positioning For CSE

Neuraxial blocks are often performed with the patients in the sitting position, especially in obese individuals, because the midline is easily recognized. Sitting position has been shown to allow better spinal flexion in the parturients.¹⁸¹ In addition, the SED was shown to be significantly greater when epidural puncture was performed in the lateral position than in the sitting position. This change in distance may cause catheter dislodgment when the patient is turned from the sitting to the lateral position , with consequent inadequate analgesia.

Yun and coworkers compared the effects of induction of CSE anesthesia in the sitting vs lateral position in healthy women undergoing elective cesarean delivery.¹⁸² The severity of hypotension, measured by the maximal percentage decrease in systolic blood pressure from control, as well as its duration, were significantly greater in the sitting group (p < 0.05). Patients in the sitting group required twice as much ephedrine to treat hypotension as those in the lateral recumbent group. The reason for the difference in the severity of hypotension is unclear. The authors postulated it to be related to a slower recovery from venous pooling in the lower extremities when assuming a supine position from an initial sitting position. These authors concluded that the position used for induction of CSE should be considered in cases associated with greater maternal or fetal risk from hypotension.

Traditional teaching is that the spread of hyperbaric intrathecal solutions follows gravity. Lewis and colleagues compared the development of spinal blocks in the left lateral position vs the supine wedge position, after performing the CSE in the sitting position.¹⁸³ The intrathecal medications consist of 2 mL of 0.5% hyperbaric bupivacaine with 15 mcg fentanyl. The left lateral position did not produce unilateral blockade. The left lateral position was associated with slower block onset (p = 0.004), but eventually produced a spinal block similar in characteristics to that obtained in the supine wedge position. The left lateral position is known to improve maternal cardiac output, and slower onset may be outweighed by the possible benefit to the fetus.

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Summary

Recent studies have shown that the CSE technique is gaining popularity^10,150 for various types of surgery and particularly in obstetrics. In our institution, CSE technique is the most commonly performed regional technique for labor analgesia (97%) as well as cesarean delivery (50%). Although it is not a perfect technique, it provides a method for administering optimal neuraxial anesthesia and analgesia in numerous clinical situations.

CSE technique offers the advantages of both spinal and epidural technique and, therefore, has a high success rate in providing regional anesthesia. CSE provides rapid onset and the ability to titrate a desired sensory level, control the duration of the block, and deliver postoperative analgesia. Another positive aspect of CSE is the ease with which the spinal needle enters the subarachnoid space. The Tuohy needle acts as a perfect introducer and guides the fine spinal needle almost to the subarachnoid space. When smaller gauge atraumatic spinal needles are used, PDPH is absent or very rare.¹⁵⁵

On the other hand, the combined technique introduces potential side effects, such as PDPH, the increased risk of catheter migration into the subarachnoid space, and transient paresthesias from the spinal needle. Although the risk is extremely low, many technical adaptations have been suggested and developed to avoid penetration of the epidural catheter through the dural hole made by the spinal needle.

The ideal length of spinal needle protrusion beyond the tip of the epidural needle is reported to be at least 12–13 mm. Longer spinal needles were shown to be associated with significantly higher transient paresthesias. Inability to obtain CSF through the spinal needle may occur with shorter needles (< 10 mm of protrusion) and result in failure of the spinal component of the technique. CSE failure is also related to a faulty puncture site or axis deviation during needle advancement. The risk of infection, hematoma, and neurologic damage increases with multiple attempts and multiple manipulations of the needles, but it is unclear if the CSE technique increases these risks. Noninvasive ultrasonic guidance has been proposed to enhance the safety and the success of the CSE technique.

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Reference

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