The combined spinal-epidural (CSE) technique

 

Epidural and spinal blocks have a long history of safe use for a variety of surgical pro­ce­dures and pain relief. Both techniques are used extensively world-wide. Nevertheless both techni­ques have well-recognized drawbacks which are particu­larly prominent in obstetric and high-risk patients. For example it is gene­rally recog­nized that a S5-T4 block is neces­sary for ade­quate analgesia during caesa­rean section. Epidural technique for such an exten­sive block may be associated with a relatively high inci­dence of hypo­tension and a poten­tial risk of toxic compli­cations because of requirement of large doses of local anaesthetic drugs. Furthermore, in spite of these large doses the block may be inadequate in 10 to 25 per cent of pati­ents, mainly be­cause of difficulty in blocking the sacral roots. Spinal anaes­the­sia is more reliable than epidu­ral anaesthesia because of its more intense motor block but the upper level of spinal block is unpredictable and the technique may be asso­ciated with a high risk of precipi­tous maternal hypotension which may be harmful for the neonate. Since spinal block is usually a "single shot" tech­nique there is no possibility of improving an inadequate block or pro­viding exten­ded postope­rative pain relief.

 

The combined spinal-epidural (CSE) technique can reduce or eliminate some of the dis­advantages of spinal and epidural anaesthesia while preserving their advantages. CSE offers the speed of onset, efficacy and minimal toxicity of a spinal block combi­ned with the possi­bility of improving an inadequate block or prolonging the dura­tion of anaesthe­sia with epidu­ral supplements and extending the analgesia well into the post­operative period. For labour pain the CSE technique offers the possibility of combining almost instan­taneous intrathecal opioid analgesia with the flexibility of epidural analge­sia, this approach allows the parturient to ambulate throughout labour. These advantages are making CSE blocks in­creasingly popular especially in obstetrics and for orthopaedic sur­gery (1-3).

 

CSE for labour analgesia

One disadvantage of the epidural technique for labour analgesia is the length of time before it becomes established. This problem may be particularly important in women who experi­ence severe pain (e.g., the strongly labouring multipara and in oxytocin-augmented labour). The difficulty in predicting the duration of first stage and occasional late request for epidural anal­gesia may result in delivery before the requested epidural block has become established. Injecting local anaesthetics or opioids, or their combination intrathecally will provide rapid-onset analgesia. The epidural catheter is then used if labour continues beyond the duration of the subarachnoid block or to improve analgesia if the subarachnoid block is inadequate. Intrathecal opioids are being used increasingly by obstetric anaesthesiologists to provide labour analgesia, with the most common opioids being sufentanil and fentanyl. Morphine and meperidine are less popular in the context of labour analgesia. Some obstet­ricians claim that epidural analgesia increases the incidence of caesarean delivery and although the incidence of caesarean deliveries is now, about 20% in most developed coun­tries with on-site anaesthesia services, cause and effect are still unproven. However, one of the main limitations of intrathe­cal opioids such as sufentanil and fentanyl is the short dura­tion of analgesic effect, which necessitates additional dural puncture(s). Therefore, intra­thecal opioids would most appro­priately be used with CSE technique. In one study of 300 labouring women receiving a com­bination of intrathecal bupivacaine and fentanyl, the CSE technique provided analgesia, which also allowing most mothers to walk throughout labour. While it is unclear if ambulation in labour reduces its duration, meta-analysis of studies of labouring parturients suggest that anal­gesic requirements are reduced by ambu­lation, and that women appreciate the opportunity to ambulate even for short periods during labour.

 

A recent controlled study has demonstrated that the duration of bupivacaine-sufentanil for ambulating CSE labour analgesia can be prolonged from 100 to 140 min by the addi­tion of 25 µg epinephrine (4).

 

Other indications for CSE technique

A review of the literature shows that CSE has been used in general surgery, ortho­paedic and trauma surgery of the lower limb, urological and gynecological surgery, manage­ment of labour pain and postopera­tive pain. It has also been used as a research tool for controlled compari­son bet­ween epidu­ral and spinal techniques. The technique has been used success­fully in all age groups including ex-premature babies and in high-risk pati­ents (5).

 

CSE - technical aspects

There are several options for performing the CSE block. In the early years CSE blocks were performed with multiple-use extra long 25-30 G spinal needles which were introduced through standard Tuohy needles. In recent years special CSE needle sets have been introdu­ced. At present there are more than a dozen medical equipment companies that distribute spe­cialized CSE needle sets world-wide.

 

‘Needle-through-needle’ technique

Probably the most popular technique for CSE block is the single segment ‘needle-through-needle’ technique. With the patient in the sitting or lateral decubitus position an appropriate epidural needle is inserted at the desired intervertebral space (below L2 ) and the epidural space is identified in the usual manner. Next an extra long 27 G (or smaller diameter) spinal needle is introduced through the epidural needle and advanced until the tip of the spinal needle is felt to penetrate the dura (the dural ‘click’). When the stilette is removed correct placement of the spinal needle is confirmed by free flow (or aspiration) of CSF, the appro­priate dose of local anaesthetic and/or opioid is injected. If loss-of-resistance to air is emp­loyed to identify the epidural space any clear fluid coming out of the spinal needle will be CSF. The loss of resistance felt when the epidural space is entered can be regarded as a sign similar to the ‘click’ of dural puncture felt with the needle-through-needle technique when the spinal needle enters the subarachnoid space. This ‘click’ is not in itself an objective sign, but the flow of CSF from the spinal needle hub is objective. A subarachnoid injection of 2-3 ml hyperbaric bupivacaine 0.5% (10-15 mg) to which may be added fentanyl 20-25 µg is com­menced (Table). Whilst injecting into the subarachnoid space, the parturient is asked to report feelings of warmth under the buttocks and thighs. If this symptom is not reported within 30 sec, the dose has most probably not been delivered intrathecally. This routine enables one to detect proper intrathecal placement whilst the spinal needle is still in place.

 

It is emphasized that at this stage the spinal needle is held in place only by the dura mater, therefore there is a risk of needle displacement during syringe connection or during injection of local anaesthetic. This is a critical stage in the needle-through-needle technique). The problem can be overcome by steadying the spinal needle as shown in figure 1. Spinal needle displacement may not be a problem with the newer special CSE kits where the hub of the spi­nal needle locks into the hub of Tuohy needle. After withdrawing the spinal needle a catheter is introduced about 4-5 cm into the epidural space through the Tuohy needle. Epidural cathe­ter position is confirmed by negative aspira­tion of blood or CSF. This is followed by injection of about 1 ml saline into the epidural catheter to test its patency. The catheter is secured firmly with tape and is now available for use during or after surgery.

 

Sequential CSE technique

Sympathetic block-induced, precipitous, maternal hypotension remains one of the commonest problems associated with subarachnoid block for caesarean section. Despite prophylactic measures such as fluid preloading, prophylactic vasopressors (ephedrine), elastic support stockings and lateral tilt it may be difficult to maintain normal blood pressure. Maternal hypotension may lead to maternal cerebral hypoperfusion and parasympathetic imbalance may trigger nausea and vomiting. Uncorrected, maternal hypotension may result in fetal hypoxe­mia and acidosis due to uteroplacental hypoperfusion. To reduce the incidence and severity of hypotension a two stage sequential CSE technique has been described. This technique is quite similar to that described above, but the main differences are:

a) the block is performed with the patient in the sitting position,

b) the dose of intrathecal hyperbaric bupivacaine is intentionally kept low (5-10 mg hyper­baric bupivacaine 0.5% solution) because the aim is to achieve only a S5 to T8-9 block,

c) patient is then placed supine with a left lateral tilt and,

d) within 10 min the sensory block is extended to T4 by injecting fractionated doses of local anaesthetic (bupivacaine 0.2-0.25%) solution or normal saline into the epidural catheter (less than 1-1.5 ml for every unblocked segment is often sufficient) (Fig. 2).

 

The sequential CSE technique may be particularly advantageous in high-risk parturient, where gentler onset of sympathetic blockade is desirable. This is important in patients with pre­eclampsia, phaeochromocytoma, some cardiac disease or other conditions such as small stature where the use of subarachnoid block alone may be hazardous or difficult to control. This may also be the case with other high-risk patients in the non-obstetric population, as for instance the very old orthopaedic patient. Traditionally such patients are managed with slow epidural blockade that requires much higher total dosages than sequential CSE. By careful positioning of the patient prior to induction of subarachnoid anaesthetic and by allowing titra­tion with small incremental epidural doses to the precise level of anaesthesia desired the sequential CSE technique may enhance the safety of the central regional block.

 

Double-barrel or double-segment CSE technique

During induction of CSE block using a needle-through-needle technique it may occasionally be difficult to thread a catheter into the epidural space after the subarachnoid injection. If some minutes are spent in replacing the epidural needle the subarachnoid block may become ‘fixed’ in the dependent area. If difficulty is experienced threading the catheter, its insertion should be abandoned or attempted at another level. Subarachnoid anaesthesia may obscure paresthesia during epidural catheter insertion. Moreover, it may be difficult to verify the posi­tion of the epidural catheter because of difficulty in identifying unintentional subarachnoid or subdural injections in the presence of the existing spinal block.

 

These problems may be overcome if the epidural catheter is introduced prior to the subarach­noid injection. Placement of the epidural catheter before subarachnoid injection can be accomplished by the use of one of the single segment ‘double-barreled’ needles or by using the separate spaces technique. Yet another approach is to insert the spinal needle in the same lumbar segment adjacent to the epidural needle already in place.

 

However, prior placement of an epidural catheter does not necessarily guarantee increased success rate. A Swedish survey from 1993 showed that departments using double interspace technique for CSE (epidural first, then subarachnoid injection) reported more epidural catheter penetrations through the dura than departments using a single interspace CSE technique. since epidural catheter migration can occur over time only a recently injected epidural test dose holds signifi­cance. In our opinion an epidural test dose prior to spinal block is of little use if the epidural catheter is to be activated after surgery. Furthermore, if an epidural test dose is administered before the subarachnoid injection, a por­tion of this test dose may appear in the hub of the spinal needle and create confusion. Finally, the direction of epidural catheter pas­sage is unpredictable. Radiological and video epiduro­scopic studies have shown that epidural catheters may take unpredictable paths. A catheter may even tie itself in a knot. It is hence conceivable that a prior-positioned epi­dural catheter may divert the spinal needle.

 

Whether the epidural catheter is introduced before or after the subarachnoid injection and irre­spective of the CSE technique used it should be remembered that accidental subdural catheter placement can occur and that this is more common than generally believed. This may account for such phenomena as delayed onset, profound and extensive blockade, Horner’s syndrome and for ‘unexplained’ headaches, total spinals and neurological sequelae. The commonly used safeguards, aspiration and test dose may be unreliable because they cannot detect subdural placement.

 

So far, there is no controlled study that has compared morbidity after single versus double interspace techniques nor has morbidity been compared between ‘needle-through-needle’ and ‘double-barrel’ needle techniques. Compared with introducing needles into two interspaces, the single interspace technique may be expected to cause considerably less discomfort, trauma and morbidity from interspinous tissue penetration including backache, epidural venous puncture, hematoma, infection and technical difficulties.

 

In conclusion, it is obvious that either sequence has its advantages and disadvantages. How­ever, if the patient is experiencing severe pain, e.g. in labour, when the block is being
admini­stered, the better option is to perform the subarachnoid injection first to achieve rapid analge­sia, and then to place the epidural catheter in a calmer, more co-operative patient.

 

Summary

Although epidural and spinal blocks are well-accepted regional techniques they have seve­ral disadvantages. Combined spinal epidural technique reduces or eliminates the risks of these disadvantages. The CSE technique has attained widespread popularity for patients undergoing major surgery below the umbilical level who require prolonged and effective postoperative analgesia. Epiduroscopy and spinaloscopy, as well as the newer radiological imaging techni­ques, have revealed new insights into the anatomical structures in the lumbar epidural and subarachnoid areas, thus improving the performance and safety of central regional blocks. The CSE technique is now well established in many institutions.

 

References and suggested reading

1.       Carrie LES. Extradural spinal or combined spinal block for obstetric surgical anaesthe­sia. Br J Anaesth 1990;65:225-33.

2.       Rawal N, Schollin J, Wesström G. Epidural versus combined spinal epidural block for Caesarean section. Acta Anaesthesiol Scand 1988;32:61-6.

3.       Thorén T, Holmström B, Rawal N, Schollin J, Lindeberg S, Skeppner G. Sequen­tial com­bined spinal epidural block versus spinal block for cesarean sec­tion: effects on maternal hypotension and neurobehavioral function of the new­born. Anesth Analg 1994;78:1087-92.

4.       Gautier PE, Debry F, Fanard L, Van Steenberge A, Hody JL. Ambulatory combined spi­nal-epidural for labor. Influence of epinephrine on bupivacaine-sufentanil combi­nation. Reg Anesth1997;22:143-149.

5.       Rawal N, Van Zundert A, Holmström B, Crowhurst JA. Combined spinal-epidural techni­que. Reg Anesth 1997;22:406-423.

Cook TM. Combined spinal-epidural techniques (Review). Anaesthesia 2000;55:42-64.

Eisenach JC. Combined spinal-epidural analgesia in obstetrics. Anesthesiology 1999;91:299-302.