The combined spinal-epidural (CSE) technique was first described over 60 years ago. Although it is commonly assumed that CSE means a needle-through-needle technique, there are theoretically several ways of instituting CSE:
1. Insertion of an epidural needle into the epidural space, insertion of a long spinal needle through the epidural needle into the subarachnoid space, and finally insertion of an epidural catheter through the epidural needle after the spinal needle has been removed. This is the most commonly used technique in the UK.
2. Insertion of an epidural needle (and usually an epidural catheter) into the epidural space followed by separate insertion of a spinal needle into the subarachnoid space, either at the same or at a different lumbar interspace. This is favoured by a minority of UK anaesthetists.
3. Insertion of a spinal needle into the subarachnoid space followed by insertion of an epidural needle and catheter. This is rarely practised other than when the pain of labour is so severe that the mother is felt to be unable to lie or sit still long enough for epidural insertion.
CSE offers the certainty and speed of onset of spinal analgesia or anaesthesia and the flexibility and continuity of an epidural catheter. For the needle-through-needle technique, successful aspiration of cerebrospinal fluid (CSF) upon insertion of the spinal needle confirms correct placement of the epidural needle, which may be reassuring in difficult cases.
Problems and special considerations
Anaesthetists should be entirely familiar with the management of both spinal and epidural analgesic and anaesthetic techniques before considering CSE. Either a needle-through- needle or separate-space technique can be used, according to the equipment available and the anaesthetist’s preference. The separate-space technique has the advantage of not requiring special needles but the disadvantage of inflicting two sets of injections upon the woman, and additionally carries the theoretical risk of damage to the epidural catheter by the spinal needle if the epidural procedure is performed first and at a lower vertebral interspace. The needle-through-needle technique involves only a single injection but requires long (approximately 120 mm) and more expensive spinal needles, either singly or as part of specialised CSE kits.
Any standard Tuohy needle can be used, although most of the leading needle manufacturers produce kits containing specially matched spinal and epidural needles for needle-through-needle CSE. Some of these include locking devices for fixing the two needles together so that once CSF is obtained the spinal needle cannot move in or out during subarachnoid injection, which might help reduce the incidence of inadequate block; however, these devices may reduce the ‘feel’ as the spinal needle is advanced through the dura. Typically, an 18 G or 16 G Tuohy needle and a 25 G or 27 G spinal needle are used, as for separate epidural and spinal techniques. It is essential to check that the spinal needle will project beyond the end of the epidural needle by an adequate amount to achieve dural puncture (usually 12-15 mm). Some kits include epidural needles with a hole at the curved tip, through which the spinal needle passes (in order to maintain an axial direction rather than following the curve of the tip), but there is no evidence that this confers any advantage.
Management options
Analgesia
The use of CSE for labour analgesia varies. Some maternity units employ the technique routinely, others never. The advantages include rapid onset of pain relief (usually within 5 minutes) and absence of significant motor block in most cases. There is also evidence to suggest that the presence of a hole in the dura (even without injecting drugs intrathecally) may improve epidural analgesia. Despite these benefits, a Cochrane review concluded that there is no difference in maternal satisfaction between women who have received CSE in labour and those who have received low-dose epidural analgesia. The major disadvantage is the additional potential for complications introduced by deliberate dural puncture, and the cost implications of using an additional needle/kit. In addition, while the onset of analgesia is rapid, it may not be complete, especially if the standard low-dose epidural mixture is used (see below), and an early epidural top-up may be required.
The original regimen for the spinal component recommended in the UK was 25 µg fentanyl and 2.5 mg bupivacaine (1 ml of 0.25% solution), made up to a volume of 2 ml with saline. Further experience has suggested that smaller doses of fentanyl (5-15 µg) may be adequate; 3-5 ml of the standard ‘low-dose’ epidural mixture (bupivacaine 0.1% with fentanyl 2 µg/ml) may also be suitable. These combinations will provide approximately 60-90 minutes’ analgesia, in most cases with little motor blockade. (Spinal opioids alone are very rarely used in the UK, although they may be considered in some high-risk women with coexisting medical disease. In the USA and continental Europe sufentanil is widely used.) When further analgesia is needed, a low concentration of bupivacaine with fentanyl is given via the epidural catheter, either by intermittent bolus top-ups, an infusion or patient-controlled epidural analgesia (PCEA).
In labour, the abrupt reduction in the level of circulating catecholamines that may follow administration of intrathecal opioids, and the abolition of their tocolytic effect, may cause uterine hypertonicity and transient fetal bradycardia. The effect on the fetus may be compounded by maternal hypotension secondary to sympathectomy, which may lead to a reduction in placental perfusion. However, with close blood pressure monitoring and support after initiation of analgesia, such changes rarely persist.
Those who do not routinely use CSE analgesia point to the above disadvantages and to the fact that epidural analgesia is usually effective within a few contractions. However, many anaesthetists would consider CSE for women who request regional analgesia late in the first stage of labour, or for those needing regional analgesia for instrumental delivery.
Anaesthesia
The use of CSE for caesarean section combines the speed of onset and reliability of spinal anaesthesia with the ability to extend the block and provide postoperative analgesia through an epidural catheter. There are three different techniques of CSE for caesarean section:
1. The spinal injection is performed using a ‘full’ spinal dose of local anaesthetic, and the epidural catheter is used as a back-up in the event of inadequate anaesthesia, to extend the block if surgery is prolonged and to provide postoperative analgesia.
2. A smaller volume of local anaesthetic (e.g. 1 ml heavy bupivacaine 0.5%) is used intrathecally, with the intention of producing a limited spinal block (usually to about T8-10). Anaesthesia is then extended gradually with local anaesthetic via the epidural catheter. This technique allows a more controlled and controllable extension of block, which may be advantageous in women with systemic disease (e.g. cardiac, respiratory or neurological).
3. A small dose of local anaesthetic (e.g. 1 ml heavy bupivacaine 0.5%) is given intrathecally and the epidural catheter is then placed as usual. Saline (8-10 ml) is then injected through the epidural catheter to extend the height of the block suitable for surgery, by compression of the dural sac. It is thought that this technique (epidural volume extension, EVE) may result in less cardiovascular instability and motor block, and a reduced requirement for local anaesthetic. However, although it found some evidence of earlier recovery from motor block, a recent systematic review and meta-analysis (which included studies on non-obstetric patients) found no significant difference in the maximum sensory height achieved or in hypotension with or without EVE. The physical compressing effect of epidural solutions on the spread of spinal anaesthesia, however, means that should the subarachnoid block be inadequate, small epidural boluses (< 5 ml) of local anaesthetic may be effective in topping up the block.
Complications
It has been claimed that there is a higher failure rate of the subarachnoid component of CSE than with single-shot spinal anaesthesia. This may be the result of dislodgement of the spinal needle when using the needle-through-needle technique, such that not all of the drug is deposited in the intrathecal compartment, or failure to penetrate the dural sac if there is deviation from the midline. However, this does not appear to be a problem as experience with the technique is gained.
CSE carries similar risks to both spinal and epidural injection alone. A number of early reports of meningitis following CSE suggested that there might be an increased risk of this complication with CSE compared with a single-shot spinal; however, since CSE is widely used this could equally be an artefact of reporting. There have also been reports of neuropraxia and neurological damage with CSE, presumed to be related to needle length and design. A particular concern relates to the difficulty in identifying the correct lumbar interspace - which can be a problem even for experienced anaesthetists - and the risk that the chosen level may be above the termination of the spinal cord. In such a case, there should be no extra risk from epidural analgesia in labour, for example, so long as an accidental dural tap does not occur, but if CSE is used there is a risk of neurological damage from the spinal needle. The 3rd National Audit Project of the Royal College of Anaesthetists (NAP3) found that the incidence of permanent harm associated with obstetric CSEs was approximately six times greater than with epidurals, and approximately three times greater than with spinals (see Section 2, Part IV, Anaesthetic Problems).
It must be remembered that the epidural catheter is untested at the time of insertion, which may have implications in high-risk parturients who might require operative delivery. There is also the risk of an ‘epidural’ dose passing into the subarachnoid space, which might be increased by the presence of a dural hole (though this complication remains a rarity despite widespread use of CSE). Although rare, epidural catheter insertion or migration into the subdural or subarachnoid space has been reported with CSE techniques in obstetric patients.
Key points
• Needle-through-needle combined spinal-epidural (CSE) requires only a single injection but is more expensive than separate-space techniques.
• CSE analgesia provides pain relief usually within one or two contractions but is a more invasive and complex technique than epidural alone.
• CSE anaesthesia combines the advantages of spinal anaesthesia (speed of onset and quality of anaesthesia) with the ability to extend the level and duration of anaesthesia via the epidural route.
Further reading
Groden J, Gonzalez-Fiol A, Aaronson J, Sachs A, Smiley R. Catheter failure rates and time course with epidural versus combined spinal-epidural analgesia in labor. Int J Obstet Anesth 2016; 26: 4-7.
Heesen M, Weibel S, Klimek M, et al. Effects of epidural volume extension by saline injection on the efficacy and safety of intrathecal local anaesthetics: systematic review with meta-analysis, meta-regression and trial sequential analysis. Anaesthesia 2017; 72: 1398-411.
Simmons SW, Taghizadeh N, Dennis AT, Hughes D, Cyna AM. Combined spinal-epidural versus epidural analgesia in labour. Cochrane Database Syst Rev 2012; (10): CD003401.