Single-shot spinal analgesia is rarely used alone for labour, since its duration is usually much shorter than that of labour itself. However, it maybe useful in the later stages of labour when delivery is felt to be imminent, or to provide rapid onset of analgesia in a mother who is desperate and losing control, thus enabling her to cooperate while an epidural catheter is inserted.
Use of an intrathecal catheter to allow repeated boluses (or infusion) of local anaesthetic or other mixtures is an attractive concept, since the advantages of spinal block (rapid onset, profound block) are potentially combined with those of epidural block (flexibility, titrated effect). In addition, it may be used for rapid extension of the block for caesarean section, which may be desirable in high-risk parturients such as those with morbid obesity, significant cardiopulmonary disease or spinal abnormalities. In practice, however, continuous spinal block is uncommon in the UK.
Problems and special considerations
The main considerations for a single-shot spinal are the risk of postdural puncture headache and the choice of solution, given the requirement for maximal analgesia while minimising motor block and other side effects (see Chapter 29, Combined spinal-epidural analgesia and anaesthesia).
Modern intrathecal catheters are very fine (e.g. 28-32 G) and thus may be difficult to handle and insert. They are usually supplied in a kit with a spinal needle; originally these needles had cutting tips, but they are now available with pencil-point tips in an attempt to reduce the incidence of postdural puncture headache. However, even with fine catheters, 22-26 G spinal needles are required. Some catheters include a removable wire to make them stiffer for insertion.
A continuous catheter technique may also be used with a standard epidural kit (e.g. 16 G or 18 G catheter), either because specialist kits are unavailable or when an accidental dural puncture has occurred during attempted epidural block. A reduced incidence of headache after placement of an intrathecal catheter has been claimed when this is done, possibly related to inflammation around the dural puncture site, which leads to faster healing; however, this is uncertain since the evidence is mostly observational.
The main factor that has led to the withdrawal of microspinal catheters in the USA and that has contributed to the technique’s unpopularity in the UK is the association between their use and the development of subsequent cauda equina syndrome. This is thought to be caused by a combination of factors, including the use of lidocaine (more common in the USA), the known neurotoxic effect of high concentrations of lidocaine on neural tissue experimentally (more so than bupivacaine), the pooling of drug around the sensitive nerves of the cauda equina associated with very fine catheters placed caudally, and the use of excessive doses of drug in an attempt to extend an inadequately extensive block (resulting in more pooling around the nerves).
Management options
Management after a single-shot spinal is discussed elsewhere (see Chapter 34, Spinal anaesthesia for caesarean section).
For continuous techniques, once the catheter has been inserted, it should be clearly labelled, since accidental injection of an epidural-style dose may be disastrous. For labour analgesia, a dose can be given as for a combined spinal-epidural (see Chapter 29, Combined spinal-epidural analgesia and anaesthesia). Subsequent analgesia may be provided with repeated boluses of 0.5-1.5 ml bupivacaine 0.1-0.25% ± fentanyl 10-20 µg as required. Infusions (e.g. 0.1-0.25% bupivacaine ± fentanyl at 1-5 ml/hour) have also been used. Unless the technique is commonly used in a particular unit, it is prudent for all top-ups to be given by an anaesthetist, since midwifery and other staff are likely to be unfamiliar with it.
For caesarean section, incremental doses of bupivacaine ± opioid may be given to achieve the required level of block, as slowly as is felt appropriate for the clinical circumstances.
Whatever the indication, directing the catheter caudally should be avoided, as should repeated injections of concentrated solutions of local anaesthetic if the block is inadequate. Greater than normal doses of local anaesthetic should not be given.
Key points
• Single-shot spinal analgesia is rarely used alone for labour but may be useful when delivery is imminent, or to provide rapid onset of analgesia before siting an epidural.
• Continuous spinal techniques are acceptable for both labour and operative delivery.
• Advantages include good quality of block and ability to titrate the dose.
• Disadvantages include difficulty handling the catheters, risk of postdural puncture headache, potential for infection, cauda equina syndrome, cost and mistaking the catheter for an epidural one.
Further reading
Cohn J, Moaveni D, Sznol J, Ranasinghe J. Complications of 761 short-term intrathecal macrocatheters in obstetric patients: a retrospective review of cases over a 12-year period. Int J Obstet Anesth 2016; 25: 30-6.
Loubert C, Hinova A, Fernando R. Update on modern neuraxial analgesia in labour: a review of the literature of the last 5 years. Anaesthesia 2011; 66: 191-212.
Palmer CM. Continuous spinal anesthesia and analgesia in obstetrics. Anesth Analg 2010; 111:1476-9.