The use of subarachnoid local anaesthetic agents and narcotics for labour and delivery varies between institutions and individual anaesthetists. While practices may vary, the role of subarachnoid anaesthesia in comparison with other regional techniques can be defined in terms of the relative advantages and disadvantages of this method of anaesthesia.
Efficacy and application of blockade:
Local anaesthetics may be used intrathecally to accomplish sacral anaesthesia for instrumental vaginal deliveries and for other obstetric procedures. Subarachnoid blockade to a level above T7 may also be employed for cesarean section. Under these circumstances, subarachnoid blockade provides reliable, dense surgical anaesthesia.
Epidural anaesthesia is also suitable for both labour and delivery but, sometimes, sacral segments may be difficult to block (with a lumbar epidural) and the blocks may occasionally be patchy or asymmetrical (1).
In comparison to subarachnoid blockade, caudal blockade is only suitable for sacral anaesthesia (Chapter 2).
Opiates may also be administered by the subarachnoid route and provide good analgesia for labour but not for delivery (2). Furthermore, intrathecal opiates provide superior analgesia when compared to opiates administered via the epidural route (3). Side effects such as pruritus may be higher in patients receiving intrathecal opiates.
Speed of onset:
When compared to epidural or caudal anaesthesia, subarachnoid anaesthesia offers a rapid onset of action which is often of benefit to the patient, anaesthetist and surgeon. Unfortunately, an increased speed of onset of anaesthesia is only purchased at the price of a greater degree of hypotension (4) .
Postdural puncture headache:
Postdural puncture headache may occur in up to 20% of patients when a 25-gauge spinal needle is used (5) (Chapter 97). This miserable complication occurs more frequently in young females and is responsible for the reluctance of many anaesthetists to use this technique in the parturient. Except in cases of inadvertent dural puncture with the needle, this problem is not seen with epidural or caudal anaesthesia. The use of 26-gauge spinal needles has been shown to lower the incidence of postdural puncture headache (6). The use of 29-gauge needles has been associated with little risk of postdural puncture headache, even in young patients (7). The low incidence of headache with these small needles increases the acceptability of subarachnoid blockade in obstetric anaesthesia (Chapter 97).
Titratable level of blockade and continuous infusions:
The use of epidural catheters to provide a means by which the level of anaesthesia can titrated, topped up, or continuously infused for labour and delivery has been well established. The routine use of subarachnoid catheters for uncomplicated vaginal delivery has not gained wide acceptance in obstetric anaesthesia for several reasons. It has been stated that the large bore needles usually employed to introduce catheters would be associated with a high incidence of postdural puncture headache but this does not appear to occur in clinical practice (8). These catheters may increase the risk of infection, although again, there is very little supporting evidence for this concern. In an attempt to address these issues, microcatheters (32-gauge) which can be passed through a standard 25 or 26-gauge spinal needle have been used. Continuous spinal anaesthesia is obtained with negligible risk of local anaesthetic toxicity to the mother and fetus. Significant problems have been reported with these microcatheters and include cauda equina syndrome, kinking, difficulty in threading and catheter fracture (9) (Chapter 42) (Chapter 104).
The more recent use of combined spinal epidural techniques allows for continuous and titratable anaesthesia with the advantage of a rapid and dense subarachnoid block. The potential disadvantages of an intrathecal catheter are avoided and, with a small spinal needle, the risk of postdural puncture is minimal (Chapter 62)
Overall, because of its advantages spinal anaesthesia (especially with the use of smaller spinal needles) continues to challenge the pre-eminent role of epidural anaesthesia in obstetrics.
References:
1. Carrie LES. Extradural, spinal or combined block for obstetric surgical anaesthesia. British Journal of Anaesthesia 1990 65:225-233
2. Scott PV, Bowen FE, Cartwright P, Rao BCM, Deeley D, Wotherspoon HG, Sumrein IMA. Intrathecal morphine as a sole analgesic during labour. British Medical Journal 1980 281:351-353
3. Camann WR, Denney RA, Holby ED, Datta S . A comparison of intrathecal, epidural, and intravenous sufentanil for labor analgesia. Anesthesiology 1992 77 :884-887.
4. Parnass SM, Curran MJA, Becker GL. Incidence of hypotension associated with epidural anesthesia using alkalinized and nonalkalinized lidocaine for cesarean section. Anesthesia and Analgesia 1987 66:1148-1150.
5. Russell IF. Effect of posture during induction of spinal anaesthesia. British Journal of Anaesthesia. 1987 59:347-353.
6. Barker P. Are obstetric spinal headaches avoidable? Anaesthesia and Intensive Care. 1990 18:553-554.
7. Flaatten H, Rodt SA, Vamnes J, Rosland J, Wisborg T, Koller, ME. Postdural puncture headache. A comparison between 26- and 29-gauge needles in young patients. Anaesthesia. 1989 44:147-149.
8. Denny N, Masters R, Read J, Sihota M, Pearson D, Selander D. Postdural puncture headache after continuous spinal anesthesia. Anesthesia and Analgesia 1987 66:791-794.
9. Hurley RJ, Lambert DH. Continuous spinal anesthesia with a microcatheter technique. Anesthesia and Analgesia. 1990;70: 97-102.