CAUDAL BLOCK (Chapter 22)
Caudal epidurals in labour have become less popular because better perineal analgesia can be achieved by the use of epidural infusions and primigravidae are more likely to receive an epidural block. Also, there have been recent concerns about the risks of inadvertent intravenous and fetal injection.
A modified caudal epidural technique can provide rapid onset perineal anaesthesia without cardiovascular disturbance and with relatively little loss of expulsive power. If used for perineal anaesthesia only, caudal block is a useful, safe technique for experienced anaesthetists provided that the volume of local anaesthetic is limited to a maximum of 10 mls, injected slowly (with multiple aspirations). It should be noted that this dose is less than half that which is required to achieve full labour analgesia. The block should be inserted before the head is on the perineum (Figure 22.1).
Since it has been shown that pencil point spinal needles have a low incidence of headache (0 to 0.66% with 27G and 25G Whitacre needles) (1, 7) spinal anaesthesia is often more appropriate than lumbar or caudal epidural anaesthesia for rotational forceps, manual removal of placenta and, at times, low forceps delivery.
INDICATIONS
1. Unrelieved perineal pain.
2. Premature urge to push.
3. Low forceps delivery.
4. When lumbar epidural analgesia is contraindicated.
INCIDENCE
In most Australian hospitals, caudal blocks are being used less frequently in labour as the number of spinals has increased (Table 2.1). The major indications for caudals are perineal pain, labour pain, forceps delivery, and manual removal of placenta. Less commonly, caudals can provide anaesthesia for artificial rupture of the membranes, suturing of episiotomies and repair of vaginal lacerations.
CAUDAL ANALGESIA IN COMBINATION WITH OTHER MAJOR REGIONAL BLOCKS
At the Royal Women's Hospital, of those women who had a caudal, at least 62% also had a lumbar epidural. The lumbar epidural was either already in situ or was inserted at the same time as the caudal.
It has been shown that for the lumbar epidural route, increasing the volume of anaesthetic is more likely to secure good sacral blockade (3) than injection in the sitting position (4). However, in our experience sacral blockade can occasionally only be achieved with a caudal or spinal block.
COMPLICATIONS
l. Vascular tap and intravascular injection of local anaesthetic (Table 36.3).
2. Failed block (8%) - the sacral hiatus is absent in 5% of adults. (2, 9)
3. Subarachnoid injection - the dural sac reaches S2 .
4. Infection.
5. Fetal injection (Figure 22.1).
Modified caudal block is a safe technique with a limited specific place in modern obstetric anaesthesia.
PARACERVICAL BLOCK (Chapter 46)
The risk of complications, particularly fetal bradycardia, generally make this technique an unsuitable form of anaesthesia for obstetric patients. However, if used, it should be avoided in the presence of fetal distress or uteroplacental insufficiency and the fetal heart rate should be monitored continuously (Table 3.1) during and after insertion of the paracervical block (Figure 46.2).
COMPLICATIONS
1. Vaginal trauma.
2. Systemic local anaesthetic toxicity due to excessive dosage or intravenous injection (Table 36.3).
3. Parametrial haematoma.
4. Sacral plexus trauma.
5. Infection and deep abscess formation.
6. Fetal scalp injection of local anaesthetic.
7. Fetal bradycardia probably caused by decreased uteroplacental perfusion.
8. Needle stick injury.
PUDENDAL NERVE BLOCK (Chapter 21)
Pudendal nerve block provides anaesthesia for spontaneous vaginal delivery or low forceps delivery. The pudendal nerve (S2 - S4) (Figure 21.1) is the major sensory innervation of the lower vagina, vulva and perineum and provides motor fibres to the external anal sphincter and the perineal muscles.
Pudendal nerve block was first reported for vaginal delivery in 1916 (7). It is inadequate for rotational forceps delivery and manual removal of the placenta. Either a transvaginal or transperineal approach can be used. The bilateral success rate has been reported as 50% after the transvaginal approach and 25% after the transperineal approach. (6).
INDICATIONS.
1. Low forceps delivery.
2. Vaginal and perineal pain when lumbar or caudal epidural or spinal analgesia is unavailable, contraindicated or declined.
COMPLICATIONS
1. Vaginal trauma.
2. Systemic local anaesthetic toxicity due to excessive dosage or intravenous injection.
3. Vaginal or ischio-rectal haematoma.
4. Infection and deep abscess formation.
5. Fetal trauma or direct local anaesthetic injection.
6. Needle stick injury.
References:
1. Campbell DC, Douglas MJ, Pavy TJG, Merrick P et al. Comparison of the 25 gauge Whitacre with the 24 gauge Sprotte needle for elective caesarean section: cost implications. Can J Anaesth 1993; 40:1131-5.
2. Dawkins CJM. An analysis of the complications of extradural and caudal block. Anaesthesia 1969; 24: 554-563.
3. Erdemir HA, Sopper LE, Sweet R.B, Studies of factors affecting peridural anesthesia. Anesth Analg 1965; 44:400-404.
4. Park WY. Factors influencing distribution of local anesthetics in the epidural space. Reg Anesth 1988; 13:49-57.
5. Robson M, Boylan P, McParland P. Epidural analgesia need not influence the spontaneous vaginal delivery rate (abstract). Am J, Obstet Gynecol 1993; 168:364.
6. Scudamore JH, Yates MJ. Pudendal block - a misnomer? Lancet 1966; 1:23-4..
7. Smith EA, Thorburn J, Duckworth RA, Reid JA. A comparison of 25G and 27G Whitacre needles for caesarean section. Anaesthesia 1994; 49: 859-862.
8. Thompson JE. An anatomical and experimental study of sacral anaesthesia Ann Surg 1917; 66: 718-727.
9. Trotter M. Variations of the sacral canal: their significance in the administration of caudal anaesthesia. Anesth Analg 1947; 26: 192-202.