Caudal

Indications

• Anaesthesia and analgesia below the umbilicus. Paediatric patients do not generally tolerate surgery under regional anaesthesia alone. However in the very young a caudal block may be adequate to carry out urgent procedures such as reduction of incarcerated hernias, allowing return of normal bowel function prior to surgical repair. Anaesthesia can be provided for superficial operations such as skin grafting, perineal procedures, and lower limb surgery. A general anaesthetic will often be required in addition. Pain relief will extend into the post operative period. The duration of the block can been prolonged by the addition of an opiate (pethidine 0.5 mg/kg) to the local anaesthetic. The possibility of delayed respiratory depression from epidural opiates needs taken into account, and patients should monitored in an intensive care or high dependency unit for 24 hours following their administration.

• Obstetric analgesia for the 2nd stage or instrumental deliveries. Care should be taken as the foetal head lies close to the site of injection and there is real risk of injecting local anaesthetic into the foetus.

• Chronic pain problems such as leg pain after prolapsed intervertebral disc, or post shingles pain below the umbilicus.

Contraindications

• Infection near the site of the needle insertion.
• Coagulopathy or anti coagulation.
• Pilonidal cyst
• Congenital abnormalities of the lower spine or meninges, because of the unclear or impalpable anatomy.

Anatomy

The caudal epidural space is the lowest portion of the epidural system and is entered through the sacral hiatus. The sacrum is a triangular bone that consists of the five fused sacral vertebrae (S1- S5). It articulates with the fifth lumber vertebra and the coccyx.

The sacral hiatus is a defect in the lower part of the posterior wall of the sacrum formed by the failure of the laminae of S5 and/or S4 to meet and fuse in the midline. There is a considerable variation in the anatomy of the tissues near the sacral hiatus, in particular, the bony sacrum. The sacral canal is a continuation of the lumbar spinal canal which terminates at the sacral hiatus. The volume of the sacral canal can vary greatly between adults.

The sacral canal contains:

1. The terminal part of the dural sac, ending between S1 and S3.

2. The five sacral nerves and coccygeal nerves making up the cauda equina. The sacral epidural veins generally end at S4, but may extend throughout the canal. They are at risk from catheter or needle puncture.

3. The filum terminale - the final part of the spinal cord which does not contain nerves. This exits through the sacral hiatus and is attached to the back of the coccyx.

4. Epidural fat, the character of which changes from a loose texture in children to a more fibrous close-meshed texture in adults. - predictability of caudal local anaesthetic spread in children and its unpredictability in adults.

Choice of drugs & dosage

Drugs that are commonly used include Lignocaine 1% and Bupivacaine 0.25%, although higher concentrations may be needed for muscle relaxation. Drugs used for epidural injections should come from single use ampoules and be preservative free.

Various regimes have been produced to calculate the appropriate dose of local anaesthetic, the doses vary widely:

1. Armitage recommends bupivacaine 0.5ml/kg for a lumbosacral block, 1 ml/kg for a thoraco-lumber block, and 1.25 ml/kg for a mid thoracic block. He recommended the use of 0.25% bupivacaine for the block up to a maximum of 20 ml. For larger volumes he recommended adding one part of 0.9% NaCl to three parts local anaesthetic to produce a 0.19% mixture

Scott's lower doses are more likely to produce analgesia to the expected height, whereas Armitage will get anaesthesia. Dosages for adults are 20-30 ml for a block of the lower abdomen and 15-20 ml for a block of the lower limb and perineum.

Care is needed to avoid the use of toxic doses of drugs for high blocks. The recommended maximum dose of Bupivicaine is 2 mg/kg or Lignocaine 4 mg/kg. These dosages are the maximum for a correctly injected dose. If the drug is mistakenly injected intravenously very small dosages may cause serious toxicity