The patient is prepared as for general anaesthesia:

(1) He/she should be fasted

(2) All appropriate equipment for resuscitation must be available. Equipment for intubation, airway suction and drugs to stop fitting ie thiopentone 2-5 mg/kg or Diazepam 0.2-0.4 mg/kg.

(3) An intravenous cannula should always be inserted in an upper limb, in case of accidental intravenous injection, or profound sympathetic blockade from a high epidural block.

(4) The procedure must be carried out with a strict aseptic technique. The skin should be thoroughly prepared and sterile gloves worn. Any infection in the caudal space is extremely serious.

(5) There are three main approaches: the prone, the semi-prone, and the lateral. The choice depends on the preference of the anaesthetist and the degree of sedation of the patient.

The prone position is often easiest in the adult, as fat tends to move away from the mid-line and landmarks are easier to find. However, there could be difficulty if urgent access to the airway is required. The caudal space is made more prominent by asking the patient to internally rotate their ankles (fig. 2).

Position (a) causes contraction of the glutecal muscles. Position (b) allows relaxation of glutecal muscles.

The semi-prone position is preferred for the anaesthetised or heavily sedated patient as the airway is easier to control in this position, while still allowing reasonably easy access to the sacral hiatus. The lateral position is often used in children, as the landmarks are easier to find than in adults. Care should be taken to avoid over flexing the hips (as for lumber epidurals) as this can make the landmarks more difficult to palpate.

(6) The landmarks are palpated. The sacral hiatus and the posterior superior iliac spines form an equilateral triangle pointing inferiorly.

The sacral hiatus can be located by first palpating the coccyx, and then sliding the palpating finger in a cephalad direction (towards the head) until a depression in the skin is felt. (In an adult the distance from the tip of the coccyx to the sacral hiatus is approximately the same as the distance from the tip of their index finger to their proximal inter phalangeal joint)!

As there can be a considerable degree of anatomical variation in this region confirmation of bony landmarks is the key to success. The needle can penetrate a number of different structures mimicking the feel of entering the sacral hiatus. It is important to establish the midline of the sacrum as considerable variability occurs in the prominence of the cornua, causing problems unless care is taken.

(7) Once the sacral hiatus is identified the area above is carefully cleaned with antiseptic solution, and a 22 gauge short bevelled cannula or needle is directed at about 45° to skin and inserted till a "click" is felt as the sacro-coccygeal ligament is pierced. The needle is then carefully directed in a cephalad direction at an angle approaching the long axis of the spinal canal.

Care should be taken not to insert the needle too far as the dura lies at or below the S2 level in the child.

(8) The needle should be aspirated looking for either CSF or blood. A negative aspiration test does not exclude intravascular or intrathecal placement. Care should always be taken to look for signs of acute toxicity during the injection. The injection should never be more than 10 ml/30 seconds.

Further tests to confirm the correct position include gently moving the tip of the needle from side to side. The needle will feel firmly held. Introduction of a small amount of air will not produce subcutaneous emphysema, and will be heard as a "woosh" sound if a stethoscope is place further up the lumbar spine. Light blood staining is not uncommon and indicates entry into the sacral canal. There should be no local pain during injection. Tingling or a feeling of fullness that extends from the sacrum to the soles of the feet is common during injection.

(9) A small amount of local anaesthetic should be injected as a test dose (2-4mls). It should not produce either a lump in the subcutaneous tissues, or a feeling of resistance to the injection, nor any systemic effects such as arrhythmias, peri-oral tingling, numbness or hypotension. If the test dose does not produce any side effects then the rest of the drug is injected, the needle removed and the patient positioned for surgery.

In the post-operative period, motor function must be checked and the patient should not be allowed to try and walk until complete return of motor function is assured. The patient should not be discharged from hospital until he/she has passed urine, as urinary retention is a recognised complication.

• Intravascular or intraosseous injection. This may lead to grand mal seizures and/or cardio-respiratory arrest.

• Dural puncture. Extreme care must be taken to avoid this as a total spinal block will occur if the dose for a caudal block is injected into the subarachnoid space. If this occurs then the patient will become rapidly apnoeic and profoundly hypotensive. Management includes control of the airway and breathing, and treatment of the blood pressure with intravenous fluids and vasopressors such as ephedrine.

• Perforation of the rectum. While simple needle puncture is not important, contamination of the needle is extremely dangerous if it is then inserted into the epidural space.

• Sepsis. This should be a very rare occurrence if strict aseptic procedures are followed.

• Urinary retention. This is not uncommon and temporary catheterisation may be required.

• Subcutaneous injection. This should be obvious as the drug is injected.

• Haematoma

• Absent or patchy block.

Caudal block is an easy and safe technique which can be used provide anaesthesia and postoperative analgesia for a wide range of surgical procedures. When performed carefully complications are rare.

This article contained links to the following additional information:

Table 1 - Drug doses for caudal epidural anaesthesia

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