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Caudal epidural injection

Caudal epidural injections (or sacral foramen epidural injections) are one of a number of spinal epidural injections possible. 

Indications

Typically epidural injection are performed in patients who are currently not surgical candidates. Caudal injection can be performed when patients are on anticoagulation or when previous spinal surgery makes interlaminar epidural injection difficult. 

Contraindications

Allergy to any of the planned medications is of course a contraindication, although it is possible to perform this without contrast, provided consent includes the increased risk of intravascular or intradural injection. 

Any infection of the skin of the natal cleft is also a contraindication. 

Procedure

Positioning/room set up

The patient is placed prone on the fluoroscopy table, and the lumbar region exposed down to mid buttock. As an alcohol or iodine (or both) containing skin preparation is recommended it is essential to avoid prep running down the natal cleft to the genitalia. Although you may improve a patients back pain with the injection, a blistered scrotum/vulva is unlikely to meet with approval. This danger can be avoided by meticulous application of the prep, avoiding excess fluid and the placement of gauze in the cleft of the buttocks. It is probably worth while explaining why you are doing this. 

Equipment
  • 22-guage, 9-10cm (3.5 inch) spinal needle
  • fenestrated or chuck-drapes
  • isotonic contrast, e.g. 240 mg/mL  iohexol
  • local anaesthetic, e.g. 1% lignocaine/lidocaine
  • steroid, e.g. betamethasone sodium phosphate/betamethasone acetate suspension
  • long-acting local anaesthetic, e.g. bupivacaine
  • bandaid
Technique

Although ultrasound can be used to localise the sacral hiatus and enter the sacral canal, it is not able to confirm extradural extravascular needle placement or assess ascent of therapeutic mixture 3

The sacral hiatus is palpated, and the needle advanced at approximately 45 degrees in the midline. Screening should be performed initially in AP projection to ensure midline placement (this is usually not a problem) and then in lateral projection, visualising the needle ascending the sacral canal. Lateral screening can be used to both plan skin entry and degree of needle angulation as not everyones sacral hiatus is at 45 degrees. 

The tip of the needle should be advanced no further than S3 to avoid the risk of dural puncture. A pop can sometimes be felt as the needle passes through the sacrococcygeal ligament and into the hiatus 3

Once reached, 5-6ml of contrast in injected, confirming extradural and extravascular location, and acting as a visual marker for ascent of steroid / local anaesthetic. The therapeutic mixture is then injected (typically 3-5mL:1-2mL of betamethasone and 2-3mL of bupivicaine). The previously injected contrast should be seen to disperse, ideally no higher than L5/S1 1-2.  

Some authors advocate the use of larger volumes of dilute injectate to effectuate larger area of effect 4-5

Postprocedural care

As with other epidural injections, recovery in the department for 20-30 minutes minimum is recommended, as a proportion of patients will experience transient numbness, weakness or loss or proprioreception, making ambulation difficult and dangerous. 

Complications

As with all spinal epidural injections, care should be taken to confirm extradural location, to avoid intradural injection with resultant adhesive arachnoiditis 1. A low pressure headache can also result from dural puncture. 

Insomnia the night of the injection has been reported as common 5

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