Caudal epidural injection
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Caudal epidural injections, or sacral hiatus epidural injections, are one of several possible spinal epidural injections.
Typically, epidural injections are performed in patients who are currently not surgical candidates. The caudal injection can be performed when patients are on anticoagulation or when previous spinal surgery makes interlaminar epidural injection difficult.
Allergy to any of the planned medications is 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 (e.g. intergluteal pilonidal sinus).
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 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 worthwhile explaining why you are doing this.
- 22-gauge (25-gauge is an alternative), 9-10 cm (3.5 inches) spinal needle
- fenestrated or chuck-drapes
- isotonic contrast, e.g. 240 mg/mL iohexol
- local anesthetic, e.g. 1% lignocaine/lidocaine
- steroid, e.g. betamethasone sodium phosphate/betamethasone acetate suspension
- long-acting local anesthetic, e.g. bupivacaine
Although ultrasound can be used to localize 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 (bordered by the sacral cornua), 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, visualizing the needle ascending the sacral canal. Lateral screening can be used to both plan skin entry and degree of needle angulation as not everyone's 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, 5-6 mL of contrast in injected, confirming extradural and extravascular location, and acting as a visual marker for the ascent of steroid / local anesthetic. The therapeutic mixture is then injected (typically 3-5 mL:1-2 mL of betamethasone and 2-3 mL of bupivacaine). 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.
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 proprioception, making ambulation difficult and dangerous.
As with all epidural spinal 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 at the night of the injection has been reported as common 5.
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- 2. McGraw JK. Interventional radiology of the spine, image-guided pain therapy. Humana Pr Inc. (2004) ISBN:1588291987. Read it at Google Books - Find it at Amazon
- 3. Narouze SN. Atlas of Ultrasound-Guided Procedures in Interventional Pain Management. Springer Verlag. (2010) ISBN:1441916792. Read it at Google Books - Find it at Amazon
- 4. Waldman SD. Atlas of Interventional Pain Management. Saunders. (2009) ISBN:1416099948. Read it at Google Books - Find it at Amazon
- 5. Slipman CW, Simeone FA. Interventional spine, an algorithmic approach. W B Saunders Co. (2008) ISBN:0721628729. Read it at Google Books - Find it at Amazon