The patient is placed prone on the fluoroscopy table, with a pillow or bolster under the abdomen. While rotating the C-arm slightly may be necessary to center the relevant spinous processes,
Arrow denotes a typical skin entry site, if the target craniocaudal tilt is not routinely applied. A direct midline approach allows the needle to pass between the spinous processes to reach its target. A skin entry site is marked, usually over the upper portion of the more inferior spinous process (Fig. 3).
Standard sterile preparation and drape are followed by anesthesia of the skin and subcutaneous tissues, with 1% lidocaine buffered with sodium bicarbonate. Under intermittent fluoroscopic guidance, a 25-gauge 3.5-inch spinal needle is advanced, usually with a slight cephalad angulation. Knowing that the needle tends to track in a direction opposite of its bevel, it can usually be steered to keep it in the midline and following the appropriate angle to the target. Once the needle engages the interspinous ligament, it is less likely to deflect laterally, and the needle is advanced with lateral fluoroscopic visualization.
The needle is stopped when it crosses the posterior margin of the facets (Fig. 4). A midline position is ensured by checking the AP view. From this point the needle is advanced into the posterior epidural space utilizing the "air release technique" with anteroposterior (AP) fluoroscopic guidance. The air-release technique is performed by attaching a glass or
FIGURE 5 Contrast pooling around the needle tip confirming epidural location.
low-resistance plastic syringe (such as a Terumo 3-cc syringe) to the needle (10) and attempting to infiltrate approximately 0.5 cc of air. If the needle tip is still posterior to the epidural space, the plunger will bounce back. Continue advancing a millimeter at a time, checking with an air puff, until there is no bounce back, signaling needle tip entry into the epidural space. Contrast is then instilled via extension tubing, under continuous AP fluoroscopy. Contrast appropriately within the epidural space pools around the tip of the needle (Fig. 5). Alternatively, contrast in the thecal sac quickly diffuses and does not pool at the needle tip. If the tip is in a vein, contrast whisks away into branching or tortuous venous structures (Fig. 6).
Check the lateral projection, which should show contrast collecting along the dorsal margin of the thecal sac (Fig. 7) or extending slightly anterior to this if there is enough contrast to flow around the sides of the thecal sac. Intrathecal contrast will instead layer on the dependent ventral margin of the thecal sac (Fig. 8). Luckily, fluoroscopy helps keep this occurrence down to less than 1% of the time in our department.
If the thecal sac is inadvertently entered, the injection cannot proceed at that site. Proceeding would cause a spinal block, and the steroids would be wasted in the cerebrospinal fluid. While Silbergleit et al. terminate the procedure and reschedule in this situation (10), most authors will make a second attempt at another level and have not reported mishaps from this practice (8,37,60). Our approach is to make a second attempt if the needle is 25-gauge, but reschedule if it is 22-gauge.
When proper positioning is assured, 2 cc Kenalog-40 mixed with 5 cc preservative-free 0.5% lidocaine is instilled over one or two minutes, with intermittent visualization in the AP plane. Provided the needle has not dislodged, the contrast pool should increase briefly, from the residual amount left in the needle, and then be dispersed by the radiolucent medication. It is not unusual to elicit discomfort or even pain with the injection. This usually improves with a slower injection. Save the AP and lateral images documenting epidural contrast as well as an AP image after contrast is dispersed by the medication. These images often aid the next operator if the patient returns for another injection and can document extrathecal position if the patient subsequently develops a headache. After the medication is delivered, the needle is removed, the overlying puncture site is cleansed with alcohol, and an adhesive bandage is placed. The patient is assisted while rising slowly.
Given that these patients are almost never sedated and rarely have significant motor nerve anesthesia, they are not detained longer than the time it takes for cleanup and a short postprocedure discussion. While some patients are light headed after the procedure, this is usually due to the time spent prone with an abdominal bolster in place, and the sensation clears shortly. Patients should take it easy that day and then resume normal activities the next day. We insist all patients bring another person to drive them home.
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