The patient is placed in a prone position, with the neck slightly flexed and the forehead supported on a small sponge. The target site is the lamina at C7-T1 because there is less likely to be central stenosis at this level and a larger epidural space. The lamina of C7 is easily seen with C-arm fluoroscopy. No injection is attempted at the site of previous posterior surgical laminectomy due to epidural scarring. Following aseptic preparation and sterile draping, a 22-gauge spinal needle is directed under fluoroscopy to impact the posterior lamina using a paramidline approach (Fig. 10). The depth of the needle is marked with a small forceps attached to the needle at the junction of the skin, while injecting 2 to 3 cc of local anesthetic into the adjacent lamina and the posterior cervical muscles as the needle is withdrawn. A 20- or 22-gauge epidural needle is then inserted into the anesthetized skin and down to the bone margin of the lamina adjacent to the interlaminar space. The needle depth is corrected to the predetermined length so as to bypass the lamina and then directed toward the midline at the interlaminar gap under fluoroscopic control. Because the ligamentum flavum is thin and affords little resistance to the injection, a small volume of contrast in a 3 or 5 cc syringe with a minimum volume
FIGURE 10 Posteroanterior projection. Translaminar C7-T1 epidural block; posterior approach with the patient prone. The needle target is the posterior lamina of C7. A 22- or 25-gauge needle is inserted to touch the posterior cortex of C7 via a paramedian approach and a small forceps is used to grasp the needle above the skin before needle removal to mark the depth of the lamina.
short-extension tubing is used to observe the contrast flow into the epidural space by keeping a small constant pressure on the syringe until the contrast flows freely away from the needle tip into the epidural space. The position is checked with fluoroscopy in the true PA and both oblique projections to show a linear configuration of the contrast against the dural sac and exclude a subarachnoid injection. Usually no more than 3 to 4 cc of contrast is necessary to confirm this position (Fig. 11). A subsequent injection of 6 to 12 mg of a preservative-free corticosteriod such as betamethasone is administered into the epidural space. The use of a short-acting local anesthetic such as lignocaine is optional because there is a risk of intradural injection.
FIGURE 11 Posteroanterior projection. Translaminar C7-T1 epidural block; posterior approach with the patient prone. Contrast outlines the epidural space bilaterally from C6-T2.
Monitoring devices for blood pressure, EKG, and pulse oximetry are recommended. There should be oxygen, suction, and a ventilator available to manage cardiac and respiratory emergencies.
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