Infusion Catheter Epidural
A lumbar epidural injection of a corticoid has been the treatment of choice for radiculopathy for nearly fifty years. Patients who “fail” conservative care routinely are, in most cases, candidates for lumbar epidurals prior to consideration of surgery. Although approximately 80% of patients on whom the author performs epidurals have had some degree of pain relief, only about 50% have significant sustainable relief, and able to return to a fairly normal functional status. Unfortunately, the other 50% have either no relief, partial relief (i.e. 20% better after two epidurals), or transient relief (i.e. 90% better after three epidurals, but back to baseline by four weeks following the third epidural). After performing approximately 6,000 procedures over the past 14 years, the author has investigated why some patients do so well, and some others don’t.
Assuming all patients have the epidurals performed under flouroscopy with contrast, and that different approaches are attempted in failed patients (i.e. an interlaminar approach is attempted first with no success, and a transforaminal is attempted second, again with no success), what factors could otherwise explain this discrepancy? In the author’s opinion, variabilities in re-absorption of the corticosteroid may explain, in part, some of these clinical differences seen. The epidural space is extremely vascular, and the author has witnessed cases where the contrast dye is completely re-absorbed in as fast as three to four minutes but, at other times, may take significantly longer. One would postulate the same process must likely occur with the corticosteroid as well, particularly since corticosteroids are somewhat water-soluble. That may also explain why one may see some systemic effects of the corticosteroids in some patients but not in others. If this is true, is it possible that the corticosteroid just doesn’t linger long enough around the inflamed tissues to have a long lasting optimal effect?
Physiology of Locally Injected Corticoids
It has long been assumed that corticosteroids produce their pain-relieving effects when injected into joints or the epidural space by suppressing the inflammation, which may be either a cause or result of nerve injury. While this mechanism is at least partly responsible for the effectiveness of corticosteroid injection, it is also possible that some corticosteroids produce an anabolic effect at the cellular level.1 Varying clinical results may be obtained by various forms and analogues of cortisone. It is unknown whether corticoids metabolize while in a container or post-injection, but this is clearly possible because cortisol rapidly metabolizes into a number of compounds, such as androstenedione and dehydroepiandosterone (DHEA), which are clearly anabolic in nature.
To possibly enhance the effects in the past, corticosteroids had been injected in a reasonably insoluble base (i.e., “Depo”) form to keep the corticosteroid at the target area longer than could be achieved with a purely water-soluble corticosteroid. The corresponding enhanced clinical response, with a longer “soaking” in a “target” area, is essentially the same fundamental physiologic mechanism underlying the three-day epidural infusion technique described here. Simply put, exposing the inflamed tissues to a continuous infusion of corticosteroids may work better than just a one time bolus which is rapidly reabsorbed.
A New, Epidural Corticosteroid Infusion Technique
To achieve the advantage of longer term corticosteroid treatment, an indwelling catheter with an external infusion pump has been developed. (Infusion Catheter Epidural ICE Kit, Sgarlato Lab, San Jose, California). Previous to this report, 10 patients have been reported in a clinical trial.2 An additional 50 more patients, meeting the indications listed below, have since undergone the procedure. Results are very promising.
The technique requires an 18G Toughy spinal needle placed 1-3 levels above the affected suspect segment, using a retrograde approach, into the epidural space. The catheter, with stylet, is next advanced through the spinal needle and tunneled 1-3 segments in a caudal direction in the epidural space, securely implanting the catheter within the epidural space. Thus micro-movements of the catheter should not cause significant catheter migration, and should not dislodge the catheter out of the epidural space.
Spinal needle and catheter placement are verified with contrast dye under fluoroscopy. An initial bolus of injectate is initially given. The catheter is next externalized and subsequently tunneled in the subcutaneous tissues to further secure it and help reduce the risk of infection. The catheter is then attached to an external infusion pump. A combination of corticosteroid and normal saline are injected into the infusion pump, and a pre-set flow rate of 1cc per hour over 72 hours is implemented.
The ideal candidate for continuous corticoid epidural infusion is a patient who has had either a transient response (i.e. 80% improvement after one or two epidurals, but returns to baseline status within a few weeks) or a partial response (i.e. 25% better after two lumbar epidurals) to lumbar epidural injections. In this subset of patients, one could hypothesize that they did indeed have a favorable response to the bolus of corticosteroid injected into the epidural space based on their clinical improvement, albeit transient or partial. By now administering a greater dose of corticosteroid over a prolonged period of time (72 hours) to the inflamed tissues via a continuous infusion, one would anticipate a greater and/or more prolonged favorable clinical response. By breaking the pain cycle in these patients for a prolonged period of time, ICE may represent a surgery-sparing procedure in this population.
The infusion catheter epidural procedure is contraindicated in febrile or pregnant patients. Other contraindications include known anaphylic reaction to contrast dye, evidence of systemic or localized infection in the procedural field, a compromised immune system, bleeding diathesis, or concurrent use of anticoagulants.