Hirachand Mutagi

Type of Interventional Pain Procedure, Body Weight, and Presence of Spinal Pathology are Determinants of the Level of Radiation Exposure for Fluoroscopically Guided Pain Procedures

Abstract:  In the recent years new technology has led to the development of a bewildering array of imaging procedures. Yet, conventional radiography remains one of the most used tools to diagnose and to aid procedural interventions. Fluoroscopy guidance facilitates targeted drug delivery or radiofrequency directly to the area of pathology, a benefit that has to be balanced against the risks of radiation exposure. In this prospective observational survey of routine practice, dose area product (DAP) and screening time (ST) were recorded in 127 consecutive patients undergoing fluoroscopically guided spinal procedures along with other probable measures of potentially greater radiation exposure such as weight, type of spinal pathology, the ease of recognition of the anatomical landmarks, and the radiographic quality of the image in terms of contrast and graininess. The mean ST was 34 ± 27 seconds (range, 3 to 218 seconds), the mean DAP was 1.18 ± 1.08 Gy cm2 (range, 0.023 to 6.82 seconds). A correlation between weight and DAP was confirmed (r = 0.230, P < 0.05, Spearman’s correlation coefficient). Patients with spinal pathology (n = 33) had higher radiation exposure than those without (DAP median = 0.85, U = 978.00, P < 0.005, r = −0.28, Mann–Whitney test). The DAP values obtained compare favourably with the recommended doses for radiographs and other procedures, although they generally exceed the values for a chest X‐ray. ▪

A Cadaveric and in vitro Controlled Comparative Investigation of Percutaneous Spinal Cord Lead Anchoring.

Spinal cord stimulator lead migration is a common problem. Anchor design may be a factor in its prevention. We have undertaken a cadaveric and in vitro comparative investigation of the force required to cause lead migration with a variety of anchor types. Thirty‐eight spinal cord stimulator leads were anchored with short silastic (N = 8), long silastic (N = 16) and titanium (N = 10) devices in cadavers. Twenty‐eight further spinal cord stimulator lead anchorings were undertaken on the bench with the titanium anchor and three different octrode leads. The median force to cause lead movement in cadavers was 0.55 Newtons (N) for short silastic anchors, 0.81 N and 0.63 N for two types of long silastic anchor, and 1.3 N for the titanium anchor. There was a significant difference between long and short silastic anchors (p < 0.01) and a significant difference between the titanium anchor and the silastic anchors (p < 0.003). There was an insignificant difference in the force required to cause lead movement repeated by the same operator (p = 0.36). There was no significant difference between inexperienced and experienced operators (p = 0.88). There was no significant difference between the different leads using the titanium anchor (p = 0.06). The titanium anchor prevents simulated lead movement at greater forces that the silastic anchors with a variety of leads. For silastic anchors, movement occurred at median force below that simulated with spinal movement; for the titanium anchor, movement occurred at a median force above that simulated with spinal movement. Further in vivo investigations are warranted to assess the potential of titanium anchoring to significantly reduce spinal cord stimulator lead migration.

Use of metaraminol in patients with Familial Mediterranean Fever.

We were recently involved in the management of a 38-year-old male who was admitted to our hospital for an elective surgical procedure that mandated general anaesthesia. He was also known to suffer with Familial Mediterranean Fever (FMF). FMF is a hereditary inflammatory disease characterised by self-limited recurrent attacks of fever and serositis [1]. The recurrent attacks of fever are accompanied by severe abdominal pain, arthritis or chest pain along with a marked increase in acute phase reactants [1]. Inheritance is autosomal recessive and it affects mainly Jews, Turks, Arabs and Armenians [2]. FMF crises are characterised by an influx of polymorphonuclear leucocytes into the inflamed regions [2]. A PubMed search uncovered that attacks could be precipitated by intravenous metaraminol [3]. Indeed, the metaraminol provocative test is considered a specific diagnostic test for FMF: a 10-mg infusion of metaraminol is followed within 48 h by a typical disease-like attack [3]. As metaraminol is widely used in anaesthetic practice and cumulative doses in excess of 10 mg can be administered if hypotension is protracted, it is quite likely this could trigger a FMF crisis postoperatively. The metaraminol-induced symptoms do not occur in patients on prophylactic colchicine therapy [3]. However, colchicine treatment is often complicated by frequent gastrointestinal side-effects, reducing patient compliance [4]. We would therefore suggest anaesthetists remain vigilant to the potential risks associated with the use of metaraminol in this group of patients, especially those not taking colchicine regularly.

Dredging for the anchor.

In a recent issue of this journal, we have published a cadaveric and in vitro comparative investigation of the force required to cause lead migration, which demonstrates that titanium anchors (Titan®, Medtronic Inc., Minneapolis, MN, USA) prevent simulated spinal cord stimulator (SCS) lead movement at greater forces than silastic anchors with a variety of SCS leads (1). We wish to highlight another potential advantage of the titanium anchor. It is reported up to 46% patients with an implanted SCS system may require revision surgery, and 22.5% patients may require multiple revisions (2). Our experience has been that SCS revision procedures are often technically difficult because of fibrosis around the anchor site, often obscuring the depth and location of the anchor. Radiography fails to help, as silastic anchors are radiolucent. The surgeon, therefore, often has to resort to stereognosis, texture discrimination, and blind dissection along the SCS lead track in order to locate the anchor. In addition to the resultant tissue trauma, this also engenders the risk of inadvertent hardware damage during dissection. Titanium anchors are readily visualized on fluoroscopy (Fig. 1), allowing easier estimation of their depth and vertical location along the path of the lead, thus aiding their localization during revision surgery. However, evidence suggests the use of rigid plastic anchors is associated with increased lead failure rates on biomechanical testing compared with flexible silastic anchors (3). It remains to be seen whether the inherent rigidity of the titanium anchors outweighs their potential advantages.

Pressure Ulcers Induced by a Spinal Catheter

To the Editor: A 69-year-old woman was referred to our pain unit for management of severe, intractable back and lower limb pain secondary to acute myeloid leukemia. Her pain had been refractory to oral and parenteral opioids due to dose-limiting side effects. We decided to undertake a trial of intrathecal opioid administration and, if successful, proceed to implantation of a permanent intrathecal opiate delivery system. Accordingly, a 28-G spinal catheter (Co Span®, Kendall Ltd., Gosport, UK) was inserted intrathecally at the L3–L4 level under local anesthesia. The spinal catheter was looped at the insertion site and taped to the back with transparent dressing (Tegaderm; 3M Health Care, Loughborough, UK). It was then brought anteriorly over the right rib cage, where it was connected to a portable infusion pump delivering morphine. When the spinal catheter was removed after five days, multiple pressure sores were noted under the catheter (Fig. 1). These were dressed with aqueous povidoneiodine solution and healed in three days. Although pressure sores due to an epidural catheter have been reported previously (1), this is the first description of pressure ulcers caused by a spinal catheter. We were initially surprised that a fine (28-G) spinal catheter could cause pressure ulcers. However, this could be explained by the patient’s immobility (she was bedridden) and the pressure of the catheter against the underlying ribs. We speculate the additional stiffness of a fine-bore catheter (to prevent it kinking) was probably contributory. Although Cherng and Wong (1) advocated securing epidural catheters “along the paramedian or lateral chest line,” our experience suggests that the latter method also is fraught with risk. Ultimately, encouraging frequent position changes by the patient remains the best method of preventing this complication (1). However, meticulous attention to securing the catheter over “soft” underlying tissue (i.e., avoiding traversing over ribs, scapula) also may help.

CHEESE WIRING OF AN INTRATHECAL CATHETER: AN UNUSUAL CAUSE OF CATHETER LEAK

To the Editor: A 45-year-old man suffering from chronic low back pain following failed back surgery underwent replacement of a programmable intrathecal pump (SynchroMed, Medtronic Ltd., Minneapolis, MN, USA) that had been in situ for 5 years and was near the end if its battery life. A SynchroMed 2 pump (containing 200 mg morphine sulfate in saline) was implanted in the same subcutaneous pocket as the previous pump and connected to the existing intrathecal catheter, which was in good condition. Intrathecal morphine delivery was continued at 3.5 mg/day and the patient was discharged home 24 hours postoperatively. On the third postoperative day, however, he was readmitted to hospital with exacerbation of his back pain and symptoms of opiate withdrawal. On electronic interrogation of the implanted pump, it appeared to be functioning normally. Abdominal and thoracic X-rays did not reveal any catheter kinks or disconnection. On exploration of the pump implant site under general anesthesia, the catheter was found to be connected to the pump. However, closer inspection revealed the anchoring suture securing the catheter to the pump port had cut through the catheter, resulting in leakage of pump contents (Fig. 1). This appeared to be due to cheese wiring (cutting through) of the catheter by the anchoring suture due to excessively firm knotting. We would therefore caution against overzealously tight tying of the anchoring suture, especially when the catheter has been in situ for some time and may possibly have lost some of its elasticity, making it easier for the silk suture to cut through it.