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Anesth Analg 2003;97:984-988
© 2003 International Anesthesia Research Society

PEDIATRIC ANESTHESIA

Confirmation of Direct Epidural Catheter Placement Using Nerve Stimulation in Pediatric Anesthesia

Susan M. Goobie, MD FRCPC*, Carolyne J. Montgomery, MD FRCPC*, Rahul Basu, MD*, Jillian McFadzean, MD*, Gerald J. O’Connor, MD FRCPC*, Kenneth Poskitt, MD FRCPC{dagger}, and Ban C. H. Tsui, MSC MD, FRCPC{ddagger}

Departments of *Anesthesiology and Pain Management, and {dagger}Radiology, British Columbia’s Children’s Hospital and University of British Columbia, Vancouver, BC; {ddagger}Department of Anesthesiology & Pain Medicine, University of Alberta Hospitals, Edmonton, AB

Address correspondence to Susan M. Goobie, MD, FRCPC, Department of Anesthesia, Children’s Hospital, 300 Longwood Avenue, Boston, MA 02115. Address email to susan.goobie{at}tch.harvard.edu


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
We evaluated the success rate of using low current electrical stimulation (the Tsui test) to identify and confirm direct epidural catheter placement in a pediatric population. Thirty subjects received a standard anesthetic and administration of the Tsui test on epidural placement. The distribution of myotomal activity was recorded. The intended and actual level of the epidural catheter was compared. Myotomal activity was seen in all patients but one. The median current resulting in myotomal activity was 5.3 mA. The median difference between the intended and actual level as confirmed on radiograph was 1.8 levels. The clinical success rate was 93.9%. The positive predictive value of the Tsui test was 82%; i.e., in 23 of 28 cases, the Tsui test correctly identified the position of the epidural catheter tip within 2 vertebral levels. The test did not offer any added advantage when used in the setting of directly placed epidural catheters in our institution over "blind" methods already used to confirm catheter position when using cutaneous landmarks and test dosing.

IMPLICATIONS: A new technique to confirm epidural catheter position uses low current electrical stimulation in pediatric patients. This study evaluated the use of electrical stimulation in 30 pediatric patients for directly placed catheters. Electrical stimulation did not provide any advantage over conventional methods (e.g., cutaneous landmarks) for confirmation of catheter position.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
In pediatric anesthetic practice, epidural catheters are usually inserted after the induction of general anesthesia to provide intra- and postoperative pain management (1). An epidural catheter may be placed directly at the vertebral level that corresponds to the dermatomal area where the surgical incision occurs (direct placement) or by intentionally inserting the epidural catheter from a lower intervertebral level; i.e., using a caudal approach via the sacrococcygeal membrane, and passing the catheter cephalad along the epidural space to the desired level (indirect technique). Many pediatric anesthesiologists favor the indirect technique in infants weighing <10 kg (2,3). The direct method is routinely used when epidural catheters are placed at lumbar and thoracic levels in older children. Both insertion techniques, however, are performed blindly using cutaneous landmarks. Postoperative radiographs often reveal that catheter placement is not always at the intended level, particularly when the catheter is inserted indirectly (4). For further accuracy, the location of the catheter tip may be confirmed radiologically before administration of epidural medication (5).

An adult study detailed a method using low-current electrical stimulation (the Tsui test) to correctly identify epidural catheter placement during direct placement and concluded this test to be safe, objective, and reliable (6). The Tsui test relies on stimulation of epidural nerve roots causing visible myotomal activity (muscle twitching), thus providing electrophysiological confirmation of the level of the epidural catheter tip. The efficacy and safety of this technique to guide indirect epidural catheter placement has been described in a series of >100 pediatric patients (7).

The direct placement of epidural catheters is a standard practice in pediatrics (8–10). We evaluated, prospectively, the success rate of using low-current monopolar electrical epidural stimulation to identify and confirm direct thoracic or lumbar epidural catheter placement in a pediatric population.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
After IRB approval and informed written parental/guardian consent, 30 ASA physical status I-III elective surgery patients in a tertiary care pediatric hospital were recruited over a 5-mo period. All patients met existing institutional criteria for either direct thoracic or lumbar epidural catheter placement for the provision of perioperative analgesia. Subjects weighed between 10 and 70 kg and had a body mass index <30. Subjects who had a neuromuscular disorder, an allergy to local anesthetics, epidural opioids or latex, an implanted electronic device, previous epidural catheter insertion or spinal surgery were excluded.

The anesthetic technique was standardized for all patients. After induction using propofol 3–5 mg/kg and remifentanil 2–4 µg/kg and endotracheal intubation, patients were ventilated to an end-tidal CO2 of 35–45 mm Hg. Anesthesia was maintained with O2/N2O and isoflurane. No neuromuscular blocking drugs were administered. A standardized epidural kit (Epidural Positioning System using Tsui Test with FlexiTip Plus Catheter, TS-05430-P; Arrow International, Reading, PA) was used (7,11). The catheter was designed for indirect caudal placement and required the addition of an 18-gauge, 2-in Tuohy epidural needle (A1853–18; SIMS Smiths Industries, St. Paul, MN) and either a glass (Perifix 5 mL Loss of Resistance GLR5Ps; B. Braun, Melsungen, Germany) or plastic (SIMS Portex 7 mL Loss of Resistance 4900; Portex, Kent, UK) syringe, depending on the operator’s preference. The length of catheter threaded into the epidural space was determined by measuring, on the skin, the desired length from the insertion site to the target site and adding this to the depth of the epidural space. The insertion site was the dermatomal midpoint of the surgical incision. The catheter was threaded 2.5–5 cm into the space. The goal was to place the tip in the upper half of the dermatomal distribution of the surgical incision. Using aseptic technique, the desired lumbar or thoracic intervertebral epidural space was located using a standard preservative-free normal saline loss-of-resistance technique. The metal stylette was withdrawn completely before insertion and the catheter meticulously primed with 3 mL 0.9% normal saline to ensure an air-free column of fluid from the Johan’s connector to catheter tip (dead space of 0.6 mL).

Before stimulation, the Tuohy needle was withdrawn over the catheter so that the needle was not in contact with the skin. The catheter was connected from the Johan’s connector to the stimulating (black - cathode) electrode of a "Dakmed 750 digital" nerve stimulator (Dakmed, Tewksbury, MA). The grounding (red - anode) electrode was placed remotely from the site of stimulation (e.g., attached to the deltoid muscle during lumbar epidural insertion and the vastus lateralis muscle during thoracic epidural insertion). The current was increased stepwise from 0 mA by 2-mA increments until myotomal activity was observed. The catheter was flushed with 0.5–1 mL of normal saline after insertion and before each increase in current delivered. If myotomal activity was not observed at a current of 10 mA, the epidural catheter was withdrawn by 0.5 cm (to a minimal depth of 2.5 cm) and incremental nerve stimulation repeated. A maximum current of 15 mA was applied.

The distribution of myotomal activity was categorized as upper thoracic (T1-6), lower thoracic (T7-12), or lumbar (L1-5). This classification system was used to categorize the stimulated muscle groups that can be supplied by more than one spinal root. Upper thoracic myotomal activity (stimulation of nerve roots T1-6) was seen with peripheral intercostal muscle twitching. Lower thoracic myotomal activity (stimulation of nerve roots T7-12) was manifested as twitching of rectus abdominus and external oblique muscle groups. Lumbar myotomal activity (stimulation of nerve roots L1-4) was manifested as hip flexion. The epidural catheter was aspirated and a standard test dose of 0.1 mL/kg of 0.25% bupivacaine (2.5 mg/mL) with 1:200,000 epinephrine (5 µg/mL) (Marcaine®; Abbott Laboratories, Abbott Park, IL), to a maximum of 3 mL, was then administered (12).

During the insertion of the epidural and administration of the Tsui test, the observing investigator recorded the time to insert the epidural and administer the test, the presence and location of myotomal activity, and the current applied at the onset of visible myotomal activity.

Intraoperatively, an initial dose of epidural preservative-free hydromorphone HCl (2 mg/mL; Sabex®, Boucherville, PQ) (6–10 µg/kg) and epidural 0.25% bupivacaine with 1:200,000 epinephrine (thoracic, 0.25–0.5 mg/kg; lumbar, 0.5–1.25 mg/kg) was given. General anesthesia was maintained with isoflurane (end-tidal concentration 0.5%–1.5%) and an epidural infusion of 0.1% bupivacaine (0.1–0.5 mg/kg/hr) and hydromorphone (0.3–1.5 µg/kg/hr). The position of the epidural catheter tip was confirmed by a portable radiographic study in the postanesthetic recovery room (PACU).

Efficacy of epidural analgesia was assessed in the PACU by recording the requirement for rescue analgesia and, at discharge, Children’s Hospital of Eastern Ontario Pain Score (CHEOPS) as assessed by the PACU nurse (13). This outcome measure for pain intensity was chosen for use because self-reporting may not have been feasible in some cases as a result of the wide range of subjects’ ages. The CHEOPS range is from 6 to 13 where 6 is no pain and >9 implies inadequate pain management. When feasible, the dermatomal area of sensory block using subjective response was assessed in PACU at 1 h after admission. A global assessment of epidural efficacy at 24 h postoperatively was reported by the acute pain service attending anesthesiologist.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Thirty-one patients were recruited of 60 children receiving epidurals over a 5-mo period. The 29 patients not included either met exclusion criteria or did not consent to participate in the study. One patient was inadvertently given a muscle relaxant on induction and was therefore excluded. Of the 30 remaining patients, 18 were male and 12 were female. The median age was 8.6 yr (range, 1.8–16.7 yr), median weight was 28.8 kg (range, 11.6–71.0 kg), and median height was 125 cm (range, 88.0–165.0 cm). Data pertaining to surgical procedure and epidural placement are shown in Table 1.


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  		Table 1. Surgical Procedure and Level of Epidural Placement (n = 30)
 
Twenty-three subjects received thoracic epidurals (4 upper thoracic; T1-6, and 19 lower thoracic; T6-12) and 7 patients received lumbar epidurals, as defined by tip location on postoperative radiograph. The median number of insertion attempts was 1.4 (range, 1–3). The median insertion time was 11.6 min (range, 4–35 min). Myotomal activity was seen in all patients but one. In this patient, no myotomal activity was seen with a maximum of 15 mA; however, the epidural was functional and was located in the epidural space on postoperative radiograph at the intended dermatomal level.

The median current resulting in myotomal activity was 5.3 mA (range, 1.2–11.1 mA). There was no difference between median current required for thoracic versus lumbar levels.

The characteristics of myotomal activity are shown in Table 2. In the majority of cases, twitching was bilateral and palpable. The actual position of the epidural tip was determined radiologically in 28 of 30 patients (93%). In two patients, the exact position could not be determined accurately (one was below L2, but the catheter tip was not included in the film, and the other was in the lumbar space, but the tip location was not clearly defined on radiograph). The relationships between the desired and actual levels of the epidural catheter tip within incision ranges is shown in Figure 1. The median difference between the intended and actual levels, as confirmed on radiograph, was 1.8 levels (range, 1–5). In 19 of 28 patients (68%), the discrepancy between the intended and actual level was <=2 levels. In the remaining 9 patients, the difference between intended and actual vertebral level of the catheter tip was between 3 and 5 levels (in 4 subjects, the discrepancy was 3 levels difference, 4 subjects were out by 4 levels, and 1 was out by 5 levels). In 4 of the 9 cases (44%) where the difference between the intended and actual level was >=3, the epidural stimulation test did indicate this by producing myotomal activity clearly away from the intended level and closer to the actual level. For example, in two of these cases the intended level was low thoracic but the actual level was lumbar. The myotomal distribution of twitching in these cases was a strong hip flexion (represented by L1-4 nerve root stimulation), not rectus abdominus and external oblique twitching (T7-12 roots). Sensory evaluation was only possible in 13 subjects (43%) as a result of the inherent difficulty in obtaining sensory evaluation in pediatric patients of younger ages. The mean age of these patients was 8.2 yr.


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  		Table 2. Characterization of Myotomal Activity (n = 29)
 


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  		Figure 1. Relationship between actual and desired catheter tip location in relation to dermatomal range of surgical incision and myotomal range stimulated by the Tsui test. Boxes represent patients grouped into the 3 categories of myotomal stimulation and area within represents myotomal levels stimulated by the Tsui test.

 
In the PACU, 28 patients had CHEOPS pain scores of 6 and 2 patients scored 9. Only one subject required rescue analgesia in the PACU. At 24 h postoperatively, 3 patients had their epidurals removed. Two subjects had failed epidurals <24 h postoperatively on the basis of clinical criteria.


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
This case series examined the use of low current electrical stimulation to confirm the position of epidural catheters placed via the direct route in the pediatric population. A previous study reported the feasibility of performing this test in catheters threaded from the caudal space in children (8). Adult studies demonstrate the feasibility of using the Tsui test to identify and confirm epidural catheter placement via the direct route (6,14,15).

We found that our clinical success rate was 93.9% (2 failures of 30 patients). The positive predictive value of the Tsui test was 82%; i.e., in 23 of 28 cases, the test correctly identified the position of the epidural catheter tip within 2 vertebral levels. However, in 9 cases where the catheter tip was radiologically confirmed to be >=3 levels away from the desired dermatomal area, the test alerted the clinician in only 4 cases (44%). The remaining 5 cases were not recognized, likely because of extensive overlap of muscular innervation by spinal nerves and the use of a myotomal classification with broad ranges of upper thoracic (T1-6), lower thoracic (T7-12), and lumbar (L1-5) to record the results of Tsui testing. As stimulation of T7-10 spinal nerve roots could manifest either with corresponding intercostal (T7-10) muscle twitching or rectus abdominus (T7-12) muscle twitching, interpretation of Tsui test at these midthoracic levels can occasionally be difficult and easily mistaken. The clinical efficacy of these five epidurals was assessed to be adequate.

Despite our standardized method of measuring and threading the necessary length of catheter to achieve the intended level, in 9 of 28 cases, the difference between the actual and intended position was >=3 levels. This may be attributed to inadequate estimation of insertion of the catheter, including the inability to determine cephalad or caudad direction of threading. Despite this inaccuracy, most patients in this study had adequate postoperative pain control.

A limitation of this study was that portable AP radiographs were taken to determine the vertebral level of the epidural catheter tip. The catheter was inferred to be within the epidural space if it was in the midline. A further limitation was that no comparison group was used in this study. A control group might have allowed a better determination of the benefit of using the Tsui test in this patient population.

The safety of the Tsui test has been previously addressed (8). The milliamperage used is within the range used for patients with chronic pain disorders (4–30 mA) (16) and for intraoperative monitoring during spinal surgery (2–40mA) (17–20).

In one subject, myotomal twitching was not observed at the maximum current of 15 mAmps. The epidural worked adequately and was in the correct position on radiograph. In this case, it is quite likely that either the nerve stimulator was not functioning or the current path was not adequate because of bubbles in the system.

In conclusion, the Tsui test did not offer any added advantage when used in the setting of directly placed epidural catheters. Further studies are needed to determine if using this technique for directly placed catheters improves success rate and safety.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

  1. Krane E, Dalens B, Murat I, Murrell D. The safety of epidurals placed during general anesthesia. Reg Anesth Pain Med 1998; 23: 433–8.[Web of Science][Medline]
  2. Bosenberg A, Bland B, Schulte-Steinberg O, Downing J. Thoracic epidural anesthesia via caudal route in infants. Anesthesiology 1988; 69: 265–9.[Web of Science][Medline]
  3. Rasch D, Webster D, Pollard T, Gurkowski M. Lumbar and thoracic epidural analgesia via the caudal approach for postoperative pain relief in infants and children. Can J Anaesth 1990; 37: 359–62.[Web of Science][Medline]
  4. Blanco D, Llamazares J, Rincon R, et al. Thoracic epidural anesthesia via the lumbar approach in infants and children. Anesthesiology 1996; 84: 1312–6.[Web of Science][Medline]
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  7. Tsui B, Seal R, Koller J, et al. Thoracic epidural analgesia via the caudal approach in pediatric patients undergoing fundoplication using nerve stimulation guidance. Anesth Analg 2001; 93: 1152–5.[Abstract/Free Full Text]
  8. Hammer G. Pediatric thoracic anesthesia. Anesth Analg 2001; 92: 1449–64.[Free Full Text]
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  14. Tsui B, Gupta S, Finucane B. Confirmation of epidural catheter placement using epidural nerve stimulation in obstetric patients: the Tsui test. Reg Anesth Pain Med 1998; 23 (Suppl): 35.
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Accepted for publication May 16, 2003.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins and Stanford University Libraries' HighWire Press®. Copyright 2003 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press