Thoracic Epidural Analgesia Via the Caudal Approach in Pediatric Patients Undergoing Fundoplication Using Nerve Stimulation Guidance

Thoracic epidural analgesia in infants and children has been well described (1–2). The introduction and advancement of catheters from the caudal epidural space to thoracic levels is an alternative approach to direct thoracic placement (3–6). It has been suggested, however, that one should verify placement of the catheter tip radiologically because of the possibility of the catheter coiling and failing to advance to the appropriate level (3,6–7). Recently, the use of low current epidural stimulation to confirm the location of epidural catheters has been described (8–14). This approach may offer electrophysiologic confirmation of the myotome level of the epidural catheter tip by the demonstration of a motor response at the desired level. The purpose of this report was to examine prospectively the practicality of applying this test to guide the placement of a thoracic epidural catheter via the caudal approach. Materials and Methods Equipment Design A modified epidural catheter system was initially setup using the Arrow Flextipepidural catheter (Arrow International, Inc., Reading, PA) with removable stylet, a Johans ECGadapter and an IV T-extension. Subsequently, a commercially available product (Epidural Positioning System using Tsui Test with FlexTip Plus Catheter, TS-05430-P; Arrow International, Inc.) was developed (Fig. 1). The tip of the stylet was adjusted to lie 10 mm proximal to the distal end of the epidural catheter. The anode lead of the nerve stimulator is connected to an electrode on the patient’s arm as the grounding site. The cathode lead of the stimulator is connected to the metal hub of the adapter. After priming the setup with one to two mL of normal saline, an electrical impulse can be conducted through the fluid to the tip of the catheter. A low current (1–10 mA) is applied through the catheter (8–14). A motor response (truncal or limb movement) indicated that the catheter was in the epidural space (Table 1). The test must be performed in the absence of neuromuscular blocking drugs to elicit a muscle twitch.Figure 1: Setup for electrical epidural stimulation via epidural catheter. Equipment required was a commercially available 20-gauge epidural catheter with stylet and Johans ECG adapter assembly. The 20-gauge epidural catheter assembly was passed through an 18-gauge IV catheter. The negative lead of the nerve stimulator was connected to the metal hub of the ECG adapter. The stylet extends to 10 mm proximal to the tip of the epidural catheter. After priming the setup with 1–2 mL of normal saline, an electrical impulse can be conducted through the fluid to the tip of the catheter.Table 1: Simplified Guide for Interpretation of Motor Responses from Electrical StimulationSafety Considerations Electrical current has been applied to neural structures for neurophysiologic assessment or pain management for decades (15–16). Chronic spinal cord stimulation is a safe and effective means of pain management (15–20). Spinal cord stimulation, even with an electrode placed in the subarachnoid space, has also been used with minimal complications (21–22). In our reported clinical trials (8–14), none of the studied patients experienced any discomfort or obvious side effects from the stimulation test. Because the milliamperage used in this test was within the safety range used for patients with chronic pain, it was anticipated that the risk of a brief (seconds to minutes) electrical stimulation used in this test would be less than the risk of chronic (months to years) epidural stimulation used in chronic pain management. However, it is important to use caution to minimize the risk of complications in performing this test. Because a motor response will be elicited at a very low current (<1 mA) in the case of subarachnoid placement, the current output must be carefully increased from zero and stopped once motor activity is visible. The duration of stimulation should be as brief as possible. The Arrow Flextip Plus is an open-tip, single-orifice catheter constructed of a circumferential stainless steel coil with soft polyurethane. The stainless steel coil disposed within the lumen of the catheter tube is desirable to ensure proper conduction of electricity through the entire length of the catheter. The catheter has a flexible and soft blunted tip (23). Because the stylet ends 10 mm proximal to the tip of the epidural catheter, it is possible for the tip of the catheter to fold back on itself during insertion in a “J” configuration. This characteristic allows retention of the soft and blunted tip of the catheter and the stylet wire provides stiffness for ease of advancement from the caudal space. Study Design After institutional ethical approval and informed parental consent, 21 consecutive infants <3 yr of age, who were scheduled to have fundoplication under combined general anesthesia and epidural analgesia were enrolled. After induction of anesthesia and endotracheal intubation with 2–4 mg/kg propofol, 1–1.5 mg/kg succinylcholine, or 10–20 μg/kg alfentanil, the patients were turned to the lateral decubitus position. After sterile preparation, an 18-gauge IV catheter was inserted into the caudal space through which a 20-gauge epidural catheter was threaded. The length of the epidural catheter required was estimated by measuring the distance on the skin from the caudal space to the desired level (T7-8) for the catheter tip. An electrical current (1–10 mA) was applied through the epidural catheter as it was advanced cranially. The level of muscle twitch was observed to advance from the lower limb muscles to the upper abdominal muscles as the catheter was threaded cranially. The catheter was reinserted if it did not reach the desired level. When the catheter was optimally positioned, the IV catheter was withdrawn and the stylet removed from the epidural catheter. After securing the epidural catheter with a sterile dressing, a test dose of 0.2 mL/kg of 0.25% bupivacaine with 1:200,000 epinephrine was then administered in two aliquots. If the heart rate did not increase by more than 10 bpm within 60 s, an additional dose of 0.3 mL/kg of 0.25% bupivacaine was administered. Intraoperatively, the patient received an epidural infusion of bupivacaine 0.1% with 1 μg/mL fentanyl at 0.2–0.4 mL · kg−1 · h−1. General anesthesia was maintained with isoflurane (end-tidal concentration 0.5%–1.2%) or desflurane (end-tidal concentration 3%–5%) with a mixture of 50% nitrous oxide and 50% oxygen. Muscle relaxants were administered after epidural catheter placement. Epidural analgesia was determined clinically to be successful perioperatively based on assessment by the anesthesiologist. Failure of postoperative analgesia was defined as the requirement for IV opioid for pain management within 72 h after surgery, as judged by the anesthesiologist attending the acute pain service. Results Twenty-one patients aged 5 wk to 2.5 yr (Table 2) were studied. One child (aged 20 mo) was excluded as epidural analgesia was abandoned when the catheter could not be advanced beyond the lumbar region despite manipulation. This child received an IV morphine infusion for perioperative pain management. Of the remaining 20 patients in whom the catheter was advanced to the desired level under the guidance of nerve stimulation, clinical assessment deemed the epidural was functioning properly in all patients intraoperatively. Satisfactory postoperative epidural analgesia was achieved in 18 of the remaining 20 patients (success rate of 90%). In two patients, pain assessments could not distinguish pain from irritability. Despite radiologically confirmed correct placement of the catheters, analgesia was deemed possibly inadequate and the epidurals were discontinued. Symptom management was provided by IV morphine and diazepam. Tracheal extubation of all patients occurred at the conclusion of surgery with the exception of one 5-wk-old neonate who was extubated 12 h postoperatively. There was no evidence of postoperative neurologic injury in any studied patient. The average time required to place the epidural catheter from identification of landmarks until the epidural catheter reached the desired level was 14 min (range, 5–25 min).Table 2: Demographic dataDiscussion This study is the first case series report of pediatric epidural placement using electrical stimulation instead of radiographic imaging to guide the advancement of an epidural catheter cranially from the caudal space. One patient was excluded from the study, as we were unable to advance the catheter cranially to the desired thoracic level despite repeated attempts. Also, despite accurate placement of the catheters, epidural analgesia was abandoned in two patients. Unlike parenteral opioids, sedation is not a feature of this analgesic method. Patients may appear agitated and irritable because of the presence of nasogastric tubes, urinary catheters, and the inability to effectively communicate distress (both patients were nonverbal). There is no easily administered and widely accepted technique for assessing pain in nonverbal infants (24). Therefore in our study, the success of epidural analgesia was made by the pediatric anesthesiologists based on clinical assessment of the behavior (e.g., crying, facial expression), heart rate, and blood pressure of the infant. In retrospect, it would have been preferable to use a single pain scale for the assessment of postoperative pain. Because there was doubt as to the analgesic efficacy of the epidurals in these patients, we elected to remove the epidural catheters and provide parenteral morphine. However, both patients’ irritable symptoms were well managed only after IV diazepam was added. We suspect that our two patients were not settled most likely because of irritability from causes other than pain. Nevertheless, the overall success rate of this approach was 90% (18 of 20). Fundoplication is the most common inpatient general surgical procedure in children in our institution. These patients are ideal candidates for postoperative epidural analgesia because of the prevalence of preexisting respiratory disease and the increased likelihood of postoperative requirements for supplemental oxygen, ventilation, and admission to an intensive care unit. Most of these patients are either preverbal infants or nonverbal older children because of associated central nervous system disease that makes pain assessments more challenging. In our prior experience, we failed to achieve a high success rate for epidurals using styletted 22-gauge and 24-gauge catheters for caudal, lumbar, and thoracic approaches. Catheter placement was not confirmed radiologically because of the extra operating room time required. Hence improper placement may have been a major contribution to our failure rate. A review of the database of our pediatric acute pain service showed that 215 patients received epidural analgesia between February 1994 and May 1996. Approximately 32% of children with an epidural experienced inadequate analgesia and required conversion to an opioid infusion (success rate of 68%). During this period, 22 of 41 patients who received epidural analgesia for fundoplication were deemed unsuccessful because of the need to convert to an opioid infusion (success rate of only 46%). Discouraged by the low success rate, the use of epidural analgesia diminished to <20 cases per year in the subsequent years. After the introduction of the use of electrical epidural stimulation to confirm epidural catheter placement, our practice has changed significantly. In 1999, epidural analgesia was used in 127 children of which 91 (72%) were placed via the caudal approach. With an overall success rate of 86% (89% for the caudal approach), acceptance of this method of analgesia by anesthesiologists, surgeons, and postoperative nurses has improved considerably. We have found it useful to be able to demonstrate to parents and nursing staff the location of the catheter tip by using electrical epidural stimulation postoperatively on the nursing unit. This has facilitated our treatment of causes of distress other than pain. This easily performed clinical assessment obviates the need and inconvenience of having to obtain radiographic confirmation of the location of the catheter tip. In our study population of infants and nonverbal small children undergoing fundoplication optimization of catheter tip position using epidural stimulation aided in achieving effective pain control.

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