Anesth Analg 2002;95:326-330
© 2002 International Anesthesia Research Society
PEDIATRIC ANESTHESIA
Thoracic Epidural Catheter Placement Via the Caudal Approach in Infants by Using Electrocardiographic Guidance
Ban C. H. Tsui, MSC MD, FRCP(C),
R. Seal, MD FRCP(C), and
J. Koller, MD FRCP(C)
Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, Walter Mackenzie Health Sciences Centre, Edmonton, Alberta, Canada
Address correspondence and reprint requests to Ban C. H. Tsui, Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, 3B2.32 Walter Mackenzie Health Sciences Centre, 8440-112 Street, Edmonton, Alberta, Canada T6G 2B7. Address e-mail to btsui{at}ualberta.ca
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Abstract
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We examined the success of inserting epidural catheters via the caudal route in infants by using electrocardiographic guidance. A case series of 20 patients with thoracic epidural analgesia was studied. After the induction of general anesthesia, an 18-gauge IV catheter was inserted into the caudal space to allow threading of a 20-gauge epidural catheter. The electrocardiogram (ECG) tracings via the epidural catheter, as well as the surface ECG at the target spine level, were recorded simultaneously with a modified two-channel five-lead ECG system. The epidural catheter was advanced from the caudal space until the tip reached the target level as demonstrated by a match in the configuration of the epidural ECG tracing to that of the surface ECG tracing at the target level. The catheter tip location was verified by postoperative radiographs. All catheter tips were located within two vertebrae of the target level, and satisfactory intraoperative epidural anesthesia was achieved in all subjects.
IMPLICATIONS: Epidural electrocardiography may be used to guide the positioning of the thoracic epidural catheter tip via the caudal approach to the appropriate dermatome for optimum analgesia.
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Introduction
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Thoracic epidural anesthesia in infants and children has been well described (1,2). The safety of placing epidural catheters via the lumbar or thoracic approach under heavy sedation or general anesthesia is controversial (3–7). Some anesthesiologists consider placing thoracic epidurals to be technically difficult and hazardous in small infants, particularly when the infants are anesthetized. The introduction and advancement of catheters from the lumbar and caudal epidural spaces to the thoracic level has been suggested as an alternative technique (2–5). However, radiological verification of tip catheter placement may be advisable because of the possibility of the catheter coiling and failing to advance to the appropriate level (2,5).
The use of electrical epidural stimulation to determine the location of the epidural catheter tip has been demonstrated to be an effective alternative to radiological imaging (8–11). Recently, another new technique for determining the dermatomal location of the epidural catheter tip by use of electrocardiography (ECG) has been described (12). The purpose of this study was to prospectively examine the practicality of applying this technique as a guide to the placement of thoracic epidural catheters via the caudal approach.
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Methods
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A commercially available 20-gauge epidural catheter with a Johans ECG adapter assembly (Epidural Positioning System using Tsui Test with a FlexTip Plus catheter, Product No. TS-05430-P; Arrow International, Inc., Reading, PA) was used (Fig. 1). The tip of the stylet was adjusted to end 10 mm proximal to the distal tip of the epidural catheter. The ECG tracings via the epidural catheter, as well as the surface ECG at the target spine level, were recorded simultaneously by use of a modified two-channel five-lead ECG system with the lead II/III mode (Fig. 2). For Channel 1, a surface ECG (Lead II) was first recorded by connecting the right-arm lead to a skin electrode on the midline back at the target spinal level. The left-arm lead was then connected to the metal hub of the ECG adapter of the epidural catheter. For Channel 2, a satisfactory tracing (Lead III) was obtained when the epidural catheter was filled with saline solution, allowing the catheter tip to become a unipolar ECG electrode. The catheter was then advanced from the caudal space until the tip reached the desired level, as demonstrated by a match between the configurations of the ECG tracing obtained via the epidural catheter to the surface ECG tracing at the target level.
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Figure 1. Equipment required. A 20-gauge epidural catheter with a Johans electrocardiogram (ECG) adapter assembly (Product No. TS-05430-P; Arrow International). The 20-gauge epidural catheter (Arrow FlexTip Plus) was passed through an 18-gauge IV catheter. The black lead of the ECG monitor was connected to the metal hub of the ECG adapter. The black arrow shows an Arrow-Johans ECG adapter connected to the snap-lock connector of the epidural catheter.
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Figure 2. Electrocardiogram (ECG) connection: the setup of a two-channel five-lead ECG recording system.
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The ECG monitor (Model 68S; Hewlett-Packard, Palo Alto, CA) used in the study was equipped with special protection against electric shocks (microshock) for intracardiac applications (type CF floating input, an approved equipment with a patient applied part isolated for cardiac contact procedures according to the classification of Canadian Standards Association and International Electrotechnical Commission, which limited the possible current flow through the patient to not more than 10 µA). Because an epidural ECG does not have a direct link to the heart, it was anticipated that the risk of microshock from epidural ECG would be less than the risk encountered with intracardiac ECG monitoring. However, it must be stressed that the ECG monitor used for epidural ECG applications should still meet safety requirements for use with internal electrodes and intracardiac applications. After institutional ethical approval and informed parental consent, 20 infants <3 yr old who were scheduled to have thoracic or abdominal surgery under combined general anesthesia and epidural analgesia were enrolled.
After the induction of anesthesia and endotracheal intubation with 2–4 mg/kg of propofol and 0.5–1 mg/kg of rocuronium, the patients were turned to the lateral decubitus position. After sterile preparation, an 18-gauge IV catheter was inserted into the caudal space and a 20-gauge epidural catheter was threaded through it. The required length of the epidural catheter was estimated by measuring the distance on the skin from the caudal space to the target level for the catheter tip. The catheter was advanced to the predicted length from the caudal space until the tip reached the target level, as demonstrated by a match between the configurations of the ECG tracing obtained via the epidural catheter and the surface ECG tracing at the target level (Fig. 3). 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.
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Figure 3. Electrocardiogram (ECG) tracings. (Bottom left and middle) The amplitude of the QRS complex remained relatively small from the recording via the epidural catheter after 5 and 10 cm of epidural catheter had easily been threaded from the caudal space. (Bottom right) The amplitude of the QRS complex of the epidural ECG matched the surface ECG (top) at the T4 spinal level after 17 cm of the catheter had been inserted. The postoperative chest radiograph confirmed that the tip of the epidural catheter was at the level of the six thoracic vertebra.
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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. During surgery, the patient received an epidural infusion of bupivacaine 0.05%–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. The tip of the catheter was assessed by postoperative chest radiographs in the recovery room. Epidural analgesia was clinically determined to be successful during surgery on the basis of assessment by the anesthesiologist. Failure of postoperative analgesia was based on the requirement for IV opioids for pain management within 72 h after surgery, as judged by the anesthesiologist attending the acute pain service on the basis of clinical assessment of the behavior (e.g., crying and facial expression), heart rate, and blood pressure.
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Results
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Twenty patients aged 6 days to 3 yr (Table 1) were studied. Surgical procedures included thoracic and upper- and lower-abdominal surgery. The target catheter tip locations were high thoracic level (T4) for thoracic surgery in 3 patients, mid thoracic level (T7) for upper-abdominal surgery in 10, and low thoracic (T10) for abdominal surgery in 7. All patients were extubated at the end of the surgery. All catheter tips were located within two vertebrae of the target level. The aver-age difference between the target level and that achiev-ed was 1.05 vertebrae levels, with an SD of 0.8 levels. Satisfactory intraoperative epidural anesthesia was achieved in all 20 subjects. In one 17-mo-old child, epidural analgesia was supplemented by the use of a continuous IV infusion of morphine at 5 µg · kg-1 · h-1 for mild signs of irritability, even though radiographs documented proper epidural location. This child was noted to have been irritable before surgery. No other patients required supplemental opioids during the administration of epidural analgesia. All children had normal lower-body neurological examinations after the regression of epidural analgesia. The average time required from identification of landmarks until confirmation of the epidural catheter placement at the target level was 12 min (range, 5–15 min).
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Discussion
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Although thoracic epidural catheters inserted via the caudal route are used for pediatric patients, the study described here is the first case series report of pediatric epidural placement with ECG monitoring instead of radiographic imaging to guide the advancement of an epidural catheter cranially from the caudal space. Direct insertion of thoracic epidural catheters carries the risk of traumatic damage to the spinal cord because of the relatively narrow depth of the epidural space in small infants. Advancing epidural catheters via the caudal approach may be technically easier as well as less hazardous to the spinal cord (2–5). However, neither ease of threading of the epidural catheter nor age predicts successful placement (5–7). The major problem encountered during thoracic epidural insertion with a caudal approach is curling of the catheter, resulting in arrested advancement at levels between T12 and L5 (13). Thus, a number of studies have recommended that the position of the epidural catheter be guided radiographically when the caudal approach is used.
Ideally, one should be able to detect the epidural catheter location while performing the procedure, allowing adjustments to be made at the time of insertion. In the past, there was no objective way of determining epidural catheter location except by using radiological imaging. A recently described technique of applying an electrical stimulus to the tip of the epidural catheter can provide immediate information about the position of the catheter (8–11). Stimulation of the spinal nerve root causes muscle twitching in the distribution of the corresponding myotome. Because of the need to observe muscle movement, this test must be performed in the absence of a significant clinical effect from neuromuscular blocking drugs or the presence of local anesthetics in the epidural space. The precise level of muscle stimulation can also be occasionally difficult to detect in small infants.
With epidural ECG, the advancement of the epidural catheter tip can be guided in the presence of neuromuscular blocking drugs or local anesthetics. This technique was easy to perform and enabled optimal epidural catheter positioning. We made the assumption that the ease of epidural catheter advancement cranially confirmed that the catheter was in the epidural space. A subcutaneous catheter at the same position relative to the heart would demonstrate a similar ECG pattern. Matching the ECG obtained from the epidural catheter tip to that of the surface ECG at the target vertebral level provides the anesthesiologist with a useful new tool for improving epidural analgesia by means of optimizing the location of the epidural catheter tip.
In this study, we were able to guide the catheter tip to within two vertebral spaces in the thoracic region in all patients. With this epidural ECG technique, the left-arm lead (with Lead III selected) was connected to the epidural catheter tip. When the epidural catheter tip is positioned in the lumbar and sacral regions, the amplitude of the QRS complex is relatively small, because the recording electrode (epidural tip) is far away from the heart and the vector of the cardiac electrical impulse is at approximately a 90° angle. As the epidural tip advances toward the thoracic region, the amplitude of the QRS complex increases as the recording electrode comes closer to the heart and the ECG recording becomes more parallel to the cardiac electrical impulse. On the basis of this, the advancement of an epidural catheter from the lumbar or sacral region into the thoracic region can be monitored easily. The major problem encountered during thoracic epidural insertion via the caudal approach is kinking of the catheter in the lumbar region (13). An epidural ECG technique may minimize this problem by providing immediate identification of this event and allowing for immediate adjustment during insertion. Specifically, any failure to increase or regression of the QRS amplitude while advancing the epidural catheter may be indicative of catheter curling. Minor resistance to the passage of the catheter can usually be overcome by simple flexion or extension of the infant’s vertebral column or by the injection of a small amount of normal saline via the epidural catheter while advancing the catheter. All techniques of epidural catheter placement have the potential to cause neurological injury, although this happens rarely. Therefore, under no circumstances should any force be used to advance the catheter.
However, the limitations of this technique are encountered in discriminating spinal levels in the high thoracic region. Further QRS changes can be subtle and difficult to appreciate once the epidural catheter tip is above the level of the heart. Thus, for high thoracic placement, it is necessary to estimate the predicted length before insertion. Therefore, we advanced the catheters until the monitored epidural ECG was observed to match the features of the target surface QRS complex and the catheter depth was at our predicted catheter length. Although we have shown that catheter placement is predictable, we recommend that postoperative radiographic confirmation of the catheter position be sought. In summary, epidural catheter tips were advanced to the predicted length and were positioned within two vertebrae of the target level under epidural ECG guidance in our study population of infants and small children.
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Footnotes
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Presented in part at the International Anesthesia Research Society, 76th Clinical and Scientific Congress, San Diego, CA, March 2002.
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References
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Accepted for publication March 26, 2002.
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Abstract
Introduction
