Background and objective Thoracic epidural analgesia can significantly reduce acute postoperative pain. However, thoracic epidural catheter placement is challenging. Although real-time ultrasound (US)-guided thoracic epidural catheter placement has been recently introduced, data regarding the accuracy and technical description are limited. Therefore, this prospective observational study aimed to assess the success rate and describe the technical considerations of real-time US-guided low thoracic epidural catheter placement.
Methods 38 patients in the prone position were prospectively studied. After the target interlaminar space between T9 and T12 was identified, the needle was advanced under real-time US guidance and was stopped just short of the posterior complex. Further advancement of the needle was accomplished without US guidance using loss-of-resistance techniques to normal saline until the epidural space was accessed. Procedure-related variables such as time to mark space, needling time, number of needle passes, number of skin punctures, and the first-pass success rate were measured. The primary outcome was the success rate of real-time US-guided thoracic epidural catheter placement, which was evaluated using fluoroscopy. In addition, the position of the catheter, contrast dispersion, and complications were evaluated.
Results This study included 38 patients. The T10–T11 interlaminar space was the most location for epidural access. During the procedure, the mean time for marking the overlying skin for the procedure was 49.5±13.8 s and the median needling time was 49 s. The median number of needle passes was 1.0 (1.0–1.0). All patients underwent one skin puncture for the procedure. The first-pass and second-pass success rates were 76.3% and 18.4%, respectively. Fluoroscopic evaluation revealed that the catheter tips were all positioned in the epidural space and were usually located between T9 and T10 (84.2%). The cranial and caudal contrast dispersion were observed up to 5.4±1.6 and 2.6±1.0 vertebral body levels, respectively. No procedure-related complications occurred.
Conclusion Real-time US guidance appears to be a feasible option for facilitating thoracic epidural insertion. Whether or not this technique improves the procedural success and quality compared with landmark-based techniques will require additional study.
Trial registration number NCT03890640.
- pain management
Data availability statement
Data are available upon reasonable request to the corresponding author.
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According to the available guidelines,1 2 thoracic epidural analgesia (TEA) should be considered the ﬁrst-line approach for postoperative analgesia in major abdominal and esophageal surgeries. Therefore, TEA is an important part of the perioperative care plan in open abdominal and thoracic surgeries and is associated with significant improvement of pain control, less opioid consumption, and enhancement of clinical outcomes.3 4
Although TEA provides reliable perioperative pain relief, accessing the epidural space in the thoracic region remains technically challenging, and landmark palpation-based thoracic epidural catheter placement (TECP) is associated with a high failure rate (12%–40%).5 6 Fluoroscopy-guided TECP is considered superior to landmark palpation-based TECP because of correct identification of anatomical structures and epidural space.7 However, its use is limited to perioperative pain management because of the difficulty of using fluoroscope and the burden of radiation exposure.8 Recent advancements in ultrasound (US) applications have led to the development of sonographic technique and sonoanatomy for epidural catheter insertion. These techniques aid in preprocedural target imaging, which can be used for determining interlaminar space, bony structures, and epidural depth.9 10 Additionally, the use of real-time US guidance for epidural catheter placement has recently increased because it facilitates the visualization of needle advancement, thereby improving the success rate.11 12 However, compared with several studies which have investigated the clinical utility of US for lumbar epidural catheterization,11–13 few studies have investigated the advantages of US-guided TECP (US-TECP).6 14
Although they have shown the possibility of safe, consistent, and successful US-TECP6 14; however, data regarding the accuracy and success rate of real-time US-TECP are lacking, and detailed technical descriptions of the procedure are needed. Therefore, this study aimed to assess the success rate of real-time US-TECP by fluoroscopy and describe the technical considerations of real-time US-TECP.
Study design and patient recruitment
This prospective observational study was conducted at the Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, between July and December 2019. The trial protocol was registered at ClinicalTrials.gov (https://clinicaltrials.gov/ct2/show/NCT03890640) on March 26, 2019. Participants were enrolled from July 4, 2019 to December 12, 2019. Adult patients (20–79 years) who were scheduled for upper abdominal surgery and required patient-controlled epidural analgesia in the thoracic region were considered eligible for enrollment. Patients with allergy to local anesthetics and contrast dye or steroids, infection at the insertion site, neurological or psychiatric disorders, prior spine instrumentation near the insertion site, or coagulopathy or those taking anticoagulants or antiplatelet medication were excluded.
Protocol for real-time US-TECP
According to the previous reports of US-TECP,6 14 patients were placed in the sitting position during the procedure. However, based on our experience, maintaining the proper position of US probe is sometimes challenging when the patients are seated; hence, patients were placed in the prone position with a pillow under the upper abdomen to widen the target interlaminar space. Routine monitoring was established prior to the procedure. Although the interlaminar space between T6 and T8 has been traditionally recommended as the target space for epidural catheterization in patients undergoing upper abdominal surgery,15 we considered the interlaminar space between T9 and T12 as the target space for US-TECP in this study. This is because programmed intermittent epidural bolus (PIEB) infusion is used as our institutional protocol for patient-controlled epidural analgesia, which provides a more extensive cephalic spread of epidural medication.16 17 In addition, accessing the thoracic epidural space was relatively easy through the interlaminar space between T9 and T12 compared with the mid-thoracic region. After preprocedural scanning of the interlaminar space between T9 and T12, the interlaminar space with the best visualization of epidural structures such as the ligament flavum, posterior dura, and anterior complex (anterior dura, posterior longitudinal ligament, and vertebral body) was considered the target space. According to our standard of care, the T10–T11 interspace was most commonly selected for real-time US-TECP. Two investigators (D-HK and J-HL) with >2 years of experience in performing this procedure performed all placements.
First, a high-frequency linear US probe (12 MHz; NextGen LOGIQe, GE Healthcare, Madison, Wisconsin, USA) was placed in the longitudinal plane near the scapular line of thoracolumbar junction. Thereafter, the 12th rib on the target side was identified by caudal-to-cranial scanning. Subsequently, the probe was moved cephalo-medially to identify the intercostal space in line with the target interspace (figure 1A). In this view, the round-shaped rib and hyperechoic pleural line were detected (figure 1B). Second, the probe was further moved medially to obtain the paramedian sagittal transverse process view (figure 1C). In this view, the square-shaped transverse processes were observed (figure 1D). Third, the probe was moved slightly medially from the transverse process view to obtain the paramedian sagittal articular process view (figure 1E) to visualize the corresponding laminae, which resembled wave-like structures, and superior articular process (SAP) of inferior vertebrae between the laminae (figure 1F). Then, to obtain the paramedian sagittal oblique view, the physician laterally tilted the probe (figure 1G). Consequently, the posterior complex (ie, the ligamentum flavum and posterior dura) was observed as linear hyperechoic structures between the laminae (figure 1H). Moreover, the intrathecal space and spinal cord (anechoic) and anterior complex (hyperechoic) were visualized in this view. Subsequently, the cephalad end of the probe was pivoted medially (figure 1I). The height of laminae of the inferior vertebral body in this view was lesser than that in the paramedian sagittal oblique view (figure 1J). This ensured that the pathway of the epidural needle tip was not interrupted by laminae. The final location of the probe is indicated in figure 1I. The real-time US scanning for identification target epidural space was displayed in online supplemental video 1.
The target interlaminar space was identified and the center of the interlaminar space and both the cephalad and caudal ends of the probe were marked on the overlying skin. After local infiltration with 2% lidocaine at the intended needle entry site, an 18-gage Tuohy needle (Perifix, B Braun Melsungen AG, Melsungen, Germany) was inserted from the caudal end of the probe and was advanced in plane view under real-time US guidance until the needle tip reached in front of the posterior complex in interlaminar space (figure 2A and online supplemental video 2). Needle-beam alignment and tip visualization was more challenging than usual because it was necessary to compensate for the lateral-to-medial tilt of the probe and beam. Needle-beam alignment can be maintained by advancing the needle in a similar lateral-to-medial trajectory. The probe and beam position should be held constant to keep the target in view, and the needle trajectory adjusted to keep the tip within the beam and view at all times.
The advancement of the needle under real-time US guidance should be stopped just in front of the posterior complex; thereafter, the needle was further advanced using the loss-of-resistance (LOR) techniques to normal saline without US guidance. When the needle engages the ligamentum flavum, the physician can sense the ligamentum flavum due to its tire rubber texture,18 which can be helpful to identify the needle location without US guidance. After accessing the thoracic epidural space, the epidural catheter was advanced through the needle such that 3–5 cm of the catheter remained in the epidural space. Finally, a 0.5 mL mixture of normal saline and air was administered through the epidural catheter under real-time US monitoring. The hyperechoic epidural catheter could be observed behind the posterior complex under US guidance (figure 2B and online supplemental video 3). Hence, if the epidural catheter was present outside the epidural space, bulging around the laminae was observed.
After real-time US-TECP, the position of the catheter was determined using the fluoroscopy. As the epidural catheter was radiolucent, correct epidural access was confirmed by injecting 1 mL of non-ionic, low-osmolar contrast medium (Omnipaque 300, GE Healthcare, Little Chalfont, UK). To identify the correct position of catheter tip and to verify that there was no intravascular and subarachnoid spread of the contrast medium, fluoroscopic continuous pulsed imaging was performed for 3 s during the contrast administration (online supplemental figure 1A). Then, the catheter tip and contrast dispersion in the epidural space (patchy and honeycomb appearance) were observed. After confirming the presence of catheter in the epidural space, 4 mL of contrast medium and 2% lidocaine (1:1 mixture) was administrated to evaluate contrast dispersion (online supplemental figure 1B). Bilateral and craniocaudal dispersion of contrast were also observed.
Protocol for thoracic epidural infusion
To identify the patency of epidural catheter and provide TEA, epidural bolus of 4 mL of 0.125% ropivacaine was administered before the surgical incision. Subsequently, intraoperative epidural analgesia was instituted with an infusion of 4 mL bolus of 0.125% ropivacaine with sufentanil 0.4–0.6 µg/mL using the PIEB mode every 60 min. For postoperative analgesia, a bolus option was programmed to allow for 2 mL of epidural medication with a 20-minute lockout interval. As part of our institution’s standard of care at post-anesthesia care unit (PACU) and ward, if hypotension was developed, the amount of bolus could be reduced or TEA could be temporarily stopped. The amount of bolus could be increased if a patient exhibited insufficient pain improvement.
Primary and secondary outcomes
The primary outcome was the success rate of real-time US-TECP based on the fluoroscopic evidence (epidural spread of contrast medium), which was validated by the third investigator (JHS). Secondary outcomes were as follows: (1) time to mark spaces (the time to obtain the best US images of the target, the interlaminar space, and mark the overlying skin); (2) needling time (time to access the epidural space after skin insertion); (3) number of needle passes (first needle pass plus additional needle passes, that is, readvancement of the needle after any needle withdrawal for changing the direction); (4) number of skin punctures, (first skin puncture plus additional skin punctures, that is, reinsertion at a new location after complete needle withdrawal from the skin); (5) first-pass success rate (achievement of LOR and successful catheter placement on first needle pass and first skin puncture); (6) complications such as epidural hematoma, dura puncture, intravascular or intrathecal local anesthetic injection, and pneumothorax; (7) distance between skin and epidural space; and (8) fluoroscopic findings such as location of catheter tip at vertebral body and cranial and caudal contrast dispersion. All secondary outcomes, except fluoroscopic findings, were assessed by the fourth investigator (H-MK). Additionally, postoperative clinical outcomes such as the occurrence of hypotension and opioid requirements in the PACU at 0 hour (on admission to the PACU) and 1 hour post-surgery were assessed. Postoperative pain intensity was assessed using a single 11-point Numeric Rating Scale (NRS: 0=no pain, 10=worst pain imaginable).
Data are expressed as mean±SD, median (IQR), or number (proportion), as appropriate. Data were analyzed using the SPSS, V.21.0 (IBM SPSS Statistics).
Thirty-eight patients participated in this study. The mean age of patients was 62.5±9.9 years, and 60.5% of the patients were men (table 1).
One patient was classified as American Society of Anesthesiologists (ASA) 3 and others were classified as ASA 1 or 2. Thoracic epidural catheter was placed under real-time US guidance in the following interlaminar spaces: T9–T10, 13 (34.2%) patients; T10–T11, 24 (63.2%) patients; and T11–T12, 1 (2.6%) patient. All passes of epidural catheter insertion were successful.
The outcomes of US-guided epidural catheterization are presented in table 2. The median time for epidural needle placement was 49 (39–65) s. The mean time for marking the overlying skin for the procedure was 49.5±13.8 s. All patients underwent one skin puncture for the needle insertion. The first-pass and second-pass success rates were 76.3% (n=29) and 18.4% (n=7), respectively. The success rate at more than three passes was 5.3% (n=2). The mean distance between the skin and epidural space was 5.6±0.5 cm.
The fluoroscopic findings after real-time US-TECP are presented in (table 3). Based on contrast dispersion after injecting 1 mL of contrast medium, all catheter tips were successfully placed in the epidural space, usually between T9–T10 (n=32, 84.3%) and median epidural space (n=26, 68.4%). After injecting the 4 mL mixture of contrast medium and lidocaine, bilateral contrast dispersion was achieved in all patients. Dispersion of the contrast medium was observed to be up to T1 cranially and L3 caudally. The mean cranial dispersion of the contrast medium was up to T4, and the mean caudal dispersion of the contrast medium was up to T12 (online supplemental figure 2). Cranial and caudal dispersions were observed up to the 5.4±1.6 and 2.6±1.0 vertebral body levels.
In the PACU, one patient developed hypotension. The median NRS score at 0 hour post-surgery was 3.5 (1.0–4.0) and that at 1 hour post-surgery was 2.0 (2.0–2.5). The median opioid (fentanyl) requirement in the PACU was 50.0 (0.0–87.5) µg.
To our knowledge, this is the first study to evaluate the accuracy of real-time US-TECP using fluoroscopy. This study demonstrated that real-time US-TECP was successfully performed in all participants with a higher first-pass success rate and lesser number of skin punctures and needle passes, that were in line with those in a previous study.6 Additionally, placement of the epidural catheter tip between T9 and T10 resulted in sufficient contrast dispersion over the dermatome level corresponding to the surgical incision.
US imaging is a valuable tool to preview spine anatomy and to visualize needle advancement.11 19 Hence, US imaging can reduce the risk of lumbar epidural catheterization failure and the number of needle insertions and redirections.13 The clinical efficacy of US for thoracic epidural catheterization has been recently investigated; however, few studies on US-TECP have been conducted.6 14 Auyong et al6 reported the benefits of preprocedural US imaging, which included lower postsurgical pain scores and fewer needle skin punctures compared with those in landmark palpation-based TECP. Similarly, a decrease in the number of skin punctures was noted in our study. Only one study has reported that real-time US-TECP was successfully performed in 15 patients who underwent thoracic and upper abdomen surgery14 and provided specific technical description for real-time US-TECP for the first time. Moreover, it reported that epidural catheters were successfully placed in all patients, as in our study.14 The success rate in this case series (n=15) was based on only the clinical outcomes and not on the exact identification of the epidural catheter position. However, unlike the previous study, our study revealed the complete success rate of real-time US-TECP in relatively more participants using fluoroscopy. Overall, real-time US guidance could facilitate achieving successful TECP.
US-guided epidural placement has several advantages compared with landmark palpation-based epidural placement. First, accurate vertebral level corresponding to surgical incision can be identified by counting the ribs on US images.6 Palpation alone is known to be a poor predictor for identifying the accurate thoracic vertebral level.20 Second, the success rate of epidural catheterization can be improved by preprocedural identification of the interlaminar space, laminae, and spinous process with US imaging.13 Epidural catheter placement under real-time US guidance can facilitate the visualization of needle advancement and simultaneous identification of the epidural space between the target laminae. Furthermore, when the needle tip encounters the lamina, it causes discomfort and pain because of periosteal contact, followed by needle redirections and/or multiple skin punctures,19 but the needle tip visualization can advance the needle without encountering the lamina. Third, commonly encountered false positive LOR when accessing the thoracic epidural space can be overcome by examining the bulging surrounding laminae (improper catheter placement between the multifidus and lamina)21 during the injection of mixture (normal saline and air) under real-time US. Thus, malpositioning of the epidural catheter can be avoided by identifying the catheter position.
We added detailed considerations regarding real-time US-TECP based on the previous technical description.14 First, SAP of inferior vertebrae between the laminae can appear to be the posterior complex (ligamentum flavum and posterior dura) when failure to obtain an optimal paramedian sagittal oblique view. If the epidural space is relatively wider (especially lower thoracic vertebral level), the posterior complex, intrathecal space, and anterior complex can be visualized on the paramedian sagittal oblique view; however, when the target thoracic vertebral level is higher (especially above T9−T10), the intrathecal space and anterior complex cannot be usually visualized. At this point, the difficult distinguishment between the SAP and posterior complex may usually be observed. We have sometimes experienced failure in optimizing the probe position and angle to obtain the paramedian sagittal oblique view to identify the posterior complex. In that case, the epidural needle usually encountered the SAP and could not be advanced. In such cases, we recommend that the epidural needle should be withdrawn until 1–2 cm above the laminae and advanced more medially to access the epidural space. We believe that this approach can reduce the failure to access the thoracic epidural space during real-time US-TECP. Second, although either air or normal saline can be used for detecting LOR, LOR to saline may be more suitable in real-time US-TECP, because if air spreads around laminae and multifidus muscles, the target US view can be poor. Third, the ligamentum flavum and posterior dura may be seen as a single linear hyperechoic structure, referred to as the ‘posterior complex’ or ‘ligamentum flavum–posterior dura complex’.22 Thus, the physician cannot discriminate whether a single hyperechoic line is the ligamentum flavum or posterior dura. Moreover, the needle tip cannot be generally visualized below the laminae and at a depth of >4 cm.14 Hence, from just in front of the posterior complex, the needle should be advanced based on LOR to saline to ensure procedure safety and prevent dura puncture. These detailed clinical advisements can encourage the feasible use of real-time US-TECP for physicians interested in TECP. We anticipate that physicians with over 1 year experience in US-guided regional analgesia can proficiently achieve successful real-time US-TECP after 10 cases.
We chiefly performed real-time US-TECP in the interlaminar space at T10–T11 and the tips of the epidural catheters were usually located at T9–T10, lower than the previously recommended target level (T6–T8) for upper abdominal surgery.15 Interestingly, contrast medium sufficiently spread over the dermatome level corresponds to the surgical incision despite the relatively lower tip positioned (online supplemental figure 2), and all TEA were found to be effective in the postoperative period. In our experience, obtaining the optimal paramedian sagittal oblique view may be difficult above the T9–T10 vertebra level. Therefore, when PIEB infusion is used as patient-controlled epidural analgesia for the upper abdominal surgery, the appropriate levels for needle insertion and catheter tip position may be the interlaminar space at T10–T11 and the epidural space at T9–T10, respectively.
This study has some limitations. First, although this was a prospective observational study, the small number of participants limited the generalizability of our study and the robustness of our conclusions. However, to reduce radiation exposure to participants, the sample size should be limited. Second, unintentionally, patients with obesity were not included in the study. Real-time US-TECP may be difficult to perform in such patients because of poor visualization of the target epidural space and needle advancement. Hence, inclusion of patients with obesity may have changed the outcomes. Evaluation of the clinical usefulness of the real-time US-TECP in patients with obesity is warranted. Third, our procedural target sites were not included in mid-thoracic region, the most difficult region to access the epidural space.23 Although obtaining the ideal US image may be difficult in the mid-thoracic region, we believe that successful real-time US-TECP may be achieved in the mid-thoracic region with our described technical advisements. However, our results should be interpreted cautiously until validated in the upper mid-thoracic region.
Real-time US guidance appears to be a feasible option for facilitating thoracic epidural insertion. Whether or not this technique improves the procedural success and quality compared with landmark-based techniques will require additional study.
Data availability statement
Data are available upon reasonable request to the corresponding author.
This study was approved by the Institutional Review Board of the Asan Medical Center (2019-0320).
We gratefully acknowledge the support of the department of e-medical contents and e-learning teams of Asan Medical Center, University of Ulsan College of Medicine, for graphical representations.
D-HK and J-HL are joint first authors.
Contributors D-HK—conception, design, and conduct of the study; analysis and interpretation of data; reporting; and writing (original draft preparation). J-HL—conception, design, and conduct of the study; interpretation of data; and writing (review and editing of the manuscript). JHS—data curation and acquisition. WJ—analysis and interpretation of data. DL—data curation and acquisition. H-MK—data curation and acquisition. S-MJ—planning, conception, and design of the study; supervision; and project administration. S-SC—planning, conception, design, and conduct of the study; writing (review and editing of the manuscript); supervision; and project administration. All authors critically revised the manuscript. All authors approved the final version of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.