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Abstract
Introduction Fluoroscopy can improve the success rate of thoracic epidural catheter placement (TECP). Real-time ultrasound (US)-guided TECP was recently introduced and showed a high first-pass success rate. We tested whether real-time US-guided TECP results in a non-inferior first-pass success rate compared with that of fluoroscopy-guided TECP.
Methods In this single-center, non-inferiority, randomized trial, the primary outcome was the comparison of the first-pass success rate of TECP between real-time US guidance (US group) and fluoroscopic guidance (fluoroscopy group). Secondary outcomes included time to identifying epidural space, procedure time, total number of needle passes, number of skin punctures, final success, and cross-over success.
Results We randomly assigned 132 patients to the allocated groups. The difference in the first-pass success rate between the groups did not exceed the non-inferiority margin of 15% (US group: 66.7% vs fluoroscopy group: 68.2%; difference −1.5%, 95% exact CI: −14.9% to 11.9%). The difference in the final success rate also did not differ between the groups (98.5% vs 100.0%; difference −1.5%, 95% exact CI: −4.0% to 1.0%). The time to identifying epidural space (45.6 (34–62) vs 59.0 (42–77) s, p=0.004) and procedure time (39.5 (28–78) vs 112.5 (93–166) s, p<0.001) were significantly shorter in the US group.
Conclusions Real-time US guidance provided a non-inferior success rate and shorter time spent on preparation and procedure compared with fluoroscopic guidance in TECP.
Trial registration number KCT0006521.
- ultrasonography
- analgesia
- pain, postoperative
- regional anesthesia
Data availability statement
Data are available on reasonable request. Data are available on reasonable request to the corresponding author.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
Although fluoroscopy can improve the success rate of thoracic epidural catheter placement (TECP), real-time ultrasound (US)-guided TECP also showed a high first-pass success rate recently.
WHAT THIS STUDY ADDS
Real-time US guidance provided a non-inferior success rate and shorter time spent on preparation and procedure compared with fluoroscopic guidance in TECP.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
Real-time US guidance may be considered an alternative method in TECP.
Introduction
Thoracic epidural analgesia is effective for managing acute postoperative pain after major thoracic and upper abdominal surgery, thereby attenuating surgical stress response, decreasing pulmonary complications,1 and preventing postoperative ileus.2 However, thoracic epidural approach is regarded as a difficult technique even for experienced anesthesiologists because of the anatomical challenge of the thoracic spine, including closely positioned laminae, acute angulation of the spinous processes, and narrow interlaminar space.3–5 Accordingly, the failure rate of the landmark palpation-based method was reported to be up to 40%.5 6
Fluoroscopic guidance can improve the correct positioning of epidural catheters within the epidural space compared with the landmark-based technique since it enables the identification of anatomical structures and epidural space.6 However, there are several disadvantages to fluoroscopy use for anesthesiologists, including unfamiliarity with the equipment, uncertain availability of the device, and radiation hazard.
Meanwhile, as the application of ultrasound (US) has greatly developed in the field of regional anesthesia and analgesia, the real-time US-guided thoracic epidural catheter placement (TECP) technique has been recently introduced and shown to be feasible and useful.7 8 US guidance has the advantages of previewing the anatomy before needle insertion and visualizing the advancing needle in real time, which can improve the success rate of epidural access and reduce the number of needle passes and skin punctures.9
Considering that these procedural variables are related to procedural pain and patient satisfaction,8 achieving a high first-pass success rate can be critical. Given the limited use of fluoroscopy in real-world practice, real-time US guidance can be a feasible alternative for TECP. We, therefore, tested whether real-time US guidance provides a non-inferior first-pass success rate to fluoroscopic guidance in TECP.
Methods
Study design and participants
This study was a single-center, non-inferiority, randomized, active-controlled trial. This study was registered at Clinical Research Information Service on August 31, 2021 (https://cris.nih.go.kr/cris/search/detailSearch.do/20642, KCT0006521). This manuscript adheres to the applicable Consolidated Standards of Reporting Trials guidelines.
Participants were enrolled from October 2021 to May 2022. Patients aged 20–79 years who were scheduled for thoracic or upper abdominal surgery and required patient-controlled epidural analgesia in the thoracic region were assessed for eligibility. The exclusion criteria were as follows: allergic to local anesthetics or contrast dye, infection, coagulopathy or use of anticoagulants or antiplatelets, neurological or psychiatric disorders, scoliosis, compression fracture of thoracic vertebra, prior spine instrumentation near the insertion site, and refusal to participate in the study.
Randomization
Patients were randomly allocated to the real-time US guidance group (US group) or the fluoroscopic guidance group (fluoroscopy group) for TECP using a computer-generated random numbers table. Randomization was performed with a block size of 4 and an allocation ratio of 1:1. On the day of the procedure, investigator #1 provided an opaque, sealed envelope labeled with sequential study numbers to the physicians who conducted the TECP. The physicians and patients were not blinded to the type of procedure. Then, investigator #2, who was not blinded to the allocation groups, assessed the procedural outcomes in the operating room. In the postanesthetic care unit, investigator #3, who was blinded to the allocation groups, evaluated the subjective outcomes including patient satisfaction and procedural pain intensity.
Thoracic epidural catheter placement
The target level of interlaminar space for epidural catheterization was determined between T6 and T11 by considering the type of surgery (thoracic and esophageal surgery, T6–8; upper abdominal surgery, T8–11).2
For the US group, TECP using a high-frequency linear US probe (12 MHz; NextGen LOGIQe, GE Healthcare, Madison, Wisconsin, USA) was performed according to the protocol described in our previous report.10 The paramedian sagittal oblique view was obtained to visualize the posterior complex (eg, the ligamentum flavum and posterior dura). If preprocedural scanning revealed the absence or minimal presence of a gap that would allow a needle to pass through at the target interlaminar space with excessive osteophytes, the contralateral side or another interlaminar space one level below or above was selected as appropriate. Then, the skin was sterilized and draped. After local infiltration with 5 mL of 1% lidocaine at the needle insertion point, 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 the in-plane view under real-time US guidance until the needle tip reached the dorsal aspect of the posterior complex in interlaminar space (online supplemental figure 1A). Thereafter, the needle was further advanced using the loss of resistance (LOR) techniques to normal saline without US guidance. If the adjusted posterior complex was unclear on the paramedian sagittal oblique view and the needle encountered the superior articular process of the inferior vertebra between the laminae during needle advancement with LOR, the epidural needle was withdrawn to a point 1–2 cm above the laminae and advanced more medially to reach the epidural space.
Supplemental material
For the fluoroscopy group, TECP using the fluoroscope (Ziehm Vision RFD, Ziehm, Nuremberg, Germany) was performed according to the protocol described in our previous study.8 After identifying the target thoracic vertebra under the anteroposterior view, the patient’s skin was marked and sterilized. The needle entry point was determined to be at the junction between the mid-pedicular line and the upper endplate of the one vertebral segment below the target interlaminar space on the anteroposterior view. After local infiltration with 5 mL of 1% lidocaine, the epidural needle was inserted and advanced until it reached the pedicle level on the vertebral body in an anteroposterior image. The fluoroscopic device was then rotated at an angle of 60° obliquely to the contralateral direction to the needle tip to visualize the target interlaminar space and ventral interlaminar line (VILL), allowing ±5° of adjustment to optimize the contralateral oblique view.8 11 The epidural needle was subsequently advanced without using the LOR technique until just before the VILL. When the needle reached just before the VILL, it was further advanced cautiously using the LOR-to-normal saline technique to reach the epidural space (online supplemental figure 1B).
After accessing the thoracic epidural space in both groups, the epidural catheter was advanced through the needle and 4 cm of the catheter remained in the epidural space. All TECPs were performed by two attending anesthesiologists with more than 3 years of experience (more than 300 procedures with each modality) in the procedures according to identical protocols.
Before obtaining LOR, advancing the needle without withdrawal was considered a needle pass. If the needle was withdrawn and readvanced to change the direction, the needle advancement was regarded as another needle pass. In both groups, three needle passes were allowed on each skin puncture, where three skin punctures were allowed as the maximum. Therefore, a maximum of nine needle passes were allowed in the allocated group. If the epidural access was not acquired after the ninth needle pass, a cross-over trial was performed by allowing only one skin puncture using the other imaging modality (online supplemental figure 2).
Supplemental material
Fluoroscopic findings
After TECPs in both groups, fluoroscopic findings were assessed. By injecting 1 mL of non-ionic, low-osmolar contrast medium (Omnipaque 300, GE Healthcare, Little Chalfont, UK), the position of the catheter tip was determined and contrast dispersion in the epidural space was confirmed as patch and honeycomb appearance in the anteroposterior view.12 Intravascular and subarachnoid spread of the contrast were also excluded using real-time fluoroscopy for 3 s at this time. After the catheter was confirmed to be present in the epidural space, 4 mL of contrast medium and 2% lidocaine (1:1 mixture) were administrated to evaluate the craniocaudal and bilateral contrast dispersion. After 10 min of administration of injectates, the affected dermatome was assessed with the cold test.
Outcomes
The primary outcome was the comparison of the first-pass success rate of TECP between groups. First-pass success was defined as reaching epidural space successfully in a needle pass. Secondary outcomes included (1) time to identifying epidural space (time to finding the target point with US or fluoroscopy and marking the needle insertion point); (2) procedure time (time from skin puncture to reaching the epidural space); (3) total number of needle passes; (4) number of skin punctures; (5) final success or failure (successful achievement of TECP, confirmed using the fluoroscopy within the allowed trials in the allocated group); (6) cross-over success (successful achievement of TECP in the cross-over trial after a failed allocated trial); (7) procedural complications (eg, epidural hematoma, dura puncture, intrathecal catheterization, spinal cord injury, and pneumothorax); (8) fluoroscopic findings (eg, location of the catheter tip at the vertebral body, craniocaudal or bilateral contrast dispersion); (9) needle depth (distance from skin to epidural space); (10) affected dermatomes; (11) global perceived effect of satisfaction according to the 7-point Likert scale (grade 1=very dissatisfied, grade 2=somewhat dissatisfied, grade 3=slightly dissatisfied, grade 4=neither satisfied nor dissatisfied, grade 5=slightly satisfied, grade 6=somewhat satisfied, grade 7=very satisfied13 14 ; and (12) procedural pain intensity assessed by a single 11-point Numerical Rating Scale (NRS) (0=no pain and 10=worst pain imaginable). All patients were educated on how to grade their pain using a numerical rating scale and their satisfaction using global perceived effects before the procedure to obtain reliable numerical rating scale and global perceived effects data.
Statistical analysis
In order to calculate the sample size for this study, we assumed the first-pass success rate as 70% for fluoroscopy-guided TECP and 75% for real-time US-guided TECP by referring to previous studies.8 10 A difference of 15% (margin of non-inferiority) on the first-pass success rate was considered acceptable. With 80% power and a one-sided type 1 error of 5%, we needed 132 patients (66 in each group) to allow for a dropout rate of 5%. When the lower limit of the one-sided 95% confidence boundary for the between-group difference in the primary endpoint did not exceed 15%, the non-inferiority between the two groups could be proven. Data are expressed as mean±SD, median (IQR), or number (proportion). For comparison of clinical characteristics including procedural variables of TECP and fluoroscopic findings, χ2 test or Fisher’s exact test was used for categorical variables and the Mann-Whitney U test was used for continuous variables. To evaluate the success rates of TECP in those who are overweight (body mass index (BMI)≥25) and in the mid-thoracic region, we performed subgroup analyses according to BMI (BMI<25 vs≥ 25) and targeted thoracic level (mid-thoracic: T6–8 vs low-thoracic level: T8–11). A p<0.05 was considered to indicate statistical significance. All analyses were performed with SAS V.8.4.
Results
Among the 142 eligible patients, 8 patients were excluded according to the exclusion criteria and 2 patients declined to participate in the study. Subsequently, 132 patients were randomized into the allocated groups. After randomization, all patients received the allocated intervention and were included in the analysis (figure 1). The clinical characteristics of the patients were not significantly different between the two groups (table 1).
Characteristics and preoperative data of patients receiving thoracic epidural catheter placement
Study flow chart.
No significant difference was seen in first-pass success in both groups (US group: 66.7% vs fluoroscopy group: 68.2%; difference: −1.5, 95% exact CI: −14.9 to 11.9; table 2, figure 2). Because the lower limit of the 95% CI was lower than the prespecified non-inferiority margin (δ=15), non-inferiority was established between the two groups (p<0.001; figure 2). The difference in the rate of final success was not significantly different between the two groups (US group: 98.5% vs fluoroscopy group: 100.0%; difference: −1.5, 95% exact CI: −4.0 to 1.0; table 3, figure 2). The US group had a significantly shorter time to identifying epidural space (45.6 (34–62) vs 59.0 (42–77) s, p=0.004) and shorter procedure time (39.5 (28–78) vs 112.5 (93–166) s, p<0.001) than the fluoroscopy group. Most procedures were successful within the first skin punctures without a significant difference between the two groups (90.9% vs 86.4%, p=0.135). There was one case of failure in the US group, which was subsequently successful in the crossover trial with fluoroscopy. Procedure-related complications did not occur in both groups (table 3).
Primary endpoint and complication of thoracic epidural catheter placement
Non-inferiority graphic of first-pass and final success rates between real-time ultrasound guided thoracic epidural catheter placement and fluoroscopic guided thoracic epidural catheter placement. Error bars indicate one-sided 95% CIs. The dotted line represents the margin of non-inferiority. The non-tinted area indicates the zone of inferiority. *The non-inferiority margin pertains specifically to the first-attempt success. US, ultrasound.
Procedural outcomes of thoracic epidural catheter placement
Postprocedural fluoroscopy confirmed that the catheter tip was present in the epidural space in all procedures of both groups except one failure case in the US group in the allocated trial. Other fluoroscopic findings were not significantly different between the two groups (table 3). While procedural pain intensity was lower in the US group (1.4±1.5 vs 1.9±1.4, p=0.011), the global perceived effect of satisfaction for the procedure did not a significant difference between the two groups (6.6±0.8 vs 6.4±1.0, p=0.137; table 3). Except for pain intensity at discharge from the post-anesthesia care unit (PACU) (3.3±1.7 vs 2.7±1.4, p=0.033), the two groups did not show significant differences in postoperative pain intensity at arrival (4.9±2.6 vs 4.4±2.7, p=0.301), 30 min at PACU (4.5±2.1 vs 4.1±2.2, p=0.317), and opioid consumption at PACU (6.0±3.7 vs 5.8±4.7, p=0.642).
In the subgroup analyses, the first-pass success rates were not significantly different between the two groups in subgroups according to the mid-thoracic level (67.7% vs 74.1%, p=0.597), low-thoracic level (65.7% vs 64.1%, p=0.885), BMI<25 (68.3% vs 78.4%, p=0.316), and BMI≥25 (64.0% vs 55.2%, p=0.510) (online supplemental tables 1 and 2). The final success rates were also not significantly different between the two groups in subgroups according to the mid-thoracic level (96.8% vs 100.0%, p>0.999), low-thoracic level (100.0% vs 100.0%, p>0.999), BMI<25 (97.6% vs 100.0%, p>0.999), and BMI≥25 (100.0% vs 100.0%, p>0.999) (online supplemental tables 1 and 2). The time to identifying epidural spaces (the mid-thoracic level and BMI<25 subgroups) and procedure time (all subgroups) were significantly shorter in the US group of each subgroup, similar to the results of the entire study subjects (online supplemental tables 1 and 2).
Supplemental material
Supplemental material
Discussions
Given the challenging nature of TECP and its role in managing acute and chronic pain, reliable tools for accurate TECP are of crucial importance.15 16 However, detailed descriptions of TECP are sparse, and the method of TECP remains old-fashioned (eg, landmark-based or fluoroscopic-guided TECP).2 17 Although the recently introduced real-time US guidance can provide clinical usefulness during TECP,10 there is a lack of clear evidence. This study is the first randomized controlled trial to assess the success rate of TECP with real-time US guidance in comparison with fluoroscopic guidance. In this non-inferiority clinical trial, we demonstrated that real-time US guidance provided a high first-pass success rate of TECP equivalent to that of fluoroscopic guidance. The final success rate was also similar between the two modalities. In terms of reducing preparation and procedural time, real-time US guidance was superior to fluoroscopic guidance. In addition, subgroup analyses according to BMI and thoracic level showed similar rates of first-pass and final success between the two modalities.
Fluoroscopy decreases the failure rate of TECP to almost 0 and has thus been accepted as a gold standard for TECP.8 18 19 However, fluoroscopy is not readily available in many institutions; fluoroscopy equipment has disadvantages including being challenging to manage, requiring an assistant, and being costly. In contrast, US has recently been widely used in the field of regional anesthesia and is widely equipped in different institutions, which make it easy to use in clinical situations. Furthermore, handling US equipment alone can be a simple task and has a relatively low cost. In addition, there is no radiation exposure.
Our prior study showed a first-pass success rate of 68.3% for fluoroscopy-guided thoracic epidural access,8 which is comparable to the 68.2% observed in this study. However, our prior study on US-guided thoracic epidural access showed a first-pass success rate of 76.3%,10 while this study yielded a rate of 66.7%. This discrepancy could be attributed to the inclusion of mid-thoracic levels and the larger sample size in this study (66 participants in this study vs 38 in the previous study). Fluoroscopy can provide clear visualization of the needle tip and laminae and identify the epidural space using the contrast medium, leading to high first-pass and final success rates.8 US can also clearly visualize the targeted interlaminar space, laminae, and posterior complex.10 20 In addition, real-time US guidance can provide proper trajectory angles of the needle as well as real-time needle tracking and direction changing without radiation exposure.10 20 Consequently, these properties of real-time US guidance likely led to the non-inferior success rate compared with fluoroscopic guidance in this study. Furthermore, in the subgroup analyses, real-time US guidance provided similar success rates to fluoroscopic guidance even in patients who were expected to be difficult for TECP, such as those with high BMI and those in the mid-thoracic region. Therefore, real-time US guidance could also be useful in these populations.21
Recently, real-time US-guided TECP was shown to be superior to landmark-based TECP.22 Although fluoroscopic guidance is regarded as the gold standard for TECP, we believe that real-time US guidance should be considered an alternative tool for TECP considering several limitations of fluoroscopy in clinical practice and the high success rate and several advantages of real-time US guidance.
The time to identifying epidural space and the procedure time were shorter in real-time US guidance than in fluoroscopic guidance, which is likely due to the relative ease and simpler manipulation of US equipment. Another contributing factor could be that needle trajectory could be properly determined under real-time US guidance. Although the difference in time between skin marking and needling might not be clinically significant (13 s and 73 s), these gaps could be more extended in novice physicians, which means more prolonged radiation exposure in physicians with less experience under fluoroscopic guidance. Consequently, real-time US guidance can be more beneficial in reducing preparation and procedural time for physicians who are not experienced in TECP.
For other statistically significantly different variables, the procedural pain was lower, and postoperative pain at discharge from PACU was higher in the US guidance group. The mean differences of both variables were less than 1 of NRS, and these results were not considered clinically significant because >10 of 100 mm on the visual analog scale (>1 of 10 on the NRS) had been accepted as the minimal clinically important difference.21
This study has several limitations. First, the physicians and patients could not be blinded to the allocated intervention and the investigators could not be blinded to the measurements of the study outcomes, such as first-pass success and procedure time. Second, if a lower alpha value, a higher power, and less non-inferiority margins had been applied in this study, our findings would have been inconclusive, and a larger sample size would have been necessary. Third, although the two attending anesthesiologists had experience with more than 300 procedures performed with each modality, the learning curves and exposure to each procedure could have differed between fluoroscopy and US. Therefore, potential differences in the learning curves may have influenced the study results. Fourth, although all cases had the correct catheter position identified through fluoroscopic analysis when using real-time US, it cannot be guaranteed that real-time US-guided thoracic epidural catheter insertion will always lead to appropriate placement of an epidural catheter and local anesthetic spread in a typical clinical setting where fluoroscopy is not available for confirmation. Fifth, our study subjects include few obese individuals with BMI≥30 and further research on such individuals is needed. Sixth, prespecified subgroup analyses were not sufficient to draw significant results. Further study is needed to validate the results in specific thoracic levels or special populations such as those with high degrees of obesity.
Conclusions
The results of our non-inferiority trial demonstrated that real-time US guidance provides a similar success rate to the fluoroscopic guidance in TECP. Moreover, real-time US-guided TECP was superior in reducing the time to identifying epidural space overlying skin and procedure time. These findings suggest that real-time US guidance may be considered an alternative method in TECP.
Data availability statement
Data are available on reasonable request. Data are available on reasonable request to the corresponding author.
Ethics statements
Patient consent for publication
Ethics approval
This study involves human participants and was approved by Asan Medical Center Institutional Review Board, 2021-1174. Participants gave informed consent to participate in the study before taking part.
Acknowledgments
The authors gratefully thank the residents and clinical fellows in the Department of Anesthesiology and Pain Medicine, Asan Medical Center for their kind support in conducting this research.
References
Supplementary materials
Supplementary Data
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Footnotes
Contributors H-JK: conception, design, and conduct of the study; analysis and interpretation of data; reporting and writing—original draft preparation. J-BL: analysis of data. KL, JYS, and S-MJ: conduct of the study; analysis and interpretation of data. D-HK and J-HL: planning, conception, design, and conduct of the study; writing—review and editing of the manuscript; supervision; project administration. All authors critically revised the manuscript. All authors approved the final version of the manuscript. D-HK and J-HL (guarantor) accept full responsibility for the finished work and/or the conduct of the study.
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.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.