ABSTRACT
Background:
Neuraxial ultrasound (US), a newer modality, can be used for neuraxial imaging, helping in visualizing and aiding in epidural space catheterization. The aim of this study was to evaluate the efficacy of the US for cervical epidural access and to determine the failure rate and complication associated with this technique.
Methods:
A prospective single-arm pilot study was conducted on 21 participants. The neuraxial US image quality assessment by Ultrasound Visibility Score (UVS), epidural space depth measurement by US and by conventional loss of resistance (LOR) technique, and post-procedure epidural catheter confirmation by real-time US were the study parameters. Any procedural complications or failure rate were recorded. The Kolmogorov–Smirnov test, paired-samples t-test, and Chi-square test were used for the statistical comparison.
Results:
The pre-procedural UVS by the transverse interlaminar view (x/21) was 2.81 ± 1.94 and by the oblique paramedian sagittal view was 16.66 ± 2.39 with UVS being best in the paramedian oblique sagittal view (P- value < 0.05). The comparison of depth of the epidural space identified by USG and that by the LOR technique was statistically insignificant (P = 0.83). The average puncture attempts were 1.1 ± 0.3. Post-procedure US epidural catheter confirmation score (x/3) was 1.44 ± 0.44 with either epidural space expansion or microbubbles seen or both.
Conclusion:
The pilot study has successfully demonstrated the implication of US for visualizing and aiding in epidural space catheterization. Also, the failure rate and procedural complications were drastically minimized with the help of US as compared to the traditional blind technique.
Keywords: Anterior complex, cervical, epidural anesthesia, neuraxial, posterior complex, ultrasound
INTRODUCTION
The success of epidural access by blind technique depends on one’s ability to accurately locate the epidural space relying on the anatomical surface landmark and loss of resistance (LOR) technique increasing the multiple puncture attempts and discomfort to patient.[1,2] Ultrasound (US)-guided central neuraxial procedure, an advanced technique for the patient with difficult spinal anatomy, reduces the number of puncture attempts, improving the success rate and thus patient comfort.[1] The literature has majorly enlightened the lumbar sono-anatomy for US-guided central neuraxial blocks supporting the benefit of this approach, but its use remains an experimental and highly complex technique.[3]
This study was undertaken to evaluate the efficacy of the US for cervical epidural access and to determine the failure rate and any complications associated with this technique.
MATERIAL AND METHODS
After approval from the Institutional Ethical Committee and registering the trial with the Clinical Trials Registry—India (Reg. No. CTRI/2022/06/042997), written informed consent was obtained from 21 patients enrolled prospectively in the single-arm pilot study.
Inclusion criteria were age—18 to 60 years, American Society of Anesthesiologists (ASA)—I–II, and head and neck, airway, oral–pharyngeal–hypopharyngeal, thyroid, breast, shoulder, upper limb, hand, and thoracic surgeries. Exclusion criteria were not willing to participate in the study, clinically obvious or known spinal deformity, infection in the back, allergy to local anesthetic drugs, previous spine surgery, and coagulopathy.
METHODOLOGY
Intervention
All patients were premedicated with Tab. alprazolam 0.5 mg the night before and the morning of surgery and Tab. pantoprazole 40 mg the night before surgery. After arrival in the operating theater, Intravenous (IV) access was secured with 18 G IV cannula and all standard ASA monitoring was attached. Once baseline hemodynamic parameters were recorded, the patient was positioned sitting with the neck flexed. C7 spinous process was identified by palpation followed by T1. Pre-procedural US scan was done with the curvilinear probe (3–8 MHz), depth of 4–8 cm, and gain adjusted for best image optimization with a focus point at the posterior epidural space. The transverse sonogram of T1 vertebrae was scanned [Figure 1a] and then the probe was tilted / slided cranially for visualizing the C7-T1 interlaminar space. Both the transverse interlaminar and oblique paramedian sagittal ultrasonographic views were used for visualizing the posterior epidural space. Both the transverse interlaminar and oblique paramedian sagittal ultrasonographic views were used for visualizing the posterior epidural space. The image quality was assessed by the Ultrasound Visibility Score (UVS) [Table 1].[1] The visibility of the seven neuraxial structures was scored in real time during the scout scan, by the same investigator who performed the US scan, using a four-point numerical scale, and the total UVS was determined for every patient. The scan was considered a success, if the lamina and at least one deep soft tissue structure are seen. The US visibility of the neuraxial structures will be judged to have been good (UVS > 15), average (UVS 9–15), and poor (UVS < 9).
Figure 1.
(a) Transverse sonogram of T1 vertebra. (b) Transverse sonogram at C7-T1 interspace. (c) Paramedian sagittal oblique scan at C7-T1 level. (d) Paramedian sagittal oblique scan at C6-C7-T1 level. A—anterior, AC—anterior complex, Ca—caudal, Cr—cranial, ES—epidural space, ESM—erector spinae muscle, ITS—intrathecal space, L—left, LF—ligamentum flavum, P—posterior, PC—posterior complex, PD—posterior dura, R—right, SP—spinous process
Table 1.
US Visibility Score (UVS)
| Structure seen | Score [0/1/2/3]# |
|---|---|
| Lamina | |
| Interlaminar space | |
| Ligamentum flavum | |
| Epidural space | |
| Posterior dura | |
| Intrathecal space | |
| Anterior complex | |
| Total score (out of 21) |
#(0, not visible; 1, hardly visible; 2, well visible; 3, very well visible, maximum score possible=21)
Once the image optimization was done, the posterior epidural space was positioned in the center of the US image and depth was measured in mm from the skin. The center of both the long axis and short axis of the US probe was marked with skin marker. These points were intersected to determine the point of insertion. Under all aseptic precautions, local infiltration with 1% lignocaine at the point of insertion of the Tuohy needle was done. The LOR-to-saline (LORS) technique was used for epidural space identification followed by epidural catheter insertion of 3–4 cm in the epidural space. Post-procedure, under all aseptic precautions cervical epidural sonography was demonstrated in the same view for confirming the position of epidural catheter. Pressurized agitated saline flush was used to confirm the position of epidural catheter using the US catheter confirmation score [Table 2]. The visibility of any of the three parameters in the same US scan view as that obtained for visualization of epidural space with good or higher UVS was scored, by the same investigator who performed US scan, using a two-point numerical scale. A score ≥ 1 will confirm the position of epidural catheter in the epidural space.
Table 2.
US catheter confirmation score
| Parameter | Score* |
|---|---|
| Microbubbles seen in epidural space | 0/1 |
| Expansion of the epidural space | 0/1 |
| Epidural catheter visualization | 0/1 |
| Total score | _/3 |
*(0—not visible, 1—visible)
Once the catheter position was confirmed, sterile dressing was applied. After a negative test dose, the epidural block was activated. The desired level of sensory block was assessed by both touch perception and cold test. Opioid-free general anesthesia was administered to all patients, and perioperative pain was managed according to the institutional protocol. Any complications related to the cervical epidural procedure perioperatively were noted.
Statistical analysis
The data were analyzed using OpenEpi software (Version 3.01). The Kolmogorov–Smirnov test was used to test the normality of the data recorded. The data were presented as mean Standard Deviation (SD) when normally distributed and median (range) when not normally distributed. For normally distributed data, the paired-samples t-test was used for the statistical comparison. For categorical data, the Chi-square test was used. A P-value of < 0.05 was considered statistically significant.
RESULTS
The cervical epidural technique under the guidance of US through the transverse interlaminar and oblique paramedian sagittal plane was conducted by a single experienced operator in 21 adult patients, ASA I–II, of either sex with mean age, weight, and height being 39 ± 9.14 (years), 71.67 ± 7.41 (kgs), and 165.43 ± 7.05 (cm), respectively. Of the 21 study populations, the study was successfully conducted on 20 patients. However, in one patient because of procedural complication the procedure was abandoned and unsuccessful.
In all 21 patients, the pre-procedural UVS by the transverse interlaminar view and by the oblique paramedian sagittal view was statistically significant with UVS being best in the paramedian oblique sagittal view (P-value < 0.05) [Table 3]. The UVS in pre-procedural US scan was good in 66.67% of the study population by the oblique paramedian sagittal view as compared to 0.0% by the transverse interlaminar view. Thus, the oblique paramedian sagittal view provides more promising view for visualization of epidural space as compared to the transverse view and hence was used for calculating the depth of epidural space from the skin [Table 4 and Figure 1b-d]. The depth of epidural space measured by the US in the oblique paramedian sagittal view and that obtained by the LORS technique was comparable (P = 0.83) [Table 5 and Figure 1c and d].
Table 3.
Pre-procedural UVS
| Pre-procedural UVS by transverse interlaminar view (x/21) | Pre-procedural UVS by oblique paramedian sagittal view (x/21) | P | |
|---|---|---|---|
| Mean±SD | 2.81±1.94 | 16.66±2.39 | <0.0000001 |
Table 4.
Ultrasound Visibility scoring system in transverse interlaminar and oblique paramedian sagittal view
| UVS | Good (UVS >15) | Average (UVS=9–15) | Poor (UVS <9) | P |
|---|---|---|---|---|
| Pre-procedural UVS by transverse interlaminar view (n=21) | 00 (0.0%) | 00 (0.0%) | 21 (100%) | <0.0000001 |
| Pre-procedural UVS by oblique paramedian sagittal view (n=21) | 14 (66.67%) | 07 (33.33%) | 00 (0.0%) |
Table 5.
Depth of epidural space measured by US oblique paramedian sagittal view and LORS technique
| Depth of ligamentum flavum by oblique sagittal paramedian plane (n=20) | Depth of epidural space encountered by LORS through the paramedian approach (n=20) | P | |
|---|---|---|---|
| Mean±SD | 42.85±6.54 | 42.76±6.88 | 0.8281 |
In the transverse interlaminar US view, the structure visible was the posterior complex (hyperechoic structure), the intrathecal space (gray structure), and the anterior complex (hyperechoic structure) [Figure 1b]. The posterior epidural space was well appreciated in all cases in oblique sagittal paramedian scan [Figure 1c and 1d]. In two cases, we required two puncture attempts for identifying epidural space through the paramedian approach by LORS technique, but in other cases only a single attempt was required with an average attempt score of 1.1 ± 0.3.
Post-procedure US epidural catheter confirmation score (x/3) was 1.44 ± 0.44 with the most important findings where either epidural space expansion or microbubbles were seen as reverberation effect in the epidural space or both [Figure 2]. An epidural catheter, however, was not visualized in any of the subjects.
Figure 2.
Postprocedure neuraxial ultrasound scan for epidural catheter confirmation. (a) Paramedian sagittal oblique scan at C4-C5-C6 level before saline flush test. (b) Paramedian sagittal oblique scan at C4-C5-C6 level after saline flush test demonstrating epidural space (ES) expansion. (c) Paramedian sagittal oblique scan at C4-C5-C6 level before saline flush test. (d) Paramedian sagittal oblique scan at C4-C5-C6 level after saline flush test demonstrating agitated saline in epidural space seen as the reverberation effect. (e) Paramedian sagittal oblique scan at C4-C5-C6 level before saline flush test. (f) Paramedian sagittal oblique scan at C4-C5-C6 level after saline flush test demonstrating epidural space expansion and agitated saline in epidural space seen as the reverberation effect. A—anterior, Ca—caudal, Cr—cranial, ES—epidural space, L—left, P—posterior, R—right
Two complications were reported in the study with the incidence of 9.52%, one is the procedural complication in which the patient had severe bradycardia during epidural catheter insertion, which was treated with Inj. atropine 0.6 mg IV Stat, and the procedure was abandoned. The patient recovered uneventfully. The other one was the post-procedural complication in the late postoperative period where the patient was complaining of left upper limb (non-operated side) weakness, which was resolved by changing the epidural infusion concentration from 1.25% to 0.0625% of Inj. bupivacaine.
In one case, false LOR was encountered approximately 7 mm earlier than that measured by US guidance. In this study, the incidence of failure rate by the blind LOR technique was 4.76%. While confirming the catheter position during post-procedural US, the saline flush was seen spreading into muscular tissue just above the posterior epidural space [Figure 3]. Hence, the catheter was removed and the procedure was repeated successfully with LORS encountered at approximately the same depth as that measured on USG. The catheter position was then reconfirmed in post-procedural US as microbubbles (reverberation effect) in the epidural space.
Figure 3.
(a) Post-procedure neuraxial ultrasound scan showing saline accumulation in ESM (an echogenic area shown by arrow) (b) Repeat saline flush test demonstrating expansion and increased an echogenecity (more saline accumulation) A—anterior, Ca—caudal, Cr—cranial, ES—epidural space, ESM—erector spinae muscle, L—left, P—posterior, R—right
DISCUSSION
In this pilot study, the cervical epidural technique was successfully performed with confirmation of catheter position under the guidance of US. The cervical epidural technique is challenging because of its complex anatomy and narrower cervical epidural space, measuring 3–4 mm in width as compared to 5–6 mm at the lumbar level.[4] In the Magnetic resonance imaging (MRI) study of 100 patients, the distance from ligamentum flavum to dura averaged 0.3 cm (C6-C7) and 0.4 cm (C7-T1).[5] Most cervical epidural techniques are done at C7-T1 level, the reason being the easy palpation of C7 spine, and the epidural and interlaminar space gets narrower and higher.[6] In this pilot study, C7-T1 interspace was preferred for performing the procedure. The ligamentum flavum is thinnest at the cervical level.[7] The most common methods used for cervical epidural space identification are the hanging drop method and LOR technique.[8] The false LOR with nonimage guide injection is quite common in cervical epidural technique, with the incidence being 53 to 76%.[9,10] Considering the above challenges, there is a strong argument to be made for image guidance. The two most common image-guided techniques for cervical imaging are fluoroscopy and US.[7] A pilot study on US-guided cervical epidural steroid injection concluded that US is an effective, safe, and simple radiation or magnetization-free procedure.[11] Hence, in this study US modality was preferred over fluoroscopy and the traditional blind technique because the latter was associated with more failure rate and complications.[12] Of the five basic ultrasonographic view of spine, the most promising view is the paramedian oblique sagittal view.[13] In this study, the transverse interlaminar and paramedian oblique sagittal view was used with UVS being best in the paramedian oblique sagittal view (P-value < 0.05). The posterior complex was seen in the transverse interlaminar view in 11 patients, but the posterior epidural space was not very well appreciated in any of the cases with poor UVS [Figure 1b and Table 4]. However, in the paramedian oblique sagittal view, the ligamentum flavum, posterior epidural space, and posterior dura were well appreciated with UVS > 15, and hence, this view was used for measuring the depth of the posterior epidural space from the skin and also determining the point of insertion in this study [Tables 3 and 4, Figure 1c and 1d]. There are various factors that affect the quality of the US images, two most important being obesity and elderly.[14] In this study, both of these factors were not present.
Cervical Epidural Anaesthesia (CEA) has been used for various types of surgeries involving head and neck, airway, oral–pharyngeal–hypopharyngeal, thyroid, breast, shoulder, upper limb, hand, and cardiac and thoracic surgeries.[7] Nerves are not blocked by the needle but by the local anesthetic. While performing the real-time US of peripheral nerve block, it is mandatory either to visualize the entire needle or at least the tip to avoid any untoward complications. However, in this study US was used only for pre-procedural estimation of posterior epidural space depth from the skin, the point of needle insertion, and post-procedural epidural catheter confirmation. The depth of posterior epidural space measured by USG and that encountered by the LORS technique were comparable (P > 0.05). Once the epidural space was identified by the blind LORS technique, the catheter position was confirmed by real-time US by flushing agitated saline in the epidural catheter and observing either epidural space expansion or microbubbles in epidural space. In this study, the epidural catheter position was successfully identified by this method with the post-procedure US epidural catheter confirmation score (x/3) of 1.24 ± 0.44. Habib and colleagues believe that this visual confirmation offers a more precise endpoint for epidural access than the standard LOR technique by removing operator subjectivity and variability.[15] Karmakar et al.[1] have described the sonographic changes in lumbar epidural space at the level of the Tuohy needle insertion immediately after LOR. Anterior displacement of posterior dura and expansion of posterior epidural space with compression of thecal sac were observed at the point of needle entry in epidural space with the LOR technique. In this study, the cervical epidural sonographic changes were observed after the insertion of catheter by blind LORS technique. Expansion of the epidural space or microbubbles in the epidural space seen as the reverberation effect or both was observed during the confirmation of epidural catheter in the epidural space by pressurized saline flush [Figure 2]. No anterior displacement of the posterior dura was seen in this study, the reason being the close proximity of spinal cord to the posterior dura at the cervical level.
Grau and colleagues have described a technique of real-time US visualization, through a paramedian sagittal scan, of an advancing epidural needle that was inserted through the midline during a combined spinal-epidural (CSE) procedure at the lumbar level. US-guided lumbar epidural catheterization has been reported in children performed by two operators where one operator identifies the epidural space through the paramedian approach and the second operator performs the epidural catheterization through the midline approach.[16,17] The literature search reveals limited data published for performing cervical epidural technique under US guidance. However, many articles are published for US-guided cervical transforaminal block for chronic radicular pain. This study describes a novel technique of performing US guidance paramedian epidural access in the cervical region. No real-time US was used in our study, the reason being
Requires two operators
Small width of cervical epidural space
Close proximity of cervical cord to the posterior dura
Non-echogenicity of the Tuohy’s needle used
More acute insertion of the Tuohy needle with that of the US probe challenging its visibility while performing the real-time US and thus its complication.
The traditional guidance techniques that rely solely on anatomical landmarks and/or fascia clicks used in regional anesthesia have consistently failed to meet this perfectly logical requirement and are known to produce serious complications.[12] In this study, two complications, one procedural and the other post-procedural, were reported with an incidence of 9.52%. Various serious complications caused by this traditional blind CEA technique have been reported. This includes dural punctures reported in three reports, respiratory difficulties to complete paralysis reported in four reports, neurological complications reported in four reports, technical failures reported in four reports, and serious hemodynamic and cardiac complications reported in five reports.[7] No deaths have been reported; however, significant long-term morbidity and cardiac arrest were reported.[7]
There is no proper definition of epidural failure rate in the literature, but it may range anywhere from technical failure to that of inadequate epidural analgesia.[18] Pre-procedural US can actually reduce the incidence of technical failure rate and thus improve the success rate. In one case, false LOR ~ 7 mm earlier than that measured by US guidance was encountered. Post-procedural US scan confirmed the catheter position in the erector spinae muscle [Figure 3]. Hence, the catheter was removed and the procedure was repeated successfully with LORS encountered at approximately the same depth as that measured on ultrasonography. In this study, both pre-procedural and post-procedural US scans have reduced the incidence of failure rate caused by a blind technique by confirming the incorrect position of the epidural catheter. Thus, in the image-guided technique the incidence of false LOR, which is 53–76% in non-image-guided technique, can be drastically reduced and thus the procedure failure rate.[9,10] Pak MH et al.[10] in their study concluded that pre-procedural US measurement of cervical epidural space can be beneficial in excluding the false LOR and increases the success rate. Vallejo and colleagues[19] studied 370 labor epidurals with or without guidance from a pre-procedural US scan performed and concluded that the failure rate in the US-assisted patient group was significantly lower (1.6% vs 5.5%, P < 0.02). Shaikh and colleagues[20] observed a 79% reduction in the overall procedure failure rate when US guidance was used.
Epidural anesthesia has numerous advantages on hemodynamics, pulmonary function, and the central nervous system perioperatively including superlative pain relief through continuous epidural infusion and good compliance to physiotherapy in both noncardiac and cardiac surgery.[21,22] However, in cardiac surgery, with the use of anticoagulants there is an increased risk of epidural hematoma and hence the fear of using epidurals.[23] The risk of epidural blockade-induced hematoma during cardiac surgery is 1:3552 (95% confidence interval (CI): 1:2552–1:5841 and 99% CI: 1:2344–1:7326).[23] Advanced age, female gender, bony spinal pathology that may necessitate multiple attempts, and coagulopathy increase the risk of patients developing an epidural hematoma after the epidural block.[24] Hence, the use of pre-procedural US for aiding epidural access can limit the number of punctures attempt, thus decreasing the incidence of neuraxial hematoma in cardiac surgeries.
The limitation of this study is that it is a descriptive pilot study with a smaller sample size, from a single center. However, the aim of the study was to evaluate the feasibility of the US for cervical epidural access, which has been successfully demonstrated. Spinal sonography is still in its infancy and requires great expertise. Very few pilot studies, randomized control trial, and case report have demonstrated the feasibility of neuraxial sonography for lumbar epidural. Neuraxial sonography has numerous advantages from determining the depth of the epidural space to the optimal site and angle for needle insertion.[16,25-27] Pre-procedural US has improved the success rate of epidural access on the first attempt and reduced multiple puncture level and number of attempts.[16,26,27] In this study also, the number of puncture attempts required was 1.1 ± 0.3 with only two cases (10% of study population) requiring two attempts, but it does have a few shortcomings, the most important being experience in both the neuraxial anatomy and sonography. The operator who is experienced in both cervical epidural technique and neuraxial ultrasonography has become the minimum prerequisite to perform the US guidance cervical epidural technique.
CONCLUSION
The pilot study has demonstrated the feasibility of periprocedural US for visualization of epidural space and also confirmed the position of catheter. However, a study with a large population size has been planned in our institute to establish the role of real-time US for cervical epidural access in clinical practice and also to determine the precise failure rate and its complications.
Financial support and sponsorship
Nil.
Conflicts of interest
This manuscript had been conferred Janak Mehta Young Scientist Award - 2023 in IACTACON 2023.
Acknowledgment
Firstly, the author would like to thank his wife Dr. Soumya Das for her love and constant support, for all the late nights and early mornings, for keeping him sane over the past few months, and for being his muse, editor, proofreader, and sounding board. Most of all, the author thanks her for being his best friend. He owes her everything.
The author would also like to express his gratitude to Mr. Manjeet Verma for invaluable help and support.
The author would also like to thank each and every staff of the Dept. of Anaesthesiology and Critical Care, All India Institute of Medical Sciences (AIIMS) Nagpur, for their constant support.
REFERENCES
- 1.Karmakar MK, Li X, Ho AMH, Kwok WH, Chui PT. Real-time ultrasound-guided paramedian epidural access: Evaluation of a novel in-plane technique. Br J Anaesth. 2009;102:845–54. doi: 10.1093/bja/aep079. [DOI] [PubMed] [Google Scholar]
- 2.Oh TT, Ikhsan M, Tan KK, Rehena S, Han NLR, Sia ATH, et al. A novel approach to neuraxial anesthesia: Application of an automated ultrasound spinal landmark identification. BMC Anesthesiol. 2019;19:1–8. doi: 10.1186/s12871-019-0726-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Karmakar MK, Chin KJ. Spinal sonography and applications of ultrasound for central neuraxial blocks-NYSORA |NYSORA. [Last accessed on 2022 Nov 22]. Available from:https://www.nysora.com/techniques/neuraxial-and-perineuraxial-techniques/spinal-sonography-and-applications-of-ultrasound-for-central-neuraxial-blocks/
- 4.Cousins MJ, Bridenbaugh PO, Lippincott PJB. Neural blockade in clinical anesthesia and management of pain. Anesthesiology. 1981;55:490. [Google Scholar]
- 5.Aldrete JA, Ul Mushin A, Zapata JC, Ghaly R. Skin to cervical epidural space distances as read from magnetic resonance imaging films: Consideration of the “hump pad.”. J Clin Anesth. 1998;10:309–13. doi: 10.1016/s0952-8180(98)00033-6. [DOI] [PubMed] [Google Scholar]
- 6.Goel A, Pollan JJ. Contrast flow characteristics in the cervical epidural space:an analysis of cervical epidurograms. Spine (Phila Pa 1976) 2006;31:1576–9. doi: 10.1097/01.brs.0000222020.45794.ac. [DOI] [PubMed] [Google Scholar]
- 7.Shanthanna H, Mendis N, Goel A. Cervical epidural analgesia in current anaesthesia practice: Systematic review of its clinical utility and rationale, and technical considerations. Br J Anaesth. 2016;116:192–207. doi: 10.1093/bja/aev453. [DOI] [PubMed] [Google Scholar]
- 8.Lirk P, Kolbitsch C, Putz G, Colvin J, Colvin HP, Lorenz I, et al. Cervical and high thoracic ligamentum flavum frequently fails to fuse in the midline. Anesthesiology. 2003;99:1387–90. doi: 10.1097/00000542-200312000-00023. [DOI] [PubMed] [Google Scholar]
- 9.Stojanovic MP, Vu TN, Caneris O, Slezak J, Cohen SP, Sang CN. The role of fluoroscopy in cervical epidural steroid injections: An analysis of contrast dispersal patterns. Spine (Phila Pa 1976) 2002;27:509–14. doi: 10.1097/00007632-200203010-00011. [DOI] [PubMed] [Google Scholar]
- 10.Pak MH, Lee WH, Ko YK, So SY, Kim HJ. Ultrasonographic measurement of the ligamentum flavum depth;Is it a reliable method to distinguish true and false loss of resistance? Korean J Pain. 2012;25:99–104. doi: 10.3344/kjp.2012.25.2.99. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Zhang X, Shi H, Zhou J, Xu Y, Pu S, Lv Y, et al. The effectiveness of ultrasound-guided cervical transforaminal epidural steroid injections in cervical radiculopathy: A prospective pilot study. J Pain Res. 2018;12:171–7. doi: 10.2147/JPR.S181915. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Marhofer P, Greher M, Kapral S. Ultrasound guidance in regional anaesthesia. Br J Anaesth. 2005;94:7–17. doi: 10.1093/bja/aei002. [DOI] [PubMed] [Google Scholar]
- 13.Grau T, Leipold RÜW, Horter J, Conradi R, Martin EO, Motsch J. Paramedian access to the epidural space: The optimum window for ultrasound imaging. J Clin Anesth. 2001;13:213–7. doi: 10.1016/s0952-8180(01)00245-8. [DOI] [PubMed] [Google Scholar]
- 14.Chin KJ, Karmakar MK, Peng P. Ultrasonography of the adult thoracic and lumbar spine for central neuraxial blockade. Anesthesiology. 2011;114:1459–85. doi: 10.1097/ALN.0b013e318210f9f8. [DOI] [PubMed] [Google Scholar]
- 15.Habib AS, George RB, Allen TK, Olufolabi AJ. A pilot study to compare the episure autodetect syringe with the glass syringe for identification of the epidural space in parturients. Anesth Analg. 2008;106:541–3. doi: 10.1213/ane.0b013e3181606c0a. [DOI] [PubMed] [Google Scholar]
- 16.Grau T, Leipold RW, Fatehi S, Martin E, Motsch J. Real-time ultrasonic observation of combined spinal-epidural anaesthesia. Eur J Anaesthesiol. 2004;21:25–31. doi: 10.1017/s026502150400105x. [DOI] [PubMed] [Google Scholar]
- 17.Rapp HJ, Folger A, Grau T. Ultrasound-guided epidural catheter insertion in children. Anesth Analg. 2005;101:333–9. doi: 10.1213/01.ANE.0000156579.11254.D1. [DOI] [PubMed] [Google Scholar]
- 18.Hermanides J, Hollmann MW, Stevens MF, Lirk P. Failed epidural: Causes and management. Br J Anaesth. 2012;109:144–54. doi: 10.1093/bja/aes214. [DOI] [PubMed] [Google Scholar]
- 19.Vallejo MC, Phelps AL, Singh S, Orebaugh SL, Sah N. Ultrasound decreases the failed labor epidural rate in resident trainees. Int J Obstet Anesth. 2010;19:373–8. doi: 10.1016/j.ijoa.2010.04.002. [DOI] [PubMed] [Google Scholar]
- 20.Shaikh F, Brzezinski J, Alexander S, Arzola C, Carvalho JCA, Beyene J, et al. Ultrasound imaging for lumbar punctures and epidural catheterisations: Systematic review and meta-analysis. BMJ. 2013;346:f1720. doi: 10.1136/bmj.f1720. doi:10.1136/bmj.f1720. [DOI] [PubMed] [Google Scholar]
- 21.Chakravarthy M, Jawali V, Patil TA, Srinivasan KN, Jayaprakash K, Mahajan V, et al. High thoracic epidural anesthesia as the sole anesthetic for redo off-pump coronary artery bypass surgery. J Cardiothorac Vasc Anesth. 2003;17:84–6. doi: 10.1053/jcan.2003.16. [DOI] [PubMed] [Google Scholar]
- 22.Liem TH, Williams JP, Hensens AG, Singh SK. Minimally invasive direct coronary artery bypass procedure using a high thoracic epidural plus general anesthetic technique. J Cardiothorac Vasc Anesth. 1998;12:668–72. doi: 10.1016/s1053-0770(98)90240-3. [DOI] [PubMed] [Google Scholar]
- 23.Landoni G, Isella F, Greco M, Zangrillo A, Royse CF. Benefits and risks of epidural analgesia in cardiac surgery. Br J Anaesth. 2015;115:25–32. doi: 10.1093/bja/aev201. [DOI] [PubMed] [Google Scholar]
- 24.Horlocker TT, Wedel DJ. Anticoagulation and neuraxial block: Historical perspective, anesthetic implications, and risk management. Reg Anesth Pain Med. 1998;23(6 Suppl 2):129–34. doi: 10.1016/s1098-7339(98)90137-7. [DOI] [PubMed] [Google Scholar]
- 25.Currie JM. Measurement of the depth to the extradural space using ultrasound. Br J Anaesth. 1984;56:345–7. doi: 10.1093/bja/56.4.345. [DOI] [PubMed] [Google Scholar]
- 26.Grau T, Leipold RW, Conradi R, Martin E, Motsch J. Ultrasound imaging facilitates localization of the epidural space during combined spinal and epidural anesthesia. Reg Anesth Pain Med. 2001;26:64–7. doi: 10.1053/rapm.2001.19633. [DOI] [PubMed] [Google Scholar]
- 27.Grau T, Leipold RW, Conradi R, Martin E, Motsch J. Efficacy of ultrasound imaging in obstetric epidural anesthesia. J Clin Anesth. 2002;14:169–75. doi: 10.1016/s0952-8180(01)00378-6. [DOI] [PubMed] [Google Scholar]