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Introduction
Evidence supports the feasibility, efficacy and safety of ultrasound (US) use to facilitate the insertion of lumbar neuraxial blocks.1 2 However, there is limited research on thoracic US-assistance (pre-procedural US scanning and skin markings).3–5 We aimed to compare the conventional anatomic landmarking technique with a novel approach of US assistance to allow advancing the needle without purposely contacting the lamina. Our hypothesis was that US assistance would lead to reduction in the number of needle redirections.
Methods
With research ethics approval from Mount Sinai Hospital (11-0230-E) Toronto, Canada, we conducted a single-center, parallel-group, randomized controlled trial (Consolidated Standards of Reporting Trials, clinicaltrials.gov: NCT01449214.Oct 11 2011). Enrollment in elective open abdominal surgeries under general anesthesia and thoracic epidural analgesia. Exclusion criteria: marked spinal deformities, previous spinal surgery, body mass index≥35 kg/m2, and pregnancy. Subjects were randomized and allocated to palpation of anatomical landmarks (palpation group) or US-assisted method (US group).
Palpation group
The traditional palpation technique was carried out with the needle contacting bone and “walking-off” the lamina in the paramedian approach.
US-assisted group
For standardization, only one study investigator (CA) performed all the preprocedural scanning (5–2 MHz curved array probe, Zonare Medical Products Canada, Beaverton, ON, Canada). While the patient positioned in a standard sitting position with the back and neck flexed, a paramedian sagittal plane view was obtained and the probe slightly tilted towards the midline. The interlaminar level was selected by counting up the laminae from the level of the sacrum, and according to the mid-dermatome level of the planned surgical vertical incision. Within the interspace, we identified and centered on the screen two parallel hyperechoic structures: posterior complex (ligamentum flavum and dorsal dura mater unit) and anterior complex (ventral dura mater, posterior longitudinal ligament and vertebral body). The skin was pen marked at the midpoint of the cephalad and caudad aspect, and at the midpoint of the right or and left aspect of the transducer (figure 1). The optimal needle insertion point and needle trajectory was established by the intersection of these marks and the estimated subjective angle of the US beam.
Preprocedural ultrasound scanning in a volunteer model. (A.1) Scanning in the transverse median plane; (A.2) midline skin mark in the transverse median plane; (B.1) scanning in the paramedian sagittal plane; (B.2) interlaminar space transverse-skin mark (Transv-mark) in the paramedian sagittal plane; (C.1) interlaminar space longitudinal-skin mark (Longmark) in the paramedian sagittal plane; (C.2): skin marks: midline, interlaminar space transverse mark (Transv-mark) and longitudinal mark (Long mark); (D.1 and D.2) skin indentation with a plastic tip on the intersection of the transverse and longitudinal interlaminar space skin marks from the paramedian sagittal plane. Note: only one mark is shown per each skin marking: cephalad and right sides.
Outcomes
The primary outcome was the number of epidural needle redirections defined as the need to withdraw the needle for the purpose of advancing in a different angle (sagittal or axial plane). Secondary outcomes included bony contacts, needle reinsertions, epidural procedure duration, and complications (vascular puncture, dural puncture, paresthesia).
Sample size considered 46 subjects based on power analysis: number of redirections mean 1.45 for US-assisted thoracic epidurals5; mean±SD 2.6±1.4 for palpation in difficult lumbar epidurals from US-assistance study in obstetrics6; power of 0.8 and a two-tailed type I error of 0.05.
Results
Forty-seven subjects were analyzed (Palp group: n=24, mean age 58.2±11.3 years, 21 (88%) women; US group: n=23, mean age 58.1±15 years, 11 (48%) women). The number of needle redirections was not different between groups (median (IQR): Palp group=2.5 [5], US group=2 [4]; p=0.7), and<3 redirections in over 60% of cases (frequency (%); Palp group=15 (62.5), US group=15 (65.2), p=1). Only when the preprocedural US scanning time was included in the US group, the duration was significantly longer than Palp group (table 1). No difference in secondary outcomes and successful intraoperatively and postoperatively epidural analgesia as per follow-up by the acute pain service.
Epidural procedures
Discussion
This US-assisted thoracic epidural approach study found no significant difference in the number of needle redirections or the duration of the actual epidural needling when compared with the standard landmarking technique. On the contrary, when the time for preprocedural US scanning is included, the whole procedure duration was longer. Obtaining clear spinal anatomy (midline, depth to lamina, level) in the US group showed no potential advantage probably due to good to fair anatomical landmarks in both study groups. Further research is warranted in US assistance for challenging thoracic epidural procedures (obesity, spinal deformities).
Ethics statements
Patient consent for publication
Ethics approval
This study involves human participants and was approved by Institutional Board: Mount Sinai Hospital Research Ethics Board. ID:11-0230. Participants gave informed consent to participate in the study before taking part.
Acknowledgments
We acknowledge our patients and colleagues supporting this research study at Mount Sinai Hospital and University of Toronto, Canada.
Footnotes
Contributors CA, MB, ZF and YG contributed to study conception and design. CA, MB, AM and ZF contributed to study conduct. CA and AM contributed to data analysis. All authors contributed to manuscript preparation. CA is the guarantor for the overall content.
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.