After obtaining the approval of research Ethics Committee of Beijing Chaoyang Hospital, Capital Medical University and written informed consent from the subject, a total of 18 American Society of Anesthesiologists physical status (ASA) I–III patients scheduled for lower extremity surgery, in whom a CSE anesthesia was planned, were enrolled for this study. Patients were excluded if they had a body mass index (BMI) > 28 kg/m2, clinically obvious or known spinal deformity, infection in the back, allergy to local anesthetic drugs, previous spine surgery, or coagulopathy.
The intravenous access was established and the electrocardiography (ECG), heart rate, non-invasive or invasive arterial pressure, and arterial oxygen saturation were monitored after the patient arrived at the operating room. Then, the patients were positioned in the lateral decubitus position, with the affected side downward. Sufentanil (5 - 10 μg) was administered intravenously, immediately before the positioning, to those who complained of fracture-associated pain. The US scan was performed by an experienced anesthetist (Dr. Yun Wang), who is skilled in spine US imaging and familiar with spine-related interventional injections.
All US scans were performed using a Sonosite Turbo (Philips Healthcare, Andover, MA, USA) ultrasound system and a curved array transducer (C5-2, 5-2 MHz). Some US gel was applied to the skin over the lumbar region for adequate acoustic coupling. The target vertebral level (L2-L3-L4) for the neuraxial block was identified by locating the lumbosacral junction (L5-S1 gap) on a paramedian sagittal scan, and then counting cranially to locate the lamina and transverse processes of the L2, L3, and L4 vertebrae (9). The paramedian transverse scan through the articular process was then performed with the transducer positioned 3 - 5 cm lateral to the midline in the transverse orientation at the L2-L3 or L3-L4 intervertebral level (Figure 1). The transducer was also directed medially so that the US beam was insonated in a paramedian transverse oblique plane. This was performed to ensure that the incident US signal entered the spinal canal through the interlaminar space (Figure 2). The orientation marker of the ultrasound transducer was oriented laterally during the US scans in all patients. The US scout scan was recognized as successful if the articular process, ligamentum flavum, posterior dura, intrathecal space and anterior dura were visualized at the L2-L3 or L3-L4 intervertebral level. The patients with successful US scout scan underwent the following CSE procedure under US guidance.
The transducer was finally positioned over the L2/L3 or L3/L4 intervertebral spaces after the important spinal and neuraxial structures were visualized following the scout scans (Figure 3). The position of the transducer was marked on the patient’s back using a skin marking pen to ensure that the transducer was returned to the same position after sterile preparations were made before the intervention. After sterile preparations, the CSE anesthesia was performed by Dr. Yun Wang (single operator technique). The US transducer with its cable was covered by a sterile plastic sleeve, with no air trapped between the footprint and plastic sleeve, after the transducer was prepared by applying a layer of US gel on its footprint. No US gel was applied directly to the skin over the area scanned, and Iodophor, which was applied using a sterile swab, was used as a substitute coupling agent. The transducer was held in the non-dominant hand of the operator. With the spinal and neuraxial structures such as ligamentum flavum, posterior dura or anterior dura in view on the US monitor, the operator used the dominant hand to infiltrate local anesthetic (lidocaine 1%, 2–3 ml) to the skin and underlying tissue, 1 cm lateral to the spinal midline at the US beam plane. The 18 G Tuohy needle (BD, Suzhou, China) was then inserted from the skin infiltration wheal, with its tip directed towards the interlaminar space (L2/L3 or L3/L4) on the US image.
This target interlaminar space was always viewed in the bottom-right of the US image (10). The trajectory for needle insertion was optimized while the needle was still in the erector spinal muscle. The Tuohy needle was gradually advanced to the interlaminar space, under real-time US guidance, until the tip was judged to have engaged in the ligamentum flavum (Figure 4). This was also confirmed by testing for ‘resistance to air injection’ through the Tuohy needle using the standard LOR syringe included in the kit. Since the Tuohy needle was inserted in the plane of the US beam, it was possible to follow the advancing needle in real time. The position of the needle tip could be inferred by observing tissue movement on the US scan. The needle-syringe assembly was then stabilized by the dominant hand holding it on the patient’s back. The needle-syringe assembly was then gradually advanced, until the operator felt the sudden loss of resistance to pressure on the plunger. Then, the syringe and US probe were removed and a 27 G spinal needle was threaded into the Tuohy needle to perform the dural puncture. Once a free flow of cerebrospinal fluid (CSF) was seen, the spinal needle was fixed and 2.5 – 3 ml of hyperbaric ropivacaine (0.5%, diluted in 10% glucose) was injected at a rate of 1 ml every 6 s. The spinal needle was removed and 3–4 cm of an epidural catheter was immediately inserted into the epidural space through the Tuohy needle and secured to the back. The patients were then returned to the supine position and no local anesthetic was injected through the epidural catheter unless the level of sensory block after the spinal injection was inadequate for surgery. Electrocardiography (ECG), oxygenation saturation and arterial pressure were monitored continuously for the duration of surgery. Hypotension (defined as < 20% decrease in systolic arterial pressure from the baseline) was treated using intravenous ephedrine (10 mg bolus). The level of sensory block was detected 10 min after the initial intrathecal injection. The oxygen (5 litre/min) was administered via a facemask to the patients.
Data Collection and Analysis
The following parameters were recorded during the study. The visibility of the six spinal and neuraxial structures (articular process, ligamentum flavum, epidural space, posterior dura, intrathecal space, and anterior dura) at the L2/L3 or L3/L4 lumbar interspace were scored during the scout scan, by Dr. Yun Wang who performed the US scan, using a four point numerical scale (0, not visible; 1, hardly visible; 2, well visible; 3, very well visible, maximum score possible = 18), and the total US visibility score (UVS) was determined for every patient (7,9). The scan was considered a success if both posterior and anterior dura were seen on the US imaging. The US visibility of the spine and neuraxial structures was judged to have been good, if the mean total UVS was > 12, average if the score was 6–12, and poor if the score was < 6 (7, 11). The number of attempts it took to access the epidural space was also recorded.
Complications directly related to the technique or inadequate block that required rescue epidural injection of local anesthetic during surgery was also recorded. The data were analyzed using SPSS for Windows (version 19, SPSS. Inc., Chicago, IL, USA). The Kolmogorov–Smirnov test was used to test the normality of the data recorded. The data are presented as mean (SD) when normally distributed and as median (range) when not normally distributed. The categorical variables are presented as n (%).