Study Design and Participants
This prospective, randomized controlled trial was approved by the hospital’s Institutional Review Board (Ethics Committee of The First Affiliated Hospital of Guangzhou University of Chinese Medicine; Y 042; February 11, 2019) and written informed consent was obtained from all patients participating in the trial. This study was registered prior to patient enrolment at the Chinese Clinical Trial Register (identifier, ChiCTR1900020819; principal investigator, Y.L.; date of registration, January 20, 2019). The trial was performed from February 2019 to September 2019 in The First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, China, and adhered to the applicable Consolidated Standards of Reporting Trials guidelines (Fig. 1).
A total of 80 patients were recruited. The inclusion criteria comprised (1) patients who were scheduled to receive CSE anesthesia for elective hip fracture surgery; (2) age ≥ 65 years; (3) body mass index (BMI) ≤ 30 kg/m2; and (4) an American Society of Anesthesiologists (ASA) classification of I to III. Exclusion criteria are as follows (1) severe cardiopulmonary diseases; (2) a contraindication to CSE anesthesia (e.g., coagulopathy, hypovolemia, raised intracranial pressure, infection in puncture area, allergy to local anesthetics, or lack of cooperativity); and (3) a history of lumbar surgery.
The patients were randomized (using a computer-generated randomized number table) to receive CSE anesthesia using either a landmark-guided technique (n = 40) or an ultrasound-assisted technique (n = 40). The allocation of patients was determined by sequentially numbered, sealed envelopes after the patients were moved into the operating room. During the procedure, patients were blinded to group allocation.
Three anesthesiologists conducted the trial, and each had previously performed more than 40 ultrasound-assisted neuraxial blocks and ample experiences (> 15 years in average) in conducting CSE anesthesia. In the landmark group, ultrasound and CSE anesthesia were performed by distinct operators, while the whole procedure in the ultrasound group was performed by the same operator.
After the patients were moved to the operating room, routine monitoring (non-invasive blood pressure, 3-lead electrocardiogram, oximetry) and face mask oxygen at a flow rate of 1–2 L/min were applied, and peripheral intravenous access was established. During the whole procedure, no sedative was administered. An ultrasound-guided fascia iliaca compartment block was performed with 20 mL of 0.375% ropivacaine to reduce pain for all patients [31, 32]. After 15 minutes, the patient was assisted in assuming a lateral decubitus position with the fracture side up. In both groups, the anesthesiologists palpated the surface landmark and graded the ease of palpation using a 3-point scale (easy, moderate, and difficult) as described in a previous study .
For the landmark group, the procedure was done following these three steps:
- Identification of the needle insertion point. The needle insertion point was marked on the skin by traditional palpation. The first anesthetist subsequently left the operating room.
- Ultrasound scan. A portable ultrasound machine (Konica Minolta, SONIMAGE HS1, Japan) with a low frequency (2–5 MHz) curved array probe with a depth of 8 cm was used. Due to safety concerns, a second anesthesiologist conducted an ultrasound to check if the skin mark was above the L1-L2 interlaminar space; if so, the anesthetist was required to perform CSE anesthesia at a lower interlaminar space . Ultrasound images were saved.
- Administration of CSE anesthesia. CSE anesthesia was performed by the first anesthesiologist, using the paramedian approach.
For the ultrasound group, the entire procedure was carried out using the following six steps:
- Marking of the midline. The probe was placed at the transverse midline (TM) plane for the evaluation of spine anatomy. The probe was tilted to obtain optimal ultrasound images. Midpoints of the long edge of the ultrasound probe were marked as the midline of the spine.
- Identification of the interlaminar space. The probe was placed at the parasagittal oblique (PSO) plane, 1–2 cm to the midline. The scan was performed upwards from the sacrum; the L5-S1 to L2-L3 interlaminar spaces were identified successively by the “counting-up” approach. The primary and secondary choice of interlaminar space for puncture were determined by the ultrasound image quality and the length of the anterior/posterior complex.
- Identification of the needle insertion point. The probe was adjusted to achieve the best ultrasound image at the determined interlaminar space. Then, the upper edge of the inferior laminar was placed at the center of the ultrasound screen. Skin marks were made at the midpoints of the long and short borders of the probe. The intersection of two connecting lines indicated the needle insertion point.
- Measurement of the suggested insertion angles. The built-in tool in the ultrasound unit was used to measure the maximum cephalad angle (∠α in Fig. 2a) between (1) the connecting line from the insertion point to the far end of the posterior complex and (2) the midline of the ultrasound screen; 1/2 ∠α was the suggested cephalad angle. The probe’s tilt to the median plane indicated the medial angle (∠β), and was measured using a 180° protractor (Deli, Shanghai, China) (Fig. 2b).
- Measurement of the needle insertion depth. The distance from the insertion point to the posterior complex, which was the presumed minimum insertion depth, was measured using the ultrasound clipper tool (Fig. 2a).
- Administration of CSE anesthesia. CSE anesthesia was conducted using the paramedian technique according to the marked insertion point, suggested insertion angles, and presumed depth. After the needle reached the subcutaneous tissue and became stable, a low temperature plasma sterilized protractor (Deli, Shanghai, China) was used to correct the needle insertion angle (Fig. 2c). When the puncture was successful, the actual needle insertion angles (cephalad and medial) were measured (Fig. 2d).
In both groups, an aseptic technique was strictly applied throughout the entire process. CSE anesthesia was performed using a needle-through-needle approach, with a 25/16-gauge CSE kit (Kindao Interventional Medical Co., Ltd., Guangzhou, China). When the backflow of clear cerebrospinal fluid was observed, 0.5% ropivacaine (9.75-12.75 mg) was injected. Then, a 20-gauge multi-orifice epidural catheter (Kindao Interventional Medical Co., Ltd., Guangzhou, China) was inserted through the Touhy needle, up to 5 cm into the epidural space. If three attempts failed, the secondary interlaminar space was used. If attempts at two different interlaminar spaces failed, an alternative technique was allowed (palpation, ultrasound guidance, midline approach, another anesthetist). In the event that the alternative technique failed, general anesthesia was induced.
The patient satisfaction score was rated using a 5-point scale (from 1: completely dissatisfied to 5: completely satisfied) after anesthesia . The block level was tested by loss of cold sensation, 15 minutes after anesthesia. The quality of the ultrasound image was assessed as good (the posterior complex and anterior complex were both visible), moderate (either the posterior complex or anterior complex was visible), or poor (neither the posterior nor anterior complex was visible) [24, 29, 33]. The discrepancy (Δ) between the suggested and actual angle was classified as accurate (0° ≤ Δ ≤ 5°), acceptable (5° < Δ ≤ 10°), or inaccurate (Δ > 10°). During the entire procedure, data were recorded by a research assistant; for all measurements, the mean of three readings was calculated. A postoperative follow-up was conducted within 48 hours after the surgery.
The primary outcome in this study was the first-pass success rate of CSE anesthesia. A first-pass success was defined as the needle reaching the subarachnoid space within a single insertion attempt, without redirection.
Secondary outcomes were as follows:
- First-attempt success rate: defined as the needle reaching the subarachnoid space within a single insertion attempt and allowing redirection.
- Number of needle insertion attempts: each skin puncture was considered as a separate attempt.
- Number of needle passes: total number of insertion attempts and needle redirections.
- Locating time: the time from when the operator touched the patient’s skin to the marking of the insertion point on the skin (landmark group), and the time from when the probe was placed on the skin to the marking of the insertion point (ultrasound group).
- Puncture time: interval between the contact of the skin with the Touhy needle, and the observation of cerebrospinal fluid from the spinal needle.
- Total time: the sum of the locating time and puncture time.
- Level of block: measured by testing the loss of cold sensation.
- Procedural adverse reactions: radicular pain, bloody tap, unintentional dural puncture.
- Postoperative complications: including paresthesia, backache, and post-dural puncture headache.
- Patient satisfaction score: 1 (completely dissatisfied), 2 (dissatisfied), 3 (moderate), 4 (satisfied), 5 (completely satisfied). It was defined as the overall comfort level the patients experienced during the procedure, which includes (i) the back pain the patients felt, (ii) radicular pain the patient felt (iii) the discomfort due to the repositioning after a failed needle insertion and (iv) the overall anxiety or fear the patients felt. One negative response to these situations will deduct the satisfaction score by one point.
The sample size was calculated using PASS software Version 15.0 (NCSS, Kaysville, USA). Based on our pilot study, the first-pass success rates in patients using the conventional palpation and ultrasound-assisted technique were 22% and 59%, respectively. With an α error of 5% and a β error of 10% (90% power), a sample size of 35 patients per group was required. We increased the target sample size to 40 patients per group to allow for dropouts.
Data were analyzed using SPSS 25.0 (IBM Corporation, NY, USA). Continuous data were tested for normality using the Kolmogorov-Smirnov test. Normally distributed data (mean ± standard deviation [SD]) were compared using the Student’s t-test. Non-normally distributed data (median [interquartile range]) were compared using the Mann-Whitney U test. Categorical variables were presented as n (%) and were compared using the χ2 test or Fisher’s exact test. The primary outcome (first-pass success rate) was compared using the χ2 test. Spearman’s rank correlation was used to determine the relationship between the presumed minimum needle insertion depth and actual insertion depth. For the differences in success rates for a selected number of passes and attempts between two groups, 95% confidence intervals (CI) were calculated. A two-tailed P < 0.05 was considered statistically significant.
Pre-specified sub-group analysis was conducted to investigate the effect of scoliosis to the first-pass success rate, number of needle passes and needle insertion attempts, locating time, puncture time, total time and patient satisfaction. Sub-group analysis was performed for all 12 patients with scoliosis, 6 patients in each group.