Preprocedural ultrasound versus landmark techniques for spinal anesthesia performed by novice residents in elderly: a randomized controlled trial

Spinal anesthesia is traditionally performed using the palpation of bony landmarks to identify the level and point of the needle insertion, together with haptic feedback during needle insertion. Ultrasound (US) imaging has become an increasingly popular tool among anesthesiologists to guide neuraxial blockade. Studies have shown that pre-procedural US facilitates the performance of spinal anesthesia in patients in whom technical difficulties are expected [1, 2] and is not of significant benefit over the traditional landmark technique when it is performed for patients without lumbar spine abnormalities [3‐5].

According to a practice survey amongst UK anesthesiologists, the conventional midline approach is the most commonly used technique for spinal anesthesia [6]. However, the paramedian palpation approach has shown to be useful in geriatric population, since it is less influenced by spinal osteoarthritic changes, and is associated with a higher success rate than palpation midline approach in the elderly (85% vs. 45%) [7].

Most of the studies on pre-procedural US-guided neuraxial techniques are limited to a midline approach using a transverse median (TM) view. The parasagittal oblique (PSO) view allows for a wider ultrasound window of the epidural space, providing an enhanced visibility of the neuraxis and surrounding structures compared to the TM view [8]. However, it is still not evident whether these superior PSO views lead to an easier paramedian needle insertion. In the literature, there are no studies directly comparing the US-guided paramedian approach using the PSO view, the US-guided midline approach using the TM view, and the conventional landmark midline approach to perform spinal anesthesia by novice residents in elderly patients.

In this prospective, randomized, controlled study, we hypothesized that both midline and paramedian pre-procedural US-guided spinal anesthesia would result in different success rates at first attempt when compared with the conventional landmark-guided midline technique in elderly patients. All procedures were executed by first year clinical anesthesia residents (CA-1) under direct staff anesthesiologist supervision.

This study was approved by the American University of Beirut Institutional Review Board and written informed consent was obtained from all patients and from the 14 residents participating in the trial. The study adheres to the CONSORT guidelines and was retrospectively registered at clinicaltrials.gov (NCT02658058, principal investigator: Sahar Siddik-Sayyid, date of registration: January 18, 2016).

Patients scheduled for surgery under spinal anesthesia, were more than 60 years old, with American Society of Anesthesiologists physical status 1 to 4, were considered eligible for enrollment. Patients who were unable to give informed consent, refused spinal anesthesia or had contraindications to spinal anesthesia, including allergy to local anesthetics or a bleeding diathesis were excluded.

After obtaining informed consent, a computer-generated block randomization schedule was used to randomize patients to receive spinal anesthesia into one of three treatment groups: the conventional surface landmark-guided midline technique (group LM), the pre-procedural US-guided paramedian technique (group UP), or the pre-procedural US-guided midline technique (group UM). Group allocation was concealed from study investigators until the procedure time. Due to the nature of the study, blinding of the residents performing the procedure and observer collecting data was not possible. Only patients were blinded to the study group.

Baseline patients characteristics recorded were: age, gender, body mass index, and presence of any spinal abnormalities (including significant scoliosis on physical exam and previous spine operations with instrumentation). Upon arrival to the operating room, standard monitoring (three-lead electrocardiogram, noninvasive blood pressure, and pulse oximeter) and intravenous access were established. The operator performing the procedure was a CA-1 under direct supervision of one attending anesthesiologist (MR) with fifteen years of clinical experience. All US imaging of the lumbar spine were performed by the same attending anesthesiologist trained and experienced in US-assisted neuraxial block. The Sonosite (TM, Bothell, WA 98021 USA) with a low frequency (2 to 5 MHz) curvilinear probe was used for this study. The pre-procedural spinal US was performed in a nonsterile manner. Thereafter, all spinal procedures were carried out with the patient in the sitting position and under sterile technique. All patients were requested to maintain a lumbar flexion posture. The lumbar interspaces selected were presumably between L2 and L5.

Each resident was randomly allocated procedures in subject allocation blocks of six. Each subject allocation block contained randomly two landmark-guided midline techniques, two pre-procedural US-guided paramedian techniques, and two pre-procedural US-guided midline techniques. Each resident did six spinal blocks in a row and had to complete two to three subject allocation blocks. Residents chosen were novices who had performed less than five spinal attempts since the beginning of their residency. They were instructed about the three spinal techniques by watching 3 cases of each before the beginning of the study, in addition to the standardized teaching about spinal anesthesia that included teaching videos and reading material.

Twelve of the 14 residents did two subject allocation blocks (4 procedures of each group) and the remaining two did 3 subject allocation blocks (6 procedures of each group). We randomized 209 patients of whom twenty-nine did not receive the allocated intervention for the following reasons: the surgical procedure was canceled by the surgical team (4 patients), the attending anesthesiologist with the expertise in the US-guided technique was unavailable (11 patients), it was deemed that there was insufficient time to perform study assessments (3 patients), or there was a change in the anesthesia type (11 patients). The final number of patients included was 60 patients for each group (Fig. 1). No patients were lost to follow-up. The three groups were similar regarding baseline demographics and type of surgery (Table 1). None of our patients had scoliosis or previous spine operations.

The successful dural puncture rate on first attempt (primary outcome) was higher in groups LM and UM (77 and 73% respectively) than in group UP (42%; P < 0.001). The median number of attempts was lower in groups LM and UM (1 [1] and 1 [1–1.75] respectively) than in group UP (2 [1–2]; P < 0.001). Also, the median number of passes was lower in groups LM and UM (2 [0.25–3] and 2 [0–4]; respectively) than in group UP (4 [2–7.75]; P < 0.001) (Table 2).

The ease of landmark palpation was similar between the three groups, and grading by US was similar between the US groups. The time taken to perform the spinal anesthetic was not different between groups LM and UM (87.24 ± 79.51 sand 116.32 ± 98.12 s respectively) but shorter than in group UP (154.58 ± 91.51 s; P < 0.001). Less verbal attending assistance was required in groups LM and UM (53 and 48% respectively) compared to group UP (85%; P < 0.001) (Table 2).

More complications (paresthesia, blood tap, and radicular pain) occurred in patients in group UP, and patients with complications were followed-up to 24 h as per hospital protocol with no consequences. Also, percentage of patients satisfied during the procedure was less in group UP (Table 2). All spinal anesthetics were successful and patients achieved complete sensory block to the T₇ dermatome or higher. All failed dural punctures by the residents were achieved successfully by the attending anesthesiologist using the same technique as the resident except for one patient in group UP and three patients in group UM who had the spinal procedure using the LM technique.

Our study showed that both preprocedural US-assisted modalities (midline or paramedian) did not prove more efficacious than the landmark-based midline approach in facilitating spinal anesthesia performed by CA-1 residents in elderly patients. In fact, while the first attempt and overall success rates of dural puncture in the midline US and the conventional landmark groups were not significantly different, they were higher than the rates achieved with preprocedural US-guided paramedian spinal technique. Furthermore, time to perform spinal anesthesia, need for verbal attending assistance, as well as the number of attempts and passes were all significantly less in the midline US and conventional groups compared to the paramedian US group.

Metanalyses suggest that preprocedural US leads to reduction of the risk of failure and a lower number of needle passes compared to conventional palpation approach [10‐12]. This is particularly true in patients with whom technical difficulties are expected such as those with high body mass indices, nonpalpable landmarks, or difficult spinal anatomy. Of note, most of these studies are limited to a midline approach using a TM view.

Geriatric population, similar to our study population, also may present with higher likelihood of technical difficulties during spinal anesthesia due to narrowed interspinous spaces and interlaminar spaces as a result of ossification of the interspinous ligaments and hypertrophy of the facet joints respectively [1]. However, our findings did not demonstrate an improved outcome with the US midline vs landmark. This may be explained by the fact that the spinal procedures in our elderly population using the landmark midline technique were not difficult enough and easier than expected, thus limiting the benefit of a preprocedural US. In fact, the first success rate in the LM and UM groups (77 and 73% respectively) were higher than that reported in a previous study conducted by Chin et al. in a nonobstetric patient population with difficult anatomic landmarks (32% in landmark group and 65% in US group), even though operator in all cases in the aforementioned study was a clinical fellow in regional anesthesia or consultant with more than 5 year clinical experience [1].

As for the paramedian approach, it should theoretically be valuable in the elderly since the interlaminar spaces are less affected by aging offering a better view of LFD and PLL compared to midline view [13], and it does not require flexing of the spine (an advantage in elderly patients with fractures). Even with these advantages, a lower first attempt success rate with the paramedian approach was obtained compared to both landmark- and US-guided midline approaches. As a matter of fact, the paramedian approach has been shown to be superior to the midline approach in some previous studies [7, 14, 15] but not in others [16‐18]. It must be noted that we found only two studies in the literature that describe the use of paramedian US techniques to facilitate spinal anesthesia with contradictory results [4, 9]. Lim et al. compared an US-assisted paramedian vs a conventional paravertebral approach for orthopedic and other types of surgery and found no intergroup difference in first skin puncture-success rate, number of needle redirections, and complications [4]. In another study, Srinivasan et al. compared an US-assisted paramedian vs a palpation at midline approach for an elderly orthopedic population and showed that US technique required fewer passes and attempts to reach the subarachnoid space [9]. We found a much lower success rate at first attempt in the US paramedian group (42%) compared to those in the Lim et al. and Srinivasan et al. studies (64% vs 84% respectively). This may be explained by that our operators were CA-1 residents as opposed to the other two studies where operators were either trainees at variable level of experience (up to three years of experience) [4] or attending anesthesiologists [9].

In our study, the higher number of attempts in the UP group resulted in more blood taps, paresthesia, and radicular pain than in the other two groups. Also, patients in the UP group had more periprocedural pain and lower satisfaction than the other two groups, probably because the needle has to cross the erector spinae muscle before reaching the dura. These findings can be due to the fact that the paramedian approach to the neuraxis is intrinsically more difficult to perform and is utilized by few anesthesiologists.

Studies with junior residents acting as operators during preprocedural US scanning of the spine are present in the obstetric literature with mixed results. All investigators used the midline approach prior to the spinal block. While Sahin et al. found a high level of success in the prepuncture US-determined insertion point by anesthesia residents [2], Turkstra et al. reported similar results to our findings with no observed benefit to preprocedural US examination for junior residents performing spinal anesthesia [5].

Third, the potential learning effect over the course of the study could be present; however, it was mitigated by performing all spinal blocks in a row and minimizing the number of procedures done outside study. Yet, it must be noted that as per Kopacz et al., notable improvement in the spinal anesthesia technique among novice residents require at least 20 procedures to be performed [17]. In our study, 12 residents performed each 12 spinal blocks and only 2 residents performed each 18 spinal blocks, all of which are below minimal required number.

Finally, we found some challenges with the use of the US-assisted approach in general: the difficulty to mark the point for needle insertion that can change if the patient moves between the time of skin marking and the actual procedure, the tissue distortion particularly in the elderly with mobile and loose skin, and to guarantee that the trainee will follow the exact direction of the probe despite the clear instruction about the angle at which the needle should be inserted. It is important to highlight on the different definitions of attempts, passes, and redirections in the literature as a redirection without withdrawal is sometimes considered in some reports as an additional attempt, thus making comparison of measured outcomes difficult among studies.

In conclusion, our study showed that preprocedural US scanning did not improve the ease of midline and paramedian spinal anesthesia as compared to the conventional landmark midline technique when performed by junior residents in an elderly population. Thus, there was no observed additional value to preprocedural US, whether using the TM or the PSO views for anesthesiologists in training. Our results should be confirmed with the use of the newer modality of real-time US guidance in the future.