The ideal technique for spinal anaesthesia requires successful dural puncture with a single needle pass.1 Multiple puncture attempts are associated with an increased risk of needle trauma, postdural puncture headache, spinal haematoma, backache and paraesthesia.1–6 Minimising the number of attempts is desirable to reduce the risk of complications and improve patient satisfaction.7
Spinal anaesthesia has traditionally relied on a technique guided by surface landmarks, something that may be challenging in the elderly because of degenerative changes in the spine.2,3,8–11 Ultrasonography might improve the efficacy of spinal anaesthesia12–14 by improving the accuracy of identification of intervertebral levels, depth measurement of the intrathecal space13,14 and location of the interlaminar window that permits needle passage.12 Compared with the landmark-guided technique, ultrasound-assisted spinal anaesthesia decreases the number of puncture attempts and improves the success rate at the first attempt in patients with potential technical difficulties.2,15
However, previous studies that have employed ultrasound-assisted anaesthesia in surgical patients in general have reported no significant advantages compared with the landmark-guided technique.16–19 There is little support for the routine use of ultrasound for spinal anaesthesia.16,19 In particular, it is unclear which groups of patients might benefit from this technique.20 Moreover, previous trials have mainly employed the midline approach,2,18,21 and the ultrasound-assisted paramedian approach has not been fully evaluated.3 As the paramedian sagittal oblique (PSO) view provided by ultrasound provides a consistently superior view compared to the transverse midline view,3,10,12 offers promise for an ultrasound-assisted technique. In a previous trial, the ultrasound-assisted paramedian approach required fewer needle passes than the landmark-guided midline technique.3 However, as the paramedian approach has been shown to facilitate spinal anaesthesia in elderly patients,1,22,23 it remains to be determined whether the ultrasound-assisted paramedian technique is better than the landmark-guided paramedian approach in this group.
The current study aimed to evaluate whether ultrasound-assisted paramedian spinal anaesthesia in the elderly can achieve successful dural puncture with fewer needle passes compared with the conventional landmark-guided paramedian technique.
Study design and participants
The current randomised controlled study was approved by the institutional review board of Seoul National University Hospital (no. 1708-113-879; on 13 October 2017) and was registered with ClinicalTrials.gov (NCT03316352; on 16 October 2017). We have prepared this article in accordance with the Consolidated Standards of Reporting Trials guidelines.24
We included all consenting patients aged at least 60 years with American Society of Anesthesiologists physical status I/II/III, who were scheduled to undergo elective orthopaedic surgery with spinal anaesthesia between October 2017 and January 2018 at Seoul National University Hospital, Seoul, Republic of Korea. All patients provided written informed consent. Patients with contraindications to spinal anaesthesia, marked spinal deformity and previous spinal surgery were excluded from the study as were those unwilling to participate or unable to communicate.
Randomisation and minimisation of bias
Patients were randomly assigned to receive spinal anaesthesia by the paramedian approach by either conventional surface guided palpation (landmark group) or preprocedural ultrasound-assisted (ultrasound group) using a computer-generated table of random numbers. Group allocation was concealed using a sequentially numbered, sealed opaque envelope, which was opened only by the attending anaesthesiologist immediately before the procedure. All spinal procedures were performed by one of three anaesthesiologists (S-KP, SY or J-TK), each having performed over 30 ultrasound-assisted neuraxial blocks before this study. Block randomisation was performed to balance the allocation of each of the three anaesthesiologists to the two intervention arms.
Spinal anaesthesia was administered with patients lying in the lateral decubitus position. Sedatives were not administered before or during administration of spinal anaesthesia. In the ultrasound group, preprocedural skin marking was performed using the 4C-RS convex probe (frequency, 2.0 to 5.5 MHz) of a portable ultrasound system (Vivid-i Ultrasound System; GE Healthcare, Little Chalfont, UK) and a regular-tip skin marker (Devon; Covidien, Dublin, Ireland). Both PSO and transverse midline images were acquired as previously described.3,12,17,25 Preprocedural ultrasound-assisted paramedian spinal anaesthesia was administered using the following systematic seven-step protocol.
- In the transverse midline view, the neuraxial midline was marked on the skin (Fig. 1a and b). This midline mark was used to aid the medial angulation of the needle and estimate the distance from the midline to the paramedian insertion point.
- The probe was rotated by 90°, and a PSO view was acquired approximately 1 to 2 cm lateral to the midline. The sacrum was identified first, then, the transducer was moved cephalad to identify individual interlaminar spaces from L5/S1 to L2/3, the ‘counting-up’ approach.
- The interlaminar space, showing the posterior (ligamentum flavum, epidural space and posterior dura) and anterior (anterior dura, posterior longitudinal ligament and vertebral body) complexes12 as clearly as possible, was centred on the screen. With the probe positioned to obtain the clearest image, the skin was marked at the midpoints of the long and short borders of the probe (Fig. 1c and d). The midpoint of the probe indicated the needle-insertion point. A vertical line indicating the centre on the screen represented the imaginary needle trajectory (Fig. 1d).
- The intervertebral level that provided the largest interlaminar space was selected as the site for the first attempt, and the skin was carefully marked at this level. The skin was also marked at the other intervertebral levels for preparation, and these sites were used only if the first attempt was unsuccessful (Fig. 2a).
- The medial angle of the probe providing the clearest image in the PSO view was estimated (Fig. 1c) and used as the angle of needle insertion. The needle was directed towards the observed angle off the sagittal plane, and there was no cephalad angulation in the first attempt (Fig. 2b; Supplemental Video S1, http://links.lww.com/EJA/A208).
- The required needle-insertion depth was estimated by measuring the distance from the skin to the posterior complex.
- The PSO and transverse midline images were graded as good (both posterior and anterior complexes visible), intermediate (posterior or anterior complex visible) or poor (neither complex visible).3,26
After skin marking, the ultrasound gel was wiped off to ensure that the needle-entry site was free of the gel. In the ultrasound group, the anaesthesiologist did not palpate the landmarks until completion of spinal injection.
In the landmark group, the anaesthesiologist palpated the surface landmarks and graded the ease of palpation on a four-point scale (easy, moderate, difficult or impossible).2,3 Spinal anaesthesia was administered on the basis of palpation, using a conventional paramedian approach described in a standard textbook.27 The needle was inserted 1 cm lateral and 1 cm caudal to the caudal edge of the more superior spinous process, 10 to 15° off the sagittal plane in the cephalomedial plane.27 After injection, the intervertebral level at which the injection was administered was identified by ultrasound.
In both groups, strict aseptic techniques were used throughout the procedure. Spinal anaesthesia was administered using a 25-gauge Quincke bevel spinal needle (TaeChang Industrial Co., Gongju, Republic of Korea). After confirming the backflow of clear cerebrospinal fluid, 0.5% heavy bupivacaine was injected intrathecally, with the dose determined at the discretion of the anaesthesiologist who was also allowed to give 20 μg of intrathecal fentanyl. The operator could use alternative techniques (ultrasound group, midline approach/landmark palpation; landmark group, midline approach/ultrasound-assisted technique) if dural puncture was not achieved after five attempts.
The primary outcome was the number of needle passes (defined as the number of forward advancements of the needle, or the number of needle redirections without exiting the skin, including first pass).
Secondary outcomes included the following:
- Number of needle-insertion attempts (separate skin punctures).
- Time for identifying landmarks (ultrasound group: time from the first placement of the probe on the skin to the operator's declaration of completion of skin marking; landmark group: time from the first touch for palpation to completion of palpation).
- Time for administering spinal anaesthesia (the time from needle insertion to either completion of intrathecal local anaesthetic administration by the allocated method or the anaesthesiologist's declaration to use an alternative method).
- Incidence of radicular pain, paraesthesia and blood tap by the spinal needle.
- Periprocedural pain score on an 11-point numeric scale (0, no pain; 10, worst pain imaginable).
- Periprocedural discomfort score on an 11-point numeric scale (0, no discomfort; 10, worst discomfort imaginable).
- Level of sensory block tested by loss of cold sensation.
The outcomes were evaluated by two independent observers. Because of the skin markings in the ultrasound group, the primary observer who assessed outcomes during administration of spinal anaesthesia could not be blinded to group allocation. However, the second observer, who measured the level of block, periprocedural pain and discomfort scores, entered the operating room only after the designated procedure was completed and was blinded to group allocation. Patients were specifically asked to rate the pain in their back during administration of spinal anaesthesia. After rating their pain scores, patients were asked to rate their discomfort during the entire neuraxial procedure, including that due to positioning or anxiety as a whole. The numbers of passes and attempts were recorded until either completion of spinal anaesthesia or a change to an alternative technique.
Based on a previous study, we assumed the average number of passes (mean ± SD) for an experienced anaesthesiologist to be 3.3 ± 3.1.28 We hypothesised that ultrasound assistance would decrease the number to 1.3.3 To achieve a power of 0.8 and an alpha error less than 0.05, 38 patients were needed in each group. To allow for dropout, 40 were randomised to each group.
Data were analysed using SPSS Statistics for Windows (version 23.0; IBM Corp., Armonk, New York, USA) and R software (version 3.1.0; R Foundation for Statistical Computing, Vienna, Austria). All data were analysed on an intention-to-treat basis. Continuous data were tested for normality using the Kolmogorov–Smirnov test. Normally distributed data (mean ± SD) were compared using Student's t test. Nonnormally distributed data (median [interquartile range]) were compared using the Mann–Whitney U test. Among nonnormally distributed data, the numbers of passes and attempts, time variables, pain and discomfort scores were reported with minimum and maximum values. Categorical data [n (%)] were compared using the χ2 or Fisher's exact test, as appropriate. For the success rates for selected numbers of attempts and passes, the 95% confidence intervals (95% CIs) of differences in proportion between the two groups were calculated. The relative risk of binary variables was presented with 95% CI. Two-tailed P values less than 0.05 were considered statistically significant.
Of 101 patients who were assessed for eligibility, 80 patients, aged 71.1 ± 6.6 years, were randomised and completed the study (Fig. 3). The baseline characteristics of the two groups were comparable (Table 1). The median numbers of passes (1.0 vs. 4.5) and attempts (1.0 vs. 1.5) required for dural puncture were both significantly lower in the ultrasound group than in the landmark group (both P < 0.001; Table 2). The rates of successful dural puncture at first pass (65.0 vs. 17.5%) and first attempt (90 vs. 50%) were significantly greater in the ultrasound group than in the landmark group (both P < 0.001; Table 2). For all patients in the ultrasound group, dural puncture was successful within two attempts. In the 35% of patients in the ultrasound group who required needle redirection, the redirections involved mostly a few adjustments of the medial–lateral angulation. There was no evidence of interoperator differences in number of passes/attempts (Supplemental Table S1, http://links.lww.com/EJA/A209).
Compared with palpation, ultrasonography required significantly more time to establish landmarks but less time to administer spinal anaesthesia (Table 2). In total, the median total procedure time was significantly longer in the ultrasound group than in the landmark group. Patients in the ultrasound group reported significantly lower periprocedural pain and block-associated discomfort scores than those in the landmark group (Table 2).
In the landmark group, five patients required alternative techniques (midline approach, one; ultrasound-assisted technique, four) for successful dural puncture (Supplemental Table S2, http://links.lww.com/EJA/A209). None of the patients in the ultrasound group required an alternative technique. There was no significant difference between the two groups in the incidence of radicular pain, paraesthesia or bloody tap (Supplemental Table S2, http://links.lww.com/EJA/A209). These patients were followed up for 24 h after surgery, and none exhibited persistent symptoms. None of the patients in either group required general anaesthesia, and spinal block was adequate for the entire procedure.
There were significant intergroup differences in the intervertebral level of anaesthesia administration (P = 0.005; Table 3). Approximately half of the patients in the landmark group had surface landmarks that were easily palpated (47.5%; Supplemental Table S3, http://links.lww.com/EJA/A209). In the ultrasound group, PSO images had better quality than transverse midline images (Supplemental Table S3, http://links.lww.com/EJA/A209).
The current study shows that the ultrasound-assisted paramedian technique reduces the technical difficulty of spinal anaesthesia in the elderly. Compared with the landmark-guided paramedian technique, the use of ultrasound reduced the number of needle manipulations required for success, increased the first-attempt success rate and reduced block-associated pain and discomfort.
Information on the comparative efficacies of the ultrasound-assisted and landmark-guided paramedian techniques for spinal anaesthesia has been lacking. A previous clinical study3 showed the ultrasound-assisted paramedian technique had fewer needle manipulations compared with the landmark-guided midline approach in orthopaedic patients (age 64.3 ± 12.8 years).3 However, as there were several reports that the paramedian approach was superior to the midline in the elderly,22,23,29,30 we considered that the direct comparison of ultrasound-assisted paramedian approach with landmark-guided paramedian approach was required to verify the advantage of ultrasonography in this group. We deliberately used the paramedian approach in the landmark group because we considered that there was sufficient evidence supporting the use of the paramedian approach in the elderly.22,23,29,30 As a result, our data strongly indicate an advantage in ultrasound assistance for spinal anaesthesia in the elderly. Our findings are consistent with the earlier study which showed that ultrasound imaging increase the first-attempt success rate of combined spinal–epidural anaesthesia in the elderly.31
Although ultrasound assistance reduces the technical difficulty in patients with difficult surface anatomy,2,15 studies in pregnant women with easily palpable spines18 and in surgical patients in general population16,19 have shown no benefit. Recently, Chin et al.20 have suggested that ultrasound assistance is beneficial for neuraxial anaesthesia in pregnant women with easily palpable spines. The current study participants had low BMI and no spinal deformities and, although 77.5% of patients in the landmark group had easily or moderately easily palpated surface landmarks, the performance in this group was poorer than that in the ultrasound group. Our results suggest that old patients with easily palpable landmarks can benefit from neuraxial ultrasound.
Although several studies have reported improved patient satisfaction with ultrasound,16,21,32 others have found no significant improvement.3,18,20 We observed significantly lower periprocedural pain and discomfort in the ultrasound group than in the landmark group. Our results indicate that ultrasound-assistance significantly promotes patient comfort during spinal anaesthesia compared with the conventional technique. Although the total procedure time was longer in the ultrasound group, we consider it may not be clinically relevant when weighed against the benefits in patient comfort. In addition, we suggest that total procedure time can be much shortened if skin marking is done only at the intervertebral level with the widest interlaminar space that will be used for actual approach.
The ultrasound-assisted paramedian technique in this study appeared to be highly efficient for the following probable reasons. First, ultrasonography can be used to overcome the technical drawbacks of the paramedian approach. Although the paramedian route allows a larger permeable window than the midline route in patients with narrow interspaces,29,33 it requires greater three-dimensional insight29 and entails greater intersubject variability in optimal insertion point and angle. By using ultrasound, the approach can be individually planned. Second, the paramedian approach could potentially be easier than the midline approach because PSO views offer a better sonographic view than transverse midline views.3,33 Third, the paramedian approach was accomplished without cephalad angulation because we considered it to be the most direct way of translating ultrasound waves into the needle trajectory. We visualised the window that permitted the ultrasound waves to reach the intrathecal space and inserted a needle through the optimal window. Our results indicate that this method is highly effective and not associated with any complications. Lastly, we believe that individualisation is a key element of minimising technical difficulties. Because of the large intersubject variability in anatomy, generic approaches using the ‘blind’ technique have an inherent theoretical upper limit of success rate.7 The only way to improve upon these limits is to use individualised planning or guidance methods.7 Through individualised planning, we obtained success rates of 90 and 100% at the first attempt and within two attempts, respectively, in the ultrasound group.
Arguably, the question of cephalad angulation in the ultrasound-assisted paramedian technique needs discussion in more detail. As Chin34 describes in their recent review, the optimal paramedian approach was considered to involve some cephalad angulation. In this ‘paraspinous’ approach, the needle insertion site should be slightly inferior to the transverse plane.34,35 However, we had intentionally chosen an ultrasound-assisted paramedian approach without cephalad angulation for the reasons mentioned above, and the insertion point and needle trajectory were on the same transverse plane in the middle of the interlaminar space. The paramedian approach can be unsatisfactory when the insertion site is too lateral to the midline, making the estimation of correct needle trajectory difficult.35 Thus, care was given to ensure the insertion point was not too far from the neuraxial midline in the current study. As a result, the median distance between the midline and the insertion point was 1.7 cm in the ultrasound group. This may partly explain why our results were favourable to the ultrasound group and differed from the results of Lim et al.,16 although they did not mention cephalad angulation. However, it should be noted that some cephalad angulation with the needle insertion site slightly inferior to the transverse plane might be helpful in patients with severely narrowed interspaces where an adequate sonographic transverse view into vertebral canal cannot be obtained.35
The L5/S1 interspace is the widest interlaminar space and is least affected by degenerative changes36 or poor positioning.19,37,38 In our study, most patients in the ultrasound group (57.5%) successfully received spinal anaesthesia at the L5/S1 interspace, which was also the level selected for the first attempt after ultrasound imaging. In contrast, fewer patients in the landmark group (19.4%) received spinal anaesthesia at the L5/S1 interspace. A previous study reported a nonsignificant trend towards a lower number of passes at the L5/S1 interspace than at other levels.3,19 However, a randomised study that compared the ultrasound-assisted technique at the L5/S1 interspace with the landmark-guided technique did not find any benefit with the former in terms of number of needle manipulations.19 Therefore, one of the most important benefits of using neuraxial ultrasound might be the identification of the widest intervertebral level, pointing the anaesthesiologist to the best level for a successful first attempt. In our study, dural puncture in the ultrasound group was easier than that in the landmark group, not because the level was at the L5/S1 interspace, but because it was individually selected after imaging each patient's own anatomy.
The current study has several limitations. First, neither the primary outcome assessor nor operator could be blinded to group allocation because of the nature of the study. Second, we did not employ a real-time ultrasound-guided technique because it remains experimental.13,14 We chose the preprocedural ultrasound-assisted technique instead, because we considered it to be more easily applicable in more hospitals and under differing circumstances. Third, the preprocedural technique has an inherent degree of inaccuracy owing to the use of a curved-array probe and the presence of loose skin in elderly subjects. Moreover, in this study, the angle of insertion relied on the memory of the anaesthesiologist and not on the measurements. Further studies are required to evaluate whether the real-time technique despite its technical complexities, can overcome this drawback of preprocedural scanning.1,3,12 Fourth, the study subjects were mostly women with relatively low BMI, and this might undermine the generalisability of our results. Lastly, because the grade of the ease of palpation was not recorded in the ultrasound group, we were unable to compare the quality of surface landmarks between the groups.
In conclusion, ultrasound-assisted paramedian spinal anaesthesia significantly reduces the number of needle manipulations required for success, increases the success rate at first pass and decreases periprocedural pain and patient discomfort compared with the landmark-guided paramedian technique in the elderly. Our results suggest that the neuraxial ultrasonography enhances the efficacy and comfort of spinal anaesthesia in the elderly.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: none.
Conflicts of interest: none.
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