European Journal of Cardiovascular Medicine

Subarachnoid block remains one of the most commonly employed regional anaesthetic techniques for surgeries involving the lower abdomen and lower limbs. Its popularity is attributed to rapid onset, reliable sensory and motor blockade, minimal drug requirements, and reduced systemic complications when compared to general anaesthesia.[1] However, successful spinal anaesthesia depends largely on accurate identification of lumbar intervertebral spaces and correct needle placement. This task becomes challenging in patients with poorly palpable anatomical landmarks due to obesity, advanced age, degenerative spinal changes, or increased subcutaneous tissue.[2]

Conventional landmark guided spinal anaesthesia relies on palpation of surface landmarks such as the iliac crest and spinous processes. In patients with obscured landmarks, this approach often results in multiple needle passes and attempts, which may cause patient discomfort and increase the risk of complications including post dural puncture headache, paraesthesia, spinal hematoma, and backache.[3,4] Repeated redirection of the spinal needle has also been associated with increased procedural failure rates and reduced patient satisfaction.[5]

The paramedian approach to spinal anaesthesia bypasses the supraspinous and interspinous ligaments and may offer technical advantages in patients with degenerative changes or calcified ligaments.[6] Despite this, accurate localization of the interlaminar space remains difficult when surface landmarks are poorly palpable. In recent years, ultrasonography has emerged as a useful adjunct for neuraxial procedures by allowing visualization of vertebral anatomy, identification of interlaminar spaces, and estimation of needle depth.[7,8]

Preprocedural ultrasound guidance has been shown to improve first attempt success and reduce needle passes in midline spinal anaesthesia.[9,10] However, evidence regarding its utility in paramedian spinal anaesthesia, particularly in patients with difficult surface anatomy, remains limited. The paramedian sagittal oblique ultrasound view offers a consistent acoustic window for identifying the interlaminar space and may be especially beneficial in such patients.[11,12]

This study was undertaken to compare ultrasound aided and landmark guided paramedian spinal anaesthesia in patients with poorly palpable anatomical landmarks, with emphasis on procedural efficacy and performance characteristics.

This prospective randomized controlled study was conducted after obtaining institutional ethical committee approval. Fifty adult patients aged between 18 and 80 years with poorly palpable lumbar anatomical landmarks scheduled for elective surgery under spinal anaesthesia were enrolled after obtaining informed consent. Patients with infection at the puncture site, coagulopathy, severe spinal deformity requiring alternate techniques, or refusal for spinal anaesthesia were excluded. Poorly palpable landmarks were defined as moderate or difficult palpation based on a four point palpation scale assessed by the attending anaesthesiologist. Sample size was calculated based on expected differences in number of needle passes from previous literature, with power of 80 percent and alpha error of 0.05. Patients were randomized using sealed envelope technique into two groups. Group A (Landmark Guided) included 25 patients who received landmark guided paramedian spinal anaesthesia. Group B (Ultrasound Guided) included 25 patients who received ultrasound aided paramedian spinal anaesthesia. In the landmark guided group, spinal anaesthesia was performed using the conventional paramedian approach after palpation of surface landmarks. In the ultrasound guided group, preprocedural lumbar spine ultrasonography was performed in the sitting position using a curvilinear transducer. The optimal interlaminar space and needle insertion point were identified and marked before performing paramedian spinal anaesthesia. The number of needle passes, number of attempts, time for landmark identification, time for administration of spinal anaesthesia, and total procedural time were recorded. Complications and periprocedural discomfort were also noted. Statistical analysis was performed using IBM SPSS version 24. Continuous variables were expressed as mean and standard deviation and categorical variables as frequency and percentage. Independent sample t test and chi square test were used for group comparisons. A p value less than 0.05 was considered statistically significant.

All 50 randomized patients completed the study. Baseline demographic and clinical characteristics were similar between groups. Mean age in group LG was 61.2 ± 9.8 years and in group UG was 60.1 ± 10.4 years (p = 0.68). There were 16 males (64 percent) in group LG and 17 males (68 percent) in group UG (p = 0.75). Mean body mass index was 27.8 ± 3.6 kg/m2 in group LG and 28.2 ± 4.1 kg/m2 in group UG (p = 0.68). ASA physical status distribution was comparable with the majority ASA II in both groups.

Mean number of needle passes was 2.52 ± 1.36 in group LG compared with 1.44 ± 0.58 in group UG, and this difference was statistically significant (p = 0.003). First attempt success was observed in 10 of 25 patients (40.0 percent) in group LG and 19 of 25 patients (76.0 percent) in group UG (p = 0.006). Mean number of attempts was 1.77 ± 0.83 in group LG and 1.10 ± 0.31 in group UG (p < 0.001).

Mean time for landmark identification was 17.9 ± 3.2 seconds in the landmark guided group and 109.8 ± 17.6 seconds in the ultrasound guided group (p < 0.001). Mean time for administering spinal anaesthesia was 90.8 ± 34.1 seconds in group LG and 54.6 ± 13.2 seconds in group UG (p < 0.001). Mean total procedural time, calculated as identification plus administration time, was 108.7 ± 36.9 seconds in group LG and 164.4 ± 25.9 seconds in group UG (p < 0.001).

Complication rates were low; there were two bloody taps in group LG and one in group UG, one transient paresthesia in group LG and none in group UG, and no major neurological complications. Periprocedural discomfort scores were not significantly different between groups.

In this randomized study of 50 patients with poorly palpable anatomical landmarks, ultrasound aided paramedian spinal anaesthesia resulted in fewer needle passes, higher first attempt success, and shorter time to intrathecal access compared with landmark guided paramedian spinal anaesthesia, although ultrasound increased the time required for landmark identification and therefore prolonged total procedural time. Mean needle passes were 1.44 in the ultrasound group versus 2.52 in the landmark group, and first attempt success rates were 76.0 percent and 40.0 percent respectively. These findings support existing evidence that preprocedural ultrasonography improves the technical performance of neuraxial blocks in patients with difficult anatomy.

Park and colleagues conducted a randomized trial in 80 elderly patients comparing ultrasound assisted and landmark guided paramedian techniques, reporting a median of 1.0 needle pass in the ultrasound group versus 4.5 in the landmark group, and first pass success rates of 65.0 percent versus 17.5 percent respectively, with longer identification but shorter administration times in the ultrasound group.[13] Our study demonstrates the same directional benefit, although absolute values differ because Park et al. studied older patients and reported medians with interquartile ranges. Their median identification times of 117.5 seconds for ultrasound and 17.5 seconds for landmark guidance closely parallel our mean values of 109.8 and 17.9 seconds, suggesting comparable scanning effort and localization accuracy.[13]

Chin and colleagues similarly reported that preprocedural ultrasound in adults with difficult surface landmarks increased scanning time but reduced spinal administration time, particularly in patients with high BMI or poorly palpable landmarks.[9] Their administration times of 5.0 minutes in the ultrasound group versus 7.3 minutes in the landmark group are consistent with our findings, although our timings were recorded in seconds, reinforcing that ultrasound facilitates faster intrathecal access once the optimal site is identified.[9]

Qu et al. evaluated a modified ultrasound assisted paramedian technique in elderly patients with hip fractures and reported first attempt success rates of 85 percent in the ultrasound group versus 42.5 percent in the landmark group, with fewer attempts overall.[10] Their results are comparable to our first attempt success of 76.0 percent and further support the effectiveness of ultrasound in anatomically difficult patients. Larger randomized trials by Zeng et al. also demonstrated significant reductions in attempts and improved first pass success with ultrasound guided paramedian approaches.[11] Srinivasan et al. reported similar reductions in needle passes when comparing landmark midline and preprocedural ultrasound guided paramedian techniques, indicating that ultrasound is beneficial even when applied before a paramedian approach.[12]

Rizk et al. studied novice residents performing spinal anaesthesia in elderly patients and found that ultrasound did not uniformly improve outcomes across all subgroups, highlighting the influence of operator experience and the learning curve associated with neuraxial ultrasonography.[14] In contrast, ultrasound scanning in our study was performed by experienced anesthesiologists, which likely contributed to the higher first attempt success observed.

Regarding timing, Park et al. showed that ultrasound prolonged landmark identification but shortened spinal administration time, with total procedure time remaining longer in the ultrasound group.[13] Our results mirror this pattern, with longer identification times but shorter administration times in the ultrasound group. The smaller magnitude of administration time reduction in our study may reflect differences in operator technique, needle type, or patient characteristics, but the direction of effect is consistent.

Complication rates were low and comparable between groups, aligning with previous randomized studies reporting similar or slightly improved safety profiles with ultrasound guidance.[9,10,11,13] The low incidence of bloody tap and transient paresthesia suggests that ultrasound did not increase adverse events and may reduce needle related trauma by limiting repeated attempts.

Limitations

Limitations of this study include longer total procedural time with ultrasound, which may affect workflow in high volume settings, and limited generalizability to operators without ultrasound experience. The sample size was sufficient to detect differences in technical outcomes but not rare complications. Future studies should focus on training strategies to reduce the ultrasound learning curve and evaluate the cost effectiveness of routine neuraxial ultrasound in patients with difficult surface anatomy.

Ultrasound aided paramedian spinal anaesthesia significantly reduces the number of needle passes and improves first attempt success in patients with poorly palpable anatomical landmarks. Despite requiring additional time for landmark identification, ultrasound guidance offers clear procedural advantages and should be considered a valuable adjunct in difficult spinal anaesthesia.

[1]           Auroy Y, Narchi P, Messiah A, et al. Serious complications related to regional anesthesia. Anesthesiology 1997;87:479-86.

[2]           Broadbent CR, Maxwell WB, Ferrie R, et al. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia 2000;55:1122-6.

[3]           Turnbull DK, Shepherd DB. Post-dural puncture headache. Br J Anaesth 2003;91:718-29.

[4]           Horlocker TT. Complications of spinal and epidural anesthesia. Anesthesiol Clin North America 2000;18:461-85.

[5]           Vallejo MC. Anesthetic management of the obese patient. Int Anesthesiol Clin 2007;45:61-76.

[6]           Rabinowitz A, Bourdet B, Minville V, et al. The paramedian technique: a superior initial approach to continuous spinal anesthesia in the elderly. Anesth Analg 2007;105:1855-7.

[7]           Grau T, Leipold RW, Horter J, et al. The lumbar epidural space: an ultrasound study. Anesth Analg 2001;92:1270-4.

[8]           Grau T, Bartusseck E, Conradi R, et al. Ultrasound imaging improves neuraxial block success. Reg Anesth Pain Med 2003;28:544-9.

[9]           Chin KJ, Perlas A, Chan V, et al. Ultrasound imaging facilitates spinal anesthesia in adults with difficult surface anatomic landmarks. Anesthesiology 2011;115:94-101.

[10]         Qu B, Chen L, Zhang Y, et al. Landmark-guided versus modified ultrasound-assisted paramedian techniques in combined spinal-epidural anesthesia for elderly patients with hip fractures: a randomized controlled trial. BMC Anesthesiol 2020;20:248.

[11]         Zeng W, Shi Y, Zheng Q, Du S. Ultrasound-assisted modified paramedian technique for spinal anesthesia in elderly. BMC Anesthesiol 2022;22:242.

[12]         Karmakar MK, Li X, Kwok WH, et al. Sonoanatomy and practical use of paramedian sagittal oblique view for neuraxial blockade. Br J Anaesth 2012;109:130-6.

[13]         Park SK, Yoo S, Kim WH, et al. Ultrasound-assisted versus conventional landmark-guided paramedian spinal anaesthesia in the elderly: a randomized controlled trial. Eur J Anaesthesiol 2019;36:763-71.

[14]         Rizk MS, Zeeni CA, Bouez JN, et al. Preprocedural ultrasound versus landmark techniques for spinal anesthesia performed by novice residents in elderly: a randomized controlled trial. BMC Anesthesiol 2019;19:208.