Strategies for Successful Lumbar Neuraxial Anaesthesia and Analgesia in Patients with Challenging Anatomy

Learning objectivesBy reading this article you should be able to:•Describe the technical performance and patient-centred benefits of the paraspinous approach to lumbar neuraxial anaesthesia.•Discuss the application of spinal ultrasound imaging to the paraspinous approach and real-time ultrasound-guided techniques.•Develop strategies to increase success in performing spinal anaesthesia in challenging scenarios, such as patients with degenerative spinal disease, suboptimal positioning, obesity and scoliosis.Key points•Poorly palpable spinous processes or narrowed interspinous spaces can make a midline approach to lumbar neuraxial blockade challenging.•A paraspinous approach to spinal analgesia and anaesthesia can increase the success rate and reduce complications.•Ultrasound imaging before the procedure facilitates both midline and paraspinous approaches.•Real-time ultrasound-guided neuraxial anaesthesia is feasible but requires advanced imaging and needling skills.•The L5–S1 interlaminar space is widest and often remains patent in spinal disease. By reading this article you should be able to:•Describe the technical performance and patient-centred benefits of the paraspinous approach to lumbar neuraxial anaesthesia.•Discuss the application of spinal ultrasound imaging to the paraspinous approach and real-time ultrasound-guided techniques.•Develop strategies to increase success in performing spinal anaesthesia in challenging scenarios, such as patients with degenerative spinal disease, suboptimal positioning, obesity and scoliosis. •Poorly palpable spinous processes or narrowed interspinous spaces can make a midline approach to lumbar neuraxial blockade challenging.•A paraspinous approach to spinal analgesia and anaesthesia can increase the success rate and reduce complications.•Ultrasound imaging before the procedure facilitates both midline and paraspinous approaches.•Real-time ultrasound-guided neuraxial anaesthesia is feasible but requires advanced imaging and needling skills.•The L5–S1 interlaminar space is widest and often remains patent in spinal disease. Lumbar neuraxial anaesthesia is a core skill for all anaesthetists. It is associated with improved outcomes compared with general anaesthesia in surgeries such as hip and knee arthroplasty.1Memtsoudis S.G. Cozowicz C. Bekeris J. et al.Anaesthetic care of patients undergoing primary hip and knee arthroplasty: consensus recommendations from the International Consensus on Anaesthesia-Related Outcomes after Surgery group (ICAROS) based on a systematic review and meta-analysis.Br J Anaesth. 2019; 123: 269-287Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar These outcomes include lower risks of pulmonary and renal complications, venous thrombosis, blood transfusion and possibly mortality.1Memtsoudis S.G. Cozowicz C. Bekeris J. et al.Anaesthetic care of patients undergoing primary hip and knee arthroplasty: consensus recommendations from the International Consensus on Anaesthesia-Related Outcomes after Surgery group (ICAROS) based on a systematic review and meta-analysis.Br J Anaesth. 2019; 123: 269-287Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar However, multiple factors can contribute to technical difficulty, including spinal degenerative disease, scoliosis, obesity, previous spinal surgery, and hindrances to optimal positioning of the patient. A large multicentre randomised controlled trial (RCT) in hip fracture surgery, a group that embodies many of these factors, reported a failure rate of 8.6% with spinal anaesthesia.2Neuman M.D. Feng R. Carson J.L. et al.Spinal anesthesia or general anesthesia for hip surgery in older adults.N Engl J Med. 2021; 385: 2025-2035Crossref PubMed Scopus (186) Google Scholar This article presents high yield strategies for successful neuraxial anaesthesia in the patient with challenging anatomy, specifically the paraspinous or paramedian approach and the application of spinal ultrasound imaging. Whereas the focus is on spinal anaesthesia, the principles for successful needle insertion into the interlaminar space can be extrapolated to lumbar epidural anaesthesia. Fluoroscopic guidance has also been described to assist with difficult spinal anaesthesia, but this is limited to one case report.3Eidelman A. Shulman M.S. Novak G.M. Fluoroscopic imaging for technically difficult spinal anesthesia.J Clin Anesth. 2005; 17: 69-71Crossref PubMed Scopus (14) Google Scholar It is not feasible in labour epidural analgesia because of the radiation exposure, and its main role in anaesthesia to date has been to assist thoracic epidural catheter insertion. One RCT demonstrated that fluoroscopy increased correct catheter placement within the thoracic epidural space from 74% to 98% compared with the conventional loss-of-resistance technique alone.4Parra M.C. Washburn K. Brown J.R. et al.Fluoroscopic guidance increases the incidence of thoracic epidural catheter placement within the epidural space: a randomized trial.Reg Anesth Pain Med. 2017; 42: 17-24Crossref PubMed Scopus (32) Google Scholar Fluoroscopic guidance in lumbar neuraxial anaesthesia is likely to remain a niche application as it requires a degree of expertise not possessed by most anaesthetists unless trained in chronic pain interventions, and we therefore consider it outside the scope of this article. The fundamental reason for using the paraspinous approach is to avoid having to locate and traverse the midline interspinous space accurately. This space can be difficult to identify in patients with poor-quality surface landmarks, or it may be narrowed by degenerative disease and inadequate lumbar flexion resulting from suboptimal positioning. It is thus a useful technique where these considerations apply, and a valuable fallback option if there is persistent bony contact when attempting a midline needle approach. We favour the term paraspinous instead of paramedian in describing the needle approach as it emphasises a critical principle that simplifies the technique and increases success: insert the needle close to the midline (spinous process) at a small lateral-to-medial angle.5Veering B.T. Cousins M.J. Epidural neural blockade.in: Cousins M.J. Bridenbaugh P.O. Carr D.B. Horlocker T.T. Cousins and Bridenbaugh's neural blockade in clinical anesthesia and pain medicine. 4th Edn. Lippincott Wilkins & Williams, Philadelphia2008: 241-295Google Scholar,6Chin K.J. Perlas A. Chan V. The ultrasound-assisted paraspinous approach to lumbar neuraxial blockade: a simplified technique in patients with difficult anatomy.Acta Anaesthesiol Scand. 2015; 59: 668-673Crossref PubMed Scopus (13) Google Scholar This is a subtle but important variation on the traditional paramedian approach, which is often taught as needle insertion in a lateral-to-medial direction starting at a skin insertion site up to 2 cm or a fingerbreadth away from the midline.7Puigdellívol-Sánchez A. Reina M.A. Sala-Blanch X. et al.Pythagoras and cosines: the skin-dural sac distance and optimal angles in paramedian spinal anesthesia.Clin Anat. 2016; 29: 1046-1052Crossref PubMed Scopus (5) Google Scholar However it then becomes challenging to triangulate the needle trajectory accurately in order to enter the interlaminar space, as the appropriate angle varies both with this distance and the depth to the space. Without knowledge of the depth to the space, the anaesthetist is faced with a wide range of potential lateral-to-medial angles to choose from during initial insertion and subsequent redirections. Redirection is further complicated by the choice of appropriate cranial angulation. An inappropriate lateral-to-medial angle will potentially contact the bony surface of not just the lamina, but also the spinous process (too medial) or the articular processes (too lateral) (Fig. 1). Distinguishing between these bony structures based on tactile feedback can be challenging for novice anaesthetists. They may not appreciate the difference in needle insertion depth when contacting the side of the spinous process (shallower) vs the lamina (deeper), or the significance of back pain localised to one side that often accompanies needle contact with the articular processes and facet joint. An inability to make a reasoned deduction as to what bony structure is being contacted by the needle will hamper decision-making around corrections to needle trajectory on subsequent passes. As the entire premise of the paraspinous approach is merely to avoid the midline interspinous space, the needle only needs to be inserted immediately lateral to the spinous process. By starting much closer to the midline, the lateral-to-medial angle can be kept small, allowing the needle to slide alongside the spinous process. We recommend a skin insertion site no more than 0.5–1 cm lateral to the midline and a lateral-to-medial angle of 5–15°, typically about 10°. In this trajectory, depending on the transverse plane of the skin insertion site relative to the interlaminar space, the needle tip will either (i) pass directly from paraspinous muscle into the ligamentum flavum, a transition that is clearly signalled by a distinct and characteristic change in tactile feedback from the soft buttery feel of muscle to the firm rubbery resistance of ligamentum flavum; or (ii) contact a bony surface, which will almost inevitably be the vertebral lamina (Fig. 1). In the latter instance, incremental cranial angulation will walk the needle tip off the superior edge of the lamina and into the ligamentum flavum, which will again be clearly signalled by its feel and ability to advance the needle deeper. The advantage of the paraspinous approach compared with the traditional paramedian technique was demonstrated in a magnetic resonance imaging study, which found that a skin insertion site 1 cm lateral to the midline, instead of 2 cm, resulted in less variation in the optimal lateral-to-medial angle of insertion with increasing depth to the subarachnoid space.7Puigdellívol-Sánchez A. Reina M.A. Sala-Blanch X. et al.Pythagoras and cosines: the skin-dural sac distance and optimal angles in paramedian spinal anesthesia.Clin Anat. 2016; 29: 1046-1052Crossref PubMed Scopus (5) Google Scholar Successful needle entry at the usual depths from skin to the vertebral canal (4–8 cm in adults) could be achieved with a narrower range of lateral-to-medial angles (5–15o), thus reducing the guesswork involved in selecting an appropriate trajectory (Fig. 2). This principle was confirmed by a large RCT that found significantly higher first-attempt success rates of lumbar spinal (59% vs 20%), epidural (65% vs 14%) and combined spinal-epidural (CSE) blockade (47% vs 15%) among trainees who utilised a needle insertion point 0.5 cm lateral to the midline vs 1 cm lateral.8Chen S.H. Chen S.S. Lai C.L. et al.Modified paramedian versus conventional paramedian technique in the residency training: an observational study.BMC Med Educ. 2020; 20: 211Crossref PubMed Scopus (6) Google Scholar In the the epidural and CSE groups that used the closer insertion point of 0.5 cm there was also a lower complication rate (composite of post-dural puncture headache, infection, haematoma) and lower rates of epidural catheter-related mishaps (difficulty threading, dural puncture, intravascular placement).8Chen S.H. Chen S.S. Lai C.L. et al.Modified paramedian versus conventional paramedian technique in the residency training: an observational study.BMC Med Educ. 2020; 20: 211Crossref PubMed Scopus (6) Google Scholar In summary, inserting the needle closer to the midline demands less precision when considering an appropriate lateral-to-medial angle, thus simplifying the technique and increasing the odds of success. In addition to the benefits described above, technical advantages of the paraspinous approach over the midline approach have been demonstrated, particularly in older patients who are more likely to have narrowed interspinous spaces. In particular, lumbar epidural catheters were easier to insert with less frequent paraesthesia.9Leeda M. Stienstra R. Arbous M.S. et al.Lumbar epidural catheter insertion: the midline vs. the paramedian approach.Eur J Anaesthesiol. 2005; 22: 839-842Crossref PubMed Scopus (28) Google Scholar A study using epiduroscopy in cadavers found that epidural catheters inserted in a midline approach caused more dural tenting and tended to deviate laterally or turn caudally, whereas paraspinous catheters threaded more consistently in a cranial direction.10Blomberg R. Technical advantages of the paramedian approach for lumbar epidural puncture and catheter introduction. A study using epiduroscopy in autopsy subjects.Anaesthesia. 1988; 43: 837-843Crossref PubMed Scopus (56) Google Scholar Possible reasons for these observations include the steeper cranial angle of insertion usually used with the paraspinous approach vs the more perpendicular angle of a midline approach, and the presence of posterior epidural ligaments that may impede midline catheter advancement. The paraspinous approach may confer additional patient-centred benefits. Randomised controlled trials have shown that back pain after the procedure is less common with the paraspinous vs midline approach.11Lee J.H. Yoon D.H. Heo B.H. Incidence of newly developed postoperative low back pain with median versus paramedian approach for spinal anesthesia.Korean J Anesthesiol. 2020; 73: 518-524Crossref PubMed Scopus (7) Google Scholar,12Singh B. Sohal A.S. Singh I. et al.Incidence of postspinal headache and low backache following the median and paramedian approaches in spinal anesthesia.Anesth Essays Res. 2018; 12: 186-189Crossref PubMed Google Scholar In one study, the overall incidence of back pain after a single pass with a 25 G spinal needle was 16% in the paraspinous group compared with 36% in the midline group.11Lee J.H. Yoon D.H. Heo B.H. Incidence of newly developed postoperative low back pain with median versus paramedian approach for spinal anesthesia.Korean J Anesthesiol. 2020; 73: 518-524Crossref PubMed Scopus (7) Google Scholar This suggests that needle trauma to supraspinous and interspinous ligaments, rather than paraspinal muscles, may be a more important factor in back pain after neuraxial blockade. A lower incidence of post-dural puncture headache has also been observed with the paraspinous vs midline approach.12Singh B. Sohal A.S. Singh I. et al.Incidence of postspinal headache and low backache following the median and paramedian approaches in spinal anesthesia.Anesth Essays Res. 2018; 12: 186-189Crossref PubMed Google Scholar In an RCT of 100 patients undergoing spinal anaesthesia with a 25 G needle for lower abdominal surgery, the incidence of mild-moderate headache over the following 7 days was 4% when a paraspinous approach was used vs 20% with a midline approach.12Singh B. Sohal A.S. Singh I. et al.Incidence of postspinal headache and low backache following the median and paramedian approaches in spinal anesthesia.Anesth Essays Res. 2018; 12: 186-189Crossref PubMed Google Scholar It is postulated that the cranial angulation of the needle in a paraspinous approach results in perforations of the ligamentum flavum, the densely multilayered dura mater and the arachnoid mater, that are slightly offset relative to each other. As a result, the edges of each layer overlap one another, creating a flap-valve effect that minimises cerebrospinal fluid (CSF) leakage. There are four fundamental steps to the anatomical surface landmark-guided paraspinous approach. The ultrasound-assisted method is described in a later section.(i)Determine the needle insertion site.(a)Establish the position of the tips of the lumbar spinous processes and the interspinous spaces by palpation. Choose a desired interspinous space and palpate the superior border of the lower spinous process.(b)We recommend using two fingers of the non-dominant hand for palpation, rolling the fingertips over the protrusions of the spinous processes and down into the depressions of the intervening interspinous spaces. The fingers are then separated slightly to straddle the width of the spinous process tips and chosen interspinous space, and to stabilise the overlying skin relative to the bony landmarks.(c)The appropriate needle insertion site is in the same transverse plane as the superior border of the lower spinous process, and ∼0.5–1 cm lateral to the neuraxial midline—the midpoint of your fingertip is a useful marker for judging this distance (Fig. 3).(ii)Scout the planned trajectory of the spinal needle with the local anaesthetic skin infiltration needle.(a)Infiltrate the skin and deeper underlying paraspinal muscles with local anaesthetic along the planned trajectory of the spinal needle. There should be no resistance to injection or advancement. Readjust the needle insertion site and angle as needed if the tip engages the bony spinous process or midline ligaments rather than passing smoothly through muscle.(iii)Insert the introducer or spinal needle with an initial trajectory comprising a lateral-to-medial angle of ∼10° with little to no cranial angulation (Fig. 4).(a)There should be a characteristic soft feel as the needle tip advances through paraspinal muscle. This will be followed by either a change in tactile feedback to the typical rubbery resistance of ligamentum flavum, or bony contact. If there is bony contact at a shallow depth <3 cm, this is likely to be the lateral aspect of the spinous process and signifies that the lateral-to-medial angle is too large (Fig. 1). Deeper bony contact is almost always the lamina. Gentle contact should not elicit any pain. If the patient reports back pain localised to the side of insertion, this usually represents contact with the ipsilateral facet joint and signifies that the lateral-to-medial angle is too small or that there is a rotational scoliotic deformity.Fig 4The introducer/spinal needle is inserted 0.5–1 cm from the midline in the same transverse plane as the superior edge of the lower spinous process bordering the chosen interspace. The initial needle trajectory should be at a lateral-to-medial angle of approximately 10o, with little-to-no cranial angulation. If the needle tip contacts bone this will almost inevitably be with the lamina of the lower vertebra. The needle should then be re-inserted with small incremental changes in cranial angulation to walk the needle tip off the lamina and into the interlaminar space. This is signalled by a perception of the needle tip advancing deeper and engaging the ligamentum flavum with its characteristic rubbery feel.View Large Image Figure ViewerDownload Hi-res image Download (PPT)(iv)Perform systematic incremental redirections as needed.(a)If the lamina is contacted, the needle should be redirected cranially without altering the lateral-to-medial angle, to walk the tip of the needle off into the interlaminar space. This is signalled by an increase in needle insertion depth and the tactile feedback from penetrating the ligamentum flavum (Fig. 4). It is critical that the redirections are small and incremental to avoid overshooting the interlaminar space. Smaller-gauge needles should be handled carefully to avoid flexion of the needle shaft and inadvertent deviation during advancement. If the patient is in the lateral decubitus rather than the sitting position, the anaesthetist's mental construct is now rotated 90⁰ when computing angles and redirecting the needle. The principles governing site and angle of needle insertion relative to the spine itself remain the same. The needle should be inserted from the dependent side of the body to allow gravity-assisted CSF backflow. Depending on patient position and handedness of the operator, the fingers of the non-needling hand will straddle either the upper or lower spinous process bordering the chosen interspace, as illustrated in Figure 3. Ultrasound imaging before the procedure is very useful in delineating spinal anatomy and thus is invaluable in patients with poorly palpable surface landmarks or anatomical distortion. The standard technique of ultrasound imaging and skin marking for a midline approach is well established and described in detail elsewhere.13Kalagara H. Nair H. Kolli S. et al.Ultrasound imaging of the spine for central neuraxial blockade: a technical description and evidence update.Current Anes Reports. 2021; 11: 326-339Crossref Scopus (9) Google Scholar In this section, familiarity with the basic principles of neuraxial ultrasound is assumed and the focus will be on aspects pertinent to the paraspinous approach. The pre-procedural ultrasound-assisted (PPUSA) paraspinous technique involves using ultrasound imaging to first obtain a parasagittal oblique (PSO) view and perform a qualitative assessment of the patency and size of paraspinous interlaminar spaces on either side, based on the length of the gap between bony lamina shadows and visible anterior complexes (Fig. 5A). Visualisation of an anterior complex confirms that this trajectory will successfully enter the vertebral canal. In patients with narrowed interlaminar spaces, the anterior complex may not be visible. In this same PSO view, the transverse plane of a suitable intervertebral space is marked on the skin. The transverse midline view is then used to identify and mark the location of the spinous processes (Fig. 5B). An appropriate skin insertion point is 0.5–1 cm lateral to the marked midline and 0.5–1 cm caudad to the selected interspace, so that the needle trajectory adheres to the principles outlined in the surface landmark-guided paraspinous approach (Fig. 6).6Chin K.J. Perlas A. Chan V. The ultrasound-assisted paraspinous approach to lumbar neuraxial blockade: a simplified technique in patients with difficult anatomy.Acta Anaesthesiol Scand. 2015; 59: 668-673Crossref PubMed Scopus (13) Google Scholar Needle advancement is guided by tactile feedback as described above.Fig 6Paraspinous approach using pre-procedural ultrasound imaging to identify landmarks. This is especially useful in obese patients as illustrated here. The location of the spinous processes can always be identified by their characteristic hyperechoic tip with acoustic dropout shadow, and then marked on the patient's skin (blue arrows) together with the midline. The interlaminar space should lie somewhere between adjacent spinous processes (red arrow). The appropriate skin insertion point (yellow circle) can be estimated from these marks using the principles described earlier. Incremental cranial angulation, while maintaining a constant lateral-to-medial angle, will walk the needle tip off the lower vertebral lamina and into the interlaminar space.View Large Image Figure ViewerDownload Hi-res image Download (PPT) It is important to note that this method differs significantly from the PPUSA paramedian technique described elsewhere in the literature.14Srinivasan K.K. Iohom G. Loughnane F. et al.Conventional landmark-guided midline versus preprocedure ultrasound-guided paramedian techniques in spinal anesthesia.Anesth Analg. 2015; 121: 1089-1096Crossref PubMed Scopus (56) Google Scholar, 15Srinivasan K.K. Leo A.M. Iohom G. et al.Pre-procedure ultrasound-guided paramedian spinal anaesthesia at L5-S1: is this better than landmark-guided midline approach? A randomised controlled trial.Indian J Anaesth. 2018; 62: 53-60Crossref PubMed Scopus (23) Google Scholar, 16Rizk M.S. Zeeni C.A. Bouez J.N. et al.Preprocedural ultrasound versus landmark techniques for spinal anesthesia performed by novice residents in elderly: a randomized controlled trial.BMC Anesthesiol. 2019; 19: 208Crossref PubMed Scopus (14) Google Scholar, 17Park S.K. Bae J. Yoo S. et al.Ultrasound-assisted versus landmark-guided spinal anesthesia in patients with abnormal spinal anatomy: a randomized controlled trial.Anesth Analg. 2020; 130: 787-795Crossref PubMed Scopus (30) Google Scholar In these studies, a PSO view of the interlaminar space is obtained and the needle insertion site is marked by the intersection point of two lines joining the midpoints of long and short borders of the probe. The lateral-to-medial angulation of the probe is noted for later replication when inserting the needle. The main drawback of this technique is that the large footprint of a curved probe invariably results in a more lateral needle insertion site and a larger lateral-to-medial angle. This re-introduces the challenges of triangulation and correct replication of the angulation of the curvilinear probe that produced the required image, thus increasing the chance of error.18Wardhan R. Smith C.R. A Miss is as good as a mile: ultrasound estimation of needle angulation cannot be overlooked in paramedian spinal approach.Anesth Analg. 2020; 131: e24Crossref PubMed Scopus (2) Google Scholar These challenges may explain conflicting results in the literature. One study reported the PPUSA paramedian technique to be more effective in patients with abnormal spinal anatomy compared with a surface landmark-guided technique using either a midline or paramedian approach (at the operator's discretion) when performed by experienced anaesthetists.17Park S.K. Bae J. Yoo S. et al.Ultrasound-assisted versus landmark-guided spinal anesthesia in patients with abnormal spinal anatomy: a randomized controlled trial.Anesth Analg. 2020; 130: 787-795Crossref PubMed Scopus (30) Google Scholar However, other studies involving consultant anaesthetists have failed to demonstrate any advantages over a surface landmark-guided midline technique.14Srinivasan K.K. Iohom G. Loughnane F. et al.Conventional landmark-guided midline versus preprocedure ultrasound-guided paramedian techniques in spinal anesthesia.Anesth Analg. 2015; 121: 1089-1096Crossref PubMed Scopus (56) Google Scholar,15Srinivasan K.K. Leo A.M. Iohom G. et al.Pre-procedure ultrasound-guided paramedian spinal anaesthesia at L5-S1: is this better than landmark-guided midline approach? A randomised controlled trial.Indian J Anaesth. 2018; 62: 53-60Crossref PubMed Scopus (23) Google Scholar On the contrary, in the hands of novice practitioners, the PPUSA paramedian technique resulted in more needle passes compared with either a surface landmark-guided or PPUSA midline technique (median of 4 vs 2 vs 2), and a longer block performance time (mean of 155 vs 87 vs 116 min).16Rizk M.S. Zeeni C.A. Bouez J.N. et al.Preprocedural ultrasound versus landmark techniques for spinal anesthesia performed by novice residents in elderly: a randomized controlled trial.BMC Anesthesiol. 2019; 19: 208Crossref PubMed Scopus (14) Google Scholar Block performance time, compared with a landmark-guided or PPUSA midline approach, was also a median of 67 s and 38 s longer, respectively, in the hands of novice practitioners.16Rizk M.S. Zeeni C.A. Bouez J.N. et al.Preprocedural ultrasound versus landmark techniques for spinal anesthesia performed by novice residents in elderly: a randomized controlled trial.BMC Anesthesiol. 2019; 19: 208Crossref PubMed Scopus (14) Google Scholar We therefore recommend that ultrasound imaging be used only to identify the location of spinous processes and to confirm the presence of a patent interlaminar space. The position and angle of the probe should not determine the needle insertion site or lateral-to-medial needle insertion angle. These should instead follow the principles outlined for the surface landmark-guided paraspinous approach. Real-time ultrasound-guided (RTUSG) neuraxial blockade is an advanced technique that requires expertise with both conventional spinal ultrasound imaging and neuraxial blockade. It invariably utilises a paraspinous needle approach to the interlaminar space, although multiple variations using different imaging views have been described.19Chen L. Huang J. Zhang Y. et al.Real-time ultrasound-guided versus ultrasound-assisted spinal anesthesia in elderly patients with hip fractures: a randomized controlled trial.Anesth Analg. 2022; 134: 400-409Crossref PubMed Scopus (8) Google Scholar A recent RCT involving three experienced anaesthetists compared RTUSG paraspinous and PPUSA paraspinous techniques of neuraxial blockade in elderly patients with hip fractures.19Chen L. Huang J. Zhang Y. et al.Real-time ultrasound-guided versus ultrasound-assisted spinal anesthesia in elderly patients with hip fractures: a randomized controlled trial.Anesth Analg. 2022; 134: 400-409Crossref PubMed Scopus (8) Google Scholar They observed that the RTUSG technique was significantly more difficult, as demonstrated by lower first-pass success rates (32% vs 63%), more needle passes overall (median of 3 vs 1) and longer block performance times (median of 488 vs 200 s). Furthermore, CSF backflow was absent in 14% of the RTUSG group; in these patients, successful spinal anaesthesia was obtained with crossover to the PPUSA technique. The authors postulated several reasons for this including needle blockage, and misplacement of the needle tip because the insertion point was too lateral or deviated from the intended trajectory. The RTUSG technique cannot therefore be recommended for routine use at this time. Nevertheless, we have occasionally found it helpful in certain circumstances, notably where the target interlaminar space was adequately seen but so small as to require a degree of precision that could only be obtained with real-time guidance. It should also be noted that concerns have been raised regarding potential toxicity of ultrasound gel introduced into the neuraxial space.20Carter H.K. Wong E.M. Safety of ultrasound gel in real-time scanning of the lumbar spine in obstetric anaesthesia.Int J Obstet Anesth. 2022; 52103594Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar This can be avoided by applying gel sparingly and meticulously cleaning the site of needle puncture, or by using saline as an alternative medium for probe-skin contact. If the patient is in a lateral decubitus position, adopting a modified Sims position, in which the patient's back slants away from the operator, can be helpful as it provides a more stable position and creates more space between the needle hub and bed surface during insertion, particularly if using a long needle >90 mm in length. However, this slant of the surface of the patient's back must be factored in when estimating the lateral-to-medial angle of needle trajectory relative to the horizontal plane of the patient's bed (Fig. 7). Flexion of the hips and lumbar spine is not critical to successful paraspinous neuraxial blockade, as the width of the paraspinous interlaminar space is minimally affected.21Podder S. Kumar N. Yaddanapudi L.N. Chari P. Paramedian lumbar epidural catheter insertion with patients in the sitting position is equally successful in the flexed and unflexed spine.Anesth Analg. 2004; 99: 1829-1832Crossref PubMed Scopus (21) Google Scholar This is a distinct advantage when optimal positioning is not feasible, such as in hip fracture. However, a recent RCT found that elevating the chest and shoulders by 30° significantly improved metrics of technical performance in elderly patients with hip fracture (Fig. 8).22Zhang W. Wang T. Wang G. et al.Elevated lateral position improves the success of paramedian approach in subarachnoid puncture in spinal anesthesia before hip fracture surgery in elderly patients: a randomized controlled study.Med Sci Monit. 2020; 26 (-1–e923813-8)e923813Crossref Scopus (3) Google Scholar This was attributed to widening of the dependent paraspinous interlaminar space created by lateral flexion in the thoracolumbar spine and is a concept worthy of further investigation. In some older patients, the skin insertion site may have to be >1 cm lateral to the neuraxial midline. This is because age-related calcification of the supraspinous ligaments can distort and widen the tip of the spinous process, creating a 'mushroom top' shape (Fig. 9). This is often evident during palpation but will also be signalled by gritty or bony needle contact during local anaesthetic skin infiltration. The skin insertion site should be adjusted as needed until it is lateral to the enlarged tip of the spinous process and the needle can pass unimpeded through the paraspinal muscles. The lateral-to-medial angle should be increased slightly up to 15–20° to geometrically compensate for this lateral shift in insertion site (Fig. 9). Accurate localisation of the spinous processes by palpation may be difficult in patients with obesity. Their approximate position can sometimes be determined by deep palpation and then confirmed by using the skin infiltration needle to probe for bony contact or injection resistance, signifying engagement of supraspinous or interspinous ligaments. Ultrasound imaging is also extremely helpful as the location of the midline and spinous processes can always be ascertained, even if the anterior and posterior complexes signifying interlaminar windows cannot be clearly seen (Fig. 6). Other major challenges in obesity are the increased needle insertion depth and mobility of overlying soft tissues. This can lead to inadvertent deviations in needle trajectory during insertion. The precision of needle handling demanded by a midline approach thus makes it more susceptible to failure, particularly if the patient also has narrowed interlaminar spaces. As discussed earlier, the paraspinous approach is more forgiving of imprecision during needle insertion. Systematic redirection is also simplified by the fact that deep bony contact almost certainly signifies the ipsilateral lamina and incremental cranial angulation is therefore the logical next step to eventual success (Fig. 1). For these reasons, we often adopt the paraspinous approach as the first-line technique in patients who are very obese. Finally, when using needles >90 mm in length, regardless of approach, we recommend using 22 G (vs 25 G) Quincke-tip needles to reduce tissue resistance to insertion and the risk of needle shaft flexion and deviation. Related to this, some anaesthetists suggest a CSE technique to achieve spinal anaesthesia in patients with challenging anatomy, citing the greater rigidity and better tactile feedback of the epidural needle. One RCT demonstrated non-inferiority, but not superiority, of the CSE technique compared with single-injection spinal anaesthesia in morbidly obese patients undergoing Caesarean section.23Ross V.H. Dean L.S. Thomas J.A. Harris L.C. Pan P.H. A randomized controlled comparison between combined spinal-epidural and single-shot spinal techniques in morbidly obese parturients undergoing cesarean delivery: time for initiation of anesthesia.Anesth Analg. 2014; 118: 168-172Crossref PubMed Scopus (24) Google Scholar It should be further noted that reported incidences of spinal haematoma and other instances of permanent injury are several orders of magnitude greater with CSE and epidural anaesthesia compared with spinal anaesthesia.24Cook T.M. Counsell D. Wildsmith J.A.W. Major complications of central neuraxial block: report on the third national audit project of the royal college of anaesthetists.Br J Anaesth. 2009; 102: 179-190Abstract Full Text Full Text PDF PubMed Scopus (629) Google Scholar,25Moen V. Dahlgren N. Irestedt L. Severe neurological complications after central neuraxial blockades in Sweden 1990-1999.Anesthesiology. 2004; 101: 950-959Crossref PubMed Scopus (765) Google Scholar We therefore do not advocate this strategy of using an epidural needle purely for its handling characteristics in non-obstetric and particularly in older patients. The CSE technique remains a valuable clinical option where the flexibility of extending the duration or height of neuraxial anaesthesia is desired. Challenges with a midline approach in scoliotic patients include narrowed interspinous spaces and rotational deformity. It is critical to identify the direction of the lateral scoliotic curve in the lumbar spine; this will be opposite to that of the thoracic curve, which is often more clinically obvious. The paraspinous interlaminar spaces are widened on the convex side of the curve and narrowed on the concave side, and the needle should thus always be inserted on the convex side (Fig. 10). A lateral curve of the spine is always accompanied by an axial rotational deformity of the vertebrae, with the body of the vertebrae rotating towards the convex side of the lateral curve. This means that little to no lateral-to-medial angulation may be needed for entry into the vertebral canal with a paraspinous approach. Conversely, medial-to-lateral angulation is now required if inserting the needle along a midline approach (Fig. 11). Ultrasound imaging is very helpful in identifying the direction and degree of curvature and rotation in these patients, in locating suitably wide paraspinous interlaminar spaces and in planning the appropriate needle trajectory.Fig 11A scoliotic curve in the spine is always accompanied by a rotational deformity (inset image A). This is evident on ultrasound imaging as a midline acoustic shadow (yellow dashed line) that is tilted away from the vertical when the probe is placed in a transverse orientation with the beam perpendicular to the surface of the back (image 1A and 1B). The direction and angle of rotation is determined by rocking the probe in the transverse plane to bring the midline acoustic shadow back to the vertical (image 2A and 2B). This medial-to-lateral probe-beam angle must be replicated for successful needle insertion using a midline approach (image 3).View Large Image Figure ViewerDownload Hi-res image Download (PPT) The L5–S1 interlaminar space tends to remain patent in degenerative spinal disease and is thus a useful option in challenging neuraxial blockade. The original description, Taylor's approach, was for spinal anaesthesia in the prone position in elderly patients and advocated a paramedian approach utilising a needle insertion point 1 cm medial and 1 cm caudal to the posterior superior iliac spine, with subsequent craniomedial redirections to walk the needle off the sacrum into the interspace. This bony surface landmark is difficult to reliably ascertain, especially in the obese. However, the L5–S1 space can be easily located with ultrasound imaging and its patency simultaneously confirmed.13Kalagara H. Nair H. Kolli S. et al.Ultrasound imaging of the spine for central neuraxial blockade: a technical description and evidence update.Current Anes Reports. 2021; 11: 326-339Crossref Scopus (9) Google Scholar A PPUSA midline or paraspinous approach can then be performed. Note that the S1 foramen can sometimes mimic the sonographic appearance of the L5–S1 space. The latter is characterised by the sawtooth appearance of the L5 lamina and its constant visibility with small lateral-medial sliding motions of the probe. One important consideration when targeting the L5–S1 space for spinal anaesthesia is adequate cranial distribution. Insufficient block height is a common cause of secondary spinal anaesthesia failure even when injection is performed at higher levels.26Fettes P.D. Jansson J.R. Wildsmith J.A.W. Failed spinal anaesthesia: mechanisms, management, and prevention.Br J Anaesth. 2009; 102: 739-748Abstract Full Text Full Text PDF PubMed Scopus (152) Google Scholar A recent dose-finding study reported that sensory loss above the T10 dermatome with Taylor's approach was only consistently obtained with a relatively large dose of at least 25 mg of plain bupivacaine 0.5%.27Liu Y. Yang S. Yao W. et al.Minimum effective dose of plain bupivacaine 0.5% for ultrasound-guided spinal anaesthesia using Taylor's approach.Br J Anaesth. 2020; 124 (–e231): e230Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar A detailed discussion of baricity and the most appropriate local anaesthetic solution for spinal anaesthesia performed at the L5–S1 space is beyond the scope of this journal. Although the densities of plain local anaesthetic solutions are numerically lower than CSF, their distribution within the CSF is not affected by postural changes in as predictable a manner as hyperbaric solutions.28Richardson M.G. Wissler R.N. Densities of dextrose-free intrathecal local anesthetics, opioids, and combinations measured at 37 degrees C.Anesth Analg. 1997; 84: 95-99Crossref PubMed Google Scholar,29Hocking G. Wildsmith J.A.W. Intrathecal drug spread.Br J Anaesth. 2004; 93: 568-578Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar Using hyperbaric or hypobaric local anaesthetic solutions should be considered, in conjunction with appropriate positioning of the patient after the block to achieve the desired cranial distribution.30Srinivasan K.K. Leo A.M. Iohom G. Loughnane F. Lee P.J. Pre-procedure ultrasound-guided paramedian spinal anaesthesia at L5-S1: is this better than landmark-guided midline approach? A randomised controlled trial.Indian J Anaesth. 2018; 62: 53-60Crossref PubMed Scopus (23) Google Scholar, 31Faust A. Fournier R. Van Gessel E. Weber A. Hoffmeyer P. Gamulin Z. Isobaric versus hypobaric spinal bupivacaine for total hip arthroplasty in the lateral position.Anesth Analg. 2003; 97: 589-594Crossref PubMed Scopus (24) Google Scholar, 32Vergari A. Frassanito L. Nestorini R. et al.Hypobaric versus isobaric spinal levobupivacaine for total hip arthroplasty.Minerva Anestesiol. 2017; 83: 361-368Crossref PubMed Scopus (7) Google Scholar Lumbar neuraxial analgesia and anaesthesia is a core skill for all anaesthetists but can be technically challenging to perform in patients with abnormal spinal anatomy. Using some combination of the strategies presented in this article should help to maximise success when difficulty is anticipated or encountered.