Recommendations on the Use of Ultrasound Guidance for Adult Lumbar Puncture: A Position Statement of the Society of Hospital Medicine

Literature Search

A total of 4,389 references were pooled from four different sources: a search by a certified medical librarian in December 2015 (3,212 citations) that was updated in November 2016 (380 citations), January 2018 (282 citations), and October 2018 (274 citations); working group members’ personal bibliographies and searches (31 citations); and a search focusing on ultrasound-guided LP training (210 citations). A total of 232 full-text articles were reviewed, and the final selection included 77 articles that were abstracted into a data table and incorporated into the draft recommendations. Details of the literature search strategy are presented in Appendix 3.

Four domains (clinical outcomes, technique, training, and knowledge gaps) with 16 draft recommendations were generated based on a review of the literature. Selected references were abstracted and assigned to each draft recommendation. Rationales for each recommendation were drafted citing supporting evidence. After two rounds of panel voting, five recommendations did not achieve agreement based on the RAND rules, one recommendation was combined with another recommendation during peer review, and 10 statements received final approval. The degree of consensus based on the median score and the dispersion of voting around the median are shown in Appendix 5. Nine statements were approved as strong recommendations, and one was approved as a conditional recommendation. Therefore, the final recommendation count was 10. The strength of the recommendation and degree of consensus for each recommendation are summarized in Table 1.

Terminology

LP is a procedure in which a spinal needle is introduced into the subarachnoid space for the purpose of collecting CSF for diagnostic evaluation and/or therapeutic relief.

Throughout this document, the phrases “ultrasound-guided” and “ultrasound guidance” refer to the use of ultrasound to mark a needle insertion site immediately before performing the procedure. This is also known as static ultrasound guidance. Real-time or dynamic ultrasound guidance refers to direct visualization of the needle tip as it traverses through the skin and soft tissues to reach the ligamentum flavum. Any reference to real-time ultrasound guidance is explicitly stated.

Clinical outcomes

1) When ultrasound equipment is available, along with providers who are appropriately trained to use it, we recommend that ultrasound guidance should be used for site selection of LPs to reduce the number of needle insertion attempts and needle redirections and increase the overall procedure success rates, especially in patients who are obese or have difficult-to-palpate landmarks.

Rationale. LPs have historically been performed by selecting a needle insertion site based on palpation of anatomical landmarks. However, an estimated 30% of patients requiring LP in emergency departments have lumbar spine landmarks that are difficult to palpate, most commonly due to obesity.¹³ Furthermore, lumbar puncture performed based on palpation of landmarks alone has been reported to fail in 28% of patients.¹⁴

Ultrasound can be used at the bedside to elucidate the lumbar spine anatomy to guide performance of LP or epidural catheterization. Since the early 2000s, randomized studies comparing the use of ultrasound guidance (ultrasound-guided) versus anatomical landmarks (landmark-guided) to map the lumbar spine for epidural catheterization have emerged. It is important to recognize that the exact same ultrasound technique is used for site marking of LP, epidural catheterization, and spinal anesthesia—the key difference is how deep the needle tip is inserted. Therefore, data from these three ultrasound-guided procedures are often pooled. Currently, at least 33 randomized controlled studies comparing ultrasound-guided vs landmark-guided site selection for LP, epidural catheterization, or spinal anesthesia have been published.^22-49 We present three meta-analyses below that pooled data primarily from randomized controlled studies comparing ultrasound-guided vs landmark-guided site selection for LP or spinal anesthesia.

In 2013, Shaikh et al. published the first meta-analysis with 14 randomized controlled studies comparing ultrasound-guided vs landmark-guided site selection for LP (n = 5) or epidural catheterization (n = 9). The pooled data showed that use of ultrasound guidance decreased the proportion of failed procedures (risk ratio 0.21, 95% CI 0.10-0.43) with an absolute risk reduction of 6.3% (95% CI 4.1%-8.4%) and a number needed to treat of 16 (95% CI 12-25) to prevent one failed procedure. In addition, the use of ultrasound reduced the mean number of attempts by 0.44 (95% CI 0.24-0.64) and reduced the mean number of needle redirections by 1.00 (95% CI 0.75-1.24). The reduction in risk of a failed procedure was similar for LPs (risk ratio 0.19 [95% CI 0.07-0.56]) and epidural catheterizations (risk ratio 0.23 [95% CI 0.09-0.60]).¹⁶

A similar meta-analysis published by Perlas et al. in 2016 included a total of 31 studies, both randomized controlled and cohort studies, evaluating the use of ultrasound guidance for LP, spinal anesthesia, and epidural catheterization.⁵⁰ The goal of this systematic review and meta-analysis was to establish clinical practice recommendations. The authors concluded (1) the data consistently suggest that ultrasound is more accurate than palpation for lumbar interspace identification, (2) ultrasound allows accurate measurement of the needle insertion depth to reach the epidural space with a mean difference of <3 mm compared with the actual needle insertion depth, and (3) ultrasound increases the efficacy of lumbar epidural or spinal anesthesia by decreasing the mean number of needle passes for success by 0.75 (95% CI 0.44-1.07) and reducing the risk of a failed procedure (risk ratio 0.51 [95% CI 0.32-0.80]), both in patients with normal surface anatomy and in those with technically difficult surface anatomy due to obesity, scoliosis, or previous spine surgery.

Compared to the two earlier meta-analyses that included studies of both LP and spinal anesthesia procedures, the meta-analysis conducted by Gottlieb et al. in 2018 pooled data from 12 randomized controlled studies of ultrasound guidance for LPs only. For the primary outcome, pooled data from both adult and pediatric studies demonstrated higher procedural success rates with ultrasound-guided vs landmark-guided LPs (90% vs 81%) with an odds ratio of 2.1 (95% CI 0.66-7.44) in favor of ultrasound; however, there were no statistically significant differences when the adult and pediatric subgroups were analyzed separately, probably due to underpowering. For the secondary outcomes, data from the adult subgroup showed that use of ultrasound guidance was associated with fewer traumatic LPs (OR 0.28, 95% CI 0.14-0.59), shorter time to procedural success (adjusted mean difference –3.03 minutes, 95% CI –3.54 to –2.52), fewer number of needle passes (adjusted mean difference –0.81 passes, 95% CI –1.57 to –0.05), and lower patient pain scores (adjusted mean difference –2.53, 95% CI –3.89 to –1.17).

At least 12 randomized controlled studies have been published comparing the use of ultrasound guidance vs landmarks for the performance of LP or spinal anesthesia in adult patients, which were not included in the abovementioned meta-analyses. These individual studies demonstrated similar benefits of using ultrasound guidance: reduced needle insertion attempts, reduced needle redirections, and increased overall procedural success rates.^{17,31,37,40,41,43-49}

It is important to recognize that four randomized controlled studies did not demonstrate any benefits of ultrasound guidance on the number of attempts or procedural success rates,^23,33,41,51 and three of these studies were included in the abovementioned meta-analyses.^23,33,51 Limitations of these negative studies include potential selection bias, inadequate sample sizes, and varying levels of operator skills in procedures, ultrasound guidance, or both. One study included emergency medicine residents as operators with varying degrees of ultrasound skills, and more importantly, patient enrollment occurred by convenience sampling, which may have introduced selection bias. Furthermore, most of the patients were not obese (median BMI of 27 kg/m²), and it is unclear why 10 years lapsed from data collection until publication.³³ Another study with three experienced anesthesiologists as operators performing spinal anesthesia enrolled only patients who were not obese (mean BMI of 29 kg/m²) and had easily palpable bony landmarks—two patient characteristics associated with the least benefit of using ultrasound guidance in other studies.²³ Another negative study had one experienced anesthesiologist marking obstetric patients with ultrasound, but junior residents performing the actual procedure in the absence of the anesthesiologist who had marked the patient.⁴¹

In general, the greatest benefit of using ultrasound guidance for LP has been demonstrated in obese patients.^{24,32,34,35,52,53} Benefits have been shown in specific obese patient populations, including obstetric,^31,54,55 orthopedic,^24,56,57 and emergency department patients.³⁰

By increasing the procedural success rates with the use of ultrasound at the bedside, fewer patients may be referred to interventional radiology for fluoroscopic-guided LP, decreasing the patient exposure to ionizing radiation. A randomized study (n = 112) that compared site marking with ultrasound guidance versus fluoroscopic guidance for epidural steroid injections found the two techniques to be equivalent with respect to mean procedure time, number of needle insertion attempts, or needle passes.⁵⁸ Another randomized study found that the performance time of ultrasound guidance was two minutes shorter (P < .05) than fluoroscopic guidance.⁵⁹