Consider ultrasound-guided transgluteal sciatic nerve blocks for those with refractory pain
Evaluating and managing low back pain in the emergency department is often (and appropriately) focused squarely on identifying syndromes such as cauda equina or epidural abscess, critical tasks of the emergency physician. But this patient group makes up a small minority of the millions who present for debilitating back pain each year.
The available data suggest we do a pretty good job with back pain, with only a small fraction of patients returning with a serious condition (most often a spinal abscess) within 30 days. (Ann Emerg Med. 2019;74:549; https://bit.ly/3vXaYM7.) Effectively treating pain and enabling a safe return to the activities of daily living take a backseat to our diagnostic charge, but may benefit from a renewed focus and fervor, particularly as these patients present with increasing frequency and complexity.
Initial evaluation and management is pretty straightforward and largely homogenous for most patients presenting to the ED with non-serious low back pain. Some data suggest that about a third of patients with back pain complaints will undergo diagnostic imaging (Spine [Phila Pa 1976]. 2010;35:E140; https://bit.ly/3WbIwAF), but the ACEP-endorsed Choosing Wisely campaign pleads for rationality and evidence-based minimalism in lumbar spine imaging for most patients. (https://bit.ly/3GDXYQA.)
A certain amount of therapeutic nihilism seems to have penetrated the emergency medicine community from a treatment perspective, perhaps borne of multiple discouraging investigations, including a trial where diazepam failed to improve symptoms over placebo, another randomized, controlled trial where cyclobenzaprine and oxycodone fell similarly short, and even a disappointing study where acetaminophen did not affect recovery time compared with placebo. (Ann Emerg Med. 2017;70:169; https://bit.ly/3GXrEtg; JAMA. 2015;314:1572; http://bit.ly/3Xcd72v; Lancet. 2014;384:1586; https://bit.ly/3CFxvRm.)
Nonetheless, patients often receive some combination of these or similar medications upon arrival at the emergency department; there's more than one ED where some refrain of “Tylenol/Toradol/lidocaine patch” has rung out.
A litany of randomized trials have attempted to parse prednisone's role in low back pain, but a recent Cochrane review's conclusion rings likely true: Systemic corticosteroids appear to be slightly effective at improving short-term pain and function in most people with radicular low back pain and probably of limited utility in patients with non-radicular low back pain or pain caused by spinal stenosis. (Cochrane Database Syst Rev. 2022;10:CD012450; https://bit.ly/3W8Llmj.)
Steroids are unlikely to be profoundly helpful acutely in the ED, however, and further use of muscle relaxers, procedures, opioids, and non-opioid adjuncts varies widely in a landscape that's scarce on evidence but heavy on need. It's not a benign question; evidence shows that many patients with nonspecific low back pain will continue to have symptoms for many months (if not years), and ineffective early analgesia is well-appreciated as a trigger for chronic pain syndromes. (Eur J Pain. 2013;17:5; https://bit.ly/3QHKWpS.) Effective pain control can also sometimes make the difference between a patient who can seek outpatient care compared with one who requires admission for pain control and resource management.
Additional analgesic strategies are worth attempting for well-selected patients with refractory and debilitating low back pain in the emergency department. As an osteopath, I'd be remiss not to mention the role of osteopathic manipulative treatment to treat back pain. These techniques may not come to mind quickly, but some evidence supports their use by those trained and comfortable in their implementation. (BMC Musculoskelet Disord. 2014;15:286; http://bit.ly/3vWCcCA.)
A lot can be said for the benefits inherent in manipulative techniques, which may help parse the underlying etiology of a patient's pain, but they are unlikely to make the difference between admission and discharge in a patient with severe symptoms.
I've written previously about the role of TCAs in treating radicular low back pain in the emergency department, and since then, using 10 mg nortriptyline has become a reliable staple in my analgesic toolkit. (EMN. 2019;41:19; http://bit.ly/3CI3wIB.) Unfortunately, gabapentin seems to lack a strong evidence base for its use outside the ED. (Am Fam Physician. 2019;100:309; http://bit.ly/3ZvM9EF.)
And the great James Roberts, MD, warned previously of some of the dangers associated with the class, concluding, “Emergency physicians would rarely initiate the use of gabapentinoids.” (EMN. 2018;40:8; http://bit.ly/2jm5WUh.) Similarly, IV lidocaine has been adopted into some ALTO protocols, but it appears unlikely to be a gamechanger in low back pain management. (J Emerg Med. 2014;47:119.)
Physicians have grown more aware of and comfortable with using ketamine as an effective opioid-sparing analgesic, and—anecdotally—I have found back pain to have a higher success and response rate to ketamine analgesia than other painful conditions. Opioids have their role, but they come with a long list of drawbacks, including exacerbation of a public health epidemic that continues to rage.
Oxytocin holds some promise as an analgesic adjunct, and may play a future role (potentially alongside ketamine) for acute exacerbations of chronic pain in the ED. (EMN. 2019;41:1; http://bit.ly/2HH86dE.) There is even a conversation to be had about the efficacy of antibiotics in certain patients with chronic low back pain and Modic changes on MRI; empiric amoxicillin may sterilize low-virulence anaerobic organisms that cause chronic pain and morphologic changes in the spine. Finally, trigger point injections are simple, fast, and effective and worth considering at the bedside for patients with myofascial pain syndromes (and often non-radicular pain). (J Emerg Med. 2020;59:364; EMN. 2020;42:17; https://bit.ly/2QICasP.)
Effectiveness of TGSNB
A recent patient refractory to everything I could offer sent me searching for additional techniques or therapies, and I discovered a growing world of ultrasound-guided regional anesthesia techniques with significant promise (and subsequent success) in helping patients with refractory radicular pain. Case reports of piriformis and erector spinae plane blocks suggest these techniques are technically feasible and potentially efficacious for managing radicular pain, and ultrasound-guided transgluteal sciatic nerve block can be safe, easy, and effective for diagnosis and therapy in patients with ambulation hindered by severe sciatica. (Pain Manag. 2021;11:631.)
A recent emergency medicine case series provided an early foundation for increased utilization of ultrasound-guided transgluteal sciatic nerve block (TGSNB). (Am J Emerg Med. 2020;38:1792; https://bit.ly/3GDyHpr.) TGSNB has been used for decades by pain specialists to control post- and perioperative pain, and burgeoning investigations suggest that its incorporation into the ED toolbox could lead to significant patient- and system-oriented improvements.
One reasonably informative emergency department-based study in four hospitals gave emergency physicians just 20 minutes of focused training on TGSNB anatomy, technique, and protocol before enrolling a small convenience sample for block performance. (Ann Emerg Med. 2022;80:S108; https://bit.ly/3GDLDvw.) Each TGSNB was performed with 10 mL of 0.5% bupivacaine mixed with 8 mg of dexamethasone. (Note that the addition of steroids certainly improves the duration of blocks, but it does come with some potential downsides, including disfiguring skin dimpling, so patient-specific risks and benefits of each medication should be considered.)
The training and block implementation had profound effects. Physicians estimated before TGSNB that 50 percent (16/32) of patients would require observation unit or hospital admission, but only 19 percent (6/32) did post-block (p<0.01). The patient and system benefits are plainly obvious with this nearly one-third reduction in the need for hospital admission.
Fast and Effective Analgesia
TGSNB potentially allows for interruption of a maladaptive nociceptive nidus, allowing systemic analgesia to kick in, bridging the patient until the anti-inflammatory action of NSAIDs or steroids can do its work or until multimodal analgesia can reach a critical threshold. Some may harbor concerns that the transient nature of nerve blocks means that the patient is simply likely to return in a few hours once the medications have worn off, but the prevailing evidence and clinical experience very much intimates the concept of an “activation energy” to pain consistent with clinical experience that early effective pain control leads to better downstream therapeutic success. (Rev Argent Radiol. 2021;85:91.)
TGSNB isn't particularly difficult. Put the patient in a lateral decubitus position, place the curvilinear (abdominal) ultrasound probe midway between the greater trochanter and the sacral hiatus, oriented perpendicular to the axis of the femur. This should reveal the bulky sciatic nerve, typically large and hyperechoic, 6-8 cm below the skin surface. It's deep to the gluteus maximus, superficial to the quadratus femoris, and nestles between the greater trochanter of the femur and the ischial tuberosity. Most available resources recommend an out-of-plane approach (not dissimilar to US-guided peripheral IVs), and instillation of your selected anesthetic should further hydrodissect the sciatic nerve from its soft tissue and vascular neighbors, allowing adequate anesthesia once sufficient anesthetic has infiltrated around the nerve.
I've had good success with TGSNB in a handful of applications. A truck driver with refractory symptoms that were seriously affecting his ability to make a living, a mother unable to keep up with her toddlers because recurrent pain kept her bedbound and immobile, an older man with an aversion to opioids but no relief with nonopioid modalities, the list goes on, but TGSNB permitted fast and effective analgesia with minimal risk of adverse events, and, at least according to the limited evidence available, marked improvement in patient satisfaction with significant reduction in hospital length of stay and resource utilization.
Overall, managing low back pain in the emergency department prioritizes the identification of serious conditions over the effective treatment of pain and enabling a safe return to daily activities, but the emergency physician holds the capacity for safe, effective, and judicious analgesia via a growing number of systemic medications and regional anesthesia techniques. Diagnostic imaging is frequently utilized and medications such as opioids and muscle relaxers are commonly prescribed, but the evidence supporting their effectiveness is limited. Alternative strategies, including regional anesthesia, may be worth considering for patients with refractory and debilitating low back pain.
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Dr. Pescatoreis clinical faculty and an attending emergency physician at Einstein Healthcare Network in Philadelphia. Follow him on Twitter@Rick_Pescatore.
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