ACEP News
September 2007
By Michael Murphy, MD
and Arun Nagdev, MD
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Heinrich Quincke first developed the traditional landmark-guided lumbar puncture procedure in 1891. The landmark-guided technique is performed by palpating important anatomical landmarks (i.e., the iliac crests and the lumbar spinous processes) to determine the site of optimal spinal needle introduction. Certain patient variables, such as pregnancy, obesity, or generalized edema are predictive of difficulty localizing landmarks and performing the lumbar puncture.1-3 Even in patients with clearly palpable lumbar landmarks, studies have demonstrated clinician error in correctly identifying vertebral and interspace level by palpation technique.4,5
In the emergency department, lumbar punctures are most commonly performed to determine the presence of an infectious process (meningitis, encephalitis, sepsis, etc.) or subarachnoid hemorrhage. In cases in which the procedure is unsuccessful, the emergency physician must often utilize other services, specifically fluoroscopic guidance, to obtain cerebrospinal fluid (CSF). Unfortunately, during nighttime or weekend hours, reliance on other services can be problematic, possibly leading to compromised patient care. For example, in treating a patient with a suspected central nervous system infectious process, the emergency physician may be forced to use empiric antibiotic therapy without appropriate CSF cultures.
Also, transportation of a potentially critically ill patient from the ED can be troublesome because it requires multiple personnel and places the patient at risk for clinical deterioration in the radiological suite. An immediately accessible bedside procedure facilitating lumbar puncture performed by the treating emergency physician would be ideal in these situations.
Ultrasound-guided lumbar puncture was first described in the Russian anesthesia literature in 1971.6 Subsequent evidence from the anesthesia literature demonstrates that there is a reduction in the number of attempts and interspaces accessed and in repositioning of the needle in patients with pre-procedural ultrasound visualization as compared to traditional landmark identification for spinal and epidural anesthesia.7-11
Recent pediatric literature demonstrates efficacy of ultrasound guidance for introduction of a spinal needle in neonates, with some recognizing it as the preferred method of "rescue" in cases of failed landmark-guided lumbar punctures.12 With the increasing availability of bedside ultrasound equipment and training over the past decade, emergency physicians have incorporated bedside ultrasound visualization during various emergent procedures (central venous access, pericardiocentesis, thoracentesis, etc.).
In 2005 the first published emergency medicine case series described the utility of bedside ultrasound in pre-puncture localization in three emergency department patients in whom an experienced provider was unable to obtain CSF.13 Recently, two observational studies demonstrated the ability of trained emergency physicians to identify accurately the pertinent lumbar landmarks by ultrasound.1,2 Further, in patients with poorly palpable or non-palpable spinal landmarks, ultrasound was found to identify relevant structures that could help guide a lumbar puncture in 76% of these patients.2 Currently no prospective, randomized trials exist demonstrating the efficacy of bedside ultrasound for procedural guidance either before or during lumbar puncture in the emergent setting.
Key Basic Principles of Ultrasound
Reflection occurs when sound waves encounter tissues with different acoustic impedance. Impedance, in simple terms, is resistance to propagation of ultrasound waves. Bone has very high tissue impedance and reflects a hyperechoic (white) image back to the transducer, with an area of anechoic (black) "shadowing" directly behind the reflective image. In spinal imaging the identification of bony landmarks is imperative in locating the interspinous space. The specifics of performing a pre-procedure ultrasound-guided lumbar puncture will be detailed in the following sections.
The Procedure: Ultrasound-Guided Lumbar Puncture
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Patient Positioning: A recent observational trial demonstrates increased interspinous distance by placing the patient in a sitting position with feet supported, which may yield an improved success rate for lumbar puncture.14 However, patient positioning should be determined by patient tolerance and comfort.
Probe selection: Linear (high frequency) probes allow for higher resolution of superficial structures, making these the most commonly used transducers for imaging of spinal anatomy. In patients with large body mass and correspondingly deep spinal structures, changing to a curvilinear (low frequency) probe to delineate the vertebral spinous processes may be a prudent alternative (pic1).
Probe orientation: In lumbar spinal imaging, two main probe orientations are used: the transverse and the longitudinal views. The goal of the transverse view is to determine an accurate anatomic midline by identification of the hyperechoic spinous process. This view is obtained by placing the probe perpendicular to the long axis of the spine (pic2). The purpose of this cross-sectional image is to identify the lumbar spinous process and center it on the image display. The bony spinous process will appear as a "hyperechoic" white convex rim with an anechoic shadow. We recommend looking for a solitary anechoic shadow if the hyperechoic rim is not seen, as this may be the only landmark visualized.
Often, paired hyperechoic structures (transverse processes, facet joints, or laminae) may be visualized surrounding the spinous process, adding support for midline confirmation (pic3). Once the midline is localized, it should be marked and labeled as described in the next section.
Once the midline landmarks are identified, the longitudinal view should be obtained, always maintaining reference to the midline located in the transverse view. The goal of the longitudinal view is to determine the spinal interspace while placing the probe's long axis parallel to the long axis of the spine (pic4). Again, the key structure to identify is the spinous process, which will appear as a hyperechoic convexity with a deep anechoic shadow (pic5). The spinous process should be the most superficial hyperechoic structure, and we recommend moving the probe in a lateral direction in an attempt to confirm that the structure is, in fact, the superficial spinous process and not a similar-appearing deeper and lateral structure.
Once the spinous process is identified, the probe should be moved cephalad and caudad, always maintaining the previously identified midline. If midline position is not maintained, inadvertent imaging of the similar-appearing lateral transverse processes may occur, leading to improper pre-puncture localization. The goal is to identify a contiguous spinous process and then center the probe and image between the contiguous spinous processes over the hypoechoic grey interspace (pic5). This interspace is the optimal location for needle insertion for lumbar puncture.
Physicians more experienced with identification of spinal anatomy may be able to locate deeper structures through this visualized interspace, such as the ligamentum flavum, which is the fibrous structure that lies just superficial to the epidural space, dura, and subarachnoid space. Ultrasound imaging can be used to measure the depth from the skin to this ligament and can be an accurate adjunct to guide spinal needle introduction.10 Once the interspace is identified, it should be marked and labeled as described below.
Pre-procedural Labeling: Pre-procedural ultrasound guidance is useful only if accurate skin markings are made of the optimal lumbar puncture location. In the transverse view the probe and resultant image should be centered over the spinous process with a physical marking made on the patient's skin adjacent to both sides of the probe.
In the longitudinal view the probe and image are centered over the desired interspace with another physical mark made adjacent to the probe, corresponding to interspace level. We recommend using a surgical tissue marking pen because standard aseptic skin cleansing technique can remove common pen markings. Of note, removal of the excess gel from the edges of the probe before skin marking can increase adherence of the ink to skin (pic6).
Another simple tool that may be used to promote accurate labeling is described by Lin et al in February's ACEP News.15 One slides a straightened paper clip between the transducer and the patient's skin, creating a reverberation artifact on the monitor. In the transverse view, the paper clip artifact should be centered over the spinous process and marked, indicating anatomic midline. The probe is then placed in a longitudinal view, and the paper clip and resultant reverberation artifact should be centered and marked over the spinous interspace. The intersection of these two points is the optimal pre-puncture location.
After labeling has been accomplished, the standard aseptic preparation may be performed. The lumbar puncture may be carried out utilizing the labeled landmarks with "X marking the spot" for needle introduction, remembering to introduce the needle with slight cephalad angulation to follow the contours of the spinous processes. Lastly, it is very important that patients maintain their positioning between ultrasound guided labeling and performance of the lumbar puncture, because patient movement may change the relationship between the labeled surface marks and the underlying spinal structures.
Bibliography
- Ferre RM, Sweeney TW. Emergency physicians can easily obtain ultrasound images of anatomical landmarks relevant to lumbar puncture. Am J Emerg Med 2007;25(3):291-6.
- Stiffler KA, Jwayyed S, Wilber ST, Robinson A. The use of ultrasound to identify pertinent landmarks for lumbar puncture. Am J Emerg Med 2007;25(3):331-4.
- Grau T, Bartusseck E, Conradi R, Martin E, Motsch J. Ultrasound imaging improves learning curves in obstetric epidural anesthesia: a preliminary study. Can J Anaesth 2003;50(10):1047-50.
- Broadbent CR, Maxwell WB, Ferrie R, Wilson DJ, Gawne-Cain M, Russell R. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia 2000;55(11):1122-6.
- Furness G ea. An evaluation of ultrasound imaging for identification of lumbar intervertebral level. Anesthesia 2002;57:277-80.
- Bogin IN, Stulin ID. [Application of the method of 2-dimensional echospondylography for determining landmarks in lumbar punctures]. Zh Nevropatol Psikhiatr Im S S Korsakova 1971;71(12):1810-1.
- Cork RC, Kryc JJ, Vaughan RW. Ultrasonic localization of the lumbar epidural space. Anesthesiology 1980;52(6):513-6.
- Currie JM. Measurement of the depth to the extradural space using ultrasound. Br J Anaesth 1984;56(4):345-7.
- Grau T, Leipold, Conradi, R, Martin, E, Motsch, J. Efficacy of Ultrasound imaging in Obstetric Epidural Anesthesia. Journal of Clinical Anesthesia 2002;14:169-75.
- Grau T, Leipold RW, Conradi R, Martin E, Motsch J. Ultrasound imaging facilitates localization of the epidural space during combined spinal and epidural anesthesia. Reg Anesth Pain Med 2001;26(1):64-7.
- Grau T, Leipold RW, Fatehi S, Martin E, Motsch J. Real-time ultrasonic observation of combined spinal-epidural anaesthesia. Eur J Anaesthesiol 2004;21(1):25-31.
- Coley BD, Shiels WE, 2nd, Hogan MJ. Diagnostic and interventional ultrasonography in neonatal and infant lumbar puncture. Pediatr Radiol 2001;31(6):399-402.
- Peterson MA, Abele J. Bedside ultrasound for difficult lumbar puncture. J Emerg Med 2005;28(2):197-200.
- Sandoval M, Shestak W, Sturmann K, Hsu C. Optimal patient position for lumbar puncture, measured by ultrasonography. Emerg Radiol 2004;10(4):179-81.
- Lin M, Washington C. Tricks of the Trade: Ultrasound-Guided Lumbar Puncture. ACEP News 2007 2007(February):23.
Contributors
Dr. Michael Murphy is an attending physician, department of emergency medicine, at the Warren Alpert School of Medicine of Brown University. Dr. Arun Nagdev is an assistant professor, department of emergency medicine, the Warren Alpert School of Medicine of Brown University. Medical Editor Dr. Robert C. Solomon is an attending emergency physician at Trinity Health System in Steubenville, Ohio, and clinical assistant professor of emergency medicine at the West Virginia School of Osteopathic Medicine.
Disclosures
In accordance with the Accreditation Council for Continuing Medical Education (ACCME) Standards and American College of Emergency Physicians policy, contributors and editors must disclose to the program audience the existence of significant financial interests in or relationships with manufacturers of commercial products that might have a direct interest in the subject matter.
Dr. Murphy, Dr. Nagdev, and Dr. Solomon have disclosed that they have no significant relationships with or financial interests in any commercial companies that pertain to this educational activity.
"Focus On: Ultrasound-Guided Lumbar Puncture" has been planned and implemented in accordance with the Essential Areas and Policies of the Accreditation Council for Continuing Medical Education (ACCME).
ACEP is accredited by the ACCME to provide continuing medical education for physicians. ACEP designates this educational activity for a maximum of one Category 1 credit toward the AMA Physician's Recognition Award. Each physician should claim only those credits that he or she actually spent in the educational activity.
"Focus On: Ultrasound-Guided Lumbar Puncture" is approved by ACEP for one ACEP Category 1 credit.
Disclaimer
ACEP makes every effort to ensure that contributors to College-sponsored programs are knowledgeable authorities in their fields. Participants are nevertheless advised that the statements and opinions expressed in this article are provided as guidelines and should not be construed as College policy.
The material contained herein is not intended to establish policy, procedure, or a standard of care. The views expressed in this article are those of the contributors and not necessarily the opinion or recommendation of ACEP. The College disclaims any liability or responsibility for the consequences of any actions taken in reliance on those statements or opinions.