Needle-tissue interaction forces--a survey of experimental data.

Objective To determine whether ultrasound imaging can reduce the risk of failed lumbar punctures or epidural catheterisations, when compared with standard palpation methods, and whether ultrasound imaging can reduce traumatic procedures, insertion attempts, and needle redirections. Design Systematic review and meta-analysis of randomised controlled trials. Data sources Ovid Medline, Embase, and Cochrane Central Register of Controlled Trials up to May 2012, without restriction by language or publication status. Review methods Randomised trials that compared ultrasound imaging with standard methods (no imaging) in the performance of a lumbar puncture or epidural catheterisation were identified. Results 14 studies with a total of 1334 patients were included (674 patients assigned to the ultrasound group, 660 to the control group). Five studies evaluated lumbar punctures and nine evaluated epidural catheterisations. Six of 624 procedures conducted in the ultrasound group failed; 44 of 610 procedures in the control group failed. Ultrasound imaging reduced the risk of failed procedures (risk ratio 0.21 (95% confidence interval 0.10 to 0.43), P Conclusions Ultrasound imaging can reduce the risk of failed or traumatic lumbar punctures and epidural catheterisations, as well as the number of needle insertions and redirections. Ultrasound may be a useful adjunct for these procedures.

https://www.bmj.com/content/bmj/346/bmj.f1720.full.pdf

Ultrasound imaging for lumbar punctures and epidural catheterisations: systematic review and meta-analysis

The role of ultrasound in central neuraxial blockade has been underappreciated, partly because of the relative efficacy of the landmark-guided technique and partly because of the perceived difficulty in imaging through the narrow acoustic windows produced by the bony framework of the spine However, this also is the basis for the utility of ultrasound: an interlaminar window that permits passage of sound waves into the vertebral canal also will permit passage of a needle In addition, ultrasound aids in identification of intervertebral levels, estimation of the depth to epidural and intrathecal spaces, and location of important landmarks, including the midline and interlaminar spaces This can facilitate neuraxial blockade, particularly in patients with difficult surface anatomic landmarks In this review article, the authors summarize the current literature, describe the key ultrasonographic views, and propose a systematic approach to ultrasound imaging for the performance of spinal and epidural anesthesia in the adult patient

/pdf/ultrasonography-of-the-adult-thoracic-and-lumbar-spine-for-10sb9bqweu.pdf

Ultrasonography of the Adult Thoracic and Lumbar Spine for Central Neuraxial Blockade

https://rapm.bmj.com/content/rapm/41/2/251.full.pdf

Lumbar Neuraxial Ultrasound for Spinal and Epidural Anesthesia: A Systematic Review and Meta-Analysis.

Minimum variance (MV) based beamforming techniques have been successfully applied to medical ultrasound imaging. These adaptive methods offer higher lateral resolution, lower sidelobes, and better definition of edges compared to delay and sum beamforming (DAS). In standard medical ultrasound, the bone surface is often visualized poorly, and the boundaries region appears unclear. This may happen due to fundamental limitations of the DAS beamformer, and different artifacts due to, e.g., specular reflection, and shadowing. The latter can degrade the robustness of the MV beamformers as the statistics across the imaging aperture is violated because of the obstruction of the imaging beams. In this study, we employ forward/backward averaging to improve the robustness of the MV beamforming techniques. Further, we use an eigen-spaced minimum variance technique (ESMV) to enhance the edge detection of hard tissues. In simulation, in vitro, and in vivo studies, we show that performance of the ESMV beamformer depends on estimation of the signal subspace rank. The lower ranks of the signal subspace can enhance edges and reduce noise in ultrasound images but the speckle pattern can be distorted.

Eigenspace Based Minimum Variance Beamforming Applied to Ultrasound Imaging of Acoustically Hard Tissues

Purpose
In conventional practice of epidural needle placement, determining the interspinous level and choosing the puncture site are based on palpation of anatomical landmarks, which can be difficult with some subjects. Thereafter, the correct passage of the needle towards the epidural space is a blind “feel as you go” method. An aim-and-insert single-operator ultrasound-guided epidural needle placement is described and demonstrated.

/pdf/single-operator-real-time-ultrasound-guidance-to-aim-and-532wyyv1xl.pdf

Single-operator real-time ultrasound-guidance to aim and insert a lumbar epidural needle

BACKGROUND: Ultrasound is receiving growing interest for improving the guidance of needle insertion in epidural anesthesia. Defining a paramedian ultrasound scanning technique would be helpful for correctly identifying the vertebral level. Finding surrogate measures of the depth of the epidural space may also improve the ease of scanning. METHODS: We examined 20 parturients with pre-epidural ultrasound in the paramedian plane, and the predicted depth was compared with the actual midline depth. The actual depth was also compared with subject biometrics, depth of transverse process, and thickness of lumbar fat. RESULTS: The scanning technique allowed the depth of the epidural space to be measured in all subjects. The depth measured in ultrasound was strongly correlated to the actual depth (R 2 = 0.8 and 95% limits of agreement of -14.8 to 5.2 mm), unlike patient biometrics (R 2 < 0.25), the depth of the neighboring transverse processes (R 2 = 0.35 and 95% limits of agreement of -13.8 to 19.1 mm), or the thickness of overlying fat (R 2 = 0.66). The duration of the ultrasound scan was 10 min at the beginning of the trial and 3 min for the last subjects. CONCLUSIONS: Paramedian ultrasound can be used to estimate the midline depth to the epidural space. The surrogate measures are not sufficiently correlated with the depth to the epidural space to recommend them as a replacement for the actual depth to the epidural space measurement.

Preinsertion Paramedian Ultrasound Guidance for Epidural Anesthesia

Ultrasound has been proposed for aiding epidural needle insertion, but challenges remain in differentiating spinal structures due to noise, artifacts, and inexperience by anesthesiologists in ultrasound interpretation. Moreover, the anesthesiologist needs to measure relevant distances while preserving sterile conditions; therefore, interaction with the ultrasound controls must be minimal. Automated measurement is needed. Beam-steered ultrasound images are captured and spatial compounding is used to improve image quality. Phase symmetry is used to enhance bone (lamina) and ligamentum flavum (LF) ridges. A lamina template is matched to this ridge map using Pearson's cross-correlation, and the most likely lamina positions are found. Then, the lamina is traversed using a LF template with the Pearson's cross-correlation, and the location of the LF is obtained. Tests are performed on 39 sets of compounded ultrasound images in the L2-3 and L3-4 levels of the spine in the paramedian plane. The proposed algorithm can detect the laminas in 38 of the 39 images, and the LF in 34 of the 39 images. In successful detections, the automatic detections versus manual segmentation has an rms error of 0.64 mm and average error 0.04 mm, versus independent sonographer-measured depth has a root-mean-squared error of 3.7 mm and average error 2.5 mm, and versus the actual needle insertion depth has a root-mean-squared of 5.1 mm and average error -2.8 mm. The computational time is 4.3 s on a typical personal computer. The accuracy, reliability, and speed suggest this method may be valuable for helping guide epidurals in conjunction with the traditional loss-of-resistance method.

Automatic Detection of Lumbar Anatomy in Ultrasound Images of Human Subjects

Epidural anesthesia is the most common form of anesthesia in obstetrics. The loss-of-resistance to saline injection is used to confirm when the needle tip enters the epidural space. This procedure is highly dependent on skill and expertise, so it is useful to quantify the tissue resistance during insertion. Sensors are used to measure the force and displacement of the plunger of the syringe and the pressure at the needle tip. A model is also developed to estimate the pressure from the force and displacement. Tests are first performed on porcine tissue to compare the continuous-pressure and intermittent-pressure versions of the technique and to compare the paramedian and midline needle approaches. The accuracy of the pressure model is 12% of peak pressure for the continuous technique and 20% for the intermittent technique. Significant differences in injection flow rate were also found for the muscle, interspinous ligament, and ligamentum flavum encountered in the two approaches. A small clinical study on human subjects was performed and again significant differences were found in flow rate for different tissues. These quantitative results improve the understanding of small differences in feel that have been previously known qualitatively and may help in the development of simulators.

Instrumentation of the Loss-of-Resistance Technique for Epidural Needle Insertion

Background
Ultrasound has been shown to facilitate accurate identification of the intervertebral level and to predict skin-to-epidural depth in the lumbar epidural space with reliable precision. We hypothesized that we could accurately predict the skin-to-epidural depth and the intervertebral level in the thoracic spine with the use of ultrasound.

/pdf/utility-of-prepuncture-ultrasound-for-localization-of-the-ip5gp4ueln.pdf

Denis Tran

Papers

Single-operator real-time ultrasound-guidance to aim and insert a lumbar epidural needle

Preinsertion Paramedian Ultrasound Guidance for Epidural Anesthesia

Automatic Detection of Lumbar Anatomy in Ultrasound Images of Human Subjects

Instrumentation of the Loss-of-Resistance Technique for Epidural Needle Insertion

Utility of prepuncture ultrasound for localization of the thoracic epidural space