The Dorsomedian Ligamentous Strand: An Evaluation In Vivo with Epiduroscopy.

Several anatomical studies have described the morphology of the spinal space; however, researchers do not all agree on the presence of the dorsomedian ligamentous strand (DLS), which divides the epidural space. The possible existence of this structure still influences some clinical practice, such as locoregional anesthesia and pain therapy. Since the number of procedures occurring inside the epidural space have increased, this study's primary objective was to describe the composition of this space through epiduroscopy. We conducted a retrospective analysis of video recorded during epiduroscopy. Two independent doctors performed blind analyses of morphological aspects of peridural space visualized during the procedure in each patient for the maximum possible extension depending on the underlying pathology in the tract from S1 to L1. We enrolled 106 patients who underwent epiduroscopy; 100% of patients presented no medial longitudinal segmentation dividing the epidural channel at any level of the spinal tract investigated, including in the epidural space with pathological fibrotic scars and in those with no adherence. The main finding of our study was the visual absence of any anatomical structure dividing the epidural channel. We report that in vivo, in our experience, with direct epiduroscopy, the DLS is not visible.

Estimation of the relationship between the sacral hiatus and other dorsal sacral parameters using principle component analysis.

PURPOSE: Correct localization of the sacral hiatus is essential for administering a successful caudal epidural block. The purpose of this study is to create a statistical model of sacral hiatus from dorsal sacral parameters to improve the location of the hiatus and thus, reduce the failure rate. The aim of this investigation was to examine the relationship of sacral hiatus morphology and dimension with sacral curvature. This study further examines the dorsal sacral parameters that could affect the sacral hiatus dimension. METHODS: Adult, human, dry sacra and three-dimensionally reconstructed sacra from computed tomography imaging of normal subjects were included in the study and measured using digital Vernier calipers of 0.01 mm accuracy and Geomagic freeform plus software, respectively. RESULT: The most frequent shape of the sacral hiatus was an inverted V (48%) followed by inverted U shape (32%), an irregular shape (12.3%), an M shape (4.7) and an A shape (2.8%). The data were represented by mean and standard deviation. Sacra with M-shaped hiatus had the lowest hiatal length (14.21 ± 5.44 mm), whereas sacra with an inverted V-shaped hiatus had the highest length (25.41 ± 11.3 mm). The anteroposterior diameter of the sacral hiatus at the base in males and females was found to be 3.46 ± 1.48 mm and 2.79 ± 0.83 mm, respectively (P < 0.001). The distance between the caudal end of the median sacral crest and the apex of the sacral hiatus (7.90 ± 6.74 mm, 4.4 ± 5.86 mm) also revealed sexual dimorphism (P < 0.001). CONCLUSION: The correlations between most of the dorsal sacral parameters and length of the sacral hiatus are significant. The intercornual distance is also moderately correlated with the distance between right and left lateral sacral crest S1 level. Dorsal sacral parameters predicts variance of the sacral hiatus dimension from 40 to 73% and this could be utilized for statistical model of the sacral hiatus.

Transverse plane ultrasound-guided caudal epidural injections: sonographic anatomy and stepwise technique.

PURPOSE: The present study aims to provide a step-by-step procedural and anatomical familiarization guide for transverse plane ultrasound (US)-guided caudal epidural (CE) injection. METHODS: The study cohort consisted of 23 chronic low back pain patients (23-67 years old) previously unresponsive to conservative management. A transverse plane US-guided CE injection was performed, with each procedure step documenting and emphasizing sonographic anatomy. Several Thiel's method fixed cadaveric specimen dissections were also performed to demonstrate relevant CE injection-related anatomy. RESULTS: The sacral hiatus location can be estimated by visually forming an equilateral triangle between the posterior superior iliac spines and the sacral apex (trigonum sacrale). Follow-up palpation locates the sacral cornua, guiding transducer placement visualizing over the paired cornua 'bull frog's eye's appearance, with the epidural space visualized as a hypoechoic line, between the eyes. Then, 2-3 ml of 1% lidocaine is injected subcutaneously at the mid-point between the sacral cornua and superficial to the posterior sacrococcygeal ligament (SCL). Although keeping the cornua, superficial posterior SCL and epidural space in view, the needle is slowly advanced to the epidural space at around a 20 degree cephalad angle till the tip becomes visible. Expansion of the epidural space is monitored under the transverse sacral ligament as the injectant is slowly introduced. CONCLUSION: The present study demonstrated the anatomical landmarks necessary for the transverse ultrasound caudal epidural technique and that the cornua, superficial posterior SCL, CE space, and other relevant sacral hiatal anatomy are well visualized with this technique.

Conventional landmark palpation vs. preprocedural ultrasound for neuraxial analgesia and anaesthesia in obstetrics - a systematic review and meta-analysis with trial sequential analyses.

The aim of this systematic review and meta-analysis was to examine the efficacy, time taken and the safety of neuraxial blockade performed for obstetric patients with the assistance of preprocedural ultrasound, in comparison with the landmark palpation method. The bibliographic databases Central, CINAHL, EMBASE, Global Health, MEDLINE, Scopus and Web of Science were searched from inception to 13 February 2020 for randomised controlled trials that included pregnant women having neuraxial procedures with preprocedural ultrasound as the intervention and conventional landmark palpation as the comparator. For continuous and dichotomous outcomes, respectively, we calculated the mean difference using the inverse-variance method and the risk ratio with the Mantel-Haenszel method. In all, 22 trials with 2462 patients were included. Confirmed by trial sequential analysis, preprocedural ultrasound increased the first-pass success rate by a risk ratio (95%CI) of 1.46 (1.16-1.82), p = 0.001 in 13 trials with 1253 patients. No evidence of a difference was found in the total time taken between preprocedural ultrasound and landmark palpation, with a mean difference (95%CI) of 50.1 (-13.7 to 113.94) s, p = 0.12 in eight trials with 709 patients. The quality of evidence was graded as low and very low, respectively, for these co-primary outcomes. Sub-group analysis underlined the increased benefit of preprocedural ultrasound for those in whom the neuraxial procedure was predicted to be difficult. Complications, including postpartum back pain and headache, were decreased with preprocedural ultrasound. The adoption of preprocedural ultrasound for neuraxial procedures in obstetrics is recommended and, in the opinion of the authors, should be considered as a standard of care, in view of its potential to increase efficacy and reduce complications without significant prolongation of the total time required.

The anatomy of the peridural membrane of the human spine.

A peridural membranous layer exists between the bony wall of the spinal canal and the dura mater, but reports on the anatomy of this structure have been inconsistent. The objective of this study is to give a precise description of the peridural membrane (PDM) and to define it unambiguously as a distinct and unique anatomical entity. Thirty-four cadaveric sections of human thoraco-lumbar spines were dissected. On gross examination, the PDM appears as a smooth hollow tube that covers the bony wall of the spinal canal. An evagination of this tube into the neural foramen contains the exiting spinal nerve. The entire epidural venous plexus, including its extension into the neural foramina, is contained in the body of the PDM. Histological examination of the PDM shows a variable distribution of veins arteries, lymphatics, and nerves embedded in a continuous sheath of fibrous, areolar, and adipose tissue. The posterior longitudinal ligament may be considered a dense condensation of fibrous tissue within the membrane. Thus, the PDM is a unique, continuous, and complete anatomical structure. In the spinal canal, the PDM is adjacent to the periosteum. In the neural foramen, suprapedicular PDM and pedicular periosteum separate anatomically to form a suprapedicular compartment, bounded anteriorly by the intervertebral disc and posteriorly by the facet joint. Trauma or degeneration of the disc or facet joint may lead to inflammation and pain sensitization of PDM. This protective mechanism may be of considerable importance for the functioning of the spine under conditions of strain.

The crossed-leg position increases the dimensions within the acoustic target window for neuraxial needle placement in term pregnancy: a prospective observational study.

INTRODUCTION: Neuraxial anesthesia in obstetric patients may be difficult to achieve due to anatomical changes in pregnancy. The crossed-leg position may help in optimizing patient position. We prospectively evaluated the utility of the crossed-leg position compared with a standard position using ultrasound measurements. METHODS: Thirty women with term singleton pregnancy admitted for vaginal delivery were recruited. Women with a history of spinal trauma or surgery, congenital spinal abnormality, advanced first stage of labor or a language barrier were excluded. Two anesthesiologists, blinded to each other's measurements, scanned each subject in the crossed-leg position and standard position. Measurements of the lengths of the posterior longitudinal ligament, ligamentum flavum and interlaminar distance were recorded at the L3-L4 interspace. Comfort level in each position was scored on a Likert Scale. RESULTS: Twenty-nine women completed the study (complete data n=28). Significant increases were observed in the lengths of the posterior longitudinal ligament (mean difference 2.2 mm, 95% CI 1.3 to 3.2; P <0.001), ligamentum flavum (mean difference 1.4 mm, 95% CI 0.7 to 2.1; P <0.001) and interlaminar distance (mean difference 1.4 mm, 95% CI 0.4 to 2.5; P=0.006) in the crossed-leg position. No significant differences in comfort were observed. CONCLUSION: We demonstrated a significant increase in the sonographically measured lengths of the posterior longitudinal ligament, ligamentum flavum and interlaminar distance in the crossed-leg position when compared with the standard position. Both positions were comfortable. Further studies should explore whether these findings translate clinically into easier needle placement in the crossed-leg position.

[Correlation of the epidural space measured intraoperatively and estimated by MRI or US: an observational study]. / Correlação entre a profundidade do espaço peridural medida no intraoperatório e a estimada por RM ou US: estudo observacional.

BACKGROUND AND OBJECTIVES: To assess the agreement between the epidural depth measured from the surgical site with the epidural depths estimated with magnetic resonance imaging (MRI) and ultrasound scanning. METHODS: Fifty patients of either sex, scheduled for L4-5 lumbar disc surgery under general anesthesia were enrolled in this prospective observational study, and the results of 49 patients were analyzed. The actual epidural depth was measured from the surgical site with a sterile surgical scale. The MRI-derived epidural depth was measured from the MRI scan. The ultrasound estimated epidural depth was measured from the ultrasound image obtained just before surgery. RESULTS: The mean epidural depth measured from the surgical site was 53.80 ± 7.67mm, the mean MRI-derived epidural depth was 54.06 ± 7.36mm, and the ultrasound-estimated epidural depth was 53.77 ± 7.94mm. The correlation between the epidural depth measured from the surgical site and MRI-derived epidural depth was 0.989 (r2 = 0.979, p < 0.001), and the corresponding correlation with the ultrasound-estimated epidural depth was 0.990 (r2 = 0.980, p < 0.001). CONCLUSIONS: Both ultrasound-estimated epidural depth and MRI-derived epidural depth have a strong correlation with the epidural depth measured from the surgical site. Preprocedural MRI-derived estimates of epidural depth are slightly deeper than the epidural depth measured from the surgical site, and the ultrasound estimated epidural depths are somewhat shallower. Although both radiologic imaging techniques provided reliable preprocedural estimates of the actual epidural depth, the loss of resistance technique cannot be discarded while inserting epidural needles.

Correlation of the epidural space measured intraoperatively and estimated by MRI or US: an observational study / Correlação entre a profundidade do espaço peridural medida no intraoperatório e a estimada por RM ou US: estudo observacional

Abstract Background and objectives: To assess the agreement between the epidural depth measured from the surgical site with the epidural depths estimated with magnetic resonance imaging (MRI) and ultrasound scanning. Methods: Fifty patients of either sex, scheduled for L4‒5 lumbar disc surgery under general anesthesia were enrolled in this prospective observational study, and the results of 49 patients were analyzed. The actual epidural depth was measured from the surgical site with a sterile surgical scale. The MRI-derived epidural depth was measured from the MRI scan. The ultrasound estimated epidural depth was measured from the ultrasound image obtained just before surgery. Results: The mean epidural depth measured from the surgical site was 53.80 ± 7.67 mm, the mean MRI-derived epidural depth was 54.06 ± 7.36 mm, and the ultrasound-estimated epidural depth was 53.77 ± 7.94 mm. The correlation between the epidural depth measured from the surgical site and MRI-derived epidural depth was 0.989 (r2 = 0.979, p < 0.001), and the corresponding correlation with the ultrasound-estimated epidural depth was 0.990 (r2 = 0.980, p < 0.001). Conclusions: Both ultrasound-estimated epidural depth and MRI-derived epidural depth have a strong correlation with the epidural depth measured from the surgical site. Preprocedural MRI-derived estimates of epidural depth are slightly deeper than the epidural depth measured from the surgical site, and the ultrasound estimated epidural depths are somewhat shallower. Although both radiologic imaging techniques provided reliable preprocedural estimates of the actual epidural depth, the loss of resistance technique cannot be discarded while inserting epidural needles.

Resumo Justificativa e objetivos: Avaliar a concordância entre a profundidade peridural medida no campo cirúrgico com a profundidade peridural estimada pela Ressonância Magnética (RM) e ultrassonografia. Métodos: Cinquenta pacientes de ambos os sexos agendados para cirurgia de disco lombar L4-5 sob anestesia geral foram incluídos neste estudo observacional prospectivo, e os resultados de 49 pacientes foram analisados. A profundidade peridural real foi medida no campo cirúrgico com uma régua cirúrgica estéril. A profundidade peridural obtida pela Ressonância Magnética (RM) foi medida a partir das imagens do exame de RM. A profundidade peridural estimada pelo ultrassom foi medida a partir da imagem do ultrassom obtida imediatamente antes da cirurgia. Resultados: A profundidade peridural média medida no campo cirúrgico foi de 53,80 ± 7,67 mm; a profundidade peridural média da RM foi de 54,06 ± 7,36 mm; e a profundidade peridural estimada por ultrassom foi de 53,77 ± 7,94 mm. A correlação entre a profundidade peridural medida no campo cirúrgico e a profundidade peridural derivada da RM foi de 0,989 (r2 = 0,979; p < 0,001); e a correlação correspondente com a profundidade peridural estimada por ultrassom foi de 0,990 (r2 = 0,980; p < 0,001). Conclusões: Tanto a profundidade peridural estimada por ultrassom quanto a profundidade peridural derivada da RM mostram forte correlação com a profundidade peridural medida no campo cirúrgico. As estimativas pré-operatórias da profundidade peridural derivadas da RM são um pouco mais profundas do que a profundidade peridural medida no campo cirúrgico, e as profundidades peridurais estimadas por ultrassom são um pouco mais rasas. Embora ambas as técnicas de imagem radiológica tenham fornecido estimativas pré-operatórias confiáveis da profundidade peridural real, a técnica de perda de resistência não pode ser descartada durante a inserção da agulha peridural.

Does the Technique for Assessing Loss of Resistance Alter the Magnitude of Epidural Needle Tip Overshoot?

INTRODUCTION: Postdural puncture headache due to accidental dural puncture is a consequence of excessive needle tip overshoot distance after entering the epidural space via a loss of resistance (LOR) technique. We are not aware of any quantitative comparison of the magnitude of needle tip overshoot (distance traveled by the needle tip beyond the point where LOR can be discerned) for the various LOR assessment techniques that are taught. Such a comparison may provide insight into contributing factors of accidental dural puncture and associated postdural puncture headache. METHODS: A custom-built simulator was used to evaluate the following 3 LOR assessment techniques: incremental needle advancement, intermittent LOR assessment (II); continuous needle advancement, high-frequency intermittent LOR assessment (CI); and continuous needle advancement, continuous LOR assessment (CC). RESULTS: There were significant mean differences in maximum overshoot past a virtual LOR plane due to technique (F(2,124) = 79.31, P < 0.001) (Fig. 2). Specifically, maximum overshoot was greater with technique II [mean = 3.8 mm, 95% confidence interval (CI) = 3.4-4.3] versus either CC (mean = 1.9 mm, 95% CI = 1.5-1.8, P < 0.001) or CI (mean = 1.4 mm, 95% CI = 0.9-2.3, P < 0.001). Differences in maximum overshoot between CC and CI were not statistically different (P = 0.996). Maximum overshoot was greater at 4 cm (mean = 3.0 mm, 95% CI = 2.6-3.4) compared with 5 cm (mean = 2.3 mm, 95% CI = 2.0-2.5, P = 0.044), 6 cm (mean = 2.0 mm, 95% CI = 1.9-2.2, P = 0.054), 7 cm (mean = 1.9 mm, 95% CI = 1.7-2.1, P = 0.002), and 8 cm (mean = 1.8 mm, 95% CI = 1.6-2.1, P = 0.001). In addition, maximum overshoot at 5 cm was greater than that at 7 cm (P = 0.020) and 8 cm (P = 0.037). The other LOR depths were not statistically significantly different from each other. Depth did not have a significant interaction with technique (P = 0.517). Technique preference had neither a significant relationship to maximum overshoot (P = 0.588) nor a significant interaction with LOR assessment technique (P = 0.689). DISCUSSION: Technique II LOR assessment produced the greatest needle overshoot past the simulated LOR plane after obtaining LOR. This was consistent across all LOR depths. In this bench study, the II technique resulted in the deepest needle tip maximum overshoot. We are in the process of designing a clinical study to collect similar data in patients.

Prospective observational investigation of body habitus measurements and relationship to epidural depth in term pregnant women.

BACKGROUND: High body mass index (BMI) can predict difficult neuraxial block; however, fat distribution may also be important. The primary study aim was to identify body habitus and fat distribution measurements that correlated with ultrasound measured epidural depth. We hypothesized that measurements such as midarm and subscapular fatpad thicknesses and length of cervical spine may correlate better with ultrasound measured epidural depth than a global measure of BMI. METHODS: Prospective IRB approved study of term pregnant women requiring neuraxial block. We measured height, weight (BMI, kg/m2 ), subscapular, midarm fatpad thickness (digital caliper, mm), vertebral column length (C7 to sacral hiatus, cm) and epidural depth (ultrasound, mm). Four experts assessed photographs to assign anticipated difficult neuraxial block in sitting and lateral positions (5-point Likert scale, 1 = very easy, 5 = very difficult). RESULTS: In all, 131 women completed body habitus measurements. Measured mean (standard deviation) BMI was 30.3 (5.4) kg/m2 . Measured BMI, subscapular fatpad and midarm fatpad thickness were significantly correlated with ultrasound depth to epidural space (R2 0.733, 0.626 and 0.633, respectively, P < .0001) but vertebral column length was not. The experts had a high level of agreement (Cronbach's alpha >0.7) for assessment of anticipated difficult block in the sitting and lateral positions; however, anticipated difficult block was not correlated with epidural depth measured by ultrasound for sitting position, R2  = -0.015, P = .87; and lateral position, R2  = -0.087, P = .33. CONCLUSIONS: Measurements of body habitus and fat distribution were no better than measured BMI to anticipate greater ultrasound measured depth to epidural space. Clinical trial number: Non-interventional observational study, not registered.

Abdominal girth has a strong correlation with actual and ultrasound estimated epidural depth

Background/aim/AIM: This study aimed to assess the correlations of actual epidural depth (ND) and ultrasound estimated epidural depth in the paramedian sagittal oblique plane (ED/PSO) and transverse median plane (ED/TM) with the abdominal girth (AG), body mass index (BMI), and weight of patients. Materials and methods: One hundred and thirty patients of either sex scheduled for unilateral inguinal hernia repair were enrolled. ED/PSO and ED/TM were assessed with a 2­5 MHz curved array probe at the L3­4 intervertebral space. The epidural needle was marked with a sterile marker upon locating the epidural space. The ND was assessed by measuring the distance from the sterile marker to the tip of the epidural needle with a linear scale. Anthropometric measures of the patients were recorded. Results: ED/PSO was 49.6 ± 7.9 mm, ED/TM was 49.5 ± 7.9 mm, and ND was 50.0 ± 8.0 mm. AG was 99.8 ± 12.9 cm. The Pearson correlation coefficient between ND and ED/PSO was 0.997 and with ED/TM was 0.996 (P < 0.001 for both). Pearson correlation coefficients for ND with AG, BMI, and weight were 0.757, 0.547, and 0.638, respectively (P < 0.001 for all). Conclusion: AG, weight, and BMI have strong correlations with ND.

Cadaveric Porcine Spines as a Model for the Human Epidural Space.

Most patients who undergo epidural anesthesia are pregnant and thus a protected population, which has limited investigations of the human epidural space. Among the several species studied as models for the human spine, the porcine spine has been used as a model for spine instrumentation. Although the spread of colored dye within the porcine epidural space has been investigated, no model has demonstrated in situ spread by using radiopaque contrast dye. To this end, we here used 10 Yorkshire swine cadavers through an approved tissue sharing agreement. Epidural catheters were placed by using a landmark-based loss-of-resistance technique; placement was confirmed through radiography. The catheters were connected to epidural infusion pumps to ensure consistent dosing, 2-mL boluses of contrast dye were injected into the space, and radiographs were taken and recorded after each bolus. The total spread of the contrast dye was analyzed. We demonstrated consistent and reliable spread of fluid in the epidural space among the animals used, with low variability between animals of different weights. Our results support the use of the epidural space of cadaveric swine as a model for the human epidural space. Furthermore, the technique for epidural administration by using the landmark-based loss-of-resistance demonstrated in this model was validated, thus supporting future investigations of medication delivery into the epidural space.

Randomized comparison of two methods of the epidural space identification during regional labour analgesia.

OBJECTIVES: Conventional loss of resistance (LOR) technique for identifying the epidural space (EDS) predominantly depends on experience of the anaesthetist. A technique using automated syringe for EDS identification was invented as an alternative to the traditional method. The aim of the study was to compare the efficacy and risk for complications between automatic LOR syringe - Epimatic® (Vygon, Ecouen, France) and conventional LOR - Perifix® (B.Braun Melsungen AG, Melsungen, Germany) techniques for EDS identification. MATERIAL AND METHODS: A total of 170 patients were enrolled into the study and 153 cases were analysed. Number of at- tempts, time to EDS identification, ease of EDS identification, complication rate and patient procedure-related discomfort were evaluated and compared. RESULTS: No statistically significant differences were found in the number of needle insertion attempts (1.3 in both groups), time to EDS identification (31 sec. vs. 27 sec.), efficacy of epidural analgesia (100% in both groups), or complication rate between both groups. CONCLUSIONS: The automatic and the conventional LOR techniques are comparable in terms of efficacy and safety for the epidural space identification.

The Posterior Lumbar Epidural Space: Three-Dimensional Reconstruction of High-Resolution MRI: Real and Potential Epidural Spaces and Their Content In Vivo.

OBJECTIVE: Our aim was to study the posterior lumbar epidural space with 3D reconstructions of magnetic resonance images (MRIs) and to compare and validate the findings with targeted anatomic microdissections. DESIGN: We performed 3D reconstructions of high-resolution MRIs from seven patients and normal-resolution MRIs commonly used in clinical practice from 196 other random patients. We then dissected and photographed the lumbar spine areas of four fresh cadavers. RESULTS: From the 3D reconstructions of the MRIs, we verified that the distribution of the posterior fat pad had an irregular shape that resembled a truncated pyramid. It spanned between the superior margin of the lamina of the caudad vertebra and beyond the inferior margin to almost halfway underneath the cephalad lamina of the cranial vertebra, and it was not longitudinally or circumferentially continuous. The 3D reconstructions of the high-definition MRI also consistently revealed a prelaminar fibrous body that was not seen in most of the usually used low-definition MRI reconstructions. Targeted microdissections confirmed the 3D reconstruction findings and also showed the prelaminar tissue body to be fibrous, crossing from side to side anterior to the cephalad half of each lamina, and spanning from the dural sac to the laminae. CONCLUSIONS: Three-dimensional reconstructions and targeted microdissection revealed the unique appearance of posterior fat pads and a prelaminar fibrous body. The exact consistency, presence, prevalence with age, presence in other regions, and function of this body are unknown and require further research.

Skin-to-epidural distance in the Southeast Asian paediatric population: multiethnic morphometrics and international comparisons.

INTRODUCTION: Paediatric epidurals can present technical challenges due to wide variations in age and weight among children, ranging from neonates to teenagers. This study evaluated the skin-to-epidural distance in the thoracic and lumbar regions to determine the relationship between age, weight and ethnicity and depth to the epidural space in our Singapore paediatric population. METHODS: Data from the Acute Pain Service was prospectively collected over 16 years. Details included patient demographics, level of epidural performed and distance from skin to epidural space. Multivariable regression analysis was performed to determine the association of weight, age, ethnicity and gender with the depths to the thoracic and lumbar epidural spaces. A simple linear regression was calculated to predict the depth to both thoracic and lumbar epidural spaces based on body weight. Equations were formulated to describe the relationship between weight and depth of epidural space. RESULTS: A total of 616 midline epidurals were studied. Regression analysis was performed for 225 thoracic epidurals and 363 lumbar epidurals. Our study revealed a clear correlation between skin-to-lumbar epidural distance and weight in children. The best correlation was demonstrated between skin-to-lumbar epidural distance and body weight (R2 = 0.729). This relationship was described by the formula: depth (mm) = (0.63 × weight [kg]) + 9.2. CONCLUSION: Skin-to-lumbar epidural distance correlated with weight in children. Our results highlighted the clinical significance of differences between Southeast Asian paediatric populations when compared to other populations.

A systematic review of the diagnostic accuracy of epidural wave form analysis to identify the epidural space in surgical and labor patients.

INTRODUCTION: Epidural failure due to misidentification of the epidural space is not uncommon. Epidural wave form analysis has been suggested to identify the epidural space. EVIDENCE ACQUISITION: A systematic literature search (Medline, Epub, Embase.com (Embase plus Medline), Cochrane Central, Web of Science, and Google Scholar) was performed to identify studies comparing epidural wave form analysis (index test) to epidural analgesia (reference test). EVIDENCE SYNTHESIS: Eight studies (3901 patients) were retrieved that provided data on diagnostic accuracy. These studies had a low risk of bias and of applicability concerns, as assessed by the quality assessment of diagnostic accuracy studies (QUADAS-2) tool. One study did not observe an epidural wave form in parturients, a finding that was not corroborated in another study. Because the reference test was different across the studies we decided not aggregate the data. The sensitivity values of the individual studies varied between 0.81 and 1.00, for the specificity values between 0.42 and 1.00 were found. CONCLUSIONS: Our study suggests that epidural wave form analysis is a reliable method for identification of the epidural space that could become a useful adjunct especially in anticipated difficult catheter placements or in teaching situations. Further research is warranted to define the role of epidural wave form analysis in pregnant women.

Examining the association of body mass index and the depth of epidural space, radiation dose exposure and fluoroscopic screening time during transforaminal nerve block injection: a retrospective cohort study.

OBJECTIVE: The primary objective of this study was to examine the association between body mass index (BMI) and the depth of tissue overlying the epidural space. Secondary objectives examined the association between BMI and (1) radiation dose exposure and (2) fluoroscopic screening time during transforaminal nerve block (TFNB) injections. METHODOLOGY: This is a retrospective cohort study including patients aged ≥ 16 years who underwent unilateral single-level TFNB in a single centre over a 28-month period, by a single spinal orthopaedic surgeon. Demographic data, BMI (kg/m2), fluoroscopic screening time (seconds) and radiation dose exposure (centi-gray per square centimetre squared (cGy-cm2)) were recorded. Exposure of interest: BMI. PRIMARY OUTCOME: depth of epidural space. SECONDARY OUTCOMES: (1) radiation dose exposure, (2) fluoroscopic screening time. Descriptive statistics for study participants' demographics are presented. Spearman's rank (r) coefficient and linear regression analysis was performed examining the association between BMI and the outcome measures. RESULTS: A total of 362 patients met inclusion criteria; n = 45 patients were excluded due to incomplete data, final analysis included 317 patients. Mean age was 62.6 years (IQR 53-74). Male:female ratio was 37.9% (n = 120):62.1%(n = 197). Mean BMI was 26.9 kg/m2 (IQR 24.4-28.9 kg/m2). Following adjustment for age, gender and spinal comorbidities there is a statistically significant association between BMI and the depth of tissue overlying the epidural space (adjusted coefficient 2.41, (95% CI (2.14, 2.68), p < 0.001)). We also found a significant association between BMI and both secondary outcomes, radiation dose exposure (adjusted coefficient 1.45, (95% CI (0.84, 2.06), p < 0.001)) and fluoroscopic screening time (adjusted coefficient 0.11, (95% CI (0.02, 0.20), p = 0.02)). CONCLUSION: This study has demonstrated a significant association between increasing BMI and increased depth of the epidural space. Furthermore, significant associations between increasing BMI, radiation dose exposure and fluoroscopy screening time have been identified. BMI may represent a modifiable risk factor with a view to decreasing patient exposure to medical ionised radiation.