Depth Of Epidural Space Research Articles

Abstract PR207

Background & Objectives: We conducted a service evaluation of anaesthesia in morbidly obese parturients in our unit. Our aims were to quantify the extent of the issue locally, identify the level of anaesthetist involved and make recommendations. Materials & Methods: Following hospital governance approval, cases were identified from the Anaesthesia Obstetric Database. Women with a Body Mass Index (BMI) more than 40 kg/m2 who required an anaesthetic intervention between 1st of January 2014 to 31st of December 2014 were included. Two hundred and fourteen individual cases were identified out of 5,848 deliveries. We obtained 151 case notes. Seventeen cases were excluded due to missing data or discrepancies, leaving 134 cases for analysis. Data was collected for demographics, mode of delivery, analgesia technique, anaesthesia, complications (resites, bloody taps, dural punctures), grade of anaesthetist and outcomes. Results: BMI ranged between 40 to 65 kg/m2 at term. Sixty-one women were seen in our dedicated antenatal high BMI clinic. Seventy-three women underwent a Lower Segment Caesarean Section (LSCS). There were six category 1 Caesarean sections with five general anaesthesia cases and one epidural top-up. A Decision to Delivery Interval time (DDI) of less than 30 minutes was achieved in all cases. Seven women had assisted vaginal delivery and fifty-four a normal vaginal delivery. Our rate of labour epidural/CSE in morbidly obese patients was 69.81%, with a failure rate of 17.15%. We found a poor correlation between the antenatally ultrasound estimated depth of epidural space and the actual depth found in labour. The following complications were identified: eight cases of multiple attempts (one being impossible), three cases of accidental dural punctures and three bloody taps. Our super-morbidly obese patients (BMI more than 50 kg/m2) were managed by senior anaesthetists (seventeen cases) and three cases were by juniors. Conclusion: Our data is similar to internationally published studies of morbidly obese parturients in terms LSCS incidence (54.47%), rate of labour epidural and regional anaesthesia failure.1 We recommended threading more length of epidural catheter in the space to account for its movement with position related tissue expansion.2 There should be senior anaesthetic involvement with all super-morbidly obese patients. The demographic data from this audit was used to inform a successful bid for equipment funding from the Department of Health.

Lumbar Epidural space depth has better relations to the Weight than Height of the Patient

This study was carried out on one hundred and fifty male patients undergoing TURP and Cystoscopy under lumbar epidural anaesthesia in urology department mayo hospital with age between 30 years to 100 years with mean 64.29 years, weight 37kg to 96kg with mean 59.21kg and height between 140cm to 187cm with mean 165.34cm. All patients were administered single shot-lumbar epidural anesthesia with tuohy needle no 16 with bupivacain 0.5% volume ranging 15cc to 20cc at level of L3-4 or L4-5 level. Two patients developed lumbar puncture and managed conservatively. The lumbar epidural space ranged between 3.5cm to 6.5cm with mean depth 4.38±0.563. It was concluded statistically that lumbar epidural space depth had better relation to the weight of patients than height.

Comparison of ultrasound imaging in transverse median and parasagittal oblique planes for thoracic epidurals: A pilot study.

Background and Aims:The use of ultrasound (US) scanning to assess the depth of epidural space to prevent neurological complications is established in current practice. In this study, we hypothesised that pre-puncture US scanning for estimating the depth of epidural space for thoracic epidurals is comparable between transverse median (TM) and paramedian sagittal oblique (PSO) planes.Methods:We performed pre-puncture US scanning in 32 patients, posted for open abdominal surgeries. The imaging was done to detect the depth of epidural space from skin (ultrasound depth [UD]) and needle insertion point, in parasagittal oblique plane in PSO group and transverse median plane in TM group. Subsequently, epidural space was localised through the predetermined insertion point by ‘loss of resistance’ technique and needle depth (ND) to the epidural space was marked. Correlation between the UD and actual ND was calculated and concordance correlation coefficient (CCC) was used to determine the degree of agreement between UD and ND in both the planes.Results:The primary outcome, i.e., the comparison between UD and ND, done using Pearson correlation coefficient, was 0.99 in both PSO and TM groups, and the CCC was 0.93 (95% confidence interval [95% CI]: 0.81–0.97) and 0.90 (95% CI: 0.74–0.96) in PSO and TM groups respectively, which shows a strong positive association between UD and ND in both groups.Conclusion:The use of pre-puncture US scanning in both PSO and TM planes for estimating the depth of epidural space at the level of mid- and lower-thoracic spine is comparable.

Acoustic puncture assist device: A novel technique to identify the epidural space

Background:Acoustic puncture assist device (APAD) is designed to detect and signal the loss of resistance during the epidural procedure. We aimed to evaluate this device in terms of successful identification of the epidural space and the incidence of accidental dural puncture.Patients and Methods:Following Institutional Review Board approval and written informed consent obtained from all patients, 200 adult patients (107 males) American Society of Anesthesiologists I-III who underwent lower limb orthopedic surgery under lumbar epidural anesthesia using APAD were enrolled in the study. APAD system was connected to the epidural needle using normal saline prefilled extension tube. Numbers of successful epidural attempts and accidental dural tap were documented.Results:The mean values of the depth of epidural space and the time to perform epidural puncture were 5.8 ± 1.0 cm and 3.3 ± 1.4 min, respectively. In 63% of patients, epidural puncture was successful from the first attempt and in 1% it was successful from the fourth attempt. Epidural anesthesia by APAD was successful in 198 cases (99 %). Dural tap occurred in 2 cases (1%).Conclusions:Using APAD, the success of identifying the epidural space was high and reliable.

Using computed tomography scans and patient demographic data to estimate thoracic epidural space depth.

Background and Objectives. Previous studies have used varying methods to estimate the depth of the epidural space prior to placement of an epidural catheter. We aim to use computed tomography scans, patient demographics, and vertebral level to estimate the depth of the loss of resistance for placement of thoracic epidural catheters. Methods. The records of consecutive patients who received a thoracic epidural catheter were reviewed. Patient demographics, epidural placement site, and technique were collected. Preoperative computed tomography scans were reviewed to measure the skin to epidural space distance. Linear regression was used for a multivariate analysis. Results. The records of 218 patients were reviewed. The mean loss of resistance measurement was significantly larger than the mean computed tomography epidural space depth measurement by 0.79 cm (p < 0.001). Our final multivariate model, adjusted for demographic and epidural technique, showed a positive correlation between the loss of resistance and the computed tomography epidural space depth measurement (R 2 = 0.5692, p < 0.0001). Conclusions. The measured loss of resistance is positively correlated with the computed tomography epidural space depth measurement and patient demographics. For patients undergoing thoracic or abdominal surgery, estimating the loss of resistance can be a valuable tool.

No rent is small for migration of epidural catheter into sub-arachnoid space.

Sir, Epidural analgesia forms the mainstay of pain relief in abdominal surgeries.[1,2] Epidural needle placement and catheter insertion are preferably performed under local anaesthesia, before induction of general anaesthesia.[3] Dural puncture by the epidural needle is a known complication, and the reported incidence of accidental dural puncture varies from 0.4% to as high as 6%.[4] Dural puncture precludes the catheter placement in the same inter-vertebral space because rent created in the dura mater may allow intra-thecal migration of the epidural catheter. We report a case of inadvertent intra-thecal migration of the epidural catheter through a dural puncture by a 26 gauge needle. A 38-year-old male patient, height 167 cm and weight 63 kg. was posted for hepato-jejunostomy for the benign stricture of the common bile duct. After a written informed consent, patient was taken up for the surgery. As part of perioperative anaesthesia care, epidural catheter placement was planned in the sitting position. With all sterile precautions, inter-vertebral space between 8th and 9th thoracic vertebra was marked and was punctured with a 26 gauge 1½ inch long needle, for infiltration of local anaesthesia. An aspiration check before injecting the local anaesthetic revealed that probably dura mater had been punctured, and fluid, possibly cerebro-spinal fluid (CSF) was getting aspirated. A note of the depth at which dura mater was punctured was made. Because the dura mater was punctured with a 26 gauge needle, too small to be of concern, it was decided to use the same inter-vertebral space for epidural catheter placement. Epidural space was identified by the loss of resistance technique with a 16 Gauge 12 cm long Tuohy epidural needle (with catheter stabiliser). Skin to epidural space distance was 4 cm. There was no CSF leakage at the hub of the epidural needle. The epidural catheter was easily inserted through the needle but just as the catheter had crossed the mark of 14 cm at needle hub, fluid was seen flowing into the catheter. Fluid was aspirated into a syringe, and it was confirmed as CSF (temperature and sugar content of the aspirated fluid). Epidural catheter was then withdrawn and was placed in an inter-vertebral space higher up. Rest of the course of the hospital stay of the patient was uneventful. Dural puncture by epidural catheter on its own is not possible, though arachnoid puncture by the epidural catheter has been shown in an experimental study.[5] In our patient since dura mater and the arachnoid mater were punctured with a 26 G needle, it would have created a weak point through which subsequently the epidural catheter would have travelled into the intra-thecal space. Robbins et al. had also reported a similar case where accidental intra-thecal insertion of an extradural catheter happened during combined spinal-extradural anaesthesia.[6] They used a 26 gauge Whitacre spinal needle through 16 gauge Tuohy extradural needle. Physical characteristics like height and weight can be used to predict the depth of the epidural space to guide epidural needle placement. Ravi et al. in their study had concluded that the mean depth of epidural space in patients of body mass index (BMI) <30 is 41.60 ± 5.80 mm on the basis of a formula (Depth [mm] = a + b [BMI]. where a = 17.7966 and b = 0.9777).[7] Our patient with a calculated BMI of 22.6, the predicted depth of the epidural space was 39.89 mm. Whereas skin to sub-arachnoid space depth (SSD) in Indian males is reported to be 4.81 ± 0.68 cm,[8] the formula derived for determining SSD in the Indian population, 2.71 + 0.09 × BMI, predicts SSD of 4.74 cm for our patient.[8] We located the epidural space at 4 cm depth from the skin that was well within the predicted depth for epidural space, and was short of the predicted SSD. This also supports our observation that the epidural needle was indeed in the extradural space. In our case, that the epidural catheter migrated into the sub-arachnoid space in the absence of any undue force warrants caution. We suggest that caution should be exercised even while puncturing inter-vertebral space for infiltration for local anaesthesia and in case dural puncture happens, epidural puncture should not be attempted in the same inter-vertebral space.

Measurements of Epidural Space Depth Using Preexisting CT Scans Correlate with Loss of Resistance Depth during Thoracic Epidural Catheter Placement.

Background. Thoracic epidural catheters provide the best quality postoperative pain relief for major abdominal and thoracic surgical procedures, but placement is one of the most challenging procedures in the repertoire of an anesthesiologist. Most patients presenting for a procedure that would benefit from a thoracic epidural catheter have already had high resolution imaging that may be useful to assist placement of a catheter. Methods. This retrospective study used data from 168 patients to examine the association and predictive power of epidural-skin distance (ESD) on computed tomography (CT) to determine loss of resistance depth acquired during epidural placement. Additionally, the ability of anesthesiologists to measure this distance was compared to a radiologist, who specializes in spine imaging. Results. There was a strong association between CT measurement and loss of resistance depth (P < 0.0001); the presence of morbid obesity (BMI > 35) changed this relationship (P = 0.007). The ability of anesthesiologists to make CT measurements was similar to a gold standard radiologist (all individual ICCs > 0.9). Conclusions. Overall, this study supports the examination of a recent CT scan to aid in the placement of a thoracic epidural catheter. Making use of these scans may lead to faster epidural placements, fewer accidental dural punctures, and better epidural blockade.

Evaluation of the skin to epidural and subarachnoid space distance in young children using magnetic resonance imaging.

Epidural catheters placed for perioperative analgesia in young children confer clinical benefits but are technically challenging to insert. Approximations of the skin to epidural space depth in this population are limited to direct needle measurement and ultrasonography. Magnetic resonance imaging (MRI) is the most comprehensive imaging modality of the spine. This study aims to produce a more clinically useful formula from MRI data to estimate pediatric epidural depth. Seventy children with normal lumbar spine MR images were enrolled. After determination of epidural depth, linear regression was used to estimate a weight-based formula. Analysis of variance and bootstrap methods were used to evaluate this formula against 4 commonly cited formulae. The quality of predictions was evaluated using the mean absolute prediction error. The estimated weight-based formula as derived by MRI data is given by: skin to epidural depth (mm) = 9.00 + 0.62 * weight in kilograms. The mean absolute prediction error was 2.56 mm (95% confidence interval [95% CI], 2.12-3.04) for the new formula. Additional derived formulae are skin to dorsal dura depth (mm) = 13.52 + 0.71 * weight in kilograms (mean absolute prediction error, 2.48 mm; 95% CI, 2.00-3.03) and skin to ventral dural depth (mm) = 23.08 + 0.86 * weight in kilograms (mean absolute prediction error, 2.50 mm; 95% CI, 2.04-3.06). We provide the first predictive formulae, based on MRI data, for pediatric epidural depth estimation.

THU0335 Identification of the Optimum Puncture Level by A Lumbar Spine Ultrasonography Decreases the Pain during the Epidural Injection Procedure in Patients with A Presumed Difficult Puncture

BackgroundUltrasound (US) is widely used in rheumatology to study and guide infiltration of peripheral joints. This imaging modality can also provide useful information about the anatomy of the lumbar spine....

The Use of Ultrasound to Measure the Depth of Thoracic Epidural Space

The use of ultrasound to aid in regional blocks has increased in recent years as a result of improvement in ultrasound technology. Ultrasonography can be used to measure the depth of thoracic epidural spacewith a good correlation with the actual depth as detected by the loss of resistance technique.

Cervical Epidural Depth: Correlation Between Needle Angle, Cervical Anatomy, and Body Surface Area

Prior to performing a cervical interlaminar epidural steroid injection (CIESI), knowledge of the depth from lamina to epidural space may assist in preventing cord injury. This is a prospective analysis of data including gender, age, weight, height, previous surgery, neck circumference, distances from tip of chin to sternal notch, occiput to C7 vertebral prominence, and ear lobe to tip of shoulder, pain score, angle from C7 vertebral prominence to the back, depth at which the Tuohy needle contacted T1 vertebral lamina and depth at which the epidural space was entered was conducted with 92 subjects, average age (± standard deviation [SD]) 41.3 ± 13.2 years underwent fluoroscopically guided C7-T1 intralaminar epidural steroid injections. Depth to lamina was the best individual predictor with an r value of 0.86. Weight, neck circumference, and body mass index (BMI) positively correlated with depth to epidural space with r values of 0.66, 0.62, and 0.61, respectively. A linear regression model of depth to lamina for predicting depth to epidural space was accurate to within ± 0.5 cm of the actual depth in 69% of subjects. However, when comparing predicted with actual depth to epidural space for individual subjects, the prediction was inaccurate by as much as 1.6 cm deep or 1.7 cm shallow. While statistically significant correlations do exist between both quantitative external body characteristics and depth to cervical epidural space and T1vertebral lamina to depth of cervical epidural space for fluoroscopically guided interlaminar epidural steroid injections at C7-T1, even the most optimal regression models do not permit clinical confidence in predicted depth to epidural space.

Ultrasound-guided Epidural Blood Patch

* Department of Anesthesiology, University of Massachusetts Memorial Medical Center Worcester, Worcester, Massachusetts, issam.khayata@umassmemorial.orgA 35-YR-OLD woman presented with a postdural puncture headache for epidural blood patch. The procedure was performed in the lateral position. A curvilinear ultrasound probe with sterile cover was used to visualize the epidural space. A 20-G epidural needle was used to identify the space by the loss-of-resistance technique. Blood was then injected into the epidural space under real-time ultrasound scanning (fig.). In the preinjection insert, the ligamentum flavum and posterior dura as well as the anterior dura and the posterior longitudinal ligament were in close proximity. In the postinjection picture, the posterior epidural space (PES) increased from less than 1 mm to 3 mm and the anterior epidural space (AES) increased from less than 1 mm to 2.5 mm.Ultrasound scanning to measure the epidural space depth has been well studied.1However, performing an epidural injection under real-time ultrasound guidance has been limited. In one study where real-time ultrasound guidance was used for needle placement, the authors2described widening of the posterior epidural space during injection of local anesthetics into the epidural space. The use of ultrasound imaging for epidural needle placement has also been described in children, but real-time guidance is lacking.3Confirmation of proper placement of injectate into the epidural space is essential. Though fluoroscopy use is well established, it carries the risk of radiation exposure—particularly among pregnant patients. The increase in the use of ultrasound technology will determine whether this guidance technique can provide an alternative portable method that might be superior to performing epidural injections blindly.

Anesthesia for Bariatric Surgery

Bariatric surgery has a lot of problems in anesthesia. We retrospectively compared anesthesia for bariatric surgery in yellow race with that in normal weight patients. Twenty patients who received bariatric surgery and 20 normal body weight patients who received abdominal surgery in Japan were enrolled. Induction condition, depth of epidural space, dose of anesthetics, duration of the effects of muscle relaxants, ventilation, and fluid management in bariatric surgery were analyzed and compared with those in normal body weight patients. An epidural catheterization was successful under ultrasound guide in the bariatric group. The depth epidural space was significantly larger in the bariatric group. Cormack and Lehane classification and the number of intubation attempt were not different between the two groups, while one bariatric case was once awakened to intubate blindly. Pressure-controlled ventilation was used in the bariatric group. Four bariatric patients were continuously ventilated after surgery. The doses of anesthetics and fluid infusion rate were not different between the two groups when calculated by ideal body weight in the bariatric group. The duration of the effects of rocuronium and pancuronium were shorter in the bariatric group. For anesthesia of yellow race patients undergoing bariatric surgery, intravenous anesthetics and acetate Ringer's solution with 1% glucose could be administered per ideal body weight, the effects of muscle relaxants lasted shorter, pressure-controlled ventilation could keep oxygenation with adequate carbon dioxide, and ultrasound assist was useful in epidural catheterization in the bariatric patients.

Lumbar epidural space was narrower in parturients than that in nonpregnant women by ultrasound assessment

Labor epidural is commonly used to provide both regional anesthesia and postoperative pain relief. Epidural space is supposed to be narrower and deeper in a parturient than that in a nonpregnant woman. The aim of this study was to explore the difference of epidural spaces between parturient and nonpregnant women by ultrasound assessment. Thirty nonpregnant female volunteers and 30 parturients undergoing labor epidurals were enrolled to receive ultrasound examination. A low-frequency (2–5 MHz) curved-array ultrasound probe was used to obtain spinal sonoanatomy for each subject. The longitudinal paramedian scanning plane was used to obtain optimal ultrasound image for spinal sonoanatomy. Primary outcome was evaluated by the diameter and depth of epidural space at three lumbar interspaces (from L2 to L5). The quality of ultrasound images was also compared between the groups by a numerical scoring system (from 0 to 3). The mean diameters of lumbar epidural spaces were 3.03 ± 0.45 mm and 4.44 ± 0.49 mm ( p < 0.05) for parturients and nonpregnant women, respectively. The mean depths of lumbar epidural spaces for parturients and nonpregnant women were 3.53 ± 0.62 cm and 3.25 ± 0.63 cm, respectively ( p < 0.05). The mean scores for epidural space image quality were 2.58 ± 0.58 and 2.63 ± 0.53 for parturients and nonpregnant women, respectively ( p = 0.08). Epidural space is narrower and deeper at lumbar interspaces in obstetrics by ultrasound examination. The quality of ultrasound images did not differ significantly between the groups. These quantitative results improve the understanding of the differences between two groups that have been previously known qualitatively and may help in avoiding complications.

Ultrasound decreases the failed labor epidural rate in resident trainees

Background Epidural analgesia is widely used for pain relief during labor. The purpose of this study was to determine if ultrasound measurement of the depth from skin to epidural space before the epidural technique decreases the failure rate of labor analgesia. A secondary objective was to correlate ultrasound depth to the epidural space with actual depth of the needle at placement. Methods In this prospective, randomized, non-blinded study, 370 parturients requesting labor epidural analgesia were randomized to receive their epidural technique by first year anesthesia residents with or without prior ultrasound determination of epidural space depth. Outcome variables included the incidence of epidural catheter replacement for failed analgesia and the number of epidural attempts and accidental dural punctures. Results The ultrasound group had fewer epidural catheter replacements ( P < 0.02), and epidural placement attempts ( P < 0.01) compared to the control group. Pearson’s correlation coefficients comparing the actual versus ultrasound estimated depth to the epidural space in the longitudinal median and transverse planes were 0.914 and 0.909, respectively. Pearson’s correlation coefficient comparing the ultrasound estimated depths to the epidural space in the transverse and longitudinal median planes was 0.940. No significant differences were noted with respect to staff interventions, top-ups, accidental dural punctures, and delivery outcome. Conclusions Ultrasound measurement of the epidural space depth before epidural technique placement decreases the rate of epidural catheter replacements for failed labor analgesia, and reduces the number of epidural attempts when performed by first year residents and compared to attempts without ultrasound guidance.

A Service Evaluation of Ultrasound Assessment of the Epidural Space: A Retrospective Audit

Interest in the ultrasound assessment of the epidural space prior to regional anaesthesia is becoming extremely popular. The published data to date comes mainly from single operators performing scans in clinical trial settings. The clinical data from a busy teaching unit has been examined to see how it compares with standards in the published literature. 114 scans were performed by a total of 6 consultant anaesthetists as part of their normal clinical work. The majority of scans were performed for either maternal obesity (72%) or training (18%). The difference between the ultrasound assessed depth and needle depth was 0.25 +/– 0.7 (mean +/– sd) cm. The correlation coefficient (r) for these two variables was 0.86. This data suggests that the ultrasound reliably measure depth of epidural space in a routine clinical setting.

The Development and Use of a Phantom to Aid Training in Depth Measurement with Ultrasound for Epidural Procedures

Background: Within obstetric anaesthesia, the use of ultrasound to measure the depth of epidural space is increasing. There are, however,clinical governance issues surrounding its use and teaching of ultrasound skills.Method: We have developed a model for use in training anaesthetists in the skill of measuring depth using ultrasound.Results: The mean ultrasound measured depths ranged between 0.36 and 5.86 cm, which correlates well with the direct depth measurements.Bland-Altman analysis was carried out. The range of differences between ruler measured and ultrasound measured depths was � 0.31 to1.87 cm.Conclusions: The results gained from depth measurements on the model were comparable to both our local clinical data and publishedliterature. The model is easy to produce and a useful training aid for ultrasound skills, in particular measurement of depth.

Evidence for the Use of Ultrasound in Neuraxial Blocks

To summarize the existing evidence behind the role of ultrasonography in neuraxial anesthesia techniques. A literature search of the MEDLINE, PubMed, ACP Journal Club databases, and the Cochrane Database of Systematic Reviews was performed using the term ultrasonography combined with each of the following: spinal, intrathecal, epidural, and lumbar puncture. Only studies related to regional anesthesia or acute pain practice were included. Case reports and letters to the editor were excluded. Seventeen relevant studies were identified and included in this review. Neuraxial ultrasonography is a recent development in regional anesthesia practice. Most clinical studies to date come from a limited number of centers and have been performed by very few and highly experienced operators. The existing evidence may be classified in 2 main content areas: (a) ultrasound-assisted neuraxial techniques and (b) real-time ultrasound-guided neuraxial techniques. Neuraxial ultrasonography has been recently introduced to regional anesthesia practice. The limited data available to date suggest that it is a useful adjunct to physical examination, allowing for a highly precise identification of regional landmarks and a precise estimation of epidural space depth, thus facilitating epidural catheter insertion. Further research is needed to conclusively establish its impact on procedure success and safety profile, particularly in the adult nonobstetric population.

A prospective, observational study of the relationship between body mass index and depth of the epidural space during lumbar transforaminal epidural steroid injection.

Previous studies have concluded that transforaminal epidural steroid injections (ESIs) are more effective than interlaminar injections in the treatment of radiculopathies due to lumbar intervertebral disk herniation. There are no published studies examining the depth of epidural space using a transforaminal approach. We investigated the relationship between body mass index (BMI) and the depth of the epidural space during lumbar transforaminal ESIs. Eighty-six consecutive patients undergoing lumbar transforaminal ESI at the L3-L4, L4-L5, and L5-S1 levels were studied. Using standard protocol, the foraminal epidural space was attained using fluoroscopic guidance. The measured distance from needle tip to skin was recorded (depth to foraminal epidural space). The differences in the needle depth and BMI were analyzed using regression analysis. Needle depth was positively associated with BMI (regression coefficient [RC], 1.13; P < 0.001). The median depths (in centimeters) to the epidural space were 6.3, 7.5, 8.4, 10.0, 10.4, and 12.2 for underweight, normal, preobese, obese I, obese II, and obese III classifications, respectively. Sex (RC, 1.3; P = 0.02) and race (RC, 0.8; P = 0.04) were also significantly associated with needle depth; however, neither factor remained significant when BMI was accounted as a covariate in the regression model. Age, intervertebral level treated, and oblique angle had no predictive value on foraminal depth (P > 0.2). There is a positive association between BMI and transforaminal epidural depth, but not with age, sex, race, oblique angle, or intervertebral level.

Estimating lumbar epidural space depth in infants and children of Korea.

Lumbar epidural block is now a popular technique for anesthesia and post operative analgesia. It may be helpful for prevention of complication during this procedure to know the depth from the skin to the lumbar epidural space before the procedure. This study was undertaken to evaluate the depth from the skin to the lumbar epidural space and to determine any potential relationship between a patient's data (age, weight, and height) and the measured depth in Korean children. We investigated the electronic records of 662 Korean children who were received urologic surgeries with epidural catheterization for postoperative analgesia. The patients' gender, age, weight, height and epidural depth were recorded and analyzed with multiple linear regression test using SPSS 13.0 (SPSS Co., Ilinois, USA). The patient's age and weight were significantly correlated to the skin-epidural space depth in Korean children. Body weight was more significant variable than age on the epidural depth. The empirical formula derived from the results was as follow; epidural depth (mm) = 9 + 0.5 x body weight (kg) - 0.2 x age (months). We suggest that the depth of skin-lumbar epidural space can be estimated with the empirical formula based on body weight and age.