Prediction of the distance from skin to epidural space for low-thoracic epidural catheter insertion by computed tomography

Background. It may be clinically useful to predict the depthof the epidural space. Methods. To investigate the accuracy of preoperative abdominalcomputed tomography (CT) in prediction of the distance for low-thoracicepidural insertion, a single group observational study was conductedin 30 male patients undergoing elective major abdominal surgeryrequiring epidural analgesia for postoperative pain relief.Using the paramedian approach, low-thoracic epidural insertionat T10–11 interspace was performed with a standardizedprocedure to obtain an actual insertion length (AIL). Accordingto the principles of trigonometry, an estimated insertion length(EIL) was calculated as 1.26 times the distance from skin toepidural space measured from the preoperative abdominal CT. Results. The mean (SD) EIL and AIL were 5.5 (0.7) and 5.1 (0.6)cm, respectively, with a significant correlation (r=0.899, P<0.01).The EIL tended to have a higher value than the AIL (0.4 (0.3)cm). There were significant correlations of both EIL and AILwith weight (P<0.01), BMI (P<0.01), and body fat percentage(P<0.01), but not with height (P>0.05). Conclusions. We conclude that the preoperative abdominal CTis helpful in prediction of the distance for low-thoracic epiduralinsertion using the paramedian approach. Br J Anaesth 2004; 92: 271–3     

Depth from the skin to the thoracic paravertebral space in infants and children

The actual depth from the skin to the paravertebral space (S-PVS depth) was determined in twenty paediatric ASA 1 patients (age range: 1-175 months, weight range: 3.8-61.0 kg) receiving a thoracic paravertebral block for renal surgery or cholecystectomy. The S-PVS depth correlated well to patient weight (r= 0.94) and the S-PVS depth can be predicted by the following equation: S-PVS depth (mm) = 21.2 + 0.53 × (weight in kg). Our previously reported equation for the prediction of the S-PVS depth, derived from computed tomography scans, was found to significantly (P= 0.0023) differ from the regression line generated in the present study and will underestimate the S-PVS depth by approximately 2.5-3.0 mm compared to the present results. The reader is, thus, recommended to use the new equation for a more accurate prediction of the S-PVS depth when performing a thoracic paravertebral blockade in children.     

The distance from the skin to the epidural space

To determine whether there is any systemic relationship between the distance from the skin to the epidural space and physical constitution, the distance from the skin to the epidural space was measured in 1007 epidural punctures. The distance from the skin to the epidural space in male was greater than that in female (P 0.001). However, the analysis of the distance from the skin to the epidural space of the selected patients who had both a weight of 50–60kg and a height of 1.5–1.7m indicated no statistical difference between male and female. The best correlation was found between the distance from the skin to the epidural space and body weight. The correlation between the distance from the skin to the epidural space and height was less striking. Ninety-five percent of the patients who received epidural puncture at the thoraco-cervical area (C7-T2) had a distance to the epidural space of 4.0–6.9cm; 87% at the lower-thoracic area (T8–T10), 4.0–6.9cm; 93% at the thoraco-lumbar area (T12-L2), 3.0–4.9cm; 85% at the mid-lumbar area (L2–L4), 3.0–4.9cm. These results may be useful for young anesthesiologists to master epidural block safely and efficiently.(Hirabayashi Y, Matsuda I, Inoue S et al.: The distance from the skin to the epidural space. J Anesth 2: 198–201, 1988)     

The depth of the lumbar epidural space from the skin

The depth of the epidural space at different intervertebral interspaces was measured in 1000 parturients. Overall the median distance from the skin to the epidural space was 4.7 cm, but this varied with the lumbar interspace at which it was measured, being greatest at the third (L3-4) interspace (4.93 cm) and least at the first (L1-2) interspace (4.23 cm). The clinical significance of these findings is discussed.     

Prediction by computerised tomography of distance from skin to epidural space during thoracic epidural insertion

In this single group observational study on 29 patients, we describe a technique that predicts the depth of the epidural space, calculated from the routine pre-operative chest computerised tomography (CT) scan using Pythagorean triangle trigonometry. We also compared the CT-derived depth of the epidural space with the actual depth of needle insertion. The CT-derived and the actual depths of the epidural space were highly correlated (r = 0.88, R2 = 0.78, p < 0.0001). The mean (95% CI) difference between CT-derived and actual depths was 0.26 (0.03-0.49) cm. Thus, the CT-derived depth tends to be greater than the actual depth by between 0.03 and 0.49 cm. There were no associations between either the CT-derived or the actual depth of the epidural space and age, weight, height or body mass index.     

Block of the sacral segments in lumbar epidural anaesthesia

Background. Block of the first sacral segment is often delayedin lumbar epidural anaesthesia. The addition of either epinephrineor sodium bicarbonate to the local anaesthetic enhances theefficacy of epidural block. We assessed the block of lumbo-sacralsegments in lumbar epidural anaesthesia adding epinephrine and/orbicarbonate to lidocaine. Methods. Twenty-seven patients undergoing lumbar epidural anaesthesiawith lidocaine 2%, 17 ml at L4-5 or L5-S1 were randomly dividedinto three groups. Plain lidocaine, lidocaine with 1:200 000epinephrine or lidocaine–epinephrine–bicarbonatewas administrated via an epidural catheter. The pain thresholdafter repeated electrical stimulation was used to assess thesensory block at the L2, S1, and S3 segments. Motor block wasevaluated using the Bromage scale. Results. Patient characteristics were comparable between thegroups. The pH of lidocaine in the lidocaine–epinephrine–bicarbonategroup was significantly higher than that in other groups. Painthresholds at the S1 and S3 segments in the lidocaine–epinephrine–bicarbonategroup were significantly higher than those in the lidocaine–epinephrinegroup. However, differences in the pain threshold at the L2segment between groups were insignificant. The time to onsetof sensory block at the S1 and S3 in the lidocaine–epinephrine–bicarbonategroup was significantly shorter than that in the lidocaine group.Pain threshold by pinprick test was approximately within the30–50 mA range. Conclusion. A combination of lidocaine, bicarbonate, and epinephrineincreases the pain threshold over the sacral segments. Br J Anaesth 2003; 90: 173–8     

Spread of radioopaque dye in the epidural space in infants

BACKGROUND: This prospective study aimed to assess the extent of spread of dye in the epidural space and whether it would vary in direct proportion to the volume when injecting two volumes of dye. METHODS: Ten infants, aged 2-36 days (mean +/- SD, 13.30 +/- 13.68 days) and weighing 1.8-4.5 kg (mean +/- SD, 2.60 +/- 0.97 days), who were undergoing major thoracoabdominal surgery under epidural and general anaesthesia, were studied. At the end of surgery, two volumes of radioopaque dye (omnipaque) 0.5 ml.kg(-1) and 1 ml.kg(-1) were injected into the epidural space at a rate of 1 ml.2 min(-1). The spread was studied by taking X-rays after both injections in the left lateral position. RESULTS: There were 10 different patterns of spread in the 10 cases. Uniformly circumferential and cylindrical spread was seen only in one infant. In the others, there were segregated patches of anterior and posterior spread with or without interspersed patches of circumferential spread. There was variation in the extent, location and the density of spread, filling defects and skipped segments with both volumes. Back leak of dye along the needle track was seen in three cases. Statistically, segments were 9.30 +/- 3.68 for 0.5 ml.kg(-1), for 1 ml.kg(-1) 11.50 +/- 3.03, 3.03, S, P=0.014; circumferential spread for 0.5 ml.kg(-1) 2.70 +/- 2.16, for 1 ml.kg(-1) 5.90 +/- 3.14 3.59, P=0.006; anterior spread for 0.5 ml.kg(-1) 3.60 +/- 1.58, for 1 ml kg(-1) 7.90 +/- 2.33 5.88, P=0.001; posterior spread for 0.5 ml.kg(-1) 8.20 +/- 3.71, for 1 ml.kg(-1) 9.80 +/- 3.68 3.54, P=0.006. Doubling of spread with doubling of the volume occurred in only one patient. There was a variable increase in extent or in the density of spread with reduction of skipped segments with the 1 ml.kg-1. The probable reasons for this variable spread and the mechanism of epidural anaesthesia in the presence of such spread are discussed. CONCLUSIONS: There is a difference in quantitative as well as qualitative spread in different patients and in the same patient with different volumes. There were statistically significant increases in the number of segments, circumferential, anterior and posterior locations in the 1.0 ml group. Both extent and density of spread improve with the higher volume but not in direct proportion to volume. 1 ml.kg(-1) has a better quantitative as well as qualitative spread than 0.5 ml and has a better chance of producing adequate anaesthesia.     

Effect of ethnicity and body mass index on the distance from skin to lumbar epidural space in parturients

With the current prevalence of obesity and trends in ethnic diversity amongst parturients in UK maternity units, we performed a prospective, observational study to establish the effect of ethnicity and body mass index on the distance from skin to epidural space in parturients. A total of 1210 parturients participated in this study. The mean (SD) distance from skin to lumbar epidural space was 5.4 (1.1) cm. When tested in a multiple regression model, both body mass index and ethnicity significantly influenced the distance from skin to lumbar epidural space in parturients. The distance from skin to lumbar epidural space amongst ethnic groups differed at any given body mass index. It was significantly greater in Black/British Black and White parturients compared with their Asian and Chinese counterparts. You can respond to this article at http://www.anaesthesiacorrespondence.com.     

The effect of lumbar epidural analgesia on the neurobehavioural responses of newborn infants

The effects of maternal lumbar epidural analgesia (Th10-L5) on the neonatal neurobehavioural response were studied at the ages of 3 h, 1 day, 2 days and 4-5 days. The subjects were healthy, full-term neonates, born vaginally to 15 mothers with lumbar epidural block and 19 mothers without analgesia. Those delivered with epidural analgesia scored significantly better on alertness at the age of 3 h, 2 days and 4-5 days than the control group. No other statistically significant differences were found between the groups. The formation of the two groups according to the mothers' desire for epidural analgesia may have contributed to differences in the process of labour, but with this reservation it may be suggested that lumbar epidural analgesia may enhance the infant's recovery from the stress of labour and vaginal delivery.     

A new combined spinal–epidural apparatus: measurement of the distance to the epidural and subarachnoid spaces

A new combined spinal–epidural anaesthesia apparatus with a 27G lockable spinal needle was used in 151 patients. Two groups could be created, based on whether dural perforation was felt or not (group 1: with dural click; group 2: no dural click). Measurements of the epidural space depth and of the protrusion of the spinal needle from the epidural needle (tip-to-tip distance) were made. The mean depth of the epidural space was 5.59 cm. Correlations were found with body weight, weight-to-height ratio and body mass index (p < 0.001). The mean tip-to-tip distance measured was 7.0 mm in the patients of group 1, whereas in group 2 a distance of 8.9 mm was found. This difference was statistically significant. Correlations were found between the epidural space width and the patient's height, weight-to-height ratio and body mass index. Four patients felt paraesthesia during placement of the spinal needle and, in another four patients, aspiration was necessary to detect cerebrospinal fluid. Two patients needed epidural top-ups due to insufficient level of anaesthesia. The lockable spinal needle provides safe and stable conditions during injection and a high rate of success in reaching the subarachnoid space.     

A morphometric cadaver study of the anterior lumbar epidural space

Introduction

Free disc fragments end often up in the concavity of the anterior epidural space. This space consists of two compartments. The discrepancy between the impressive magnetic resonance imaging findings, clinical symptoms in patients and the problem of treatment options led us to the anatomical determination of anterior epidural space volumes.

Materials and methods

For the first time, the left and right anterior epidural volume between the peridural membrane and the posterior concavity of the lumbar vertebral bodies L3–S1 were determined for each segment. A CT scan and a polyester resin injection were used for the in vitro measurements.

Results

The volumes determined in human cadavers using this method ranged from 0.23 ccm for L3 to 0.34 ccm for L5. The CT concavity volume determination showed this increase in volume from cranial to caudal, as well.

Conclusion

This volume is large enough to hold average-sized slipped discs without causing neurological deficits. A better understanding of the anterior epidural space may allow a better distinction of patient treatment options.     

Dilution and microfiltration of particulate corticosteroids for spinal epidural injections: impact on drug concentration and agglomerate formation

Particulate corticosteroids have been described to lead to greater pain improvement compared with their non-particulate counterparts when used in epidural injections. It is hypothesised that filtering may significantly impact their concentration and long-term efficacy. We investigated if passing particulate suspensions through different commonly-used filters affects drug dosage. Two particulate corticosteroid formulations, triamcinolone acetonide and methylprednisolone acetate, were mixed at different concentrations with either bupivacaine hydrochloride or 0.9% sodium chloride. Solutions were passed through a 5-μm and a 0.2-μm filter. Mass spectroscopy results indicated a complete loss of corticosteroid from the solutions using both filters, and light microscopy imaging demonstrated agglomerate formation, suggesting that filtering interferes with drug dosage. The choice of diluents must also be considered to reduce large agglomerate formation. Clinicians should be aware of the consequences of filtering particulate suspensions and carefully consider the selection of diluent when considering treatment plans.     

Genesis of the ''true'' negative pressure in the lumbar epidural space

A hypothesis is suggested that the initial or 'true' negative pressure encountered when a needle first enters the epidural space is due to initial bulging of the ligamentum flavum in front of the advancing needle followed by its rapid return to the resting position once the needle has perforated the ligament. The bulging has been confirmed to occur in fresh cadavers, and pressure studies carried out during performance of epidural blocks in patients lend weight to this hypothesis.     

Lumbar and thoracic epidural anaesthesia in children

Epidural anaesthetic techniques are an established part of paediatric anaesthesia. Their positive effects on general anaesthetic requirements, stay in the recovery unit, efficient perioperative pain relief and blunting of the perioperative stress response promote the routine use of regional anaesthetic techniques in children.With increasing knowledge of the anatomy and physiology of children, refinements in equipment and increased knowledge of the pharmacology of the agents used, continuous epidural catheter techniques are considered to be safe. There is some evidence that an epidural approach via the caudal and trans-sacral route is a low-risk procedure, even if the catheter is advanced to higher levels. Despite its positive effects the direct puncture at thoracic levels will probably never reach the level of routine practice. Because of its potential risks, the use of thoracic epidural anaesthesia (TEA) should be restricted to experienced paediatric anaesthetists and specialized centres.