Resin injection studies of the lumbar extradural space

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.

Unilateral Horner's syndrome and brachial plexus anesthesia during lumbar epidural blockade

Horner's syndrome is a rare side effect of epidural analgesia. In association with ipsilateral brachial plexus block, it has only been reported once before, in French. Unilateral blockade has also been reported, although its etiology is unclear and may be multifactorial. The patient described here experienced an asymmetrical epidural blockade with a unilateral Horner's syndrome and ipsilateral brachial plexus block.

A study of epidural pressures in infants

BACKGROUND

The pressures exerted on fragile structures in the infant during epidural injections have never been studied previously.

METHODS

We measured the pressure changes in the epidural space of 20 infants during injection of local anaesthetic solutions. The pressures developed during passage of the epidural needle through the ligaments of spine and in the epidural space during the injection of 1 ml at two rates of injection, over 1 and 2 min and the residual pressure 1 and 2 min after each injection were studied.

RESULTS

The mean pressure while the needle was being advanced through the ligamentum flavum was 69.14 +/- 36.95 mmHg. The epidural pressure after needle had just penetrated the ligament without eliciting the loss of resistance was 1 +/- 9.759 mmHg. A distinct pulsatile waveform identical to the pulse waveform was observed as soon as the epidural space was entered. The pressure rise varied according to the rate of injection. The pressures were 27.79 mmHg when the rate of injection was 1 ml.min(-1), with a residual pressure after 1 min of 12 +/- 5.53 mmHg and 10.14 +/- 5.53 mmHg after 2 min of injection. When the rate of injection was 1 ml.2 min(-1), the pressures were 15.66 +/- 9.48 mmHg with a residual pressure after 1 min of 14.79 +/- 5.15 mmHg and 12.93 +/- 5.46 mmHg after 2 min of injection.

CONCLUSIONS

The residual pressures seem to vary more with the volume injected than the rate of injection or the pressures developed during the injection. The relationship between the rate of injection and pressures is significant when compared with adults where the pressures have been measured after an injection rate of 1 ml.s(-1) and 1 ml.5 s(-1). This is a very fast rate compared with our rates of injection of 1 ml over 1 and 2 min. Based on the findings of this study, we recommend a rate of 1 ml.2 min(-1) in infants. In neonates, a slower rate of injection would be preferable.

Anatomy of the lumbar epidural region using magnetic resonance imaging: a study of dimensions and a comparison of two postures

Many techniques used to investigate the epidural region may alter the anatomy. Magnetic resonance imaging (MRI) has been introduced as a non-invasive diagnostic technique. The aim of this study was to investigate the anatomy of the lumbar epidural region using MRI, studying the morphology, the dimensions and the modification that may result from a change of position. Ten young, healthy female volunteers were studied to obtain results relevant to obstetric anesthesia. The following measurements were made: anterior epidural space (AES); posterior epidural space (PES); ligamenta flava; distance between the PES and the skin (S-ES); and interspace distance (ISD). All these distances were measured with the subject supine and the lumbar spine either in a neutral or a non-lordotic (flexed) position. The S-ES ranged from 2.7 to 8.1 cm. This distance was greater in the lower than in the upper lumbar segments. No differences were observed in AES, PES and ligamenta flava between the neutral and flexed positions. Flexion of the spine did not affect the S-ES but increased the ISD (P < 0.05). The S-ES at any lumbar segment or interspace and the thickness of ligamenta flava at the L2/3 interspace correlated significantly with body weight (respectively, P < 0.01 and P < 0.02). In conclusion, MRI may clearly reveal the anatomy of the epidural region. The circumferentially and metamerically segmented compartments of the epidural space were clearly noted and measured. Ligamenta flava seem to be thinner in younger than in older subjects. This may partly explain a reduced loss of resistance sometimes perceived in obstetric patients.

Risk of catheter migration during combined spinal epidural block: percutaneous epiduroscopy study

Combined spinal epidural (CSE) block with the needle-through-needle technique has become increasingly popular during recent years. However, the risk of epidural catheter penetrating dura mater through the hole made by the spinal needle (migration) is a major concern. In 15 fresh cadavers a percutaneous epiduroscopy technique with a rigid epiduroscope and video recording was used to assess the risk of catheter migration when a CSE block is performed. The experimental sequence included (a) one dural hole made by the spinal needle, (b) multiple (five) dural holes made by the spinal needle, and (c) a dural hole made by Tuohy needle. Twenty-four experimental sequences were performed in the lumbar region. Four sequences were failures due to technical problems. In the remaining 20 cases, the anatomic structures in the epidural space were recognized easily. The epidural space appears to be only a potential space, kept open either by epiduroscope or by repeated injections of air or saline. The dural holes made by Tuohy and spinal needles, and the ease of difficulty of catheter penetration through these holes, were clearly visible. Extensive tenting of the dura was seen in all subjects. It was impossible to force an 18-gauge epidural catheter through the dural hole after a single dural puncture made by a 25-gauge spinal needle. After multiple (five) dural punctures with the spinal needle, the epidural catheter penetrated the perforated dura in 1 of 20 cases. The epidural catheter penetrated the dural hole made by the Tuohy needle in 9 of 20 cases. The distribution of fat, rather than any dorso median connective tissue band, influences the course of epidural catheter in epidural space.(ABSTRACT TRUNCATED AT 250 WORDS)

Maintained unilateral analgesia

We describe a case of a patient subjected to what proved to be an epidural puncture with catheter placement resulting in persistent unilateral analgesia. The epidurographic study by contrast medium injection through the catheter showed unilateral distribution of the contrast following the cranio-caudal axis in the anterior epidural space.

Repeat epidural analgesia and unilateral block

The use of epidural analgesia has become so widespread in recent years that many women are now requesting repeat epidural analgesia for their second or subsequent labour. This study examines the incidence of problems at insertion and of inadequate block in 71 multiparae having second epidurals compared with 150 primiparae having their first epidural. Unilateral block occurred in 6.66% of primiparae and 18.3% of multiparae (P < 0.02). There was no association between difficulty of insertion of catheter, blood in needle/catheter or paraesthesia and unilateral blockade. Epidurals were inserted at a greater dilatation (P < 0.05) and there was a shorter time to delivery (P < 0.01) in the multiparous group. We conclude that unilateral block is thus more common in women receiving repeat epidurals.

The vertebral foramen: a report concerning its contents

Thirteen subjects were randomly selected and embalmed according to Winckler's technique. After removal of the vertebral column and the head in one block the specimens were frozen. Transverse transpedicular cuts were performed at C6, T1, T6, L1, L3, and L5. After enlargement photography, the surface area of the vertebral foramen and its various contents were measured on a computer using the Canvas programme and analysed using the Statview programme. The mean area of the vertebral foramen occupied by the cord was 30.5% at C6, 26.1% at T1, 21.4% at T6, 12.7% at L1, 0.08% at L3. The mean area occupied by the nerve roots was 3.9% at C6, 3.3% at T1, 1.6% at T6, 14.2% at L1, 17.5% at L3, 12.2% at L5. The mean area of all the nervous tissue was 34.4% at C6, 29.5% at T1, 23% at T6, 26.9% at L1, 18.9% at L3, 19.3% at L5. The cerebrospinal fluid occupied a mean area of 25.2% at C6, 30.7% at T1, 31.6% at T6, 43% at L1, 43.5% at L3, and 28.1% at L5. The total neural tissue did not occupy more than a third of the vertebral foramen. These facts should be considered by surgeons who perform laminectomy or decompression in cases of vertebral trauma or congenital and osteoarthritic stenoses.

Repeated unilateral epidural blockade

Unilateral epidural analgesia occurring in a parturient three times in successive pregnancies is reported. Possible causes are reviewed, and clinical and radiological evidence in support of the most likely explanation are presented.

[Is posterior lumbar epidural space partitioned?]

The anatomy of the posterior lumbar epidural space (PLES) has been extensively studied. Besides the anatomists, surgeons, radiologists and anaesthetists have taken an interest in this. However, because each one has considered the PLES from his own specialist field, descriptions are not always concordant. In particular, the reality of a medial partition in the PLES has been suggested by epidurography and intraoperative observations. Lewit and Sereghy and Luyendijk opened the debate by reporting, on antero-posterior epidurographic films, a clear-cut, medial, vertical and narrow picture which partitioned the PLES. However, this was not constant. Savolaine et al. also recognized this partition on epidurographic CT scans. During laminectomies, Luyendijk has taken photographs of a medial fold of the dura mater which appeared to hold it to the posterior vertebral arch, being collapsed on either side of the midline. He named it "plica mediana dorsalis durae matris" (PMD). Several anaesthetists considered that this could explain why epidural analgesia sometimes acted on one side only. Husemeyer and White, and Harrison et al., have tried to confirm this experimentally by making casts with polymerizing resins in cadavers. They did not get very convincing results. Blomberg also tried to see this space by epiduroscopy in the cadaver. Unfortunately, for technical reasons, his photographs were of poor quality. He, however, reported having seen each time the PMD and a band of connective tissue fixing it to the vertebral arch in the midline. However, all these anatomical studies used methods which alter the natural structures. Their results are therefore questionable. The PLES is a virtual space. Histological studies have shown that it is filled with fatty tissue between the dura and the vertebral arch. It is therefore conceivable that any liquid injected into the PLES, such as contrast medium or local anaesthetic, must push back the dura, the only tissue which can move to give it any room. The fatty tissue could therefore be compressed and take any of the shapes which have been described on epidurography. On the other hand, should it be torn, it seems this fatty tissue could make up these haphazard fibrous tracts tensed between the dura and the vertebral arch, such as described in classical anatomy, as Bonica recalled. These can be clearly seen during surgical and anatomical dissections, and during endoscopies carried out on cadavers with sufficient optical means, as opposed to the medial fibrous band fixing the dura to the vertebral arch.(ABSTRACT TRUNCATED AT 400 WORDS)