Quinn H. Hogan

Lumbosacral Cerebrospinal Fluid Volume Is the Primary Determinant of Sensory Block Extent and Duration during Spinal Anesthesia

Background Injection of local anesthetic into cerebrospinal fluid (CSF) produces anesthesia of unpredictable extent and duration. Although many factors have been identified that affect the extent of spinal anesthesia, correlations are relatively poor and the extent of spread remains unpredictable. This study was designed to determine whether variability in the volume of lumbosacral CSF among individuals is a contributing factor in the variability of spinal anesthesia. Methods Spinal anesthesia was administered to 10 healthy volunteers with 50 mg lidocaine in 7.5% dextrose. The technique was standardized to minimize variability in factors known to affect the distribution of spinal anesthesia. The extent of sensory anesthesia was assessed by pin‐prick and by transcutaneous electrical stimulation. Motor blockade was assessed in the quadriceps and gastrocnemius muscles by force dynamometry. Duration of anesthesia was assessed by pin‐prick, transcutaneous electrical stimulation, and duration of motor blockade. Lumbosacral CSF volumes were calculated from low thoracic, lumbar, and sacral axial magnetic resonance images obtained at 8‐mm increments. Volumes of CSF were correlated with measures of extent and duration of spinal anesthesia using the Kendall rank correlation test. Results Lumbosacral CSF volumes ranged from 42.7 to 81.1 ml. Volumes of CSF correlated with pin‐prick assessments of peak sensory block height (P = 0.02) and duration of surgical anesthesia (as assessed by the duration of tolerance to transcutaneous electrical stimulation at the ankle (P < 0.05). Conclusions Variability in lumbosacral CSF volume is the most important factor identified to date that contributes to the variability in the spread of spinal sensory anesthesia.

ASRA Practice Advisory on Neurologic Complications in Regional Anesthesia and Pain Medicine

Neurologic complications associated with regional anesthesia and pain medicine practice are extremely rare. The ASRA Practice Advisory on Neurologic Complications in Regional Anesthesia and Pain Medicine addresses the etiology, differential diagnosis, prevention, and treatment of these complications. This Advisory does not focus on hemorrhagic and infectious complications, because they have been addressed by other recent ASRA Practice Advisories. The current Practice Advisory offers recommendations to aid in the understanding and potential limitation of neurologic complications that may arise during the practice of regional anesthesia and pain medicine.

Upper extremity regional anesthesia. Essentials of our current understanding, 2008

Brachial plexus blockade is the cornerstone of the peripheral nerve regional anesthesia practice of most anesthesiologists. As part of the American Society of Regional Anesthesia and Pain Medicines commitment to providing intensive evidence-based education related to regional anesthesia and analgesia, this article is a complete update of our 2002 comprehensive review of upper extremity anesthesia. The text of the review focuses on (1) pertinent anatomy, (2) approaches to the brachial plexus and techniques that optimize block quality, (4) local anesthetic and adjuvant pharmacology, (5) complications, (6) perioperative issues, and (6) challenges for future research.

Neural blockade for diagnosis and prognosis : A review

On the basis of the published material reviewed above, we conclude that there are many limitations that weaken the theoretic basis for neural blockade as a diagnostic or prognostic tool. In addition, these procedures in general lack thorough documentation of clinical usefulness. Reasonable employment of diagnostic neural blockade, therefore, requires not only care in technique and confirmation of effects, but also caution in interpretation and application of the results. This critical evaluation needs to be tempered, however, by two further observations. Experienced and observant clinicians have found these procedures may, on certain occasions, provide information that is helpful in guiding subsequent therapy, so we should not be in haste to dismiss the accumulated judgment of practitioners. Finally, the confusion and complexity that typifies diagnosis in chronic pain may justify the selective use of diagnostic blocks that make anatomic and physiologic sense, even if their validity is incompletely proved.

Lumbar epidural anatomy. A new look by cryomicrotome section.

The anatomic findings from cryomicrotome sections of 38 cadaver lumbar spines are reported. The technique produces high-resolution planar images of undisturbed epidural anatomy. Several observations differ from previous reports that used methods more prone to artifact. The epidural contents are found in circumferentially and metamerically segmented compartments, rather than in a uniform layer. Large areas of the dura are directly in contact with the spinal canal wall. The steeply arched ligamenta flava are fused in the midline to a variable degree. The space anterior to the dura is filled with veins and is isolated from the rest of the epidural space by a membranous lateral extension of the posterior longitudinal ligament. This membrane and a midline posterior fat pedicle are the only observed potential barriers to the spread of epidural solutions. These findings may be important in understanding the mechanics and pharmacokinetics of solutions injected into the epidural space and in refining techniques for needle and catheter placement.

Brachial plexus anesthesia: Essentials of our current understanding☆

Brachial plexus regional anesthesia has been a mainstay of the anesthesiologist’s armamentarium since Hall1 first reported the use of cocaine to block upper extremity nerves in 1884. The American Society of Regional Anesthesia and Pain Medicine (ASRA) has sponsored a unique educational endeavor to provide practitioners and academicians alike with a comprehensive resource pertaining to brachial plexus anesthesia. Initially presented as an all-inclusive workshop at its May 2001 meeting, the material is available in its entirety on the ASRA Web site (www.asra.com). This review is a summary that presents the essential scholarly work resulting from this effort. It strives to (1) serve as a review of pertinent brachial plexus anatomy, (2) compare the efficacy of brachial plexus approaches and techniques, (3) describe the complications inherent to brachial plexus anesthesia, and (4) present available evidence to guide selection of drugs. Because evidence-based data pertaining to brachial plexus anesthesia is incomplete, we acknowledge informational gaps and emphasize areas in which we believe further study is needed. Readers desiring a more in-depth discussion of specific topics will find it in the Web site source documents, which also include additional anatomic photographs. Brachial Plexus Anatomy

Epidural opiates and local anesthetics for the management of cancer pain

&NA; The role of epidural morphine in chronic cancer pain treatment is unresolved. In a population of 1205 cancer patients, the aggressive use of systemic opiates limited the trial of epidural analgesia to 16 cases. Successful analgesia was achieved with epidural morphine alone in 6 of these 16 cases following systemic opiate failure. The addition of bupivacaine produced analgesia in all of the 10 remaining cases and was successful chronically in 6 cases. Complications occurred in 11 of the 16 cases of epidural analgesia and included dislodged or broken catheters, pain on injection, hyperesthesia from epidural morphine and bleeding or infection related to the epidural catheter. Epidural morphine is indicated only in selected cancer pain patients and, although bupivacaine extends the efficacy of epidural analgesia, these methods are accompanied by problems and limitations.

Species and strain differences in rodent sciatic nerve anatomy: Implications for studies of neuropathic pain

&NA; Hindlimb pain models developed in rats have been transposed to mice, but assumed sciatic nerve neuroanatomic similarities have not been examined. We compared sciatic nerve structural organization in mouse strains (C57BL/6J, DBA/2J, and B6129PF2/J) and rat strains (Wistar, Brown Norway, and Sprague–Dawley). Dissection and retrograde labeling showed mouse sciatic nerve origins predominantly from the third lumbar (L3) and L4 spinal nerves, unlike the L4 and L5 in rats. Proportionate contributions by each level differed significantly between strains in both mice and rats. Whereas all rats had six lumbar vertebrae, variable patterns in mice included mostly five vertebrae in DBA/2J, mostly six vertebrae in C57BL/6J, and a mix in B6129PF2/J. Mice with a short lumbar vertebral column showed a rostral shift in relative contributions to the sciatic nerve by L3 and L4. Ligation of the mouse L4 nerve created hyperalgesia similar to that in rats after L5 ligation, and motor changes were similar after mouse L4 and rat L5 ligation (foot cupping) and after mouse L3 and rat L4 ligation (flexion weakness). Thus, mouse L3 and L4 neural segments are anatomically and functionally homologous with rat L4 and L5 segments. Neuronal changes after distal injury or inflammation should be sought in the mouse L3 and L4 ganglia, and the spinal nerve ligation model in mice should involve ligation of the L4 nerve while L3 remains intact. Strain‐dependent variability in segmental contributions to the sciatic nerve may account in part for genetic differences in pain behavior after spinal nerve ligation.

Distribution of solution in the epidural space: Examination by cryomicrotome section

Background and Objectives The routes of distribution and barriers to flow of solutions in the epidural space are incompletely determined. This study examined macroscopic details of epidural injectate spread in postmortem humans by cryomicrotome imaging. Methods Soon after death, 3 nonembalmed adult human subjects were injected with ink through epidural catheters inserted by standard techniques. Following freezing, microtome sectioning was performed to reveal anatomic features down to 100 μm. To control for effects of death, an adult baboon was injected during general anesthesia and subsequently examined in the same fashion. Results Injected ink was readily evident and showed spread as rivulets through numerous small channels rather than as a unified advancing front. The fascia that extends laterally from the posterior longitudinal ligament is an important barrier restricting solution flow. Solution preferentially traveled along the nerve root sheath through the intervertebral foramen. Conclusions Distribution of solution in the epidural space is nonuniform. Rather than a uniform advancing front, spread is directed among paths between structures according to pressures by which they are compressed. No structural barriers block flow through the intervertebral foramina or spinal canal other than the fascia of the posterior longitudinal ligament.

Epidural Catheter Tip Position and Distribution of Injectate Evaluated by Computed Tomography

BACKGROUND The distribution of solutions injected into the epidural space has not been determined. The author therefore examined the site of catheter tips and the spread of contrast material in the epidural space using computed tomographic (CT) imaging in patients receiving successful epidural analgesia. METHODS Lumbar epidural catheters were placed in 20 female patients by a midline technique. Anesthetic effect was determined by motor and sensory examinations during analgesic infusion. CT images were obtained for identification of the catheter tip and after radiographic contrast injection of 4 ml and then an additional 10 ml. RESULTS Catheter tips were most often found lateral to the dura in the intervertebral foramen. In these subjects with normally functioning epidural analgesia, there was remarkable interindividual variability in patterns of spread, including various amounts of anterior passage, layering along the dura, and compression of the dura creating a posterior fold. Accumulation becomes more symmetric with increasing injectate volume. Spread through the intervertebral foramina was seen in all subjects. Air and fat in the region of the catheter interfered with solution spread in three subjects, but only over a limited area. Asymmetry in anesthetic effect was attributable to catheter position. No substantial barriers to solution spread were observed. CONCLUSIONS A variety of catheter tip positions and patterns of solution spread underlie normal epidural anesthesia. Nonuniform distribution of injectate is common and is compatible with uniform anesthesia. Posterior midline structures play a minimal role in impeding distribution of injectate. A far lateral catheter position is a more common cause of asymmetric block than anatomic barriers to solution spread.