Year : 2016 | Volume
: 6 | Issue : 2 | Page : 70--74
Neuraxial blocks in parturients with scoliosis and after spinal surgery
Mouveen Sharma, Ian McConachie
Department of Anesthesia and Perioperative Medicine, London Health Sciences Centre, Western University, London, Ontario, Canada
Dr. Ian McConachie
458 Cottontail Crescent, London, Ontario N5X 4N4
Neuraxial blocks in parturients with scoliosis and/or previous back surgery have traditionally been avoided due to concerns such as difficulty, increased complications, and decreased efficacy. Recent studies suggest that with attention to proper anesthetic technique and improvements in surgical procedures the success rate of neuraxial blocks is improved. The use of ultrasound may also improve the success rate of neuraxial blocks and should be considered. We review the recent literature and suggest practical approaches to neuraxial blocks in these parturients.
|How to cite this article:|
Sharma M, McConachie I. Neuraxial blocks in parturients with scoliosis and after spinal surgery.J Obstet Anaesth Crit Care 2016;6:70-74
|How to cite this URL:|
Sharma M, McConachie I. Neuraxial blocks in parturients with scoliosis and after spinal surgery. J Obstet Anaesth Crit Care [serial online] 2016 [cited 2019 Jun 26 ];6:70-74
Available from: http://www.joacc.com/text.asp?2016/6/2/70/191594
Neuraxial techniques are the anesthetic modality of choice for labor analgesia. Performing neuraxial blocks in women with a history of previous spinal surgery or scoliosis is challenging and can be time-consuming. Indeed, in the past, standard textbooks promoted a largely negative attitude toward neuraxial blocks in women with these comorbidities. Evidence suggests that in many centers these attitudes prevail and a majority of such women are not offered labor epidural analgesia, mostly due to the perception of difficult catheter placement.,
In this review, we highlight the problems anesthetists may encounter in performing neuraxial blockade in parturients with surgically corrected and uncorrected scoliosis as well as those that have undergone prior spinal surgery for other indications. We also discuss approaches to minimize technical challenges and improve the success rate and patient satisfaction.
Scoliosis and Pregnancy
Scoliosis is relatively common and is present in 2-4% of the children aged between 10 years and 16 years. The prevalence of curvature greater than 30 degrees is approximately 0.2%. Girls are more likely to have more severe curvatures and are more likely to progress; therefore they are more likely to require surgical treatment. Fortunately, available evidence suggests that scoliosis curvature is unlikely to progress during pregnancy,, and mild scoliosis is unlikely to impact pregnancy and delivery. However, the possibility of an operative delivery is higher in a parturient with scoliosis.
Surgical treatment involves the use of a combination of instruments to form a stable network to correct the abnormal curvature and bony spinal fusion. The preferred surgical approach is posterior spinal instrumentation, although in some cases anterior spinal instrumentation is performed. The surgery is based on distracting the concave side of the scoliosis and fusing the posterior spine with bone grafts. The instruments themselves do not interfere with needle placement; however, spinal fusion, as discussed below, poses a problem for neuraxial blockade. The improvement in surgical techniques have resulted in sparing of the lower lumbar segments and relative sparing of the epidural space as well as better derotation of the spine using implants placed laterally outside the spinal canal.,, The evidence that neuraxial blocks are used less often in the patients with prior corrective surgery holds true for both anterior and posterior spinal instrumentations.,
Multiple challenges confront the anesthesiologist when attempting neuraxial blocks in the patients with corrected and uncorrected scoliosis.
Difficulties with positioning may occur because of limited back mobility secondary to spinal fusion and/or because of the presence of hardware and implants in the patients with prior corrective surgery. Furthermore, the need to avoid positions that exacerbate pain may make positioning to perform neuraxial blocks difficult. Rotation associated with scoliosis distorts surface anatomy, and is a factor even in patients with prior surgery, as they may have underlying uncorrected and/or progressive rotation. In the patients with prior surgery, spinous processes may not be palpable, as posterior spinal fusion involves the removal of the spinous process and decortication of laminae as far as the facet joints, followed by bone grafting. Therefore, palpation of the spinous processes, a key landmark for placement of neuraxial anesthetics, may not be reliable for orientation. Furthermore, needle placement may not be possible in fused posterior segments. Prior surgical disruption of the ligamentum flavum can make the perception of loss of resistance nearly impossible. Deviation of the midline of the epidural space occurs toward the convex aspect of the scoliotic curve relative to spinous processes. Adhesions and scarring in the epidural space may affect local anesthetic spread and efficacy.
Although, not a technical concern, it must be borne in mind that up to 35% of women with scoliosis have severe back pain during pregnancy, mandating home treatment or hospitalization, which is a rate significantly more than back pain in pregnancy among the general obstetric population. This may be a source of anxiety for the patient and should be documented before attempting neuraxial blockade.
Segments that are not fused can be identified by reviewing operative notes and radiographs or by clinical examination. The cutaneous scar usually extends below the level of fusion, and if spinous processes are palpable, it would indicate segments that are not fused. Generally, fusion spares the lumbosacral joint.
Different approaches for needle insertion have been recommended in the patients with scoliosis:
Some authors recommend that during the insertion the needle should be oriented toward the convexity of the curve where the intralaminar spaces are wider. Another approach, termed the “modified paramedian approach”, recommends that the needle be inserted perpendicular to the plane of the back, lateral to the spinous process on the side of spinal convexity, it is then advanced toward the lamina and “walked” cephalad until the interlaminar space is entered.
The type of needle insertion technique adopted may have implications on the spread of anesthetic in the epidural space. There is some evidence to suggest that when using the midline approach with needle angulated toward the spinal convexity, anesthetic is more likely to spread into the concave side of the curve, leading to an asymmetric block. This may be overcome by using increased anesthetic volumes.
Depending upon the degree of scoliosis, an algorithm has been proposed to guide the anesthesiologist in planning neuraxial blockade. The degree of scoliosis is measured by Cobb' angle (CA), which is the angle subtended by a line drawn through the superior endplate of the most angulated cephalad vertebra and the inferior endplate of the most angulated caudal vertebra.
In mild scoliosis (CA 11–25 degree), good patient positioning and proceeding with caution is recommended. In moderate scoliosis (25-50 degree), consideration must be given for the use of imaging modalities such as ultrasound or fluoroscopy, either of the techniques described above could be used for the needle insertion. For severe scoliosis (>50 degrees), imaging with ultrasound should be considered and alternative modes of pain management may be required.
Note that this algorithmic approach has not been systematically studied in randomized trials.
The Role of Ultrasound
Ultrasonography of the spine before initiation of neuraxial procedures has shown to reduce the number of attempts and necessary levels for epidural catheter placement, and improve analgesia in those who have not had back surgery., The utility of ultrasound in the context of patients with a history of severe scoliosis or scoliosis repair has also been demonstrated.,, Ultrasound plays a role in identification of interspinous spaces, assisting with the insertion angle of the Tuohy needle and in identification of the epidural space.
Outcome After Neuraxial Analgesic Blocks
In a recent prospective study, 41 parturients with previous spinal instrumentation for scoliosis correction were matched with controls, epidural bupivacaine consumption and time to placement of neuraxial technique were compared. Total bupivacaine consumption, number of manual boluses, and number of subjects requiring increased bupivacaine concentrations did not differ between the groups. However, in the scoliosis group, mean time to complete the neuraxial technique was 41% longer, the number of needle redirections and attempted interspaces required were more, and the need for a more experienced provider was more. Successful analgesia was achieved in 88% women in the scoliosis group.
Further studies are required to estimate the rate of successful and reliable conversion from epidural labor analgesia to surgical anesthesia for cesarean delivery given the high requirement of extensive dermatomal spread and denser anesthesia for an operative delivery. The conversion failure rate may be greater in women with spine instrumentation compared with analgesia, but this possibility remains unproven.
It is also worth noting that epidural blood patch is usually not possible should the patient develop a postdural puncture headache. Although the case reports are sparse, yet a case of postdural puncture headache in a nonparturient, who developed headache following spinal surgery and instrumentation, was successfully treated by computed tomography (CT)-guided translaminar epidural blood patch.
Prior Spinal Surgery
Previous spinal surgery may be included but is not limited to Harrington rod insertion to correct spinal curvature, discectomy, laminectomy, and extensive spinal surgery with instrumentation that might be required to correct trauma-related vertebral injuries. The issues related to neuraxial blocks in the patients with scoliosis and previous spine surgery have been dealt with earlier. In this section, we will review spinal surgery performed for other indications, particularly laminectomy and discectomy.
Up to 84% of individuals living in industrialized countries, mostly between the ages of 30 years and 50 years, experience low back pain. Lumbar disc prolapse is the underlying etiology in approximately 4%, and some of these patients are elected for surgical treatment when conservative management fails. There are a variety of surgical approaches in this setting, making this a heterogeneous population to study. Many of the difficulties are similar to those encountered in previous spine surgery for scoliosis, although to varying degrees, such as limited back mobility, absence of surface landmarks and inability to rely on loss of resistance during needle insertion, and inflammation and scarring in the epidural space limiting anesthetic spread. Rotation of the spine and deviation of the midline of the epidural space are less of a concern. Moreover, the extent of surgery is usually limited to a few segments.
Theoretically, the limited extent of surgery should result in restricted epidural scarring and fibrosis; however, it is noteworthy that severe epidural fibrosis is an underlying pathology in most patients with failed back surgery syndrome and persistent back pain.
A prospective observational study using epidural endoscopy involving 78 patients with persistent back pain after spine surgery showed that 83% of patients with persistent pain after back surgery had severe epidural fibrosis, while 91% had significant fibrosis. Another prospective study that followed 53 patients for 1 year after microdiscectomy surgery showed evidence of intermediate epidural scar formation in majority of the patients and extensive scar formation in only 1 patient, minimal to no scarring in 15 patients.
Various surgical techniques performed result in varying degrees of scarring and anatomical changes, making it difficult for the anesthesiologist to accurately predict the effectiveness of the epidural.
Evidence suggests that parturients with a history of prior spinal surgery have a higher likelihood of encountering a difficult labor epidural catheter placement and suffering from inadequate analgesia in comparison with the parturients who have had no surgery. In the past, previous spinal surgery was considered a relative contraindication to labor analgesia.
Early retrospective studies suggested that only about 50% of the parturients with previous spinal surgery were able to achieve adequate neuraxial labor analgesia, and 44–92% required multiple attempts at catheter insertion.,, A later prospective study demonstrated that only six out of nine parturients with a history of spine instrumentation received successful epidural analgesia. Anatomical distortion and difficulties identifying the epidural space may make catheter malplacement more common. For example, unintentional subdural catheter placement may occur.
In recent years, spinal surgery techniques have improved with smaller incisions and less distortion of adjacent structures. The epidural space may be more accessible via the midline approach, and scar tissue may be reduced within the epidural space. Current microdiscectomy techniques may also create less scarring and distortion. Potentially, this could result in increased success of subsequent neuraxial techniques?
A most recent, large study seems to support this proposition. This prospective case-controlled study on labor analgesia demonstrated that parturients with a history of lumbar discectomy surgery can undergo neuraxial labor analgesia without an increased risk of difficult block initiation, epidural catheter failure, increased analgesic drug consumption, or longer time requirement for catheter placement. No technical failures of the epidural or inadequate analgesia were noted, although 17% required greater than one interspace attempt compared to 2% in control group.
Concerns have been expressed that the introduction of bacteria via epidural catheters may result in contamination of spinal instrumentation hardware and may lead to potentially devastating consequences. Fortunately, these concerns are not borne out by the literature.
Intrathecal Analgesia for Labor and CS
There are reports in the literature of successful spinal anesthesia in parturients undergoing Cesarean delivery who have had spinal instrumentation. If epidural space loss of resistance is not obtained and the intrathecal space entered, inserting an intrathecal catheter to provide ongoing analgesia seems logical though reports are sparse. Even if the epidural space can be identified and a catheter can be inserted, scarring may restrict the spread of the local anesthetic solution. Converting to continuous spinal analgesia via spinal catheter may improve analgesia though caution should be exercised with the dose of the local anesthetic employed. There are also obvious concerns regarding infection and the potential for accidental overdose if the spinal catheter is confused with an epidural catheter.
Overall, the studies suggest that labor epidurals work in parturients with scoliosis, with or without a history of spinal surgery, but they are more difficult to place and may have a higher failure rate. Neuraxial labor analgesia should be offered, although informed consent should include a discussion of the possibility of technical difficulties and surgical anesthesia.
While performing neuraxial blocks in the patients with prior spinal surgeries such as discectomy or laminectomy, the anesthesiologist is faced with similar challenges as in the patients with corrective surgery for scoliosis. However, results are better in this group, and this likely reflects differences in the extent of postsurgical changes caused by these interventions compared with surgical correction of scoliosis.
Newer surgical techniques for both scoliosis and lumbar disc prolapse are probably better in salvaging lumbar spine anatomy, thereby making the procedure more feasible and less demanding. Ultrasound may be used to assist in the epidural catheter placement, and it is an important tool, especially for the more complicated cases.
Despite the reports of improved success in the patients with spinal problems or previous spinal surgery, it may still be prudent to warn patients about the potential for decreased efficacy and increased complications with neuraxial blocks.
(Presented, in part at the 1st World Obstetric Anesthesia Conference/8th National Conference of the Association of Obstetric Anaesthesiologists in Hyderabad, India in September 2015.)
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Conflicts of interest
There are no conflicts of interest.
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