The evaluation of neuraxial placement in the paired discectomy and control subjects is shown in Table 4. The time to place the epidural catheter did not differ between the discectomy and control subjects, median difference (95% CI) 0 minute (−1 to 2.5); P = 0.38. Although the epidural was placed at the first chosen interspace in 34 pairs of discectomy and control subjects, >1 interspace was attempted in 17% discectomy in comparison with 2% of the control subjects, difference (95% CI) 15% (2–26); P = 0.03. The estimated final interspace was also more cephalad in 8 pairs and more caudal in 3 pairs of the discectomy subjects compared to the controls. The skill level of the anesthesia providers who initiated and completed the neuraxial technique was not different between the discectomy and control subject. No epidural catheters were replaced for failed analgesia.
Hourly epidural bupivacaine consumption for maintenance of epidural labor analgesia was not different between parturients with lumbar discectomy surgery and those with no known lumbar spine pathology. In addition, there was no difference in the proportion of parturients who required an increase in bupivacaine concentration to treat breakthrough pain, nor were there any failures to initiate neuraxial analgesia or need to replace epidural catheters. These findings are consistent with those of Villevieille et al., who evaluated neuraxial labor analgesic efficacy and ease of initiation in parturients with a history of back surgery.8 None of the 16 parturients with a history of lumbar discectomy surgery experienced technical failures, but 1 patient experienced “ineffective analgesia.”8 None of the parturients who had discectomy surgery in this study who required a cesarean delivery experienced failure to convert epidural analgesia to anesthesia. This result is consistent with the findings of Hebl et al., who found no difference in efficacy of surgical anesthesia achieved by neuraxial techniques in those who had prior back surgery and those who did not, although the majority of patients had prior laminectomy surgery and only 9 had discectomy surgery.12
Most case series and prospective studies evaluating efficacy and ease of placement of neuraxial labor analgesia in parturients with prior spine surgery were in women with corrective surgery for scoliosis or decompressive laminectomies. Although the ultimate success of neuraxial placement was in the range of 85%–95%, the reported analgesic efficacy rates were only 50% to 60%.6–10,13,14 Possible reasons for difficult neuraxial initiation or ineffective analgesia in women with prior back surgery include limited back mobility, inflammation and scarring in the epidural space or surrounding nerves, and increased degenerative bone changes surrounding areas of injury or instrumentation.12,15,16 Differences in findings in previous studies in parturients with scoliosis repair and laminectomy, in comparison with our findings in patients with prior discectomy, likely reflect differences in the extent of surgical damage caused by multilevel instrumentation and bone removal or grafting, which alters the epidural space more than does isolated discectomy surgery.
Women in our discectomy group were slightly older than those in the control group. Eighty-six percent of lumbar disk herniations resolve spontaneously with conservative management and resolution is correlated with younger age; thus it is expected that women who require lumbar discectomy surgery would be older.17 Age has not been demonstrated to be an independent predictor of analgesia requirements in laboring women, and therefore it is unlikely that the age difference between our groups affected bupivacaine requirements.
The neuraxial procedure was performed at a more cephalad interspace in 8 parturients with prior discectomy than in the control subjects. The spinal cord normally terminates above the L2 vertebral body, and the majority of discectomy procedures are performed at L4/5 or L5/S1. Therefore, there is usually adequate space above the surgical site for lumbar epidural catheter placement. However, “blind” neuraxial techniques frequently result in use of a more cephalad interspace than is intended or predicted.18,19 Thus, the neuraxial technique is likely placed at closer proximity to the spinal cord in discectomy patients. It is not clear whether using an interspace cephalad to the surgical site is necessary, because Fredman et al. demonstrated successful “blind” epidural catheter placement in 17 of 20 patients at or near the level of prior discectomy surgery (confirmed via fluoroscopy) in patients receiving epidural steroid injections.20
The incidence of low back pain during pregnancy in women with a history of discectomy surgery is 76%, but is comparable to that of women with no history of back pathology.21,22 ”Failed back syndrome”—characterized by low back pain, radiculopathy, or both—occurs in 8.3% to 12% of patients after discectomy surgery, but the effects of pregnancy on this syndrome have not been studied.23–25 More severe pain and radiculopathy after spine surgery correlate with radiographic evidence of more extensive scarring and anatomical changes at the surgical site.15,16,26 Although 27% of the discectomy group had low back pain or radiculopathy and potentially more scarring or anatomical changes, this observational study was not sufficiently powered to assess differences in analgesic consumption in the subset of discectomy patients who had exacerbation of back pain from failed back syndrome or pregnancy.
Nerves with underlying pathology—when exposed to a second trauma such as surgical ischemia, stretch injury, metabolic injury, or local anesthetic toxicity—are at higher risk of neurologic injury.27,28 A retrospective study by Hebl et al. demonstrated a higher incidence of new-onset neurologic impairment in surgical patients receiving neuraxial anesthesia who had preexisting radiculopathy or neurologic deficits.12 Patients in the discectomy group with underlying low back pain or radiculopathy theoretically may have been at increased risk of new or worsening neurologic deficits due to local anesthetic exposure and peripartum nerve injuries, but our study was not powered to detect differences in postpartum neurological deficits between groups.
There are several limitations to our study, including the lack of surgical details for subjects in our discectomy group. There is evidence that discectomy and microdiscectomy surgeries are equivalent in most surgical outcome measures, but other factors make discectomy procedures heterogeneous including minimally invasive versus open techniques, ligamentum flavum-sparing techniques, translaminar versus transforaminal approaches to disk removal, amount of disk removed, presence of dural tears, and whether antiscarring agents or steroids are applied at the surgical site.29–31 This study is underpowered to account for influences of these surgical variations on bupivacaine consumption among discectomy patients.
Another limitation is that the majority of patients requesting labor analgesia received a combined spinal–epidural technique for initiation of analgesia. Combined spinal– epidural analgesia is the preferred technique at our institution because the rapid onset of analgesia is advantageous in a high-volume setting with an epidural analgesia utilization rate of 89%. Epidural analgesia is chosen for specific indications, for example, difficult airway or nonreassuring fetal status, when a functioning epidural is deemed an important component of patient safety. The average labor duration of the discectomy group was 8 hours, which allowed assessment of differences in maintenance of epidural analgesia between groups because the spinal portion of the combined spinal–epidural technique lasts approximately 60 to 100 minutes.11,32 Studies are conflicting as to whether the presence of a dural puncture upon initiation of epidural analgesia improves the overall quality of analgesia due to translocation of epidural medication into the cerebral spinal fluid.33,34 Therefore, our results may not be generalizable to women for whom analgesia is initiated with a traditional epidural and not a combined spinal– epidural technique.
This study demonstrates 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, or increased analgesic drug consumption in comparison with parturients without a history of back surgery. Studies regarding efficacy or ease of placement of neuraxial labor analgesic techniques have used a heterogenous mix of “spine surgery,” and review of these studies suggests that more extensive procedures performed with instrumentation place patients at greater risk of complications from neuraxial analgesia. Future research should focus on specific surgical procedures so that anesthesiologists may appropriately counsel patients regarding their specific back pathology. Further research is warranted on whether pregnant women who have underlying back pain or neurologic deficits are at greater risk of postpartum neurologic injury.
Dr. Cynthia Wong is the section Editor for Obstetric Anesthesiology for Anesthesia & Analgesia. This manuscript was handled by Dr. Steven L. Shafer, Editor-in-Chief, and Dr. Wong was not involved in any way with the editorial process or decision.
Name: Jeanette R. Bauchat, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Jeanette R. Bauchat has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.
Name: Robert J. McCarthy, PharmD.
Contribution: This author helped design the study, analyze the data, and write the manuscript.
Attestation: Robert J. McCarthy has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.
Name: Tyler R. Koski, MD.
Contribution: This author helped write the manuscript.
Attestation: Tyler R. Koski approved the final manuscript.
Name: Christopher R. Cambic, MD.
Contribution: This author helped conduct the study.
Attestation: Christopher R. Cambic has seen the original study data and approved the final manuscript.
Name: Amy I. Lee, MD.
Contribution: This author helped conduct the study.
Attestation: Amy I. Lee has seen the original study data and approved the final manuscript.
Name: Cynthia A Wong, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Cynthia A. Wong has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.
This manuscript was handled by: Steven L. Shafer, MD.
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© 2012 International Anesthesia Research Society
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