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Patient-perceived duration of effect of lidocaine and bupivacaine following diagnostic
medial branch blocks; a multicenter study
Byron Schneider, Mihir Joshi, Reza Ehsanian, Zachary L. McCormick, Jaymin Patel,
Patricia Zheng, Ameet S. Nagpal
PII: S2772-5944(22)00074-7
DOI: https://doi.org/10.1016/j.inpm.2022.100083
Reference: INPM 100083
To appear in: Interventional Pain Medicine
Received Date: 18 January 2022
Revised Date: 3 February 2022
Accepted Date: 15 February 2022
Please cite this article as: Schneider B, Joshi M, Ehsanian R, McCormick ZL, Patel J, Zheng P, Nagpal
AS, Patient-perceived duration of effect of lidocaine and bupivacaine following diagnostic medial branch
blocks; a multicenter study, Interventional Pain Medicine, https://doi.org/10.1016/j.inpm.2022.100083.
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© 2022 The Author(s). Published by Elsevier Inc. on behalf of Spine Intervention Society.
Patient-perceived duration of effect of lidocaine and bupivacaine following diagnostic
medial branch blocks; a multicenter study.
Byron Schneider*, MD, Department of Physical Medicine & Rehabilitation, Vanderbilt
University School of Medicine
Mihir Joshi, MD*, Department of Anesthesiology, UT Health San Antonio Long School of
Medicine
Reza Ehsanian, MD, PhD, Division of Physical Medicine and Rehabilitation, Department
of Orthopaedics and Rehabilitation, University of New Mexico School of Medicine,
Albuquerque, United States.
Zachary L. McCormick, MD, Department of Physical Medicine & Rehabilitation,
University of Utah School of Medicine
Jaymin Patel, MD, Department of Physical Medicine & Rehabilitation, Emory University
Patricia Zheng, MD, Department of Orthopedic Surgery, University of California-San
Francisco School of Medicine
Ameet S. Nagpal, MD, MS, MEd, Department of Anesthesiology, UT Health San
Antonio Long School of Medicine
*Co-first author
Corresponding Author:
Byron J. Schneider MD
2201 Children’s Way Suite 1318
Nashville, TN 37212
Byron.j.schneider@vumc.org
Conflict of Interest: None
Running title: Duration of MBBs with lidocaine/bupivacaine
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Patient-perceived duration of effect of lidocaine and bupivacaine following
diagnostic medial branch blocks; a multicenter study.
Byron Schneider*, MD, Department of Physical Medicine & Rehabilitation, Vanderbilt
University School of Medicine
Mihir Joshi, MD*, Department of Anesthesiology, UT Health San Antonio Long School of
Medicine
Reza Ehsanian, MD, PhD, Division of Physical Medicine and Rehabilitation, Department
of Orthopaedics and Rehabilitation, University of New Mexico School of Medicine,
Albuquerque, United States.
Zachary L. McCormick, MD, Department of Physical Medicine & Rehabilitation,
University of Utah School of Medicine
Jaymin Patel, MD, Department of Physical Medicine & Rehabilitation, Emory University
Patricia Zheng, MD, Department of Orthopedic Surgery, University of California-San
Francisco School of Medicine
Ameet S. Nagpal, MD, MS, MEd, Department of Anesthesiology, UT Health San
Antonio Long School of Medicine
*Co-first author
Corresponding Author:
Byron J. Schneider MD
2201 Children’s Way Suite 1318
Nashville, TN 37212
Byron.j.schneider@vumc.org
Conflict of Interest: None
Running title: Duration of MBBs with lidocaine/bupivacaine
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Patient-perceived duration of effect of lidocaine and bupivacaine following
diagnostic medial branch blocks; a multicenter study.
ABSTRACT
Objective: To quantify the duration of pain relief reported in association with lidocaine
and bupivacaine in patients suffering from axial back pain, who reported a response of
>80% relief lasting at least 30 minutes following medial branch blocks(MBB).
Design: A retrospective review
Methods, Setting & Subjects: Four academic medical centers utilized a uniform pain
diary. It was administered to consecutive patients after undergoing MBB. This pain diary
included NRS pain score and percentage of pain relief (PPR) at 12 designated time
points.
Results: One hundred and fifty pain diaries were collected and analyzed. 42 blocks
were performed in the cervical spine, 7 in the thoracic spine, and 101 in the lumbar
spine. By NRS, 32% of pain diaries indicated that the patient experienced ≥ 80% pain
relief at the 30-minute and 42.7% (64/150) did so by PPR. Mean duration of >80% pain
relief as measured by NRS in the bupivacaine subgroup was 3.5 hours (SD 8.7, 95% CI
0.6-6.5) versus mean duration of 16.4 hours (SD 19.6, 95% CI 5.4-27.4) in the lidocaine
subgroup. Mean duration of >80% pain relief as measured by PPR in the bupivacaine
subgroup was 19.2 hours (SD 19.2, 95% CI 13.3-25.1) versus mean duration of 12.2
hours (SD 15.9, 95% CI 5.6-18.8) in the lidocaine subgroup.
Conclusions: This study demonstrates that there is no discernable or statistically
significant difference in the duration of effect when comparing lidocaine to bupivacaine
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in patients that experience 80% or more relief following a medial branch block. This
data suggests any emphasis on concordant duration of relief from specific anesthetics
utilized for diagnostic medial branch blocks should be reconsidered.
INTRODUCTION
Medial branch radiofrequency neurotomy (MB RFN) is a widely-utilized procedure in the
treatment of non-radicular neck and low back pain arising from the zygapophyseal joint
(z-joints, facet joints) 12. In the lumbar spine, prevalence of z-joint pain ranges from 5-
50%.3–12 13 and in the cervical spine 25-60% 14–16 MBBs can be diagnostic and prognostic
and are required to make the diagnosis of z-joint pain and thus select patients for
therapeutic RFN due to the relatively low sensitivity and specificity of physical exam
maneuvers and diagnostic imaging has in making this diagnosis.17
The interpretation of MBBs as a selection criterion for RFN has been widely debated. In
large part, this debate centers around what an acceptable threshold is for the sensitivity
and specificity of this diagnostic test, as false positive responses are inherent. The
estimates of a false positive response after a single MBB range from range of 15-45%.2–
4,9,10,18–22 The determinate of what constitutes a “positive response” is arbitrary and
debated, with increasing thresholds of relief being required to determine a test positive
resulting in a more specific but less sensitive test. Similarly, performing the test twice
will reduce false positive findings. Recent facet guidelines advocate 50% relief after a
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single MBB for diagnosis, 22.23. North American Spine Society (NASS) current
recommendations are consistent with recently updated Medicare LCD guidelines, which
call for 80% relief after two sequential MBBs. 24 22,23
The Spine Intervention Society (SIS) endorses a more rigorous selection criteria via the
concept of controlled comparative MBBs.25 Theoretically, controlled comparative MBBs
reduce the false-positive responses by comparing the patient perceived duration of pain
relief following blocks using a short-acting (e.g. lidocaine) versus a long-acting (e.g.
bupivacaine, ropivacaine). A positive test requires not only that the patient have relief of
their pain with MBBs, but that a block with a longer-acting agent has a longer duration of
pain relief than a shorter-acting local anesthetic. This is referred to as a “concordant”
response.25
This model of comparative blocks has been evaluated in cervical MBBs.26,27
In 47 patients with chronic neck pain following whiplash injury who underwent dual
anesthetic blocks, 45 had a positive initial block, and 44 had a positive second block
(irrespective of duration). Interestingly, 4 patients (9%) had a response with lidocaine
longer than bupivacaine, but responses still “consistent with known pharmacology of the
drugs” 26. 13 patients (29%) demonstrated relief for period in excess of the reported
durations of action of either lidocaine or bupivacaine, and of that group only 7/13 had
longer relief with bupivacaine than lidocaine. Collectively, duration of action varied
widely from 35 min to several days. For lidocaine, median duration was 185 minutes
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(Q1 98 min and Q3 405 min) and for bupivacaine median 458 min (Q1 240 min and Q3
1365 min).
The same investigative group then considered comparative versus “placebo-
controlled” MBBs in fifty consecutive patients with chronic neck pain.28 In this study, only
those patients who responded to both blocks, who obtained longer-lasting relief when
the longer-acting agent was used, and had a negative block with placebo, were
considered true positive responders. Comparative MBBs considering duration of
anesthesia tested against placebo MBBs yielded a specificity of 88%, but only a
marginal sensitivity of 54%. If the definition of a positive response was expanded to all
patients with reproducible relief on both blocks done with anesthetic, irrespective of
duration, sensitivity increased to 100%, but specificity decreased to 65%. It is from this
study alone that the validity of dual comparative blocks has been evaluated. This
diagnostic paradigm has not been specifically evaluated in the lumbar spine and the
translation of the literature from the cervical spine to the lumbar spine has been
debated29. Perhaps surprisingly, there is a paucity of literature on comparative effects
between small volumes of lidocaine and bupivacaine in general. While the merits of a
comparative medial branch block paradigm continue to be debated, there is surprisingly
little published data on the duration of anesthesia patients experience when undergoing
MBB with lidocaine or bupivacaine.
The objective of this study is to quantify the duration of pain relief reported in
association with lidocaine and bupivacaine in patients suffering from axial back pain,
who reported a response of >80% relief lasting at least 30 minutes following MBB.
METHODS
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Study Design
This is a retrospective review from four academic medical centers of prospectively
collected data from a uniform pain diary administered to consecutive patients after
undergoing MBBs. Internal Review Board (IRB) exemption was granted at all four
participating institutions (IRB 181798 Vanderbilt, HSC2018-385E at UT Health San
Antonio, 18-25701 at UCSF, 107359 at Emory). The time-period of collection was from
January 2018 to June 2019. The pain diary assessed numeric rating scale (NRS) score
immediately pre-injection and at 12 different time points post injection up to 48 hours
(Appendix 1). Routine clinical decision making, including assessing the degree of pain
relief, was the sole determinate in patients progressing from MBB to RFN; patients’
participation in use of the pain diary in and of itself was not a determinate.
Participants
Inclusion criteria, consisted of adults (> 18YO) with axial pain determined, by history
and physical examination, to be most likely secondary to a facetogenic pain generator
and scheduled for a MBB. Data was collected for geographic location, sex, body-mass
index (BMI), spine segment MBB was performed upon, number of joints targeted, type
of anesthetic used, anesthetic volume, needle gauge, and pre-injection NRS pain score.
There were no exclusion criteria. Data collection occurred over an 18-month period.
Medial Branch Block Procedure
MBB procedures were performed by Physical Medicine and Rehabilitation Physicians
with fellowship training in either Interventional Spine or Pain Medicine. These
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procedures were conducted according to the Spine Intervention Society's Practice
Guidelines for Spinal and diagnostic and Treatment Procedures 30. All procedures were
performed using contrast under live fluoroscopy to minimize the risks of a false negative
block. Anesthetics used were either 0.5% bupivacaine or 2% lidocaine at the discretion
of the treating physician. Patients continued their standard of care after injection
without restriction of co-interventions.
Outcome Measure
A uniform pain diary was agreed upon between the four separate academic centers and
used as a part of routine clinical practice (Appendix 1). This pain diary included NRS
pain score and percentage of pain relief at 12 designated time points. Pain relief was
measured as current pain at the time period specified: relief lasting only 25 minutes
would be recorded as “no relief” at the 30 minute mark, complete relief of 35 minutes or
55 minutes would equally be recorded as “100%” relief at the 30 minute mark. Patients
were asked to fill out the diary in full. Missing data points were not included in data
analysis. Data was prospectively collected from these diaries.
Data Analysis
Each MBB was considered in isolation, though there were patients who returned for
multiple blocks. Greater than or equal to 80% improvement in pain at the 30-minute time
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point was considered a positive block. This was performed based upon both the (1)
“calculated” 80% improvement on the traditional NRS score, as well as (2) patient-
reported percentage of improvement. The null hypothesis was that there would be no
difference in duration of relief between lidocaine and bupivacaine after positive
response to a MBB. Mean and standard deviation and median duration of pain relief
was extracted with 95% confidence intervals (CI) for means and interquartile ranges
(IQR) for medians. Categorical responses based were calculated along with 95% CI to
evaluate if utilizing a threshold of pain relief that “wore off” between 61 minutes and 1
hour 59 minutes and another window that “wore off” between 3 hours and 3 hours 59
minutes would be able to discriminate between lidocaine and bupivacaine.
RESULTS
One hundred and fifty consecutive uniform pain diaries were collected and analyzed.
Eighty-five (56.67%) diaries emanated from a single institution. The average age of
subjects was 60.76 years. Seventy-two (48%) of the subjects were female. Average
BMI was 30.7 kg/m2. Regarding spine segment, 42 blocks were performed in the
cervical spine, 7 in the thoracic spine, and 101 in the lumbar spine. Ninety percent of
procedures were performed with a 25-gauge needle (135/150). A single joint was
targeted 29 times, two joints 85 times, and four joints 36 times. In 95.3% of cases, 0.5
mL or less was injected per nerve (143/150). In 66% of cases (99/150), bupivacaine
was used as opposed to lidocaine (Table 1).
Thirty-two percent (48/150) of pain diaries indicated that the patient experienced ≥ 80%
pain relief at the 30-minute threshold utilizing calculated data from the traditional NRS
score. Two of these 48 diaries included incomplete data and were excluded from
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analysis. Analysis of the patient reported percentage improvement in pain revealed that
42.7% (64/150) of diaries demonstrated ≥ 80% relief at the 30-minute threshold.
Subgroup analysis for those patients whose blocks were performed with lidocaine
showed positive response in 14/51 (25.4%) in the traditional NRS score subgroup and
22/51 (43%) in the patient reported percentage improvement subgroup. Similar analysis
in the bupivacaine subgroup revealed a 32/99 (32.3%) and 42/99 (42.4%) positive
response rate, respectively (Table 2).
When calculating percentage improvement in NRS score based on NRS score changes,
the average duration of >80% pain relief for positive responses in the bupivacaine
subgroup was 3.5 hours (SD 8.7, 95% CI 0.6-6.5), and the median duration was 0.5
hours (IQR 0.5-3.5). The average duration of>80% pain relief for the positive responses
in the lidocaine subgroup was 16.4 hours (SD 19.6, 95% CI 5.4-27.4), and the median
duration was 9.0 hours (IQR 0.5-48) (Table 3).
When patient-reported percentage improvement was used to define a block as
“positive”, the average duration of >80% pain relief for positive responses in the
bupivacaine subgroup was 19.2 hours (SD 19.2, 95% CI 13.3-25.1) and the median
duration was 9.0 hours (IQR 2-48). The average duration of pain relief for the positive
responses in the lidocaine subgroup was 12.2 hours (SD 15.9, 95% CI 5.6-18.8), and
the median duration was 6.0 hours (IQR 0.9-13.5) (Table 3).
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Two by two tables were also constructed to evaluate the number of positive responses
that lasted less than two hours compared to 2 hours or more. As calculated by NRS
scores, of the positive lidocaine responders 5 ((35.5%) 95% CI 10.5 - 60.5%) had a
duration of relief of less than 2 hours whereas 9 ((64.3%) 95% CI 39%-89%) had a
response of at least 2 hours or more. For bupivacaine 23 ((71.8%) 95% CI 56.2% -
87.4%) had relief for less than two hours compared to 9 ((28%) 95% CI 12.5% - 43.7%)
who had relief of 2 hours or more (table 4). Data was also evaluated using patient
reported improvements in pain (table 5). Data was similarly analyzed using a threshold
of less than 4 hours as compared to 4 hours or more for both calculated NRS, and
patient reported pain relief (table 4 and table 5).
DISCUSSION
In this study, we show that within the confines of a single diagnostic medial branch
block, there is no reliable differentiation in the patients’ duration of pain relief whether
lidocaine or bupivacaine is used. By some measures, it appears the lidocaine response
was longer than bupivacaine even. This calls into question the clinical utility of
considering the duration of relief when performing dual medial branch blocks. While this
study appears in conflict with foundational work by Lord et al in the performance of
cervical medial branch blocks, this study is not equipped to specifically evaluate the
sensitivity or specificity of dual medial branch blocks when anchored against a placebo
response28. In fact, in the work by Barnsley et al, this same phenomenon of discordant
responses or unexpectedly prolonged responses was also noted and the authors in fact
called for additional research, which we aimed to address26.
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While the pharmacokinetics of short vs long acting anesthetics is well
documented, there is in fact a paucity of literature in general that assesses the duration
of action when small volumes of anesthetic are used targeting relatively small targets.
Regional anesthesia research utilizing larger volumes of injectate do suggest longer
durations of action for bupivacaine; for example one study investigating the duration of
effect of a 30 mL injection used for a brachial plexus block found duration of lidocaine to
be 172.8 +-/ 7.8 min compared to 546.4 +/- 14.9 min for bupivacaine 31 However, it is
unknown if this is applicable to the smaller volumes used in this study.
Two studies have shown that combining smaller volumes of both lidocaine and
bupivacaine together does not delay the onset of action relative to lidocaine alone nor
decreases the duration of action relative to bupivacaine alone 32,33. Another study
comparing 0.25% bupivacaine and 1% lidocaine given as 0.2 ml of intra-dermal injection
found mean duration of effect to be 7.02 +/- 1.46 hours and 6.63 +/- 1.85 hours
respectively34. The onset of action for both anesthetics was less than 30 seconds.
While this study reported a significant p value for duration of effect, clinically a
difference of 0.39 hours (23 minutes) is insufficient for a paradigm such as
“comparative” blocks. Overall, our findings are largely consistent with this latter study.
In the work by MacVicar et al on clinical outcomes of lumbar and cervical
radiofrequency ablation, two separate blocks using lidocaine or bupivacaine were used
as selection criteria, however in both studies the “duration of relief following each block
was not a criterion for treatment”18,35. In fact, the reasoning for this as published in
these studies references commentary from one of the authors also involved in the
referenced work by Lord and Barnsley. Specifically, it was noted that “duration of relief
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has little effect on the diagnostic confidence (posttest probability) of comparative local
anesthetic blocks”36. In the study by Dreyfuss and colleagues on outcomes following
lumbar RFN, patient selection was only that pain relief after lidocaine MBBs last at least
1 hour and that relief following subsequent bupivacaine MBBs last at least 2 hours.
Neither discordant responses between anesthetics nor prolonged duration of relief
following MBBs were excluded9. Perhaps most interesting from that study, is that the
authors reported a median (range) duration of relief from lidocaine and bupivacaine
blocks and similar results to our study were seen in that there was little difference. The
median duration of relief following lidocaine was 4.4 hours (IQ range 1.3–6 hours) and
following bupivacaine was 4.9 hours (IQ range 2–6 hours). In that light, our research is
in fact consistent with previously published literature on this topic.
Indeed, the findings of this study must also be put in context to the study design.
We acknowledge that we did not compare blocks within patients (in those who had two
blocks) nor did we utilize a control saline to potentially identify placebo responders as
did Lord et al. Certainly, this resulted in some “false positive” responders being
included in our analysis. Nonetheless, in this study the incidence of a positive block
was only 32% (48/150), which is well within the accepted range of the prevalence of z-
joint pain.3–12. Pragmatically, a physician is not able to the use a placebo block in clinical
practice. Even more, after an apparently positive initial medial branch block, a treating
physician is in fact only availed to information on the duration of that single block. After
in an initial block, no comparison is available, and in that sense, it is helpful to know if
unexpectedly long duration of effects of lidocaine or unexpectedly short duration of
effects of bupivacaine should be appreciated versus be discounted. Indeed, in this
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study, the data demonstrates that the duration of that block seems unrelated to the
anesthetic agent used.
Weaknesses of this study include its retrospective design; the way data was
securely collected limited our ability to extrapolate other potentially interesting
information such comparing 2 blocks done on the same patient. We also acknowledge
that we did not prospectively follow patients to evaluate if duration of effect was
associated with outcomes following radiofrequency ablation. Similarly, this data does
not further comment on the utility of performing 1 vs 2 MBBs, or what percentage of
pain relief is the best measure. Other limitations include that the investigators were not
blinded to the injectate used, though the patients were typically blinded. A modest
proportion of patients who had 2 MBBs may have been given the same anesthetic
agent for both blocks. We considered cervical, thoracic, and lumbar blocks together,
though we are unaware of why the duration of effect would be dependent on the spinal
segment blocked. The loss to follow up percentage is also unknown, as while all
consecutive patients were given the same pain diaries in a clinical setting across all
sites, we did not prospectively enroll patients and thus had no means of tracking those
who received the pain diary but did not return it.
Strengths of this study include the pragmatic approach as well as the multi-center
design. The data compiled included a large number of pain diaries assessed with
rigorously prospectively collected data, which increases the validity of our findings. The
overall ‘N’ of this study is larger than any previously published literature we are aware of
that contains data on the duration of effect of anesthetics following MBB. We also used
two different means of assessing pain relief in patients, via both a calculated NRS scale
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as well as a direct assessment of patients’ subjective perception of pain relief. While
both measures of pain relief failed to show a difference between lidocaine and
bupivacaine, it is curious the differences seen when comparing the two different
measures of pain relief. Further investigation into the phenomenon is warranted.
CONCLUSION
This study demonstrates that there is no discernable or statistically significant difference
in the duration of effect when comparing lidocaine to bupivacaine in patients that
experience 80% or more relief following a medial branch block. This data suggests any
emphasis on concordant duration of relief from specific anesthetics utilized for
diagnostic medial branch blocks should be reconsidered.
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Numeric Rating
Scale
Percentage Pain
Improvement
≥ 80% Relief All Subjects 48 (32%) 64 (42.7%)
≥ 80% Relief Lidocaine 14 (25.4%) 22 (43.0%)
≥ 80% Relief Bupivacaine 32 (32.3%) 42 (42.4%)
Table 2. Response rates for ≥ 80% improvement in pain at the 30 minute timepoint threshold using
numeric rating scale and percentage of pain improvement. Subgroup analysis includes patients
who had their block performed with lidocaine and those who had their block performed with
bupivacaine.
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Age (Mean Years) 60.76
Gender (Female) 72 (48%)
Body Mass Index (Mean kg/m2) 30.7
Segment Blocked Cervical 42 (28.0%)
Segment Blocked Thoracic 7 (4.7%)
Segment Blocked Lumbar 101 (67.3%)
25 Gauge Needle Size 135 (90.0%)
One Joint Blocked 29 (19.3%)
Two Joints Blocked 85 (56.7%)
Four Joints Blocked 36 (24.0%)
Volume Injected ≤ 0.5 mL 143 (95.3%)
Bupivacaine Used 99 (66.0%)
Lidocaine Used 51 (34.0%)
Table 1. Patient and procedural characteristics.
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Numeric Rating Scale Percentage Pain Improvement
≥ 80% Relief All Subjects 48 (32%) 64 (42.7%)
≥ 80% Relief Lidocaine 14 (25.4%) 22 (43.0%)
≥ 80% Relief Bupivacaine 32 (32.3%) 42 (42.4%)
Table 2. Response rates for ≥ 80% improvement in pain at the 30 minute timepoint threshold using
numeric rating scale and percentage of pain improvement. Subgroup analysis includes patients
who had their block performed with lidocaine and those who had their block performed with
bupivacaine.
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Mean Pain Relief Duration (Numeric Rating Scale) In
Hours ± Standard Deviation With 95% Confidence
Interval
Mean Pain Relief Duration (Percentage Pain Improvement) In Hours
± Standard Deviation With 95% Confidence Interval
Median Pain Relief Duration (Numeric Rating Scale) In Hours ±
Interquartile Range
Median Pain Relief Duration (Percentage Pain
Improvement) In Hours ± Interquartile Range
Bupivacaine
3.5 ± 8.7 (0.6-6.5) 19.2 ± 19.2 (13.3-25.1) 0.5 (0.5-3.5) 9.0 (2.0-48.0)
Lidocaine 16.4 ± 19.6 (5.4-27.4) 12.2 ± 15.9 (5.6-18.8) 9.0 (0.5-48.0) 6.0 (0.9-13.5)
Table 3. Mean and median duration of responses in those subjects with positive response to medial branch blocks, categorized by which local anesthetic was used to perform the block.
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Categorical Evaluation of Anesthetic Duration as Measured by Calculated NRS scores
< 2 hours ≥ 2hours
Lidocaine 5 (35.5%) 9 (64.3%)
95% CI 10.5 - 60.5% 95% CI 39%-89%
Bupivacaine 23 (71.8%) 9 (28%)
95% CI 56.2% - 87.4% 95% CI 12.5% - 43.7%
< 4 hours ≥ 4 hours
Lidocaine 5 (35.7%) 9 (64.3%)
95% CI 10.6% - 60.8% 95 % CI 39.2 – 89.4%
Bupivacaine 24 (75%) 8 (25%)
95% CI 60% - 90% 95 % CI 10% - 40%
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Categorical Evaluation of Anesthetic Duration as Measured by Patient Reported Improvements in Pain
< 2 hours ≥ 2hours
Lidocaine 6 (27.3%) 16 (72.3%)
95% CI 8.6% - 45.9%
95% CI 54% - 91%
Bupivacaine 5 (11.9%) 37 (88%)
95% CI 2%-22% 95% CI 78%-98%
< 4 hours ≥ 4 hours
Lidocaine 7 (32%) 15(68%)
95% CI 12% - 51% 95% CI 49% - 88%)
Bupivacaine 13 (30.9%) 29 (69%)
95% CI 17%-45% 95% CI 55%-83%
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Mean Pain Relief Duration (Numeric Rating
Scale) In Hours ± Standard Deviation With 95%
Confidence Interval
Mean Pain Relief Duration
(Percentage Pain Improvement) In
Hours ± Standard Deviation With 95%
Confidence Interval
Median Pain Relief Duration (Numeric
Rating Scale) In Hours ± Interquartile
Range
Median Pain Relief Duration (Percentage
Pain Improvement) In Hours ± Interquartile
Range
Bupivacaine
3.5 ± 8.7 (0.6-6.5) 19.2 ± 19.2 (13.3-25.1) 0.5 (0.5-3.5) 9.0 (2.0-48.0)
Lidocaine 16.4 ± 19.6 (5.4-27.4) 12.2 ± 15.9 (5.6-18.8) 9.0 (0.5-48.0) 6.0 (0.9-13.5)
Table 3. Mean and median duration of responses in those subjects with positive response to medial branch blocks, categorized by which local anesthetic was used to perform the block.
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Categorical Evaluation of Anesthetic Duration as Measured by Calculated NRS scores
< 2 hours ≥ 2hours
Lidocaine 5 (35.5%) 9 (64.3%)
95% CI 10.5 - 60.5% 95% CI 39%-89%
Bupivacaine 23 (71.8%) 9 (28%)
95% CI 56.2% - 87.4% 95% CI 12.5% - 43.7%
< 4 hours ≥ 4 hours
Lidocaine 5 (35.7%) 9 (64.3%)
95% CI 10.6% - 60.8% 95 % CI 39.2 – 89.4%
Bupivacaine 24 (75%) 8 (25%)
95% CI 60% - 90% 95 % CI 10% - 40%
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Categorical Evaluation of Anesthetic Duration as Measured by Patient Reported Improvements in Pain
< 2 hours ≥ 2hours
Lidocaine 6 (27.3%) 16 (72.3%)
95% CI 8.6% - 45.9% 95% CI 54% - 91%
Bupivacaine 5 (11.9%) 37 (88%)
95% CI 2%-22% 95% CI 78%-98%
< 4 hours ≥ 4 hours
Lidocaine 7 (32%) 15(68%)
95% CI 12% - 51% 95% CI 49% - 88%)
Bupivacaine 13 (30.9%) 29 (69%)
95% CI 17%-45% 95% CI 55%-83%
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Declaration of interests
☐ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☒ The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
Byron Schneider reports a relationship with Spine Intervention Society that includes: board membership,
funding grants, and travel reimbursement. Byron Schneider reports a relationship with AIM Specialty
Health that includes: consulting or advisory. Byron Schneider reports a relationship with State Farm
Insurance Companies that includes: consulting or advisory. Jaymin Patel reports a relationship with
Professional Disability Associates that includes: consulting or advisory. Zachary McCormick reports a
relationship with Avanos Medical Inc that includes: funding grants. Zachary McCormick reports a
relationship with Relievant Medsystems that includes: funding grants. Zachary McCormick reports a
relationship with SPR Therapeutics that includes: funding grants. Zachary McCormick reports a
relationship with Boston Scientific Corp that includes: funding grants. Zachary McCormick reports a
relationship with Soal Therapeutics that includes: consulting or advisory. Zachary McCormick reports a
relationship with Stryker Corp that includes: consulting or advisory. Zachary McCormick reports a
relationship with FSUMobile that includes: consulting or advisory.
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