Jennie Maria Christin Strid1, Erik Morre Pedersen2, Olga Vendelbo2, Niels Dalsgaard1, Yousef Nejatbakhsh3, Jens Randel Nyengaard4, Kjeld Søballe5, and Thomas Fichtner Bendtsen1
1Department of Anesthesiology, Aarhus University Hospital, Aarhus C, Denmark, 2Department of Radiology, Aarhus University Hospital, Aarhus C, Denmark, 3Hospital Pharmacy, Aarhus University Hospital, Aarhus C, Denmark, 4Electron Microscopy Lab and Stereology, Institute of Clinical Medicine, Aarhus University, Aarhus C, Denmark, 5Department of Orthopedic Surgery, Aarhus University Hospital, Aarhus C, Denmark
Synopsis
Ultrasound guided
lumbar plexus blocks holds the potential for reducing anesthesia related complications in hip surgery
in the elderly punctum. The ultrasound guidance is, however, imprecise and
associated with epidural spread of local anesthetic due to limited
visualization. It is the overall aim of this study to improve the quality of
lumbar plexus blocks using Fusion imaging between MRI and ultrasound. Here we
report preliminary results of the impact of different MR scanning positions for
the accuracy of fusion imaging and report on the feasibility of using
gadolinium doped anesthetics for studying the distribution of local anesthetic fluid
using MRI. Purpose
To study primarily
the influence of MRI scanning position on ultrasound and MRI fusion imaging
accuracy prospectively in elderly volunteers. Secondly to explore the
feasibility of using gadolinium doped anesthetics for studying the distribution
of local anesthetic injectate following block of the lumbosacral plexus.
Methods
MR imaging in
different positions
Under the
hypothesis that the lumbosacral plexus remains in the same position during
change from the supine position normally used during MRI to the lateral
decubitus position normally used for ultrasound guided lumbosacral plexus
blocks, we scanned 25 elderly healthy volunteers in the supine and in a lateral
decubitus position with a 70 cm bore 1.5T Philips Ingenia scanner. The dS flex coverage posterior coil and a
flex coverage anterior coil with 16 elements was used for signal reception. A
3D T2-TSE sequence (VISTA) with an isotropic scanned resolution of 1.2 x 1.2 x 1.2
mm3 (overcontiguos 2.4 mm slices with 1.2 mm spacing), TE 60 ms and
TR 1200 ms was used. Coronal images of the spine and its surrounding structures
from L1 to S4 using feet-head phase encoding for minimizing artefacts due to
respiration and peristaltic (Fig. 1) were obtained with a scan time of 6:26
min.
MR imaging of local anesthetics
Physical
compatibility between the gadolinium contrast agent Dotarem®
(27.9% gadoterate meglumine) and the
local anesthetics 2% lidocaine with 0.0005%
epinephrine, 0.75%
ropivacaine hydrochloride, and 0.5%
bupivacaine hydrochloride was investigated because no documented compatibility
of the combination could be found despite previously use.1 After examination for visible color change and particle formation, subvisible
particle formation, and pH change, we confirmed that Dotarem® is physical compatible
with all three local anesthetics, 2,3 and established a MR imaging protocol for visualizing the spread of
local anesthetics.
Image analysis
The images
obtained in the supine and in the lateral decubitus positions were rigidly
registered (OsiriX, Pixmeo, Switzerland) using the lateral part of the
transverse process of L4 and L5, respectively, as reference because this is a
key reference point in the ultrasound guided procedure. The distances between
the targets of the local anesthetic, spinal nerves L3 and L4, in both positions
were measured (Fig. 2). The mean (±SD) or the median
(IQR) distance between the spinal nerves in the two positions was calculated
depending on the normality of data.
T1 weighted 3D
gradient echo breathheld mDixon water scans, visualizing the gadolinium doped injectate
(Fig. 3), were combined with DWI based visualization (B-values: 0 and 500 s/mm2)
of the target nerves. To discriminate between the injectate and the nerves, ADC
maps were used. The spread of the injectate could hereafter be compared to sensory
blockade after the injection.4 This approach was used in 26 healthy volunteers in a recent
prospective randomized controlled crossover trial aiming to compare the
effectiveness of the lumbosacral plexus block guided by ultrasound vs. guidance
with MRI/ultrasound fused images.
Results
Table 1 (Fig. 5) displays
the distances in mm between the spinal nerves in the supine and in the lateral
decubitus position recorded on MRI. The initial results of the randomized
controlled trial, comparing ultrasound guidance of lumbosacral plexus block with
MRI/ultrasound fused images guidance, demonstrated that it was possible to
obtain adequate MRI image quality to identify the nervous structures and to
perform meaningful MRI/ultrasound fusion guided blocks of the lumbosacral
plexus in all volunteers.
Discussion
Only slight
displacement were seen of the L3 and L4 spinal nerves in different MRI scanning
positions – most likely because the lumbosacral plexus is situated in the
posterior part of the major psoas muscle, juxtapositioned to the rigid lumbar vertebral column. Considering
fused images can be adjusted in all three planes, we consider these minor displacements
to be clinically acceptable. In perspective, elderly patients with a damaged
hip can be MRI scanned in a realistic supine position and have a MRI/ultrasound fused
images guided lumbosacral plexus block at the L4-L5 level in the lateral decubitus
position with a reduced risk of possible detrimental cardiovascular and
respiratory side effects. A randomized controlled trial will further explore
the possible benefits in effectiveness and safety of lumbosacral plexus blocks
guided by MRI/ultrasound fused images.
Conclusion
MRI to be used for
MRI/ultrasound fusion based regional anesthesia of the lumbosacral plexus can
be performed in a realistic supine position for fusion with ultrasound used in
the lateral decubitus position. Detailed analysis of a recently performed
prospective randomized controlled crossover study will reveal if MRI/ultrasound
imaging guidance are superior to ultrasound imaging guidance for securing
effective regional anesthesia of the lumbosacral plexus.
Acknowledgements
Thank you to the colleagues in the research group at Department of Anesthesiology at Aarhus University Hospital, Aarhus C, Denmark.References
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