Effect of local anesthetic dose versus volume on block duration of single shot ultrasound-guided axillary brachial plexus block with mepivacaine.

Peripheral nerve block (PNB) as an anesthetic technique plays an important role
in modern regional anesthesia. Duration of PNB depends on several factors such
as the choice of local anesthetic (LA), the site of injection and the dose of
LA. The dose of local anesthetic administered when performing peripheral nerve
block is determined by volume and concentration; in what way these parameters
affect duration is controversial. Using ultrasound guidance, LA spread around
the nerves can be assessed with the possibility of repositioning the needle in
case of maldistribution. Recent publications illustrate that the volume of LA
can be significantly reduced when particular regional anesthetic techniques are
performed with ultrasound guidance.
In a recent study, we compared the duration of sensory and motor block with 15
and 40 millilitres mepivacaine 1.5% for axillary brachial plexus block using
ultrasound guidance. Dose reduction from 40 mL to 15 mL (62.5%) shortened the
overall duration of sensory and motor block by approximately 17-19% in our
study. It reduced sensory and motor block duration of individual nerves with
18-40% and decreased the time to first request of postoperative analgesia with
approximately 30%. The difference in block duration in our study may be the
effect of either reducing the volume from 40 to 15 mL, or of reducing the dose
from 600 to 225 mg. In previous research, duration of analgesia reported by
Serradell et al. was 231 ± 45 min in their group receiving axillary block with
200 mg mepivacaine in 20 mL. Interestingly, the TTFR in our group 40 mL (600 mg
mepivacaine) was similar (235 ± 59 min), whereas the TTFR in our group 15 mL
(225 mg mepivacaine) was considerably shorter. Although differences in
methodology preclude making direct comparisons, these observations may indicate
that the reduction in block duration seen in our study is caused by the
reduction in volume from 40 mL to 15 mL rather than the reduction in dose from
600 mg to 225 mg. However, further study is required to substantiate this.
Therefore, the purpose of the current study is to determine the effect of
mepivacaine dose and volume on the duration of sensory axillary brachial plexus
block (overall and individual nerves).

Primary objective: to determine the effect of mepivacaine dose and volume on
the duration of sensory axillary brachial plexus block (overall and individual
nerves).
Our hypothesis (H0) is that there is no difference (less than 60 min) in
duration of ABPB using the different amounts of local anesthetic (volume and
dose) under ultrasound guidance.
Secondary objectives: effect of dose and volume on; duration of motor block
(overall and individual nerves); onset of sensory and motor block (overall and
individual nerves); number of rescue blocks; Time To First Request of
postoperative analgesia (TTFR); and satisfaction (NRS 0-10) with anesthetic
technique.

The design of this study is parallel, prospective, randomized and blind (for
patient and data collector). The study will be conducted at the Sint
Maartenskliniek, Nijmegen, The Netherlands approximately between 1-3-2012 and
01-03-2014. Patient inclusion is expected between april 2012 and april 2013,
but may be prolonged if the sample size has not yet been reached.

Using a computer-generated sequence of random numbers and a sealed envelope
technique, patients will be randomly allocated to receive single shot axillary
brachial plexus block with either 30 mL mepivcaine 1.0% (300 mg), 30 mL
mepivacaine 1,5% (450 mg) or 20 mL mepivacaine 1,5% (300 mg). This study is
blinded for patient and data collector. The attending anesthesiologist will be
aware of treatment allocation.

Axillary block will be performed by experienced anesthesiologists with a
combination of nerve stimulation and ultrasound. The musculocutaneus, median,
ulnar and radial nerve will be identified separately. Each nerve will be
blocked by either 7-8 mL (30 mL groups) or 5 mL (20 mL group). Time is
designated t = 0 upon conclusion of the axillary brachial plexus block. Surgery
will be performed under regional anesthesia alone, or supplemented with
sedation, or supplemented with general anesthesia. All patients will be treated
according to standard hospital protocol.

Baseline characteristics of participating patients will be recorded (i.e. age,
length and weight). Also, the name of the anesthesiologist performing the block
and the ease of block performance will be noted.
In the first 30 minutes after injection of local anesthetic solution, a blinded
observer will assess the onset of sensory and motor block every 5 minutes until
ABPB is complete. The sensory block of the musculocutaneus, median, ulnar and
radial nerves will be assessed by pinprick at specific sites. In addition,
sensory block of the medial antebrachial cutaneus nerve will be tested. Sensory
block will be scored on a three-point scale as 0 = absent, 1 = partial and 2 =
complete. Motor function of the musculocutaneous, median, radial, and ulnar
nerve will also be assessed on a three-point scale as 0 = no motor block, 1 =
partial and 2 = complete. A complete sensory block is defined as a total score
of 10, complete motor block is defined as a total score of 8. If necessary,
supplemental blocks will be placed if sensory block is incomplete at 30 min.
The type, side and duration of surgery will be recorded. Upon arrival at the
recovery, offset of sensory and motor block will be assessed every 15 minutes
until full recovery in the same manner as preoperatively. Full sensory and
motor recovery are defined as the time that a total score of 0 is first
obtained. In addition, the time to first request for analgesia as well as
patient satisfaction with the anesthetic technique will be recorded.

Block duration will be tested every 15 minutes postoperatively in patients who
participate in this study until the block has resolved completely. We think
this minor burden does not outweigh the information we can obtain to optimally
treat future patients. There are no specific benefits for the patient to
participate in this study, nor are there specific risks.
This study is not group related.