Obesity, Ultrasound Guided Axillary Brachial Plexus Block Clinical Trial
Title of Research Program: Ultrasound Guided Axillary Brachial Plexus Block: Influence of
Obesity on Block Failure Rate, Performance Time and Incidence of Acute Complications- A
prospective observational cohort study
Background: Axillary brachial plexus (ABP) block is commonly performed as the primary
anesthetic technique to provide surgical anesthesia and postoperative analgesia for elbow,
forearm and hand surgery. Compared to general anesthesia, ABP blocks have been shown to
result in better pain relief, less nausea and vomiting, shortened length of hospital stay,
decreased side effects of opioids painkillers and better patient satisfaction. These
beneficial effects of ABP blocks are particularly useful for patients who are overweight or
obese as this cohort is at a higher risk of experiencing complications from general
anesthesia. Traditionally, nerve blocks have been described technically challenging in obese
patients. This may not be true now with availability of high-resolution ultrasonography (US).
US imaging also allows doctors the ability to visualize the needle "live" to allow for more
accurate needle placement. This allows local anesthetic to be placed more precisely resulting
in faster onset anesthesia, decreased local anesthetic drug dosages, reduced complications
and higher success rate. Ultrasound guidance has not been used for performing ABP block in
previous studies in obese patients.
Hypothesis: We hypothesize that the block failure rate is no worse in obese compared to
non-obese patients when US guidance is used to perform ABP blocks.
Specific Objectives: The primary objective of this study is to evaluate whether obese
patients receiving US guided ABP block as their primary anesthetic modality have a block
success rate (defined by a Composite Score ≥ 14 at 30 minutes) worse than their non-obese
peers. The secondary objective is to evaluate time parameters around ABP performance,
incidence of complications and patient satisfaction.
Methods: This study will be conducted as an observational quasi-experimental multicenter
trial at St. Joseph's Health Care (SJHC), London, ON and the Nova Scotia Health Authority
(NSHA) Halifax Infirmary (HI) site, Halifax NS. There will be 250 patients taking part in
this study. One hundred and fifty patients have already completed the study in Ontario. The
duration of the study at the Halifax Infirmary is 10 months. Healthy patients (aged 18-75
years) scheduled to undergo elbow/ forearm/ or hand surgery will be invited to volunteer in
this observational study. A study investigator or resident under direction supervision of a
study investigator will perform the ABP block. There is NO experimental drug or treatment in
this study. Patient demographics including age, sex, arm circumference, height, weight and
Body Mass Index will be recorded. Nerve blocks will be performed in a designated area near
operating rooms called the block room. US will be used for identification of the nerves
supplying the arm and an ABP block will be performed with a total volume of 30 mL of 0.5%
ropivacaine according to a standardized procedure. Measurements of sensory and motor blockage
will be recorded every 5 minutes for 30 minutes following the ABP block. Block success will
be measured and is defined as a score of ≥ 14 on the Composite Score (CS) within 30 minutes
of ABP block completion. According to routine care, all patients will receive a phone call
from the investigators 24-48 hours after surgery to inquire about complications. The study
follows non-inferiority design to show that the success rate in the obese group is not worse
than the non-obese when anesthetized. In non-inferiority trials, both intention to treat and
per-protocol analysis are recommended; both approaches should support non-inferiority The
student's t-test (unpaired, two tailed) will be used for comparison of the means of
continuous, normally distributed data or Mann-Whitney U test as appropriate. Categorical data
(success rate, complication rate) are to be analyzed using χ2 test or Fisher's exact test, as
appropriate. An interim analysis will not be conducted and set at 0.05 for significance and
95% confidence intervals.
Significance/ Importance: This study would provide anesthesiologists additional information
to inform their clinical decision-making when dealing with obese patients. To date there are
no publications or any registered trials exploring the success rates and technical aspects of
ABP blockade in obese patients using US guidance technology for block performance. Therefore,
this study is novel and timely for the patient groups.
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