Magnetic Resonance Imaging of Interscalene Plexus Block
Status:
Completed
Trial end date:
2014-07-01
Target enrollment:
Participant gender:
Summary
Interscalene plexus block is a widely used technique to provide anesthesia and analgesia for
surgery at the upper extremity (shoulder and upper arm); it is standard-of-care in many
institutions worldwide. Local anesthetic is being injected around the nerves supplying the
arm (Plexus brachialis) at a specific location in the arm (between the scalenus muscles, thus
called "interscalene plexus block"). The optimal volume of injection with regard to efficacy,
safety and avoidance of untoward effects has been subject to intense debate for a long time.
In spite of evidence that small volumes (between 5 and 7 mls) are effective for adequate
postoperative analgesia, larger volumes up to 40 mls are still frequently used in many
practices. However, with the use of such large doses, adverse events are known to occur with
increased frequency, including paralysis of the diaphragm or spread of local anesthetic to
the spinal cord.
This study is intended to help evaluate the effects of small or larger injection of local
anesthetic around the brachial plexus, and to correlate the distribution with clinical
efficacy, block duration, and possible side effects. It is a randomized, controlled,
observer-blinded trial; patients undergoing shoulder or upper arm surgery will be randomly
allocated to receive either 5mls or 20mls of local anesthetic for their interscalene plexus
block. Magnetic resonance imaging will be performed immediately afterwards, followed by a
series of neurological exams during the hospital stay. Test of lung function (spirometry) and
ultrasound of the diaphragm will be used to evaluate effects of the block on respiratory
mechanics.