The supraclavicular block numbs the whole arm below the shoulder by reaching the brachial plexus where it bunches tightest, in the hollow above the collarbone. Ultrasound shows the plexus there as a cluster of small dark circles beside the subclavian artery. The first rib runs underneath as a bright line. The lung sits a little below that. The probe finds the cluster, follows the needle to it, and watches the local anesthetic spread through the plexus. The lung lying so close is the reason this block is done under direct sight. Feel alone is not safe enough here.
The spinal of the arm
The supraclavicular block is the one that takes the whole arm. At this level the trunks and divisions of the plexus are gathered into a tight bundle. A single pool of local anesthetic around them reaches almost every nerve of the limb below the shoulder. The block comes on fast. It runs deep. It earned the name the spinal of the arm for the completeness of the numbness it gives.
The bundle here carries every major nerve of the arm. The median, the ulnar, the radial, and the musculocutaneous nerves all pass through the trunks and divisions at this level, before they part and run their separate ways down the limb. One pool of drug around the bundle reaches all of them at once. This is why the block numbs the arm so fully and so evenly.
The reach suits surgery from the upper arm down to the hand. An operation on the elbow, the forearm, the wrist, or the fingers sits well within its field. The arm is made numb and still for the surgeon. Pain relief carries on for hours after the cut is closed.
The shoulder is the one part this block serves less well. The nerves to the top of the shoulder leave the plexus higher in the neck, above the level the supraclavicular reaches. A shoulder operation is given the interscalene block, set out on its own page. The supraclavicular is matched to the arm below the shoulder, where its dense, quick block is at its best.
The cluster of grapes by the artery
The supraclavicular region in cross view. The brachial plexus is drawn in yellow as the upper, middle, and lower trunks, lying beside the subclavian vessels (red artery, blue vein) and above the cut clavicle. The anterior and middle scalene muscles and the phrenic nerve are labeled. The white triangle marks a surgical exposure used for another condition, not the block needle path. Illustration: Nicholas Zaorsky, M.D., CC BY-SA 3.0.
The plexus has a look here that the eye learns quickly. The subclavian artery shows first, a round dark circle that pulses, sitting on the first rib. The plexus lies right beside it, to the upper and outer side, a clump of small round dark shapes pressed together. The clump is often likened to a bunch of grapes for the way the little circles gather.
The position around the artery is fixed enough to rely on. The plexus sits lateral and a touch above the artery, between it and the skin. The first rib runs underneath both, a bright line with dark shadow below it. The lung lies deep to the rib, on the inner side, close enough to hold in mind through every pass of the needle.
Each small circle in the clump is a piece of the plexus, a trunk or a division wrapped in its sheath. The dark centers are the nerve bundles. The bright lines between them are the tissue that binds the clump together. A block laid into this clump reaches the whole arm, since the entire supply of the limb is packed into that small space.
Positioning and the first look
The patient lies back a little, with the head turned away from the side of the block. This opens the hollow above the collarbone and brings the plexus forward toward the probe. A folded towel under the shoulders can help in a patient with a short neck. The skin is cleaned and draped for a sterile field.
The artery is the anchor the whole search returns to. It is the one structure found with ease, a bright pulsing circle that color flow lights up at a touch. From the artery the eye steps out to the cluster, down to the rib, and across to the line of the lung. A scan that starts at the artery finds the rest in order.
The probe sits in the hollow above the collarbone, angled down toward the chest to look along the plexus. The first pass is a survey. The subclavian artery is found, the clump beside it identified, the first rib and the line of the lung read off the screen. A sweep with color Doppler lights any vessel in the path, since a small artery can run through the plexus itself. A minute spent on this picture sets up everything that follows.
A high-frequency linear probe gives the fine detail the shallow plexus needs. The depth is set so the rib and the cluster fill the screen, with the line of the lung in view below. The gain is raised until the small dark circles stand out against the brighter tissue around them. A clear picture of the cluster, the artery, and the rib is the ground the whole block is built on.
The first rib, a backstop
The first rib is the steadying landmark of this block. It shows as a short bright line under the artery and the plexus, with a clean dark shadow beneath it, since sound does not pass through bone. The rib marks the floor of the safe space. A needle kept above the rib stays in the plexus, clear of the depth below.
The rib matters because of what lies past it. On the inner side, where the rib gives way, the lung begins. The bright line of the rib is a wall the needle can work against, a place to aim toward. Keeping the rib in view, and the needle shallow to it, is one of the habits that makes the block safe.
The lung itself can be seen sliding at the edge of the picture. Deep to the rib and a little medial, the bright line of the pleura shifts back and forth with each breath, a movement called lung sliding. Seeing it confirms where the lung is. The needle is kept well clear of that moving line.
The pleura below the plexus
The pleura lying close below the plexus is the fact that shapes this whole block. The lung apex rises into the base of the neck, and its lining sits a short way deep to the cluster of grapes. A needle pushed too far, or aimed too steeply toward the chest, can pierce that lining and let air into the space around the lung. The lung can then collapse away from the chest wall, the complication called a pneumothorax. This is the one risk that sets the supraclavicular block apart. It is the reason the block was once approached with caution. The block was described a century ago and was prized for the completeness it gave. The fear of the lung later held it back. Ultrasound brought it into easy use again by putting the pleura on the screen. The lung is now seen. It is no longer guessed at. The bright line of the lung surface shows on the screen, sliding with the breath. The needle is kept in front of it through every advance. The first rib gives a second guard, a bony floor to stay above. The needle enters from the outer side, in plane with the probe, so its whole length and its tip travel across the screen as a bright line. The tip is never pushed forward unless the screen is showing it. A tip lost from view, even for a moment, is brought back into the slice before it moves again. The approach aims along the plexus and over the rib, away from the line of the lung, so the spread opens in the cluster, far from the pleura. A pneumothorax from a block done this way is rare. The signs are watched for after every block. A patient who grows short of breath, or coughs, or feels a sharp pain in the chest after the block, is checked for a lung that has begun to collapse. The probe itself can look for the lung sliding that a healthy pleura shows; the loss of that sliding over the apex points to air in the space. A small pneumothorax usually settles on its own with rest and watching. A large one is drained. A quick look with the probe after the block, checking that the lung still slides on both sides, can catch a leak before the patient leaves the room. The whole weight of care in this block falls on keeping the needle in sight and the pleura in mind, from the first pass to the last drop of drug.
The corner pocket
One spot in the picture has a name of its own: the corner pocket. It is the angle where the subclavian artery meets the first rib, the inner lower corner of the safe space. The lowest part of the plexus, the bundle that becomes the ulnar nerve and supplies the little finger and the inner forearm, tends to sit down in that corner.
A spread that reaches only the upper clump can leave that lowest bundle dry. The inner forearm and the little finger then keep their feeling, a gap in a block that is otherwise complete. A small deposit of local anesthetic in the corner pocket reaches the bundle that hides there. The block of the whole arm depends on the drug reaching this low corner as well as the main clump.
The corner pocket calls for care in the same breath. It sits at the inner end of the rib, near where the lung begins. The needle is brought to it along the rib, the tip kept over the bone and in view, so the corner is filled from the safe side. The completeness of the block and the safety of the needle meet at this one spot.
Bringing the needle in
The needle enters from the outer side of the probe, in plane, so its full length is seen as it crosses to the plexus. It travels above the first rib, toward the cluster of grapes, with the tip held in view at every step. The path runs along the rib, away from the lung on the inner side.
A test dose tells the placement. Local anesthetic spreading through the clump, opening it and lifting the small circles apart, is the sign of a needle in the right plane. The drug is given slowly, the spread watched as it fills the cluster. A spread that gathers on one side is a cue to move the tip, so the whole clump is bathed and the corner pocket reached.
The aim is the drug around the bundles, drawn back from any bundle it might enter. A bundle that swells as the drug goes in, or a jolt of pain down the arm, calls the tip back at once. A small injection of plain fluid ahead of the drug can open the plane and fix where the tip sits. Each push is read on the screen before the next is given.
Many operators lay the drug at two points. A first deposit goes into the corner pocket, low against the rib, to catch the bundle that hides there. A second goes into the upper part of the cluster, to fill the rest of the plexus. The two pools join and surround the whole bundle. A single well-placed deposit can do the same when the spread is seen to reach every corner of the cluster.
Drugs and what to expect after
A moderate volume of local anesthetic fills the cluster, enough to surround the bundles and reach into the corner pocket. A long-acting drug holds the arm numb and pain-free for many hours, often well into the night after surgery. A shorter-acting drug is chosen when the numbness is needed for a brief procedure alone. An additive mixed into the local anesthetic can stretch the block a few hours longer, of use when a long night of pain lies ahead.
The block comes on quickly at this level, since the nerves are bare and packed close. The arm grows warm, then heavy, then numb, over about a quarter of an hour. The surgeon has a still, painless field by the time the drug has spread. The early, dense onset is one of the reasons this block is favored for the arm.
The numb arm needs looking after once the block has set. It hangs heavy and senseless for the hours the block lasts. The patient cannot feel it to protect it. The arm is held in a sling, kept off hard edges and out of harm. The patient is told that the dead weight of the arm is the block at work.
The patient is also told what to report. A sharp pain in the chest, a new cough, or shortness of breath in the hours after the block is a reason to call for a check, since these can be the first signs of a lung leak. The hour the block should wear off is given as well, so a block that runs long is noticed.
For pain that lasts beyond a single day, a fine catheter can be threaded into the cluster and left in place, feeding local anesthetic for as long as it is needed. The same scan that places the single shot guides the catheter. The spread is checked through it to confirm the tip still sits among the bundles. The catheter carries the block from hours into days.
The phrenic nerve and the supraclavicular
The nerve to the diaphragm runs higher in the neck, a little away from the plexus at this level. The supraclavicular block reaches it less often than the interscalene block does. A patient who cannot afford to lose a diaphragm is served better here than by a block placed higher in the neck.
The phrenic nerve is not fully out of reach. Local anesthetic spreading upward from the supraclavicular fossa can still touch it in some patients. The diaphragm on that side can then slow for the length of the block. Reports of how often this happens vary from one study to the next. The effect is less common than the near-certain paralysis of the interscalene block. A patient with poor lungs is weighed with care before either block.
The choice of the supraclavicular over a higher block often turns on the lungs. A patient with little breathing to spare is steered toward the supraclavicular, or toward a block lower still, where the diaphragm is left alone more of the time. The chest weighs in the choice as much as the arm does. The anesthesiologist checks the breathing before settling on the level of the block.
Cautions before the block
A few situations steer the choice away from this block. A patient who cannot lie still or hold the arm in place is hard to scan and to needle with safety. A patient on strong blood thinners carries a higher chance of bleeding from the deep vessels near the plexus. The block is weighed against these before it is offered.
The lung sets one firm limit. A patient with only one working lung, or with a collapsed lung on the far side, is a poor candidate for a block that risks the pleura. A block placed further from the chest is the safer path for them. The chest is checked, and the level of the block is chosen to fit it.
Among the blocks of the neck
The brachial plexus from the spinal roots out to the branches, passing through the trunks, the divisions, and the cords. The supraclavicular block works low, at the trunks and divisions, where the plexus is packed tightest. The interscalene block works higher, at the roots. The lettered points mark individual nerves, keyed on the source page. Diagram: Mattopa, public domain.
The supraclavicular block has a close cousin higher in the neck, the interscalene block, set out on its own page. Both blocks reach the same plexus. The supraclavicular catches it low, at the trunks and divisions above the collarbone, where the whole arm comes under one tight clump. The interscalene catches it high, at the roots, where the shoulder is best covered.
The surgery points to one block. An operation on the arm, the forearm, or the hand is given the supraclavicular. A shoulder operation is given the interscalene. The patient’s lungs weigh in as well, since the supraclavicular spares the phrenic nerve more often. The skill of reading the plexus and watching the spread carries from one block to the other.
Lower again, a block can be placed below the collarbone or in the armpit, where the nerves have spread into cords and branches around the axillary artery. These blocks sit further from the lung. The supraclavicular keeps its place for the fast, complete arm block, chosen when its dense numbness is the aim.
The block suits more than planned surgery. A broken forearm or a crushed hand can be made painless for the work of setting it, with no need to send the patient to sleep. The fast, dense block of the whole arm serves the emergency room as well as the operating theatre.
Staying out of trouble
Three structures set the limits of safety, and each is watched on the screen.
The lung is the first. It sits deep to the rib on the inner side. A needle driven too far can reach it. The pleura is kept in view, the needle held above the rib and in plane, the tip never advanced unseen. The first rib is the floor the needle stays above.
The subclavian artery is the second. It pulses beside the plexus, a large vessel the needle is steered around. Color Doppler marks it before the needle moves. The drug is given in small divided doses, the syringe drawn back before each to check for blood. A small artery can also run through the plexus itself. Doppler clears the path of it.
The nerves are the third. A tip pushed into a bundle, felt as a swelling on the screen or a jolt down the arm, is drawn back to the edge before more drug is given. The block is laid around the bundles, in the space that holds them. Each of these three is held off the same way, by keeping the needle and the spread in sight.
The spinal of the arm
The supraclavicular block carries an old name: the spinal of the arm. At the level above the collarbone the trunks and divisions of the plexus are packed tight beside the artery. A drug set there numbs the whole arm below the shoulder. It works fast. It gives a deep numbness across the limb. For surgery on the upper arm, the elbow, the forearm, or the hand, the block carries the case on its own.
The plexus sits shallow in the hollow, a centimeter or two down, easily within a linear probe’s reach. It shows as a clump of small dark rounds, the bunch of grapes, against the bright pulse of the artery. The corner where the artery meets the first rib is the pocket where the lower trunk hides.
The lung is the price of the spot. The pleura lies a short way below the plexus. The whole block is read with the line of the lung in view, the first rib held as a backstop under the needle. The fullest block of the arm sits closest to the lung. The picture is what keeps the two apart.
Common questions about the supraclavicular block
What is a supraclavicular block used for?
It numbs the whole arm below the shoulder for surgery on the upper arm, elbow, forearm, wrist, or hand. It reaches the brachial plexus where it is packed tightest, above the collarbone, so the block comes on fast and runs deep. It is a weak choice for the shoulder, which is served by the interscalene block.
What does the plexus look like on ultrasound here?
It sits beside the subclavian artery as a clump of small round dark shapes, often likened to a bunch of grapes. The artery is a round pulsing circle on the first rib. The plexus lies to the upper and outer side of it, between the artery and the skin, with the first rib and the lung below.
Why is pneumothorax a concern with this block?
The lining of the lung sits a short way deep to the plexus, so a needle pushed too far can pierce it and let air around the lung. Ultrasound shows the pleura sliding with the breath. The needle is kept in front of it and above the first rib. A pneumothorax done this way is rare. The signs are watched for after the block.
What is the corner pocket?
It is the angle where the subclavian artery meets the first rib, the inner lower corner of the block. The lowest part of the plexus, which supplies the inner forearm and little finger, tends to sit there. A small deposit of local anesthetic in that corner completes the block of the whole arm.
Does a supraclavicular block affect breathing?
It reaches the phrenic nerve less often than the interscalene block does, so the diaphragm is spared more of the time. Some patients still feel a temporary slowing of the diaphragm on that side. A patient with poor lungs is weighed with care before the block.
Why does a supraclavicular block work fast?
The plexus is bunched tight above the collarbone. The trunks and divisions sit close together beside the artery. A drug laid there washes over the whole bundle at once. The arm goes numb sooner than with a block placed where the nerves have spread apart.
About the Author
Julien Mercier
Senior R&D Engineer · Medical Ultrasound Transducer Development
Senior R&D Engineer with an M.S. in Applied Physics and over 15 years of experience in medical ultrasound transducer development, specializing in the design verification and performance testing of high-frequency imaging transducers. Currently leading the development and verification of the company’s next-generation high-frequency linear-array transducer, responsible for imaging performance evaluation and reliability analysis in preclinical testing. Brings extensive hands-on experience in piezoelectric element tuning, beamforming parameter optimization, and system-level performance testing.
