Anesthesiology APPLIED Exam › Regional anesthesia and acute pain

Interscalene block and its complications

Regional anesthesia and acute pain·~5 min read· Physician-reviewed✓ Sourced · 3

Stem

A 66-year-old woman, 102 kg (BMI 38), with moderate COPD (FEV1 55% predicted) and treated obstructive sleep apnea, is scheduled for an outpatient arthroscopic rotator cuff repair in the beach-chair position. Her room-air SpO2 is 93%. The surgeon asks for "the usual interscalene" for postoperative analgesia.

Question

Will you do an interscalene block in this patient, and what are the alternatives?

Ideal answer

HeadlineNot a conventional interscalene: it almost always blocks the phrenic nerve, and with COPD, obesity, sleep apnea and a saturation of 93% she may not tolerate that.¹

Name the risk: phrenic paresis. In classic large-volume studies essentially every patient had hemidiaphragmatic paresis and FVC fell about 27%;¹ 45 to 20 mL did not prevent it; FVC still fell about a third.²
Suprascapular plus axillary or infraclavicular block, which in one arthroscopy study gave similar 24-hour pain and opioid use with no diaphragmatic paresis.¹
Superior trunk or supraclavicular is an option, but I tell her they reduce rather than eliminate phrenic involvement.¹
Ultrasound, awake or lightly sedated, so she can report paresthesia or pain on injection; consented for Horner syndrome, hoarseness, nerve injury and LAST.
Oral multimodal analgesia before the block wears off; in recovery I monitor her saturation and work of breathing.

Breaking down the answer

Why the phrenic goes — it lies on the anterior scalene near C5. Low volume, extrafascial injection and distal blocks only reduce it: 5 mL instead of 20 mL cut the rate from 100% to 45%; superior trunk block still paralyzed 76%.¹
Patient selection — heart failure, contralateral phrenic palsy and previous pneumonectomy join lung disease, obesity and low baseline saturation as reasons for an alternative.¹ Contralateral pneumonectomy is an absolute no; contralateral recurrent laryngeal palsy also pushes me away. This is the judgment tested.
What sparing costs — suprascapular-based plans give somewhat less complete analgesia than an interscalene, so the multimodal plan carries more weight.
Two more safeguards — I avoid injecting against high pressure (above about 15 psi), a second safeguard against intraneural injection, and do not advance the needle more than 2.5 cm, to avoid epidural or intrathecal injection.³
Beach-chair hypotension and bradycardia — the Bezold-Jarisch reflex in a preload-depleted, hypercontractile heart, often after epinephrine-containing infiltration. Fluids, ephedrine or atropine, with cerebral perfusion pressure in mind because the brain is above the cuff.
Rebound pain — the single-shot block wears off at 12–18 hours. Changes if: the plan needs longer cover; a catheter or dexamethasone extends duration.

Follow-up question

The surgeon insists, and a colleague gives a 20 mL interscalene. In recovery she becomes dyspneic, with SpO2 89% on 2 L nasal cannula. What do you do?

Follow-up answer

HeadlineLikely phrenic paresis, but I treat respiratory distress until I have excluded worse, and I tell the nurse and surgeon.

I sit her up, increase oxygen and examine her: reduced breath sounds and paradoxical abdominal motion on the blocked side suggest phrenic paresis, but I exclude pneumothorax with lung ultrasound, looking for lung sliding, and consider LAST. Diaphragm ultrasound and a blood gas for hypercarbia matter in her COPD. Most settle with oxygen, upright positioning and reassurance; if she tires or the PaCO2 rises, non-invasive ventilation and, rarely, intubation until the block wears off. She stays overnight in a monitored bed; I document and discuss it with her.

Pitfalls that cost points

Promising a block with no phrenic involvement.
Offering an interscalene to a patient with severe COPD without discussing alternatives.
Forgetting pneumothorax and LAST in the differential for post-block dyspnea.

Rapid-fire

Q: Why Horner syndrome? A: Spread to the cervical sympathetic chain causes ptosis, miosis and anhidrosis; it is benign and resolves with the block.³

Q: Why hoarseness? A: Spread to the recurrent laryngeal nerve; dangerous only if the contralateral cord is already paralyzed.

Q: Why can a small dose cause seizures in this block? A: Inadvertent injection into the vertebral artery, which runs deep to the anterior scalene, delivers drug directly to the brain; as little as 1–2 mL can seize.

Q: Which part of the upper limb does an interscalene block miss? A: The inferior trunk (C8–T1): the ulnar distribution, so not for forearm or hand surgery;³ posterior portal skin, from upper thoracic dorsal rami, often needs local infiltration.

Numbers to know

Item	Value
Phrenic block with conventional volume	Near 100%²
FVC reduction	~27% (large volume); 32% with 20 mL at 30 min²
Low-volume interscalene	5–15 mL ropivacaine 0.5%; 5 mL still gives ~45% paresis¹
Superior trunk block paresis	~76%¹
Single-shot duration	12–18 h; longer with dexamethasone
Roots targeted	C5–C6 (upper trunk)

Sources

1.Phrenic-sparing strategies for shoulder surgery: balancing respiratory safety with effective regional anesthesia · NYSORA, 2026 · nysora.com
2.Pulmonary Function Changes During Interscalene Brachial Plexus Block: Effects of Decreasing Local Anesthetic Injection Volume · Regional Anesthesia (Urmey WF, Gloeggler PJ), 1993 · rapm.bmj.com20 mL vs 45 mL mepivacaine: hemidiaphragmatic paresis in all patients; FVC fell 32% and 41% at 30 min.
3.Interscalene block complications · OpenAnesthesia · openanesthesia.org

Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.