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Anesthesiology APPLIED Exam › Regional anesthesia and acute pain

The patient with a spinal cord stimulator or intrathecal pump

Regional anesthesia and acute pain·~5 min read· Physician-reviewed✓ Sourced · 8

Stem

A 64-year-old woman, 79 kg, is scheduled for a right total knee arthroplasty. She has a rechargeable spinal cord stimulator for persistent pain after a lumbar fusion: percutaneous leads with tips at T8–T9 entering the epidural space at T12–L1, and the generator in her left flank. She takes extended-release morphine 30 mg twice daily. She has brought her patient remote, and the device card says the system is MRI-conditional.

Question

How will you manage her stimulator and her pain for this operation?

Ideal answer

HeadlineThe stimulator is safe if I switch it off, keep cautery current away from it and stay below the leads; her morphine is baseline, not analgesia.

  1. Interrogate, then switch it off. Model and a recent normal lead impedance confirmed, output to minimum, then off with her remote.1
  2. Bipolar cautery; any monopolar pad on the right thigh. Lowest power, current path away from the device, no full-length table pad.1
  3. Spinal below the lead entry, clear of her fusion. Imaging shows lead entry and hardware; the needle must not transect the lead;1 no accessible interspace means general anesthesia.
  1. Continue her morphine; add multimodal analgesia. Morning dose, adductor canal block, acetaminophen, ketamine; missed baseline looks like uncontrolled pain.
  2. Back on before she leaves the room. Before emergence if general; settings restored, generator skin and legs examined.1

Watch for: sedation as acute opioid stacks on baseline.

Breaking down the answer

  • Why off, and why the pad — current coupled into the leads can burn at the electrode or damage the generator; device-off and a short current path are the manufacturer's conditions. Changes if: a representative reprograms it, they stay through emergence and recovery.1
  • Scar changes the block — epidural fibrosis around the leads gives patchy or failed blocks and can steer an epidural catheter caudally, so general anesthesia stays ready.1 Infection can cost her the device, so asepsis is part of the plan.1
  • MRI-conditional is model-specific — impedance must be in range, scan region and duration may be limited, and MRI mode is set and reversed afterwards.1
  • Buprenorphine, if she took it — continued, not routinely stopped.2 In a 2025 VA cohort of 1,881 operations, interruption nearly doubled postoperative opioid use (74 versus 40 mg MME/day) and raised pain scores.3
  • Methadone, if she took it — continue the daily dose. High chronic doses prolong QT, and its 24–36 h half-life outlasts naloxone, so respiratory depression needs an infusion.4
  • The pump patient — the pump is her maintenance drug: I record drug, concentration, daily dose and refill date, keep it running, and route any neuraxial or surgical approach clear of the catheter path.

Follow-up question

In the next bay, a 27-year-old man with cerebral palsy and an intrathecal baclofen pump is two hours out of a hip osteotomy. He is itching, agitated and rigid, temperature 39.2 °C, heart rate 138, blood pressure 88/50. The preoperative note says his refill was overdue. What is happening and what do you do?

Follow-up answer

HeadlineAcute intrathecal baclofen withdrawal until proven otherwise; it can kill, so I call for help and the pump team now.

Returning spasticity, pruritus and hypotension come first; advanced withdrawal mimics sepsis, malignant hyperthermia and neuroleptic malignant syndrome.5 He just had a general anesthetic, so end-tidal CO2 and a gas rule MH in or out. Treatment is restoring intrathecal baclofen: refill and interrogate the pump, image the catheter for kinking, fracture or disconnection at positioning, or give a lumbar bolus. Until then I give enteral baclofen and IV benzodiazepines, because oral baclofen alone will not halt it.5 I cool him, give fluids, check CK, potassium and coagulation, and admit to ICU, since rhabdomyolysis and organ failure follow.5

Pitfalls that cost points

  • Treating ziconotide like baclofen: it can be stopped abruptly without withdrawal; intrathecal opioids and baclofen cannot.6
  • Assuming a SynchroMed II works after an MRI: it may not, so I interrogate it after every scan.7
  • Injecting into the pump's catheter access port: that route can deliver a life-threatening overdose.5

Rapid-fire

Q: What do you need from an intrathecal pump before surgery? A: Drug, concentration, daily dose, reservoir volume and refill date, because refill intervals are calculated to prevent depletion.5

Q: How does intrathecal baclofen overdose present? A: Drowsiness, respiratory depression, seizures and rostral hypotonia progressing to coma; no antidote, so empty the pump, ventilate, and consider removing 30–40 mL of CSF.5

Q: What are ziconotide's dose limits and main toxicity? A: Label start ≤2.4 mcg/day, maximum 19.2 mcg/day;6 PACC experts start 0.5–1.2 mcg/day, rising ≤0.5 mcg/day weekly;8 boxed psychiatric and neurologic warning; CK rises in 40%.6

Q: When does the stimulator go back on after a general anesthetic? A: Before emergence, so returning pain does not complicate extubation.1

Numbers to know

Item Value
Neuraxial level Below the lead's epidural entry, on imaging1
Buprenorphine interrupted vs continued 74 vs 40 mg MME/day after surgery3
Methadone half-life 24–36 h4
Ziconotide maximum 19.2 mcg/day (0.8 mcg/h)6
Baclofen overdose CSF drainage 30–40 mL5

Sources

  1. 1.Recommendations for Managing Non-Cardiac Implantable Electrical Devices (NCIEDs) During Non-Neurologic Surgery and Procedures · APSF, 2025 · apsf.orgMorano JM, Uejima JL. APSF Newsletter, February 2025 (vol 40, no 1). Covers SCS and DBS; does not address intrathecal pumps.
  2. 2.Buprenorphine Management in the Perioperative Period: educational review and recommendations from a multisociety expert panel · ASRA Pain Medicine, 2021 · asra.comKohan L, et al. Reg Anesth Pain Med 2021;46:840-59.
  3. 3.Perioperative continuation of buprenorphine in surgical patients with opioid use disorder · NYSORA, 2025 · nysora.comSummary of Hitt JM, Elkin PL, de Leon-Casasola OA. Anesthesiology 2025;142(2): VA cohort 2010-2020, 1,881 operations.
  4. 4.Use of Methadone in the Perioperative Period · APSF · apsf.org
  5. 5.Gablofen (baclofen injection) for intrathecal use: prescribing information · FDA labeling (Drugs.com) · drugs.comBoxed warning on abrupt discontinuation; section 5.5 withdrawal; overdose section.
  6. 6.Prialt (ziconotide) intrathecal infusion: prescribing information · FDA labeling (Drugs.com) · drugs.comSection 5.1: can be interrupted or discontinued abruptly without evidence of withdrawal effects.
  7. 7.SynchroMed II infusion pump: caution after MRI · Therapeutic Goods Administration (Australia) · tga.gov.au
  8. 8.Intrathecal Ziconotide: Dosing and Administration Strategies in Patients With Refractory Chronic Pain · Neuromodulation (McDowell, Pope), 2016 · europepmc.orgExpert consensus (PACC authors): start continuous infusion at 0.5-1.2 mcg/day, titrate by <=0.5 mcg/day no more than weekly; PACC 2012 range 0.5-2.4 mcg/day, maximum 19.2 mcg/day. The PACC 2016/2017 full text could not be opened.

Facts on this page were checked against these sources on Oct 22, 2026. Guidelines change; confirm doses against current institutional protocols.

Related topics

Acute pain in the opioid-tolerant patientPCA and multimodal analgesiaSubstance use: opioids, cocaine, alcohol withdrawalAnesthesia in MRI and remote locationsPacemakers and ICDs in the operating roomMalignant hyperthermia
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