The chronic pain patient for surgery: postherpetic neuralgia and chronic low back pain
Stem
A 72-year-old woman, 64 kg, with COPD is scheduled for total knee arthroplasty. She has had postherpetic neuralgia of the left T6 dermatome for 2 years and chronic axial low back pain for a decade. Her medicines are pregabalin 150 mg twice daily, duloxetine 60 mg daily, tramadol 50 mg four times daily, and lidocaine 5% patches. She is anxious that "nothing works for my pain."
Question
How do you plan her perioperative care and analgesia?
Ideal answer
HeadlineContinue her chronic regimen so she does not withdraw or flare, build a regional, opioid-sparing plan, and watch closely for respiratory depression from layered sedatives.
- Continue pregabalin, duloxetine and tramadol through surgery, because abrupt stops cause withdrawal and rebound pain; duloxetine must be tapered, not stopped.1
- Spinal plus an adductor canal block and periarticular infiltration, because regional techniques carry the analgesia and spare opioids.
- Acetaminophen, an NSAID if kidneys allow, titrated opioid, because she is tolerant but not to large doses.
- No added gabapentinoid, and careful opioid use, because gabapentinoids plus opioids in an older patient with COPD raise respiratory depression risk.2
- Continuous oximetry, capnography and a clear expectations talk, because her goal is function, not zero pain.
Watch for: sedation and slow breathing, agitation, tremor, clonus or fever suggesting serotonin toxicity.
Breaking down the answer
- Gabapentinoids around surgery — 281 trials showed no clinically meaningful reduction in acute pain and no prevention of chronic pain, with more dizziness and visual disturbance.3 I continue her chronic dose, but do not add a perioperative one.
- Serotonergic stacking — duloxetine with tramadol, fentanyl, meperidine or methadone raises serotonin syndrome risk;1 I prefer morphine or hydromorphone for rescue. Changes if: a methylene blue or linezolid need, which requires stopping duloxetine first.1
- Her PHN regimen fits the evidence — NeuPSIG 2025 makes tricyclics, gabapentinoids and SNRIs first line, lidocaine 5% and capsaicin 8% patches second line, opioids third line.4
- Axial back pain is not neuropathic pain — axial back pain without radiculopathy was excluded from NeuPSIG;4 her back pain needs physical function goals, not more neuropathic drugs.
- Bleeding — SNRIs increase bleeding risk, especially with NSAIDs, aspirin or anticoagulants;1 relevant to her DVT prophylaxis plan.
Follow-up question
On the first evening she is drowsy with a respiratory rate of 8 and SpO2 89% on 2 L oxygen, after two doses of oral oxycodone, her usual pregabalin and a nurse-given "extra" tramadol. What do you do?
Follow-up answer
HeadlineOpioid-induced respiratory depression, compounded by pregabalin in an older patient with COPD; I wake her, support her breathing and give naloxone in small doses.
Stimulation, airway support, and naloxone in small increments titrated to breathing, not to pain, then an infusion if needed because oxycodone outlasts naloxone. I check a gas for CO2 retention. Pregabalin is held tonight and resumed at a lower dose; tramadol stops while duloxetine continues. The FDA warns of this combination, especially in the elderly and those with COPD.2 She moves to a monitored bed with capnography.
Pitfalls that cost points
- Stopping duloxetine abruptly; it causes discontinuation symptoms and loses its analgesia.1
- Ordering meperidine or extra tramadol as rescue on top of an SNRI without considering serotonin toxicity.1
- Taking off her lidocaine patches routinely; they are compatible with surgery and help the dermatome.
Rapid-fire
Q: Number needed to treat for first-line neuropathic agents? A: Tricyclics about 4.6, SNRIs about 7.4, gabapentinoids about 8.9.4
Q: Who is at risk from gabapentinoids with opioids? A: Patients on opioids or other CNS depressants, the elderly, and those with respiratory impairment such as COPD.2
Q: Do gabapentinoids reduce postoperative nausea? A: Yes, a small reduction, but with more dizziness and visual disturbance.3
Q: Third-line options for neuropathic pain? A: Botulinum toxin A, repetitive transcranial magnetic stimulation and opioids, weak recommendations.4
Numbers to know
| Item | Value |
|---|---|
| TCA / SNRI / α2δ NNT | 4.6 / 7.4 / 8.94 |
| Lidocaine 5% plaster NNT | 14.5 (very low certainty)4 |
| Capsaicin 8% patch NNT | 13.24 |
| Gabapentinoid trials pooled | 281 RCTs, 24,682 patients3 |
| FDA gabapentinoid respiratory warning | December 20192 |
Links
- Acute pain in the opioid-tolerant patient, Opioids and postoperative respiratory depression, MAOIs, lithium, antidepressants and herbal supplements, PCA and multimodal analgesia, crps
- NeuPSIG neuropathic pain recommendations (2025 update); FDA gabapentinoid warning (2019)
Sources
- 1.CYMBALTA (duloxetine) prescribing information · Eli Lilly / DailyMed · dailymed.nlm.nih.gov
- 2.FDA requires new warnings for gabapentinoids about risk of respiratory depression · FDA, 2019 · fda.gov
- 3.Perioperative use of gabapentinoids for the management of postoperative acute pain: a systematic review and meta-analysis · Anesthesiology (abstract), 2020 · europepmc.org
- 4.Pharmacotherapy and non-invasive neuromodulation for neuropathic pain: a systematic review and meta-analysis (NeuPSIG update) · Lancet Neurol (abstract), 2025 · europepmc.org
Facts on this page were checked against these sources on Nov 2, 2026. Guidelines change; confirm doses against current institutional protocols.