Acute Pain Service — PCA, Epidural Infusions, Opioid Equianalgesia + Rotation

Lockout protects against stacking — set conservatively in opioid-naive.

Hourly limits provide a safety ceiling.

Patients > 75, OSA, BMI >40, or chronic opioid use require lower starting demands + closer monitoring.

Continuous basal infusions added to PCA increase total opioid consumption + sedation + respiratory depression WITHOUT improving analgesia or sleep in opioid-naive patients (Cochrane reviews).

Reserved for chronic-opioid patients whose baseline requirement must be met to prevent withdrawal, and for selected pediatric or palliative scenarios.

When used, calculate basal from oral morphine equivalents + start low (e.g., 0.5-1 mg/hr morphine for a chronic-opioid adult).

Monitoring: continuous SpO₂ + capnography in basal-infusion patients per APSF guidance.

ASA + APSF strongly recommend continuous respiratory monitoring for any PCA with basal infusion + for opioid-naive patients with risk factors (OSA, obesity, age >65, concomitant sedatives).

Lower bupi concentration (0.0625%) for ambulation-friendly post-op (knee replacements, labor).

Higher (0.125%) for major thoracoabdominal cases.

PCEA (patient-controlled epidural analgesia): continuous infusion 4-6 mL/hr + patient demand bolus 3-5 mL with 10-20 min lockout — superior pain scores + lower total local + lower motor block vs continuous-only.

Adjuncts: clonidine 1-2 mcg/mL adds analgesia without motor block but causes hypotension + sedation.

Epinephrine 1-2 mcg/mL prolongs block + serves as intravascular marker.

Motor block: lower bupi concentration or transition to opioid-only.

Pruritus: opioid effect at spinal cord — low-dose naloxone 0.5-1 mcg/kg/hr infusion or nalbuphine.

Urinary retention: opioid-induced; foley if needed.

Respiratory depression: opioid (especially hydrophilic morphine — delayed peak 6-12 hr after dose; less concern with lipophilic fentanyl).

Catheter migration → intravascular (LAST risk — recheck test dose if dose-response changes) or intrathecal (high block, hypotension, dyspnea — stop infusion).

Epidural hematoma: alert sign is unexpected motor block after hours of stable function — MRI emergently, decompress within 8 hr to preserve neurology.

Parenteral: IV morphine 10 mg ↔ IV hydromorphone 1.5 mg ↔ IV fentanyl 100 mcg.

Oral:IV morphine ratio 3:1 (oral 30 mg = IV 10 mg).

Transdermal fentanyl: 25 mcg/hr patch ≈ 60 mg oral morphine/day; reaches steady state at 12-24 hr + half-life after removal 17 hr — never use transdermal fentanyl for acute pain.

Methadone is NON-LINEAR: when converting from another opioid at oral morphine equivalent doses >200 mg/day, reduce calculated methadone dose by 75-90% + titrate up.

Cross-tolerance is incomplete — when rotating opioids, reduce the calculated equianalgesic dose by 25-50% to account for partial tolerance + interindividual variability.

Buprenorphine: modern consensus (Anesthesiology 2021 + ASRA 2022) is to CONTINUE baseline buprenorphine perioperatively + add full-agonist opioids as needed; the partial-agonist ceiling at mu does not prevent additive analgesia from full agonists.

Methadone for OUD: continue baseline dose, dose 1x/day; treat pain with additional full agonists.

Naltrexone: discontinue 72 hr before elective surgery (PO) or transition off implant/depot per addiction medicine consult — full agonists ineffective while bound.

NSAID if not contraindicated: ketorolac 15-30 mg q6h IV (max 5 days; reduce 50% in elderly + renal impairment) or ibuprofen 600 mg q6h PO.

Gabapentinoids: gabapentin 100-300 mg TID or pregabalin 75-150 mg BID — caution with respiratory depression in combination with opioids + elderly (FDA warning 2019).

Ketamine 0.1-0.3 mg/kg/hr infusion for opioid-tolerant or refractory cases.

Lidocaine 1-1.5 mg/kg/hr infusion in select abdominal surgery.

Document the multimodal plan + escalation thresholds in the acute pain service note.