What is the recommended infusion regimen for postoperative pain management?

Recommended Infusion Regimen for Postoperative Pain Management

For postoperative pain management, the optimal infusion approach depends on the surgical procedure and patient population, but generally involves continuous epidural or regional anesthetic infusions using ropivacaine 0.2% at procedure-specific rates (5-10 mL/h for thoracic epidural, 6-12 mL/h for interscalene blocks), combined with multimodal systemic analgesia including IV lidocaine infusion limited to 24 hours maximum duration.

Epidural Infusion Regimens

Thoracic Epidural Analgesia (for thoracic/upper abdominal surgery)

• Initiate with a bolus of 5 mL ropivacaine 2.5 mg/mL (12.5 mg) after catheter placement before surgery 1
• Follow with continuous infusion of ropivacaine 1.5 mg/mL with sufentanil 0.2 µg/mL at 5-10 mL/h postoperatively 1
• Allow patient-controlled boluses of 5 mL every 40 minutes as needed 1
• This regimen provides superior pain control at rest and with mobilization compared to IV opioid PCA, with reduced nausea/vomiting and shorter postoperative ileus duration 1

Lower Abdominal Surgery Epidural Protocol

• Use ropivacaine 0.2% at 10 mL/h for optimal balance of analgesia and minimal motor block 2
• This concentration significantly reduces opioid requirements (median 7.5 mg morphine over 21 hours vs 43.3 mg with placebo) while minimizing motor block 2
• Higher concentrations (0.3%) provide similar analgesia but cause significantly more motor block 2

Regional Nerve Block Infusions

Interscalene Block (for major shoulder surgery)

• Start with initial block using 30 mL ropivacaine 7.5 mg/mL (225 mg) 3
• Begin continuous infusion 6 hours after initial block using ropivacaine 2 mg/mL at 6-9 mL/h (12-18 mg/h) 3
• Continue infusion for 48 hours maximum 3
• This regimen maintains plasma concentrations well below toxic thresholds (mean total ropivacaine 1.40 mg/L at end of infusion) with excellent pain control (median VAS ~20 mm) 3

Subacromial Infusion (for rotator cuff repair)

• Use ropivacaine 0.75% via continuous subacromial catheter 1
• Provides lower pain scores for first 12 hours compared to saline, though evidence for opioid-sparing effect is mixed 1
• Interscalene continuous infusion (levobupivacaine 0.125%) provides superior analgesia and less opioid consumption compared to subacromial infusion 1

Intravenous Lidocaine Infusion Protocol

Standard Duration and Dosing

• Administer IV bolus of 1.5 mg/kg over 10 minutes, followed by continuous infusion at 1.5 mg/kg/h (maximum 120 mg/hour) 4, 5
• Maximum initial duration should not exceed 24 hours for most patients 4
• Most patients do not benefit from prolonged infusion beyond 24 hours 4

Extension Beyond 24 Hours (if necessary)

• Decision to extend must be made by consultant anaesthetist/intensivist or acute pain team 4
• Reduce infusion rate to 50% of original rate if extending beyond 24 hours 4
• Rationale: Lidocaine exhibits time-dependent pharmacokinetics after 12 hours, with elimination half-life prolonging from 100 minutes to 3.22 hours after 24 hours 4

Critical Safety Requirements

• Lipid emulsion 20% must be readily available wherever IV lidocaine is used 4
• Monitor every 15 minutes for first hour, then hourly minimum 4
• Watch for early toxicity signs: peri-oral tingling, tinnitus, light-headedness, restlessness (these neurological symptoms precede cardiovascular changes) 4
• Ideally manage patients in monitored bedspace (HDU/level 2 care) outside operating theatre/recovery 4

Pediatric Postoperative Infusion Regimens

Ketamine/S-Ketamine Infusion

• Intraoperative bolus: 0.5 mg/kg (reduce to 0.25-0.5 mg/kg for S-ketamine) 1
• Optional continuous infusion: 0.1-0.2 mg/kg/h (maximum 0.4 mg/kg/h) 1

Dexmedetomidine Infusion

• IV bolus: 0.5-1 µg/kg 1
• Continuous infusion: 0.2-0.7 µg/kg/h until end of procedure 1

Metamizole Infusion (short-term hospital use only)

• Continuous infusion: 2.5 mg/kg/h following intraoperative loading dose 1
• Due to agranulocytosis risk with long-term use, recommend for short-term postoperative use in hospital setting only 1

Adjunctive Systemic Medications

IV Ketorolac

• Single intraoperative dose: 0.5-1 mg/kg (up to 30 mg) 1
• Postoperative: 0.15-0.2 mg/kg (max 10 mg) every 6 hours for maximum 48 hours 1
• Reduces morphine requirements by 26% when used as fixed intermittent boluses 6
• Total duration of ketorolac therapy must not exceed 5 days 6

IV Paracetamol

• Loading dose: 15-20 mg/kg 1
• Maintenance: 10-15 mg/kg every 6-8 hours 1

Common Pitfalls and Caveats

Epidural Infusion Pitfalls

• Avoid thoracic epidural in favor of paravertebral block when hypotension or urinary retention are concerns 1
• Thoracic epidural has higher failure rates (14.6% failure to identify epidural space) and more hypotension compared to paravertebral approaches 1

Regional Block Infusion Pitfalls

• Low-concentration ropivacaine infusions (0.1-0.2%) for peripheral nerve blocks may not provide adequate analgesia without supplemental systemic analgesics 7
• In axillary brachial plexus blocks, continuous infusion of 0.1% or 0.2% ropivacaine was no more beneficial than saline for postoperative pain relief 7

IV Lidocaine Pitfalls

• Never extend beyond 24 hours without reducing infusion rate by 50% due to altered pharmacokinetics 4
• Pharmacokinetics are only linear and predictable up to 12 hours of continuous infusion 5

Dosing Concentration Considerations

• For labor analgesia with epidural ropivacaine 2 mg/mL, use minimum 6 mL/h infusion rate to minimize need for rescue boluses 8
• Lower rates (4 mL/h) require significantly more top-up injections (mean 3 vs 1.4 at 10 mL/h) 8