What is the recommended postoperative pain management strategy using a continuous peripheral nerve (CPNB) block, specifically a caps block, for an adult patient with no significant medical history undergoing lower limb surgery?

Continuous Peripheral Nerve Block (CPNB) for Lower Limb Surgery

Direct Answer

For lower limb surgery in adults, continuous peripheral nerve blocks are highly effective and should be implemented as part of multimodal analgesia, with specific block selection based on surgical site: femoral nerve block for knee/anterior thigh procedures, sciatic blocks for ankle/foot surgery, and fascia iliaca blocks for hip procedures, using low-concentration local anesthetics (0.2% ropivacaine or bupivacaine) at 6 mL/hour. 1

Block Selection Algorithm by Surgical Site

For Knee Surgery

• Femoral nerve block (FNB) is the primary recommended technique based on level 1 evidence for total knee arthroplasty and can be extrapolated to other knee procedures 1, 2
• Administer initial bolus of 10-20 mL ropivacaine 0.5% (weight-adjusted), followed by continuous infusion of ropivacaine 0.2% at 6 mL/hour (0.2 mL/kg/hour, weight-adjusted) 3
• Do NOT combine femoral and sciatic blocks - insufficient evidence shows this is superior to femoral block plus systemic analgesia, and it increases motor blockade 1, 2

For Ankle and Foot Surgery

• Popliteal sciatic nerve block is the recommended approach for ankle fracture surgery and foot procedures 1
• Use ultrasound-guided technique with ropivacaine for optimal outcomes 1
• Expect substantial rebound pain when blocks subside; prepare patients and provide adequate multimodal analgesia 1

For Hip Surgery

• Fascia iliaca compartment block (FICB) is superior to opioids and should be the primary regional technique 1
• Can be administered as single-shot (30-40 mL bolus of 0.25% bupivacaine with 1:200,000 epinephrine) or continuous infusion (10-20 mL bolus of 0.2% bupivacaine, then 6 mL/hour) 1
• Reduces preoperative opioid consumption, acute confusional states, chest infections, and time to first mobilization 1

Essential Multimodal Analgesia Components

Regional blocks must be combined with scheduled systemic analgesics - never use blocks as monotherapy 1, 4

Scheduled Non-Opioid Medications

• Acetaminophen 1 gram IV every 6 hours for first 72 hours as first-line systemic adjunct 4
• NSAIDs (ibuprofen 800 mg every 6-8 hours or naproxen) unless contraindicated by renal dysfunction, bleeding risk, or cardiovascular disease 1, 4
• Continue these medications on a fixed schedule, not as-needed, to prevent fluctuations in serum levels 1

Opioid Management

• Reserve opioids strictly for breakthrough pain at lowest effective dose for shortest duration 1, 4
• For patients over 55 years, reduce opioid dosing by 20-25% per decade to minimize exposure without compromising pain control 1

Technical Considerations for CPNB

Catheter Placement

• Use ultrasound guidance in 82% of cases for optimal catheter positioning 3
• Employ strict sterile technique during placement 3
• Secure catheters properly to minimize dislodgement (occurs in 4.2% of cases) 3

Infusion Management

• Median catheter duration is 3 days (IQR 2-5 days) 3
• Provide PRN boluses of 10 mL bupivacaine 0.25% (weight-adjusted) with maximum 4 times daily if breakthrough pain occurs 3
• Expect 77-95% of patients to be pain-free at rest and 63-88% during mobilization during first 10 days 3

Critical Safety Considerations

Acute Compartment Syndrome Risk

Use low-concentration local anesthetics (0.2% or less) WITHOUT adjuvants to preserve some sensation and movement, allowing detection of breakthrough pain that may signal compartment syndrome 1

Key points for trauma cases:

• Severe pain is NOT always present in acute compartment syndrome 1
• Implement appropriate post-injury and postoperative surveillance protocols 1
• Single-shot or continuous blocks with low concentrations are NOT associated with delayed diagnosis when proper monitoring is used 1

Contraindications

• Avoid blocks in patients on therapeutic anticoagulation due to bleeding risk 4
• Do NOT use epidural techniques for lower limb surgery - increased risk of serious adverse events including limb weakness, bladder dysfunction, and delayed mobilization without superior benefits 1

Ambulatory Management

• Provide comprehensive patient and family education on catheter care and warning signs before discharge 4
• Ensure 24/7 availability of healthcare provider to address complications 5
• Monitor for catheter obstruction, migration, leakage (1.5% incidence), and local inflammation 3, 5

Common Pitfalls to Avoid

• Do NOT use lumbar plexus block (posterior approach) - femoral nerve block is equally effective with fewer complications 1, 2
• Do NOT add adjuvants (clonidine, epinephrine, neostigmine) to peripheral nerve blocks - lack of efficacy in procedure-specific studies 1, 2
• Do NOT use intra-articular local anesthetic or morphine - inconsistent analgesic efficacy 1
• Expect catheter replacement needs in 11% of cases and loss of efficacy requiring removal in 13% 3

Expected Outcomes

With proper CPNB technique:

• 79-92% of patients will not require increased opioid doses 3
• 50-67% will not require any PRN opioid doses 3
• Reduced length of hospital stay compared to systemic opioids alone 1
• Decreased risk of opioid-related adverse events including confusion, respiratory depression, and nausea 1