What is the recommended anesthesia regimen for a patient undergoing below the knee amputation, considering their medical history and potential allergies or sensitivities?

Pure Peripheral Nerve Block for Below the Knee Amputation

For below the knee amputation, a combined femoral, obturator, and sciatic nerve block provides reliable surgical anesthesia in high-risk patients, with 91% success rate and minimal hemodynamic disturbance. 1

Primary Anesthetic Technique

Combined peripheral nerve blocks (femoral + sciatic + obturator) should be used as the sole anesthetic technique for below the knee amputation, particularly in patients with significant cardiovascular comorbidities. 1, 2

• The femoral-obturator-sciatic (FOS) combination achieved successful surgical anesthesia in 91% of ASA IV patients undergoing above knee amputation, with stable intraoperative hemodynamics in the majority of cases 1
• This approach avoids the hemodynamic instability associated with neuraxial techniques and the cardiovascular stress of general anesthesia 2
• Patients receiving only femoral + sciatic blocks (without obturator) required significantly higher doses of intraoperative sedation and analgesia (p = 0.013), indicating incomplete surgical anesthesia 1

Specific Block Technique and Dosing

Use ropivacaine 0.5% with epinephrine 1:200,000 for the initial nerve blocks, with 20 mL for sciatic and 20 mL for femoral blocks. 3

• Ropivacaine 0.75% (300 mg total) or 0.5% bupivacaine (200 mg total) both provide adequate surgical anesthesia when combined with epinephrine 3
• Adding dexmedetomidine 1 μg/kg to 0.33% ropivacaine for lumbar plexus and sciatic blocks extends analgesia duration to 26 hours postoperatively in high-risk patients 4
• The addition of epinephrine 1:200,000 to long-acting local anesthetics reduces peak plasma concentrations and prolongs block duration 3

Ultrasound Guidance

Ultrasound guidance must be used for all peripheral nerve blocks to reduce complications and local anesthetic systemic toxicity. 5

Intraoperative Management

Plan for supplemental sedation and analgesia in 95% of cases, but avoid deep sedation that could compromise airway reflexes or hemodynamic stability. 1

• Light to moderate sedation with propofol infusion or intermittent midazolam allows patient cooperation while maintaining spontaneous ventilation 1
• Have rescue analgesics immediately available: fentanyl 25-50 mcg IV boluses can be titrated for breakthrough pain 1
• Monitor for signs of incomplete block (patient discomfort, movement, hemodynamic changes) and be prepared to convert to general anesthesia if necessary 1

Postoperative Analgesia Strategy

Continue peripheral nerve block analgesia with catheter-based infusions rather than relying solely on systemic opioids. 4, 6

• Ropivacaine 0.2% provides equivalent analgesia to 0.3% with lower total drug exposure; initial infusion rates should be 15 mL/h 6
• Ropivacaine 0.1% provides inadequate postoperative analgesia and should not be used 6
• Plasma ropivacaine concentrations remain below toxic levels with continuous infusions up to 72 hours when using 0.2-0.3% concentrations 6

Implement multimodal analgesia with scheduled paracetamol and NSAIDs/COX-2 inhibitors unless contraindicated. 7

• Paracetamol should be administered on a scheduled basis, not as-needed 7
• Add conventional NSAIDs or COX-2 selective inhibitors for baseline analgesia 7
• Reserve strong opioids strictly as rescue medication for breakthrough pain 7

Critical Contraindications and Pitfalls

Avoid this technique in patients with active infection at injection sites, coagulopathy, or patient refusal. 5

• Active infection or sepsis at the proposed injection site is an absolute contraindication 5
• Patient inability to cooperate or refusal makes the technique unsafe 5
• Severe coagulopathy increases bleeding risk, though peripheral blocks are safer than neuraxial techniques in this regard 5

Do not omit the obturator nerve block when performing femoral-sciatic combinations for lower limb amputation. 1

• The obturator nerve provides sensory innervation to the medial thigh and contributes to surgical field anesthesia 1
• Omitting this block results in incomplete anesthesia and significantly higher sedation-analgesia requirements 1
• Consider adding lateral femoral cutaneous nerve block for complete coverage of the anterior and lateral thigh 1

Avoid epidural or spinal anesthesia in favor of peripheral blocks for this high-risk population. 8

• Neuraxial techniques cause sympathetic blockade and hemodynamic instability that may be poorly tolerated in patients with severe cardiovascular disease 8
• A retrospective analysis of above knee amputation showed no mortality benefit with regional versus general anesthesia after propensity matching 8
• Peripheral nerve blocks provide equivalent analgesia without the hemodynamic consequences of neuraxial blockade 1, 2

Patient Selection Considerations

This technique is particularly appropriate for patients with recent myocardial infarction, severe heart failure, or multiple cardiovascular comorbidities. 2

• Peripheral nerve blocks cause minimal hemodynamic disturbance compared to general or neuraxial anesthesia 2
• The 30-day mortality in ASA IV patients undergoing above knee amputation with peripheral blocks was 12.3%, with one-year mortality of 47.4%, reflecting the severity of underlying disease rather than anesthetic technique 1
• Patients with severe sepsis and recent MI can safely undergo urgent amputation with combined sciatic-femoral blocks 2