What are the considerations for spinal anesthesia with bupivacaine (bupivacaine) 0.5% heavy plus fentanyl (fentanyl) for a below-knee amputation in a patient with chronic kidney disease (CKD) on dialysis, emphysema, and pneumonia?

Spinal Anesthesia for Below-Knee Amputation in CKD on Dialysis with Emphysema and Pneumonia

Spinal anesthesia with reduced-dose bupivacaine 0.5% heavy (<10 mg) plus fentanyl 15 mcg is the preferred technique for this patient, as regional anesthesia reduces perioperative blood transfusion requirements and avoids respiratory depression in a patient with severe pulmonary compromise. 1, 2

Critical Preoperative Considerations

Timing of Surgery and Dialysis

• Schedule surgery for the morning following dialysis when the patient is in optimal metabolic balance with eliminated circulating toxins, high intravascular volume, and ideal heparin metabolism 3
• Verify serum electrolytes are within acceptable range, as ESRD patients on dialysis have significant perioperative risk 1

Risk Stratification

• This patient has multiple independent predictors of mortality after below-knee amputation: renal insufficiency (ESRD on dialysis), cardiac issues (if present), and increased age (68 years) 4
• CKD with dialysis dependence carries up to 45% prevalence of PAD and is associated with higher rates of lower extremity amputation and readmission after revascularization 1
• The 30-day mortality rate for below-knee amputation is approximately 7%, with 34.4% experiencing complications 4

Anesthetic Technique Selection

Why Spinal Anesthesia is Preferred

• Regional anesthesia significantly reduces perioperative blood transfusion requirements (11.8% vs 16.5% with general anesthesia, p<0.001) and decreases composite postoperative complications (25.7% vs 29.1%, p<0.04) 2
• Regional anesthesia reduces intraoperative hypotension (14.6% vs 61.4% with GA), vasopressor use (14% vs 52%), and postoperative ICU admission (7% vs 14.6%) 5
• Avoids respiratory depression critical in a patient with emphysema and active pneumonia, as general anesthesia requires mechanical ventilation and higher inspired oxygen concentrations 1
• Spinal anesthesia is specifically recommended for all patients undergoing hip fracture repair (similar lower extremity surgery) unless contraindicated 1

Specific Dosing Adjustments Required

Bupivacaine Dosing:

• Use reduced doses of intrathecal bupivacaine (<10 mg) to minimize hypotension in this elderly patient 1
• Elderly patients (≥65 years) exhibit greater spread, higher maximal level, and faster onset of anesthesia than younger patients 6
• Bupivacaine is substantially excreted by the kidney, and risk of adverse reactions is greater in patients with renal impairment - dose selection must account for this 6
• Consider attempted lateralization using hyperbaric bupivacaine with the operative leg positioned inferiorly to ameliorate hypotension 1

Fentanyl Dosing:

• The planned dose of fentanyl 15 mcg intrathecally is appropriate and preferred over morphine or diamorphine, which cause greater respiratory and cognitive depression 1
• This is particularly critical given the patient's emphysema and pneumonia 1

Intraoperative Management

Hemodynamic Monitoring and Goals

• Maintain mean arterial pressure between 60-70 mmHg (or >70 mmHg if patient is hypertensive) to preserve renal perfusion pressure 1, 7
• Implement goal-directed fluid therapy with stroke volume monitoring during this major surgery to optimize renal perfusion and reduce postoperative complications 7
• Patients ≥65 years with hypertension are at increased risk for hypotension during spinal anesthesia 6
• Prepare vasopressors in titrated dosages for immediate use if hypotension develops 6

Respiratory Management

• Provide supplemental oxygen continuously during spinal anesthesia 1
• Monitor respiratory status closely given emphysema and pneumonia - spinal anesthesia avoids the respiratory depression associated with opioid-only analgesia 1
• Be prepared for potential high spinal block causing respiratory compromise, though this is less likely with reduced bupivacaine doses 6

Renal Protection

• Avoid all nephrotoxic agents and NSAIDs in the perioperative period 1, 7, 8
• Maintain adequate hydration to prevent acute kidney injury 7
• Avoid hypovolemia, which is crucial to prevent acute kidney injury in dialysis patients 7

Technical Considerations

• Aspirate for blood and cerebrospinal fluid before injecting to confirm subarachnoid entry and avoid intravascular injection 6
• Monitor onset of adequate spinal anesthesia carefully, as it is not always possible to control the level after subarachnoid injection 6
• Maintain core temperature monitoring and active warming strategies throughout, as elderly patients are susceptible to hypothermia 1

Postoperative Management

Analgesia

• Regular paracetamol (acetaminophen) should continue throughout the perioperative period 1
• Avoid NSAIDs entirely - they are contraindicated in renal dysfunction and specifically listed as drugs to avoid in hemodialysis patients 1, 8
• Use opioids with extreme caution - reduce both dose and frequency (e.g., halved) in patients with renal dysfunction 1
• Avoid codeine as it is constipating, emetic, and associated with perioperative cognitive dysfunction 1

Monitoring

• Close monitoring of renal function with regular assessment of urine output and serum creatinine is essential 7
• Check serum electrolytes if any symptoms develop postoperatively 3
• Monitor for postoperative complications including wound infection (9.3% incidence), sepsis (9.3%), and return to operating room (15.6%) 4

Critical Pitfalls to Avoid

• Do not use standard bupivacaine doses - elderly patients with renal impairment require reduced doses 6
• Do not administer spinal anesthesia simultaneously with general anesthesia - this is associated with precipitous falls in blood pressure 1
• Do not use morphine or diamorphine intrathecally in this patient with pulmonary disease - fentanyl is preferred 1
• Do not prescribe NSAIDs postoperatively - they are nephrotoxic and contraindicated in dialysis patients 1, 8
• Do not allow hypovolemia - this is critical to prevent acute kidney injury 7
• Do not inject during positioning or movement - ensure patient is stable before injection 6