Anesthetic Implications of Aortobifemoral (Aortofemoral) Bypass

1. Patient Profile and Preoperative Assessment

• Determine urgency (emergency vs. elective)
• Rule out active cardiac conditions: ACS, decompensated HF, severe valvular disease, unstable arrhythmia
• Estimate functional capacity (METs): if >4 METs without symptoms, proceed without further testing
• For poor functional capacity with elevated surgical risk, stress testing may be considered if it will change management

• Full blood count (major blood loss risk, underlying anemia)
• Coagulation studies (especially if regional anesthesia planned)
• Comprehensive metabolic panel (renal insufficiency is common; baseline needed)
• 12-lead ECG (baseline, increased MACE risk)
• Echocardiogram if LV dysfunction documented, worsening clinical status, or dyspnea of unknown origin
• Cardiac biomarkers: troponin, NT-proBNP, cystatin C, CRP increasingly studied for perioperative risk prediction

• Pulmonary disease: strong smoking-ASCVD association mandates assessment for COPD
• Diabetes and hypertension: optimize control
• Renal insufficiency: very common in this population; baseline creatinine and electrolytes essential
• Peripheral vascular exam: extent of collateral development (relevant to hemodynamic tolerance of clamping)

• Continue beta-blockers and statins perioperatively
• Aspirin/antiplatelet management per surgical team
• Antihypertensives continued with attention to the morning of surgery

2. Anesthetic Technique

General vs. Neuraxial/Regional

• Case duration (several hours)
• Need for abdominal access and muscle relaxation
• Potential for hemodynamic lability requiring airway control

• A lumbar or low thoracic epidural catheter is placed before induction
• Provides intraoperative supplementation and - critically - postoperative pain control
• Barash advises: a preinduction epidural catheter should be considered for postoperative pain control, barring contraindication
• Important caveat: local anesthetics via the epidural around the period of clamping and unclamping can worsen hemodynamic instability due to sympathetic block. Some clinicians use epidural opioids alone during this window, then resume local anesthetics after aortic unclamping once hemodynamics and volume have stabilized.
• Four randomized trials with ~450 combined aortic reconstruction patients failed to demonstrate reduced perioperative myocardial ischemia with epidural techniques. Pulmonary, cardiovascular, and renal complication rates were also not consistently reduced. Benefits relate mainly to postoperative analgesia and reduction in catecholamine response.

Induction

• A variety of IV agents (propofol, etomidate, thiopental) are suitable
• A short-acting potent opioid (fentanyl or sufentanil) blunts the hemodynamic response to laryngoscopy/intubation
• Low-concentration volatile agents during assisted ventilation can further blunt the hyperdynamic response
• Have ready for bolus during induction:
  • Esmolol 10-25 mg
  • Nitroglycerin 50-100 mcg
  • Sodium nitroprusside 5-25 mcg
  • Clevidipine 100 mcg
  • Phenylephrine 50-100 mcg

Maintenance

• Balanced anesthesia: potent opioid (fentanyl/sufentanil) + inhaled volatile (sevoflurane, desflurane, or isoflurane)
• N2O can supplement
• Pure opioid technique reserved for severe LV dysfunction
• Volatile agents provide controllable hemodynamics and some degree of cardiac preconditioning

3. Monitoring

• Routine non-selective use of pulmonary artery catheter is NOT recommended; reserve for patients with severely limited cardiopulmonary function or complex aortic reconstruction
• In patients with good LV and pulmonary function, CVP correlates adequately with LV filling pressure
• Invasive monitoring lines can be placed before or after induction; preinduction placement allows assessment of awake baseline hemodynamics

4. Physiology of Aortic Cross-Clamping and Unclamping

Cross-Clamping (Infrarenal level for AFB)

• SVR increases 20-32%
• Arterial pressure increases 7-10%
• Cardiac output decreases 9-33%
• Heart rate typically unchanged

• AIOD patients are already accustomed to high aortic resistance due to chronic obstruction
• Extensive collateral blood flow has already developed
• This contrasts with aneurysmal disease where collateral flow is limited
• Clamp position (distal aorta) is less hemodynamically significant than supraceeliac or thoracic clamping

Unclamping - the Critical Moment

• Decreased myocardial contractility
• Decreased arterial blood pressure
• Increased PA pressure
• Decreased venous return
• Decreased cardiac output

• Increased total body O2 consumption (reperfusion of ischemic tissue)
• Increased lactate (washout of ischemic metabolites)
• Decreased mixed venous O2 saturation
• Increased prostaglandins, activated complement, myocardial-depressant factors
• Metabolic acidosis
• Core temperature drop (cold blood returning from legs)

• Longer clamp duration
• More proximal clamp placement

Management of Unclamping

1. Correct fluid deficits and replace blood loss before unclamping
2. Reduce/discontinue vasodilators before unclamping
3. Reduce inspired volatile anesthetic concentration
4. Administer ~500 mL volume bolus immediately before infrarenal clamp release
5. If hypotension occurs: ask surgeon to partially re-apply or digitally compress the clamp; give vasopressors (cautiously, as re-clamping above the celiac axis with vasopressors on board can cause severe proximal hypertension)
6. Consider sodium bicarbonate for significant metabolic acidosis
7. Consider mannitol (renal protection, free radical scavenging)

5. Fluid and Blood Management

• Major blood loss is expected; transfusion triggers should be individualized
• Cell salvage (autologous blood salvage) is standard
• Warm all IV fluids and blood products
• Balanced crystalloid/colloid strategy; avoid overtransfusion during the clamp period - maintaining artificially elevated CVP during clamping leads to overtransfusion and pulmonary edema
• Coagulation monitoring (TEG/ROTEM if available) guides blood product use

6. Temperature Management

• Hypothermia is a significant risk in open abdominal surgery with large fluid shifts
• Strategies: increase ambient OR temperature before incision, warm cotton blankets, warm IV fluids, forced-air warming blanket over upper body
• Do NOT warm the lower body during the cross-clamp period - this increases metabolic demand in ischemic distal tissue, worsening ischemia-reperfusion injury
• Resume full warming after unclamping

7. Renal Protection

• Infrarenal clamping typically does not directly impair renal perfusion (kidneys are above the clamp), but hypotension during unclamping can
• Maintain adequate intravascular volume and MAP
• Avoid nephrotoxins (NSAIDs, contrast if applicable)
• Mannitol (0.25-0.5 g/kg) before unclamping: promotes osmotic diuresis, free radical scavenging
• Monitor urine output hourly; oliguria in the operative field warrants attention
• Postoperative AKI risk is elevated - baseline creatinine is valuable

8. Postoperative Care

• Pain management: epidural analgesia (if catheter placed) or IV PCA; adequate analgesia facilitates early extubation and mobilization
• ICU admission: standard for open aortic surgery; continuous hemodynamic monitoring
• Extubation: can be considered in OR if patient is hemodynamically stable, normothermic, metabolically compensated, and adequate ventilatory effort. COPD patients may need prolonged ventilation.
• Hemodynamic monitoring: continued close BP monitoring for hypertension on emergence (esmolol, nitroglycerin, clevidipine, or SNP at hand)
• Hypertension and tachycardia at emergence are aggressively controlled with short-acting agents
• Monitor for:
  • Myocardial ischemia/MI (ECG, troponin)
  • Renal dysfunction
  • Lower limb ischemia (graft occlusion/thrombosis)
  • Hemorrhage
  • Bowel ischemia (inferior mesenteric artery territory; uncommon with AFB but possible)
  • Spinal cord ischemia (very rare with infrarenal clamping, more relevant to thoracoabdominal)

Summary Table