What is the recommended protocol for evaluating a diabetic foot in a patient with peripheral vascular disease?

Protocol for Evaluation of Diabetic Foot with Peripheral Vascular Disease

All diabetic patients with foot ulcers must undergo immediate vascular assessment including ankle-brachial index (ABI), toe pressures, and Doppler arterial waveforms, with urgent vascular imaging and revascularization considered when toe pressure is <30 mmHg or transcutaneous oxygen pressure (TcPO2) is <25 mmHg. 1

Initial Clinical Assessment

History Taking

• Document symptoms of peripheral arterial disease (PAD): leg fatigue, claudication, and rest pain relieved with dependency 1
• Identify prior foot ulcers, amputations, or Charcot foot history 1
• Assess neuropathic symptoms: pain, burning sensation, or numbness 1, 2
• Record diabetes duration, smoking status, presence of cardiovascular disease, hypertension, dyslipidemia, and renal disease 1, 3
• Note that only 19-41% of diabetic patients with severe PAD report claudication, so absence of symptoms does not exclude PAD 4

Physical Examination of the Foot

• Pulse palpation: Assess dorsalis pedis and posterior tibial arteries bilaterally 1
• Vascular signs: Evaluate capillary refill time, rubor on dependency, pallor on elevation, and venous filling time 1, 2
• Skin inspection: Look for ulcers, pre-ulcerative lesions, calluses, erythema, warmth, skin breaks, dryness, and fungal infections 1, 2
• Foot deformities: Document bunions, hammertoes, prominent metatarsal heads, Charcot foot, and limited joint mobility 1, 2
• Neurological assessment: Perform 10-g Semmes-Weinstein monofilament test at plantar sites plus at least one additional test (pinprick, temperature perception, 128-Hz tuning fork vibration, or ankle reflexes) 1, 5

Mandatory Bedside Vascular Testing

Primary Screening Tests (Perform in ALL Patients with Foot Ulcers)

• Hand-held Doppler evaluation: Assess flow signals from dorsalis pedis and posterior tibial arteries; document whether signals are triphasic, biphasic, or monophasic 1
• Ankle-Brachial Index (ABI): Measure ankle systolic pressure and calculate ABI 1
  • ABI <0.9 indicates PAD 1
  • ABI <0.6 indicates significant ischemia affecting wound healing 1
  • ABI <0.5 warrants urgent vascular imaging 1
  • Critical limitation: ABI may be falsely elevated in diabetes due to medial arterial calcification and noncompressible vessels 1, 6

Secondary Vascular Tests (Essential When ABI is Unreliable or >0.9)

• Toe-Brachial Index (TBI): More accurate than ABI in diabetic patients 1, 6
  • TBI ≥0.75 largely excludes PAD 1
  • TBI <0.7 strongly suggests PAD 1
  • Critical finding: 70% of limbs with "normal" ABI still had PAD detected by low TBI 6
• Toe systolic pressure: Direct measurement of distal perfusion 1
  • Toe pressure ≥30 mmHg: Threshold for healing potential 1
  • Toe pressure <30 mmHg: Indicates severe ischemia requiring urgent vascular referral 1
  • Toe pressure >55 mmHg: Ulcers will often heal 1
• Transcutaneous Oxygen Pressure (TcPO2): Measure skin perfusion 1
  • TcPO2 ≥25 mmHg: Increases healing probability by at least 25% 1
  • TcPO2 <25 mmHg: Warrants urgent vascular imaging 1
  • TcPO2 >50 mmHg: Ulcers will often heal 1

Interpretation and Decision Algorithm

PAD is Confirmed When:

• Both foot pulses are absent on palpation 1
• Absent or monophasic Doppler signals from one or both foot arteries 1
• ABI <0.9 1
• TBI <0.7 1

Severity Stratification and Management Pathway

Mild PAD (May Attempt Conservative Management First)

• ABI >0.6 with toe pressure >55 mmHg or TcPO2 >50 mmHg 1
• Provide 6 weeks of optimal wound care with close monitoring 1
• Reassess perfusion if wound healing response is poor 1

Moderate PAD (Consider Vascular Imaging)

• Ankle pressure <50 mmHg or ABI <0.5 1
• Ulcer not improving after 6 weeks of optimal management despite any bedside test results 1
• Perform duplex ultrasound or angiography 1

Severe PAD (Urgent Vascular Referral Required)

• Toe pressure <30 mmHg 1
• TcPO2 <25 mmHg 1
• ABI <0.5 with ankle pressure <50 mmHg 1
• Refer immediately for vascular imaging and revascularization 1

Advanced Vascular Imaging

Indications for Angiography

• Severe PAD as defined above requiring revascularization 1
• Non-healing ulcer after 6 weeks optimal care regardless of bedside test results 1

Imaging Modalities (All Acceptable)

• Duplex ultrasound 1
• Computed tomography angiography 1
• Magnetic resonance angiography 1
• Intra-arterial digital subtraction angiography 1
• Requirement: Must visualize entire lower extremity arterial circulation with detailed below-the-knee and pedal arteries 1

Revascularization Considerations

Goals of Revascularization

• Restore direct flow to at least one foot artery, preferably the artery supplying the wound region 1
• Achieve minimum toe pressure ≥30 mmHg, TcPO2 ≥25 mmHg, or skin perfusion pressure ≥40 mmHg 1

Revascularization Decision-Making

• Both endovascular techniques and bypass surgery should be available 1
• Decisions made by multidisciplinary team considering PAD distribution, vein availability, comorbidities, and local expertise 1
• Limb salvage rates after revascularization: 80-85% with ulcer healing >60% 1

Exceptions to Revascularization

• Severely frail patients or life expectancy <6-12 months 1
• Pre-existing severe functional impairment unlikely to worsen with amputation 1
• Large volume tissue necrosis rendering foot functionally unsalvageable 1

Critical Pitfalls to Avoid

• Do not rely on ABI alone in diabetic patients: 70% of limbs with normal ABI had PAD detected by TBI, with 64-70% having ulceration 6
• Do not rely on pulse palpation alone: Only 25.7% of PAD cases detected by palpation versus 55.4% by Doppler 3
• Do not assume absence of claudication excludes PAD: Peripheral neuropathy blunts pain perception; patients more commonly present with ulcers than claudication 3, 4
• Do not attribute poor healing to "diabetic microangiopathy": This should not be considered the cause of poor wound healing 1
• Do not delay vascular assessment: PAD prevalence in diabetic foot ulcer patients is 43.87-70%, and PAD significantly worsens limb salvage outcomes (48.3% vs 82.3% without PAD) 7, 6

Follow-Up Protocol

• Post-revascularization patients require multidisciplinary team management as part of comprehensive care plan 1
• Patients with PAD and foot infection are at particularly high risk for major amputation and require emergency treatment 1
• Risk-stratified follow-up based on International Working Group on Diabetic Foot classification 5, 8