Investigation for Hemodialysis Patient with AV Fistula and Suspected Soft Tissue Infection
Physical examination remains the cornerstone for diagnosing AV fistula infection, with duplex ultrasound as the primary adjunctive imaging modality to confirm the diagnosis, assess extent of involvement, and exclude alternative pathologies such as pseudoaneurysm or abscess formation. 1
Initial Clinical Assessment
Perform a focused physical examination looking for:
- Erythema, warmth, and tenderness overlying the fistula site 1
- Fever and systemic signs of infection 2
- Changes in access thrill or bruit (may indicate concurrent stenosis) 1
- Skin integrity: ulceration, eschar formation, or spontaneous bleeding 1
- Presence of fluctuance suggesting abscess formation 1
- Temperature asymmetry >2°C between limbs (suggests active inflammatory process) 3
Up to 90% of accesses with abnormal physical examinations will have underlying clinically significant findings on imaging. 1
Primary Diagnostic Investigation
Order duplex ultrasound of the hemodialysis access as the first-line imaging study. 1 This modality serves multiple critical functions:
- Confirms access patency (distinguishes infection from thrombosis) 1
- Identifies fluid collections (abscess, hematoma, or seroma) regional to the access 1
- Assesses vessel wall integrity and detects wall degeneration 1
- Excludes pseudoaneurysm (contained rupture requiring urgent surgical intervention) 1
- Evaluates for underlying stenosis that may be contributing to complications 1
Blood Cultures and Laboratory Work
Obtain blood cultures before initiating antibiotics given the presence of fever and systemic signs. 2 This is essential because:
- AV fistula infections should be treated as subacute bacterial endocarditis with 6 weeks of antibiotic therapy 1
- Blood cultures guide targeted antimicrobial therapy
- Positive cultures confirm systemic involvement
Check complete blood count to assess for leukocytosis and inflammatory markers. 3
When to Consider Additional Imaging
CT scan, PET, or nuclear medicine scans (e.g., indium scan) are reasonable adjunctive diagnostic techniques when: 1
- Ultrasound findings are equivocal
- Deep tissue involvement is suspected
- Extent of infection needs better characterization
- Alternative diagnoses require exclusion
Fluoroscopy fistulography has NO role in the evaluation of suspected superficial or deep infection and should not be ordered. 1
Critical Management Decisions Based on Findings
If infection is confirmed:
- Initiate empiric broad-spectrum antibiotics covering skin flora (Staphylococcus aureus and Streptococcus species) 2
- Plan for 6 weeks of antibiotic therapy as per subacute bacterial endocarditis protocol 1
- Obtain immediate vascular surgery consultation if septic emboli are present, as fistula surgical excision is required 1
If pseudoaneurysm is identified on ultrasound:
- This represents a surgical emergency requiring immediate vascular surgery referral 1
- Do not cannulate the affected segment 1
If abscess is identified:
- Surgical drainage is typically required
- Continue to avoid cannulation of the affected area
Common Pitfalls to Avoid
Do not delay imaging while waiting for culture results – ultrasound should be performed urgently to guide immediate management decisions. 1
Do not dismiss non-painful swelling as benign – serious pathology including early infection may be painless initially. 3
Do not cannulate an access with overlying skin changes or suspected infection – this carries high risk of further exacerbation and permanent access loss. 4
Do not assume infection is the only problem – concurrent stenosis, thrombosis, or central venous obstruction may coexist and require separate evaluation. 1
Temporary Access Considerations
Establish temporary alternative access (tunneled dialysis catheter) if dialysis is needed before infection resolves. 4 The infected fistula should be rested until clinical resolution is achieved. 4