Effects of Right Arteriovenous Fistula on Hemodynamic Measurements
A right arteriovenous fistula (AVF) significantly alters systemic hemodynamics by creating a low-resistance circuit that increases cardiac output while potentially compromising perfusion to vital organs such as the brain.
Systemic Hemodynamic Effects
Cardiac Changes
- Creation of an AVF leads to immediate and significant increases in cardiac output (CO), with studies showing an average increase from 7.02 L/min to 9.19 L/min 1
- The increase in CO is primarily driven by increased heart rate rather than stroke volume 2
- Right ventricular workload increases due to elevated pulmonary artery pressures 1
- Cardiac index (CI) can increase significantly, with reductions observed when the AVF is temporarily occluded (ΔCI: -0.42 L/min/m²) 2
Vascular Resistance and Blood Flow
- AVF creation results in decreased systemic vascular resistance 2
- AVF blood flow can represent approximately 23% of total cardiac output 1
- High-flow AVFs (>2000 mL/min) show more dramatic hemodynamic changes, with greater reductions in cardiac index when occluded (-2.79 L/min/m² vs -0.24 L/min/m²) 2
- Systemic vascular resistance index (SVRI) increases significantly when an AVF is temporarily occluded (ΔSVRI: 170.1 dyn/sec/cm⁻⁵/m²) 2
Regional Perfusion Effects
Brain Perfusion
- AVF creation can lead to decreased carotid artery flow and reduced brain tissue oxygenation as measured by near-infrared spectroscopy 1
- This represents a potential "steal" phenomenon where blood is diverted from cerebral circulation to the lower-resistance AVF circuit
Coronary Circulation
- Coronary artery flow velocity increases following AVF creation 1
- This compensatory mechanism helps maintain myocardial perfusion despite altered systemic hemodynamics
Pulmonary Circulation
- Pulmonary artery pressure increases after AVF creation 3
- Patients with higher AVF flow rates (mean 2750 mL/min) are more likely to develop pulmonary hypertension compared to those with lower flow rates (mean 1322 mL/min) 3
Monitoring and Clinical Implications
Flow Measurement and Surveillance
- Direct flow measurements are preferable for monitoring AVF function compared to indirect measures 4
- Optimal functioning AVF is characterized by flow rates of 700-1,300 mL/min 5
- Hemodynamically significant stenosis is defined as 50% narrowing with at least one abnormal clinical or hemodynamic indicator 5
Risk Assessment
- High-flow AVFs may lead to high-output cardiac failure, which can be reversible with AVF occlusion 2
- When indexing AVF blood flow for body size, a value ≥603 mL/min/m²·⁷ may identify patients at higher risk for high-output cardiac failure 6
- Patients with diabetes may experience greater reductions in ejection fraction (15.5% vs 1%) after AVF creation 3
Monitoring Techniques
- Physical examination remains a valuable initial screening tool for AVF dysfunction 4
- Doppler ultrasound is recommended for preoperative vascular mapping and surveillance of AVFs 5
- Central venous oxygen saturation (ScvO₂) increases by approximately 20% after successful AVF creation and can be used to track maturation 7
Practical Approach to Hemodynamic Monitoring in Patients with Right AVF
- Perform regular physical examinations to detect abnormal thrills, bruits, or pulses that may indicate stenosis or flow problems 4
- Monitor for clinical indicators of hemodynamic compromise:
- Ipsilateral extremity edema
- Abnormal thrill (weak/discontinuous)
- High-pitched bruit
- Difficulty achieving target dialysis blood flow 4
- For patients with high-flow AVFs (>2000 mL/min), consider more frequent cardiac evaluation due to increased risk of high-output cardiac failure 2, 6
- Pay special attention to elderly patients and those with diabetes, who may be more susceptible to hemodynamic complications 3
By understanding these hemodynamic effects, clinicians can better monitor and manage patients with right AVFs to optimize outcomes and minimize complications.