Interactive tool
Calculate flow volume
Enter the directly measured TAMV, or let the calculator estimate it from PSV and EDV. Together with the diameter, flow is calculated as Q = TAMV × π × (d/2)2 × 60.
How to use it
Instructions
Measuring the two parameters correctly
- Diameter. Longitudinal view, measured intima to intima (internal lumen), midway between two branches, in a straight, non-aneurysmal segment. Average 3 measurements. The diameter error is squared in the formula: an 8% error in diameter becomes a 17% error in flow.
- Time-averaged mean velocity (TAMV). Sample volume opened to cover the whole lumen (not just the centre), insonation angle ≤ 60°, angle correction parallel to the vessel wall, mean trace calculated over at least 3 complete cardiac cycles. Do not use TAMAX (time-averaged peak velocity): it overestimates flow by about 20–30%.
- Repeat the measurement at two different points of the same vessel and use the average: intra-observer variability is 10–15%.
Where to measure in an arteriovenous fistula
- The standard site is the brachial artery, 3–5 cm above the elbow crease: the vessel is straight, flow is laminar and the calibre is stable. In distal radiocephalic fistulas, brachial flow is a good approximation of access flow.
- Avoid measuring on the outflow vein: irregular calibre, turbulent flow and compressible walls make the result unreliable.
- In prosthetic grafts, measure on the body of the graft, midway between the arterial and venous anastomoses.
- Measure before the dialysis session or at least one hour after it: during and immediately after dialysis, flow falls because of hypovolaemia.
Units
The calculator accepts the diameter in millimetres and velocities in cm/s. If a measured TAMV is not available, enter PSV and EDV to obtain an estimate: TAMV = (PSV + 2 × EDV) / 3. Conversion to ml/min is automatic. You can also enter the cross-sectional area directly, which is useful when the vessel is elliptical and you prefer to trace it by planimetry.
Clinical references
Guidelines and interpretation
Haemodialysis vascular access
| Flow | Interpretation | Management |
|---|---|---|
| < 400–500 ml/min (native fistula) | Access at high risk of thrombosis | Full morphological study and treatment of the stenosis |
| < 600 ml/min (graft) | Graft at risk of thrombosis | Fistulography / angioplasty |
| 600 – 1500 ml/min | Range usually adequate for dialysis | Regular surveillance |
| Fall > 25% from the previous value | Sign of progressive stenosis, even when the absolute value is still normal | Further investigation regardless of the absolute value |
| > 1500–2000 ml/min | High-flow access | Assess high-output heart failure and hand ischaemia (steal syndrome); consider flow-reduction procedures |
Flow alone is not enough: access surveillance combines flow data, a direct search for stenosis (velocity ratio ≥ 2 across the stenotic segment, PSV > 400 cm/s) and clinical parameters from the dialysis session (venous pressure, recirculation, cannulation difficulties). A stenosis > 50% associated with reduced flow is the classic indication for treatment; an angiographically significant stenosis without haemodynamic impact should not be treated routinely.
Fistula maturation
The rule of 6s — at 6 weeks after creation: flow ≥ 600 ml/min, vein diameter ≥ 6 mm, depth from the skin ≤ 6 mm, straight cannulable segment ≥ 6 cm — is the practical reference for considering a native fistula mature.
Supra-aortic vessels
- Vertebral artery: normal flow 60–120 ml/min per side. Values < 40 ml/min or marked asymmetry should be correlated with dominance and hypoplasia (diameter < 2.5 mm).
- Global cerebral blood flow (sum of both internal carotid and both vertebral arteries): usually 700–1000 ml/min in adults; it falls physiologically with age.
- In subclavian steal, vertebral flow is reversed or alternating: the absolute value loses meaning and what matters is the flow direction throughout the cycle.
Because the area depends on the square of the radius, the diameter is the dominant source of error. Before concluding that flow is abnormal, repeat the diameter measurement and check that the TAMV is the mean trace and not the peak one.
References
Sources
- KDOQI 2019 — Clinical Practice Guideline for Vascular Access, American Journal of Kidney Diseases.
- ESVS 2018 — Clinical practice guidelines on the management of vascular access for haemodialysis, Eur J Vasc Endovasc Surg.
- Schäberle W. — Ultrasonography in Vascular Diagnosis — method for calculating volume flow.
- Scheel PJ. et al., Stroke 2000 — Flow velocity and flow volume measurements in the extracranial carotid and vertebral arteries.
Quick-reference tool for healthcare professionals. It does not replace the original guidelines, the summaries of product characteristics or the specialist's clinical judgement. All calculations run in the browser: no patient data is transmitted to or stored on any server.