- Choose the estimation method — BIS / bioimpedance (when an absolute overhydration value from a body-composition monitor is available) or a structured clinical estimate.
- Select the weight unit and enter the current (pre-dialysis) weight. Switching the unit clears the field.
- BIS method: enter the absolute overhydration OH (L) from the BCM/BIS device; optionally add relative OH (% of extracellular water) for context.
- Clinical method: select the edema severity and tick the congestion signs present — the tool sums a rough excess-fluid estimate from category midpoints.
- Optionally enter the planned ultrafiltration this session (L) and session length (h) to compute the UF rate (mL/kg/h) against the patient's target weight.
- The result shows the estimated dry/target weight, the fluid to remove, and — if UF inputs are given — the UF rate with its risk band.
All computation runs in your browser; no values are stored or transmitted. This is a decision aid, not a substitute for serial clinical reassessment.
When to Use
Use this tool to frame a target (dry) weight and the volume to remove for a maintenance hemodialysis patient — either anchoring on an objective bioimpedance overhydration value, or building a structured clinical estimate when no body-composition monitor is available. It also flags an ultrafiltration rate that crosses thresholds associated with cardiovascular harm. The numbers are a starting point for an iterative process, not a prescription.
Appropriate use
Adult maintenance hemodialysis patients in whom you are reassessing dry weight or planning fluid removal. The BIS method is preferred when a calibrated body-composition monitor (e.g. BCM) gives an absolute overhydration (OH) in liters; the clinical method is a fallback driven by edema and congestion signs. Dry weight should then be approached gradually, guided by intradialytic blood pressure, symptoms, and serial examination.
When NOT to rely on it
Do not treat the output as a definitive dry weight. The clinical estimate in particular is a coarse approximation that overlaps widely between categories. Bioimpedance is unreliable in amputees, with metallic implants, in severe electrolyte derangement, and immediately post-prandial or post-exercise. Never remove the full estimated volume in one session if it implies an aggressive UF rate — reduce stepwise and reassess.
Pearls & Pitfalls
The normohydration band
On BCM/BIS, an absolute OH within roughly ±1.1 L (or relative OH < 7% of extracellular water) is considered normohydrated; relative OH ≥ 15% marks clear fluid overload and predicts worse cardiovascular outcomes. Bioimpedance-guided fluid management has been shown to improve blood-pressure control and surrogate cardiovascular endpoints.
Watch the ultrafiltration rate
UF rate matters as much as the total volume removed. Rates above ~13 mL/kg/h are associated with intradialytic hypotension and increased cardiovascular morbidity and mortality; aim for ≤10 mL/kg/h. If the estimated volume forces a high rate, spread removal over more or longer sessions rather than chasing dry weight in one run.
Pitfalls
(1) Dry weight is a clinical diagnosis reached by gradual, iterative reduction — not a single calculated number. (2) Over-aggressive UF causes intradialytic hypotension, cramps, and myocardial/cerebral/gut "stunning" from ischemia. (3) Under-correction leaves chronic overload, hypertension, and left-ventricular hypertrophy. (4) BIS complements but does not replace clinical judgment — bedside signs, blood pressure trend, and intradialytic tolerance always govern.
Why Use It
Misjudging dry weight is a leading driver of morbidity in dialysis. Chronic fluid overload sustains hypertension and drives left-ventricular hypertrophy and cardiovascular death, while overshooting toward an unrealistically low target produces intradialytic hypotension, cramps, and organ stunning. Pairing an objective overhydration measurement (or, failing that, a disciplined clinical estimate) with an explicit ultrafiltration-rate check helps anchor a safe, gradual approach toward true euvolemia rather than reacting to a single weight reading.
Dry Weight & Target Weight Estimator (BIS + Clinical)
Choose a method, enter the current pre-dialysis weight, then either the bioimpedance overhydration value or the clinical signs. Optionally add the planned ultrafiltration and session length to check the UF rate against safety thresholds.
⚕ BIS method: target weight = current weight − OH (1 L ≈ 1 kg). Clinical method: estimated excess = edema-category midpoint + 0.5 L per congestion sign (capped +2 L); target weight = current − estimated excess. UF rate = planned UF (mL) ÷ target weight (kg) ÷ session length (h); aim ≤10 mL/kg/h, >13 mL/kg/h is high risk. Dry weight is a clinical diagnosis reached by gradual, iterative reduction guided by intradialytic blood pressure, symptoms, and serial signs — not a single calculated number. Sources: Wabel et al. NDT 2008; Onofriescu et al. AJKD 2014; Flythe et al. Kidney Int 2011.
Next Steps
Use the result to support — not replace — clinical judgment.
- Approach the target weight gradually — typically 0.2–0.5 kg steps over successive sessions — rather than removing the full estimated volume at once.
- Reassess at every session: intradialytic blood pressure trend, symptomatic hypotension or cramps, recovery time, and bedside congestion signs all refine the true dry weight.
- If the planned removal forces a UF rate above ~13 mL/kg/h, spread it over more or longer sessions, or add an extra treatment, rather than tolerating a high rate.
- Where available, repeat the bioimpedance measurement to track absolute and relative OH back toward the normohydration band; correlate with blood pressure and LV mass over time.
- Escalate when intradialytic instability, persistent overload despite removal, or discordant data make the target unclear.
Evidence & References
Formula & Equations
| Quantity | Equation |
|---|---|
| Target weight — BIS method (kg) | current weight − OH (L), treating 1 L of fluid as 1 kg |
| Clinical excess fluid (L) | edema-category midpoint (0 / 1.5 / 3.5 / 5.5 L) + 0.5 L × (number of congestion signs), capped at +2 L |
| Target weight — clinical method (kg) | current weight − estimated excess fluid |
| Fluid to remove (L) | current weight − target weight (≥ 0) |
| UF rate (mL/kg/h) | planned UF (mL) ÷ target weight (kg) ÷ session length (h) |
| Unit conversion | weight (kg) = lb ÷ 2.2046 |
Hydration & UF-rate bands
| Parameter | Band / threshold |
|---|---|
| Absolute OH (BCM/BIS) | Normohydrated ≈ within ±1.1 L; values well above suggest overload |
| Relative OH (% of ECW) | < 7% normohydrated; ≥ 15% clearly overhydrated (worse CV outcomes) |
| UF rate ≤ 10 mL/kg/h | Target — lower cardiovascular risk |
| UF rate > 13 mL/kg/h | High risk — associated with CV morbidity and mortality (Flythe) |
These are population thresholds, not individualized targets. The clinical excess-fluid estimate is deliberately coarse — categories overlap widely — and requires confirmation by serial intradialytic tolerance, blood pressure, and examination.
Evidence & References
Bioimpedance spectroscopy (BIS), implemented in body-composition monitors such as the BCM, gives an absolute overhydration value that helps target euvolemia and predicts cardiovascular outcomes; randomized data show bioimpedance-guided fluid management improves blood-pressure and surrogate cardiovascular endpoints. Independently, the ultrafiltration rate is a modifiable risk factor: rapid fluid removal is associated with cardiovascular morbidity and mortality, supporting a ≤10 mL/kg/h target and flagging >13 mL/kg/h as high risk.
- Wabel P, Moissl U, Chamney P, et al. Towards improved cardiovascular management: the necessity of combining blood pressure and fluid overload. Nephrol Dial Transplant. 2008;23(9):2965–2971.
- Onofriescu M, Hogas S, Voroneanu L, et al. Bioimpedance-guided fluid management in maintenance hemodialysis: a pilot randomized controlled trial. Am J Kidney Dis. 2014;64(1):111–118.
- Flythe JE, Kimmel SE, Brunelli SM. Rapid fluid removal during dialysis is associated with cardiovascular morbidity and mortality. Kidney Int. 2011;79(2):250–257.
