5-Calculator-Series-Renal & Electrolytes

1- FENa (Fractional Excretion of Sodium) Calculator 

Information

The Sodium Bicarbonate Deficit calculation is used to estimate the amount of sodium bicarbonate needed to correct metabolic acidosis. It considers the patient's weight, the target increase in serum bicarbonate, and the patient's current bicarbonate level. This guides the treatment of patients with acid-base imbalances, such as those with severe renal failure or metabolic acidosis from other causes. The calculation provides an estimate of the bicarbonate amount required to raise the serkum bicarbonate to a desired level, aiding in appropriate and safe correction of acidosis.

Bicarbonate Deficit Calculation-

bicarb deficit = 0.4 × weight (kg) × (desired bicarb (mmol/L) – bicarb level (mmol/L))

References-

Koda -Kimble M, Young LY, et al. Handbook of Applied Therapeutics. Lippi ncott Williams & Wilkins; 2006. P10.3(1104).

FENa (Fractional Excretion of Sodium)

Urine Sodium (U_Na, mmol/L):
Plasma Sodium (P_Na, mmol/L):
Urine Creatinine (U_Cr, mg/dL):
Plasma Creatinine (P_Cr, mg/dL):

2- Bicarbonate Deficit Calculator

Estimates bicarbonate replacement requirement in metabolic acidosis.

Patient Weight (kg):

Desired Bicarbonate (mmol/L):

Actual Bicarbonate (mmol/L):

Formula:

Bicarbonate Deficit (mmol) = 0.5 × Weight (kg) × ( Desired HCO₃⁻ − Actual HCO₃⁻ ) Bicarbonate Deficit (mmol)=0.5×Weight (kg)×(Desired HCO₃⁻−Actual HCO₃⁻

Information

The Sodium Bicarbonate Deficit calculation is used to estimate the amount of sodium bicarbonate needed to correct metabolic acidosis. It considers the patient's weight, the target increase in serum bicarbonate, and the patient's current bicarbonate level. This guides the treatment of patients with acid-base imbalances, such as those with severe renal failure or metabolic acidosis from other causes. The calculation provides an estimate of the bicarbonate amount required to raise the serum bicarbonate to a desired level, aiding in appropriate and safe correction of acidosis.

Bicarbonate Deficit Calculation-

bicarb deficit = 0.4 × weight (kg) × (desired bicarb (mmol/L) – bicarb level (mmol/L))

References-

Koda-Kimble M, Young LY, et al. Handbook of Applied Therapeutics. Lippincott Williams & Wilkins; 2006. P10.3(1104).Fractional Excretion of Urea (FEUrea) Calculator

3- FEUrea Calculator-

Fractional Excretion of Urea helps differentiate pre-renal from intrinsic renal causes.

Urine Urea (mmol/L or mg/dL):

Plasma Urea (mmol/L or mg/dL):

Urine Creatinine (mg/dL):

Plasma Creatinine (mg/dL):

Inputs: Urine Urea Plasma Urea Urine Creatinine Plasma Creatinine ✅ Output: FEU rea (%) with interpretation (

What is FEUrea?

FEUrea is a diagnostic calculation used to help differentiate causes of acute kidney injury (AKI), especially prerenal azotemia vs intrinsic renal (e.g., ATN), in patients receiving diuretics, where FENa (Fractional Excretion of Sodium) may not be reliable.

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🔹 Formula

$$FE_{Urea} (\%) = \frac{(Urine \, Urea \, Nitrogen \times Plasma \, Creatinine)}{(Plasma \, Urea \, Nitrogen \times Urine \, Creatinine)} \times 100$$

• UUN = Urine Urea Nitrogen (mg/dL or mmol/L)

• PUN/BUN = Plasma (Blood) Urea Nitrogen

• UCr = Urine Creatinine

• PCr = Plasma Creatinine

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🔹 Interpretation-

• < 35% → Suggests Prerenal AKI (functional, hypoperfusion).

• > 50% → Suggests Intrinsic renal AKI (e.g., ATN).

• 35–50% → Indeterminate / gray zone.

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🔹 Why use FE Urea?

• In patients on diuretics, sodium handling is altered, making FENa unreliable.

• Urea reabsorption depends more on renal perfusion than sodium, so FEUrea is better in these cases.

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📌 Example:

• UUN = 400 mg/dL

• PUN = 40 mg/dL

• UCr = 100 mg/dL

• PCr = 2 mg/dL

$$FE_{Urea} = \frac{(400 \times 2)}{(40 \times 100)} \times 100 = 20\%$$

➡ Suggests prerenal AKI.

The FEUrea calculation is useful in the assessment of acute kidney injury, particularly in patients who are on diuretics. It helps to distinguish between pre-renal azotemia and acute tubular necrosis.

FEUrea Calculation

FEUrea (%) = ((Urine Urea / Serum Urea) / (Urine Creatinine / Serum Creatinine)) × 100

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