Table 2.

Sodium-based osmotherapy equations

RowDescriptionEquation
1Dialysance of sodium ionDNa = –(V/t) × LN(1 – NaAR)
DNa = QP × [(QUF + QRF)/(QP + QRF)]
2Method 1 calculation of added water volumeVRF2 = VRF1 × (NaRF1/NaRF2)
VW = VRF1 × [(NaRF1 – NaRF2)/NaRF2]
3Method 2 calculation of water exchange volumeVX = VRF1 × (NaRF1 – NaRF2)/NaRF1]
4Method 3 volume calculation of added 4 M hypertonic saline volume (23.4%)V4M = VRF1 × (NaRF2 – NaRF1)/(Na4m – NaRF2)
5Method 4 calculation of solution H fluid flow rateQH = QEff × (NaRF1 – Eff-NaRF)/(NaRF1 – NaH)
6Method 4 replacement fluid 1 (RF1) flow rateQRF1 = QEff × (Eff-NaRF – NaH)/(NaRF1 – NaH)
7Plasma flow rate calculationQP = QB × (1 – hematocrit)
8Sodium concentration at treatment time (t)PNa(t) = PNa(0) + Na(0) × (1 – e–DNa·t/V); PNa(0) = NaPre
PNa(t) = PNa(0) + (NaRF2 − NaPre) × (1 – e–DNa·t/V)
PNa(t) = NaPre + ([NaRF2 − NaPre] × NaAR)
9Replacement fluid flow rateQRF = QP × (DNa − QUF)/(QP − DNa); QUF = 0
10Sodium balance at time (t)ΣNa(t) = PNa(t) × (V − QUF × t) − (NaPre × V)
ΣNa(t) = PNa(t) × (V − QUF × t) − (PNa(0) × V)
11Sodium concentration adjustment ratioNaAR = 1 – e–DNa·t/V
NaAR = ΔNa/∇Na(0) = (NaPost – NaPre)/(NaRF2 − NaPre)
12Sodium concentration change at end-treatment time (t)ΔNa = ∇Na(0) × NaAR
ΔNa = NaPost – NaPre
13Sodium concentration gradient, initial∇Na(0) = NaRF2 – NaPre
14Sodium concentration of RF2NaRF2 = NaPre + (ΔNa/NaAR)
NaRF2 = NaPre + [ΔNa/(1 – e–DNa⋅t/V)]
15Time at which specified PNa occurs (tX)tX = –(V/DNa) × LN[(NaRF2 – PNa(tX))/(NaRF2 – NaPre)]
16Ultrafiltration rate to achieve net zero sodium balance at time (t)QUF(t) = ([NaPost × V] – [NaPre × V])/(NaPost × t)
QUF(t) = (ΔNa × V)/(NaPost × t)
17Urea reduction ratioURR = 1 – e–KUrea·t/V
URR = (BUN(0) – BUN(t))/(BUN(0) – BUNDialysate)
18Watson volumeVMan = 2.447 – 0.09156 × (age, yr)
+0.1074 × (height, cm) + 0.3362 × (weight, kg)
VWoman = –2.097 + 0.1069 × (height, cm) + 0.2466 × (weight, kg)
  • See Table 1 for definitions of variables.