Box 2.

Example- calculating spKt/V when dialysis sessions are more than 3 times per week

Problem: A 38-year old female is receiving hemodialysis 6 hours per day, 5 times a week. The dialysis days are Monday, Tuesday, Thursday, Friday, Saturday. Calculate spKt/V from the samples taken on Friday. Post dialysis blood urea (from sample taken on Thursday) is 18 mg/dl. Pre-dialysis blood urea (from sample taken on Friday) is 52 mg/dl. Weight loss is 1 L. Her weight is 57 Kg and height 165 cm.

Solution:

We will use equation 2 (given above) for calculating spKt/V, as hemodialysis frequency is high (5 times per week).

Equation 2: spKt/V = - ln (R - GFAC x T) + (4-3.5R) x 0.55 x Weight loss/V

Step 1: Here, PIDI is 1 day (Thursday to Friday).

G-Factor (GFAC) is 0.0175+0.001=0.0185 [from Table 1].

Step 2: Calculating ‘V’ by Watson’s formula for women:

V = -2.097 + (0.2466 X Weight in Kg) + (0.1069 X Height in cm)

= -2.097 + (0.2466 X 57) + (0.1069 X 165)

= -2.097+14.0562+17.6385=29.5977 L

Step 3: Calculating R

R = post-dialysis blood urea/pre-dialysis blood urea=18/52=0.3462

Using these values in equation 2:

Equation 2: spKt/V = - ln (R - GFAC x T) + (4-3.5R) x 0.55 x Weight loss/V

spKt/V = -In (0.3462-0.0185 x 6) + (4-3.5 x 0.3462) x 0.55 x (1/29.5977)

= - ln (0.3462-0.111) + (4-1.2117) x 0.55 x 0.0338

=-ln 0.2352+2.7883 x 0.0186

=-ln 0.2352+0.052

Using Ln calculator available on Rapid Tables (link provided in appendix):

= - (-1.4473) + 0.052=1.4473+0.052=1.4993