A Reference Equation for Objectively Adjusting Dwell Volume to Obtain More Ultrafiltration in Daily Practice of Peritoneal Dialysis

Figures & data

Table 1  Demographic data of study subjects (n = 88)

	1500 ml		2000 ml		Total		p
	n	%	N	%	n	%
Gender							0.078
Female	18	90	48	70.6	66	75.0
Male	2	10	20	29.4	22	25.0
Age [year-old]							0.36
<40	4	20	11	16.2	15	17.0
40–50	5	25	29	42.6	34	38.6
>50	11	55	28	41.2	39	44.3
Underlying disease							0.564
DM	2	10	10	14.7	12	13.6
CGN	17	85	54	79.4	71	80.7
CIN	0	0	3	4.4	3	3.4
SLE	1	5	1	1.5	2	2.3
CAPD duration [month]							0.401
<12	8	40	17	25.0	25	28.4
12–36	2	10	17	25.0	19	21.6
36–60	5	25	15	22.1	20	22.7
>60	5	25	19	27.9	24	27.3

*χ² test or Fisher exact test.

Abbreviations: DM = diabetes mellitus, CGN = chronic glomerulonephritis, CIN = chronic interstitial nephritis, SLE = systemic lupus erythematosus.

Table 2  Variables compared with two groups of 1500 ml and 2000 ml

	Group 1 (n = 20)		Group 2 (n = 68)		p
	Mean	SD	Mean	SD
Height (cm)	152.0	6.0	159.0	7.2	0.000^†
Weight (kg)	47.5	7.6	59.1	9.5	0.000^†
Waist circumference (cm)	77.6	8.9	86.2	9.3	0.000^†
BMI	20.4	2.9	23.3	3.3	0.001^†
Effluent volume (ml)	1779.0	140.0	2278.0	174.0	0.000^†
ΔH4-H2	0.2	0.2	0.2	0.2	0.158
UF (ml.)	279.0	140.6	278.7	174.7	0.994
Mean IPP0 (cm H2O)	50.4	7.2	48.8	10.5	0.518
Mean IPP4 (cm H2O)	16.6	3.9	18.7	6.1	0.159
ΔIPP (cm H2O)	33.8	8.7	30.1	9.8	0.132

Group 1: inflow volume 1500 ml, Group 2: inflow volume 2000 ml.

*Student's t test.

^†p < 0.05.

Abbreviations: BMI = body mass index, UF = ultrafiltration, IPP = intraperitoneal pressure at the beginning and ending of PET, DH4-H2: difference between dialysate/plasma creatinine level at hour 2 and hour 4.

Table 3  Summary statistics for various linear combinations

Angle	Weights		Sum of squares			λ
θ	w1 (Cosθ)	w2 (Sinθ)	SSt	SSw	SSb	(SSb/SSw)	F-value
0	1.000	0.000	8500	7365	1135	0.154	13.251
10	0.985	0.174	9086	7855	1231	0.157	13.483
20	0.940	0.342	9151	7896	1255	0.159	13.673
30	0.866	0.500	8687	7484	1204	0.161	13.831
40	0.766	0.643	7750	6668	1082	0.162	13.961
50	0.643	0.766	6453	5547	907	0.163	14.056
58.46	0.523	0.852	5190	4459	730	0.165	14.089
60	0.500	0.866	4953	4256	697	0.164	14.088
70	0.342	0.940	3430	2950	479	0.162	13.974
80	0.174	0.985	2067	1788	280	0.156	13.448
90	0.000	1.000	1031	909	122	0.134	11.529

Abbreviations: θ = the angle of two variables of waist circumference and body mass index (see Figure 1); w1 = Cosθ, w2 = Sinθ, SSt = total sum of squared deviation between data mean and its observed value, SSw = sum of total squared deviation between group mean and its observed value, SSb = sum of total squared deviation between data mean and its group mean, λ = SSb/SSw, F-value = (SSb ÷ degree of freedom) ÷ (SSw ÷ degree of freedom): as F goes up, P goes down (i.e., more confidence in there being a difference between two means).

Table 4  Six prediction methods for original observed volume

		Observed		Overall percentage	Predicted formula
Alternatives	Predicted	1500	2000
A	Rotation axes				Z = Cos 58.46° * waist + Sin 58.46° * BMI = 0.523 * waist + 0.852 * BMI
	1500	10^†	7	80.68%	Cutoff = 68.5, 21.5 for waist and BMI
	2000	10	61		Z cutoff = 55.65
B	DF (all groups with equal prior probability on two variables)				Z1 = −35.89 + 0.95 * waist − 0.15 * BMI
	1500	14	22	68.20%	Z2 = −44.05 + 1.02 * waist − 0.36 * BMI
	2000	6	46		Selected group = Max(Z1,Z2)
C	DF (prior probability from sample sizes on two variables)				Z1 = −36.69 + 0.95 * waist − 0.15 * BMI
	1500	3	3	77.30%	Z2 = −43.61 + 1.02 * waist − 0.36 * BMI
	2000	17	65		Selected group = Max(Z1,Z2)
D	DF (prior probability from sample sizes on four variables)				Z1 = −41.82 + 0.83 * waist + 0.2 * BMI + 7.35 * D(T4 − T2) + 0.3 * DIPP
	1500	8	3	83.00%	Z2 = −47.31 + 0.92 * waist + 0.25 * BMI + 5.6 * D(T4 − T2) + 0.26 * DIPP
	2000	12	65		Selected group = Max(Z1,Z2)
E	LR with two variables
	1500	4	3	78.40%	Z = −7.68 + 0.07 * waist + 0.16 * BMI
	2000	16	65
F	LR with four variables
	1500	8	4	81.80%	Z = −6.2 + 0.09 * waist + 0.09 * BMI − 1.39 * D (T4 − T2) − 0.05 * DIPP
	2000	12	64

^†counts in the matrix were determined by the respective predicted formula of alternatives.

Abbreviations: DF = discriminant function, LR = logistic regression.

Figure 1.  Plot of study data and new axis of Z (new axis) for alternative A.

Figure 2.  Relationships of causes and effects obtaining appropriate PD dwell volume to maximum UF volumes for continuous ambulatory peritoneal dialysis (CAPD) treatment.