Vector length as a proxy for the adequacy of ultrafiltration in hemodialysis.
BACKGROUND
Evaluation of dialysis adequacy has focused on parameters of solute (principally urea) clearance. Relatively little attention has been paid to the adequacy of ultrafiltration. At a given phase angle, the bioimpedance vector length reflects the degree of tissue hydration, as the vector lengthens with ultrafiltration.


METHODS
We determined the relative risk of death associated with different bioimpedance vector lengths in a 3009 patient hemodialysis cohort using proportional hazards regression.


RESULTS
The mean phase angle was 4.8 degrees, and the mean vector length 300 +/- 70 ohm/m (range 140 to 630 ohm/m). Vector length was much longer in women than men (mean 340 vs. 270 ohm/m) and significantly longer in African Americans and patients without diabetes. Adjusted for the effects of age, gender, race, diabetes, vintage, weight, albumin, prealbumin, creatinine, hemoglobin, ferritin, and dialysis dose, the relative risk (RR) of death was 0.75 (95% CI 0.57 to 0.88) per 100 ohm/m decrease in vector length. The effect of vector length on RR was somewhat more pronounced among men (vector length x gender interaction, P= 0.07). Considering vector length of 300 to 350 ohm/m as the referent category, the RRs of death were 1.54 (95% CI 1.08 to 2.21) and 2.83 (95% CI 1.55 to 5.14) for patients with vector length 200 to 250 and <200 ohm/m, respectively.


CONCLUSIONS
Shorter predialysis bioimpedance vectors, indicating greater soft tissue hydration, were associated with diminished survival in hemodialysis patients. These findings validate clinical observations linking longevity to maintenance of dry body weight.
Pillon
Luana
L
Division of Nephrology, Department of Medicine, New York University School of Medicine, New York, New York 10016, USA. luana.pillon@med.nyu.edu
Piccoli
Antonio
A
Lowrie
Edmund G
EG
Lazarus
J Michael
JM
Chertow
Glenn M
GM
D000328:Adult; D000368:Aged; D001834:Body Water; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000401:mortality* / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis / Q000401:mortality* / Q000592:standards; D012307:Risk Factors; D015996:Survival Rate