Linear decay of relative blood volume during ultrafiltration predicts hemodynamic instability.
BACKGROUND
Relative blood volume (RBV) changes during hemodialysis (HD) are poorly understood. We wish to define characteristics of RBV profiles at different hydration states predictive of hemodynamic instability.


METHODS
Thirty patients underwent online RBV monitoring during an HD session with intermittent ultrafiltration (UF) pulses administered until the onset of hypotension. The RBV decay constant (tau) was derived from curve fitting. Linear divergence, the net deviation of the RBV curve during UF from predicted linear decay, was computed from initial 1-minute slopes.


RESULTS
The best correlation with proximity to dry weight (PDW) was provided by linear divergence (r = 0.817; P < 0.001), its major determinant in multiple regression analysis. Other predictors were RBV at initiation of UF pulse, UF pulse volume, and UF decay constant (tau(UF)). These parameters were significantly different in UF pulses within 1 kg and 1 kg or greater of dry weight. There were no correlations with refill parameters. The occurrence of hypotension was not different at RBVs less than 90% (7.4%) or 90% or greater (5.3%). tau(UF), linear divergence, RBV at initiation of UF pulse (all P < 0.001), and UF decay amplitude (P < 0.01) were different between hypotensive and normotensive UF pulses. Hypotension was the only independent predictor of tau(UF) (R2 = 0.40; P < 0.001). The only independent predictor of linear divergence was PDW (R2 = 0.667; P < 0.001).


CONCLUSIONS
Approaching dry weight, the RBV decline during UF switched from exponential to linear decay, probably indicating failing vascular refill. Monitoring deviation from linearity may allow improved hemodynamic stability and attainment of optimal post-HD weight.
Hope Hospital, Manchester; University of Hertfordshire, Hatfield, UK. rhea2202@aol.com
Sandip
S
Mitra
Paul
P
Chamney
Roger
R
Greenwood
Ken
K
Farrington
D000328:Adult; D000368:Aged; D000959:Antihypertensive Agents / Q000494:pharmacology; D001775:Blood Circulation / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D018660:Blood Pressure Monitoring, Ambulatory / Q000706:statistics & numerical data; D001810:Blood Volume / Q000502:physiology*; D001834:Body Water / Q000187:drug effects / Q000378:metabolism; D002408:Catheters, Indwelling / Q000009:adverse effects; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007022:Hypotension / Q000097:blood / Q000378:metabolism / Q000503:physiopathology; D016014:Linear Models; D008875:Middle Aged; D015999:Multivariate Analysis; D011237:Predictive Value of Tests; D006435:Renal Dialysis / Q000009:adverse effects* / Q000706:statistics & numerical data; D014462:Ultrafiltration / Q000379:methods
D000959:Antihypertensive Agents