Model-based study of the effects of the hemodialysis technique on the compensatory response to hypovolemia.
BACKGROUND
Hemodialysis technique (dialysate composition, filter, convection/diffusion ratio, etc.) can have an impact on the patient's tendency to acute hypotension. We have examined the hypothesis that the dialysis technique affects the hypotension risk by altering the cardiovascular compensatory response to hemodialysis-induced hypovolemia.


METHODS
Twelve hypotension-prone subjects were studied during six sessions of conventional bicarbonate dialysis (BD) and six sessions of acetate-free biofiltration (AFB). Blood volume (BV) control system was used in AFB to provide a BV change equivalent to the BV change observed in BD. The efficacy of reflex compensatory mechanisms was assessed by a model-based computer analysis of the BD and AFB sessions.


RESULTS
BD sessions were complicated by hypotension more frequently than the AFB ones (34/66 BD vs. 18/66 AFB). Hypotension arose about 60 minutes earlier in BD (123 +/- 41 minutes in BD vs. 183 +/- 25 minutes in AFB, P < 0.01), and after a smaller BV reduction (hypotension BV 7.9%+/- 2.0% in BD vs. 10.9%+/- 2.6% in AFB, P < 0.05). Model-based computer analysis of the sessions without hypotension revealed differences in peripheral resistance adaptation (9%+/- 9% BD vs. 19%+/- 7% AFB, P < 0.05) as well as in the stroke volume reduction (19%+/- 8% BD vs. 10%+/- 8% AFB, P < 0.001). Model analysis of sessions with hypotension indicated that compensatory mechanisms were almost inoperative in BD, whereas a residual capacity to control peripheral resistance and cardiac contractility was present in AFB. Model simulations demonstrated that hypotension occurred later in AFB since the residual compensatory capacity in AFB was able to sustain the arterial pressure for larger BV reductions (8.3% BD vs. 11.2% AFB).


CONCLUSIONS
The increased risk of acute hypotension in BD compared to AFB is caused by a therapy-induced inhibition of reflex compensatory response to hypovolemia.
Cavalcanti
Silvio
S
Bioengineering Laboratory-DEIS, University of Bologna, Bologna, Italy. silvio.cavalcanti@unibo.it
Ciandrini
Andrea
A
Severi
Stefano
S
Badiali
Fabio
F
Bini
Stefano
S
Gattiani
Andrea
A
Cagnoli
Leonardo
L
Santoro
Antonio
A
D000222:Adaptation, Physiological; D000368:Aged; D000369:Aged, 80 and over; D001639:Bicarbonates / Q000009:adverse effects; D001794:Blood Pressure; D002319:Cardiovascular System / Q000503:physiopathology*; D003198:Computer Simulation; D018592:Cross-Over Studies; D005260:Female; D006339:Heart Rate; D017583:Hemodiafiltration / Q000009:adverse effects; D006801:Humans; D007022:Hypotension / Q000209:etiology; D020896:Hypovolemia / Q000503:physiopathology*; D007676:Kidney Failure, Chronic / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D009200:Myocardial Contraction; D011446:Prospective Studies; D006435:Renal Dialysis / Q000009:adverse effects / Q000379:methods*; D012306:Risk; D014655:Vascular Resistance
D001639:Bicarbonates