Sequential Dialysis, Osmolality, and Blood Pressure

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To the Editor: As pioneered by Bergstrom, sequential dialysis

involves separating diffusion and ultrafiltration and performing them sequentially during a dialysis treat- ment session ( 1). By providing isolated ultrafiltra- tion, one can reduce the problem of intradialytic hypotension. This blood pressure stabilization may result from a decrease in the drop in intravascular osmolality which results in less of a shift of intravas- cular fluid to the extravascular compartment. In an attempt to further study the relationship between osmolality changes and mean arterial pressure changes, we utilized four different protocols in 10 stable chronic hemodialysis patients in a cross-over design. Patients were treated with 4 hours of regular hemodialysis (RHD); standard sequential dialysis- 3 hours of RHD following by 1 hour of ultrafiltration (SSHD): reverse sequential hemodialysis- 1 hour of ultrafiltration followed by 3 hours of RHD (RSHD); and modified sequential hemodialysis-45 minutes of dialysis followed by 15 minutes of ultrafiltration each hour for 4 hours (MSHD). In order to exacer- bate any decline in blood pressure due to a falling osmolality. a dialysate sodium of 133 mEq/L was used with a Gambro 1.0 m7 dialyzer.

P.s shown in Figure 1 there was no statistically significant difference (by repeated measures analysis of variance) in mean arterial pressure (measured every 15 min), between any of the methods of dialysis studied. Utilizing hourly osmolality measurements for each patient in each protocol (549 data points), a correlation coefficient of r = 0.67 was found be- tween mean arterial pressure and plasma osmolality

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~ ~ P = 1 . 2 1 8 ( O s r n ) - 264.88

f z U

% 8 0 E I I I I I I I I I I I

284 286 288 290 292 294 296 298 300 3 0 2 304 308 OSMOLALITY (mOsmlL)

FIG. 2. Correlation between mean arterial pressure and osmo- Iality. Each point represents the mean arterial pressure and mean osmolality values for all time periods (hours 0-4) for all protocols for each of the 10 study subjects, a total of 539 osmolality and mean arterial pressure measurements.

(Fig. 2). Intradialytic weights were not significantly different for all protocols studied.

We conclude that 1 ) in stable chronic dialysis patients, intradialytic blood pressure during standard sequential dialysis does not differ significantly from that during other forms of sequential dialysis nor from that during regular hemodialysis. That such a difference might be demonstrated in a larger study or in "high-risk" patients remains a possibility. 2) Although there are many factors that may affect changes in mean arterial pressure during dialysis the correlation between changes in blood pressure and changes in osmolality support osmolality's role as one such factor, 3) To prevent declines in osmol&ty and mean arterial pressure during dialysis, high so- dium dialysate is probably superior to sequential dialysis methods. High sodium dialysis does not have the drawback of decreased diffusion dialysis that occurs with sequential dialysis methods. In addition, sequential dialysis methods have no place in the recent attempt to shorten dialysis time since a loss of diffusion time can markedly decrease clearances.

Steven J. Rosansky, MD Phillip Rosenzweig, MD William Jennings Bryan Dorn VA Hospital Columbia. SC

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TIME (HOURS) FIG. I . Change in mean arterial pressure. Mean arterial pressure

declined in each Treatment protocol. Absolute changes in mean arterial pressure were small (maximum change from time zero of 6.9 mm Hg in RHD). No significant differences in mean arterial pressures between protocols could be demonstrated.

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References I . Bergstrom J: Ultrafiltration without dialysis for removal of fluid and

2. Ogden DA: A double-blind cross-over comparison of high and low solutes in uremia. Clin h'ephrol9: 156-164. 1978

sodium dialysis. Proc Did Frunsplctnr Forum 8:157-164. 1978

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