Effect of postural change on blood volume in long-term hemodialysis patients

In healthy subjects, the blood volume (BV) increases rapidly after postural change from standing to the supine position. However, little is known abou t the effect of postural change on BV in long-term hemodialysis (HD) patien ts. Therefore, we have examined the BV change caused by adopting the supine position from standing by continuous hematocrit monitoring, using the CRIT -LINE instrument, in 8 anuric HD patients. The hematocrit was monitored for 25 min with the patient in the supine position just before HD. The percent age change in the BV (% Delta BV) was calculated from the hematocrit and ap proximated using the equation: % Delta BV = b - [1 - exp(-c x time (min)] - a x time (min). Coefficient a was the slope of the linear part in the % Del ta BV, b was the magnitude of BV increase and c was the rate of BV increase . Then we examined the relationship between the coefficients (a, b and c) a nd clinical parameters. In all patients, % Delta BV increased quickly after adopting the supine position. The mean increases were 2.8 +/- 0.6% after 5 min and 4.8 +/- 0.5% after 25 min. There was a significant correlation bet ween the value of % Delta BV calculated from the hematocrit and the value c alculated using above equation (0.92 < r < 0.99, p < 0.001). Although coeff icient a did not correlate with a clinical parameter, coefficient b showed a significant positive linear correlation with the serum albumin level (r = 0.816, p < 0.05) and coefficient c showed a significant positive linear co rrelation with the percentage change in interdialytic weight gain (r = 0.73 6, p < 0.05). Furthermore, based on the % <Delta> BV, we calculated the cha nge in total BV, which had increased by 181.5 +/- 21.9 ml after 25 min in t he supine position. In conclusion, the change in the BV with time by contin uous hematocrit monitoring using the CRIT-LINE instrument can be approximat ed by a modified monoexponential equation. BV increased quickly in HD patie nts after postural change from standing to the supine position. Copyright ( C) 2001 S. Karger AG, Basel.