Effects of Automatic Blood Volume Control over Intradialytic Hemodynamic Stability

Due to the crucial role of hypovolemia in the genesis of dialysis-induced hypotension, we have evaluated whether the automatic control of the intradialytic blood volume (BV) decrease along a preset trajectory might be beneficial to the hemodynamic stability during treatment. Five frequently hypotensive HD patients were studied and a 3-period-protocol (A1-B-A2) was adopted, each period lasting 6 sessions per patient. During the B periods the patient BV decrease was kept along a predefined profile, thanks to an automatic system with a retroactive control of both the ultrafiltration rate (UFR) and dialysate conductivity (DC); instead, during the A periods, conventional HD was performed, with linear UFR and constant DC, inducing a spontaneous decrease in BV. The intradialytic BV behaviour was much more stable during the B-periods (-10.2 ∓ 1.4% by the end of the treatment) than during the A1 (-11.2 ∓ 3%) and A2 periods (-11.5 ∓ 2.5%). Only one dialysis-hypotension episode was observed during the B periods, compared to 8 and 5 during the A1 and A2 periods, respectively (p ≤ 0.05). The automatic control of the BV changes during dialysis could improve the intra-treatment cardiovascular stability in critically-ill patients.

Hypertonic and hypovolemic stimulation of thirst in pigs

Young female pigs weighing from 15 to 45 kg were used. Plasma osmolality was slowly raised by an intravenous infusion of 15% NaCl. The behavioral threshold was when the pigs began to drink water, and the rise of osmolality was the stimulus. In 23 measurements on 8 pigs the rise of osmolality to initiate drinking was 10.4 +/- 1.4 mosmol/kg (mean +/- SE). There was also an estimated 3.8 +/- 1.4% rise of blood volume. Control infusions of 0.9% NaCl for 1 h usually resulted in no drinking, and plasma osmolality fell by 6.7 +/- 2.1 mosmol/kg, while blood volume did not change. Hypovolemia was effected using furosemide (1 mg/kg body wt) to cause excretion of nearly isotonic urine. Blood volume changes were estimated from plasma protein and packed cell volume data. In 28 measurements on 6 pigs, drinking occurred when blood volume had decreased by 6.7 +/- 1.8%. During 2-h control periods, blood volume did not change appreciably. Plasma osmolality decreased during both the furosemide treatment (by 3.5 +/- 0.7 mosmol/kg) and the controls (by 4.1 +/- 0.8 mosmol/kg).