Can haemodialysis-induced hypotension be predicted?

During haemodialysis (HD) ultrafiltration may affect the central blood volume to an extent that blood pressure decreases. Thoracic electrical impedance (TI) is applied to monitor the central blood volume and we evaluated if it can be used to predict HD-induced hypotension.

In 12 hypotensive prone (H) and 13 non-hypotensive prone (N) patients, blood pressure and heart rate were recorded during one dialysis session every 30 min, while TI, thoracic intracellular water (Th(ICW)) and total body impedance (TBI) were followed every 10 min. Hypotension was defined as a decrease in systolic blood pressure (SAP) >/=30 mm Hg or a SAP < 90 mm Hg.

All 12 H patients developed hypotension after 190 +/- 10 min (mean +/- SE) as SAP decreased 35 +/- 5 mm Hg, while the 13 N patients maintained blood pressure. TBI increased in all patients and the increase was similar (60 +/- 5 and 56 +/- 6 Omega in H and N patients, respectively). In N patients TI did not change significantly for the first 2 h of HD, while it became elevated by 2.8 +/- 0.6 Omega (1.5 kHz) and 2.3 +/- 0.7 Omega (100 kHz) by the end of the dialysis. In H patients, the increase in TI took place at the onset of HD to reach higher values (by 7.0 +/- 0.5 Omega at 1.5 kHz and 5.9 +/- 0.5 Omega at 100 kHz). Th(ICW) was changed only in H patients (decreased by 7.9 +/- 2.1 Siemens (S) 10(-4), p < 0.05), while HR increased (9 +/- 2 beats/min) in 8 of 12 H patients, while it decreased in 1 patient (by 9 beats/min).

The results suggest that in HD patients hypotension is elicited by a reduction in the central blood volume that affects heart rate and the distribution of red cells within the body. To prevent HD-induced hypotention, the ultrafiltration rate could be reduced when an increase in thoracic impedance approaches 5 Omega, or when an index of intracellular water decreases by 6 10(-4).