Hemodynamics during hemodialysis investigated by impedance cardiography

Purpose: To clarify the hemodynamic characteristics of patients experiencing a hypotensive attack during hemodialysis (HD), and predicting the attacks, Subjects: Twenty-eight patients with chronic renal failure without any signs of heart failure. Methods: An impedance cardiogram, carotid pulse waves, ECG, and PCG were recorded simultaneously during hemodialysis. The mean thoracic impedance (Zo), stroke volume (SV), cardiac index (CI), total peripheral resistance (TPR), and the systolic time interval were measured immediately before and after HD and every 30min thereafter, 12 times in total. The subjects were classified into the S group, with stable blood pressure during HD, and the D group, with a hypotensive attack during HD. The time-course changes in each of the parameters were compared between the 2 groups. Results: There were 19 S-and 9 D-group subjects. In the D group, a hypotensive attack occurred in the middle stage of HD (between 2 and 3h) in 3 cases and in the late HD stage (between 4 and 4.5h) in 6 cases. Before HD, the Zo was significantly higher in the D than in the S group, while the SV and CI were significantly lower in the D group. The two groups showed no significant differences in blood pressure, HR, Zo, dZ/dt min., SV, CI, TPR, or PEP before the hypotensive attack (4h after initiation of HD). Between 3.5 and 4h after initiation of HD, the decreases in ΔsBP and ΔmBP, prolongation of ΔPEP, shortening of ΔETc, and decrease in ΔET/PEP in the D group were significantly larger than in the S group. Discussion: It is difficult to predict hypotensive attacks during HD. In our study, the 2 groups showed no significant differences in blood pressure, SV, CI, or TPR before the attack, but abnormalities in the systolic time interval were present 30min before the attack in the D group. Thus, a circulatory failure state was already present 30min before onset of the hypotensive attack. Prediction of hypotensive attacks during HD by detecting such systolic time interval abnormalities should be possible.