Systemic vascular resistance in intradialytic hypotension determined by means of impedance cardiography.

BACKGROUND: Recurrent intradialytic hypotension still is a major source of discomfort in hemodialysis patients today, its origin being subject to extensive research. Different hypotheses have been raised to unravel this problem, without forming one coherent point of view. The aim of this study was to gain more insight into the mechanisms causing intradialytic hypotension by determining cardiovascular performance noninvasively during hemodialysis in a large group of patients.
METHODS: In the present study the variations in blood volume, stroke volume, cardiac output and systemic vascular resistance were investigated in 68 patients on chronic intermittent hemodialysis utilizing bioelectrical impedance cardiography. In addition, blood volume was monitored continuously with an on-line optical device.
RESULTS: Twenty-four patients experienced symptomatic hypotension during dialysis treatment. Compared to the hemodynamically stable patients, the hypotensive patients manifested a slightly greater decline in blood volume (mean +/- SEM; -9.4 +/- 1.2 vs. -6.5 +/- 0.8%, p = 0.04) and cardiac output (-11.8 +/- 4.2 vs. -7.3 +/-2.7%, p = NS). The main difference, however, was a highly significant decrease in systemic vascular resistance (-17.9 +/- 4.4%) in the hypotensive group compared to a rise in the stable group (+6.2 +/- 3.5%, p < 0.001).
CONCLUSION: Intradialytic hypotension seems the consequence of an inadequate compensatory response to ultrafiltration-induced blood volume reduction, resulting in a fall in systemic vascular resistance. The degree of hypovolemia itself appears to be less important in the origin of acute, intradialytic hypotensive episodes. Noninvasive monitoring during hemodialysis provides an opportunity to gain more insight into the pathophysiology of intradialytic hypotension and offers the possibility for controlled intervention and possible prevention of this complication.