Evolution of volume sensitivity during hemodialysis and ultrafiltration

This study aimed at assessing the evolution of cardiovascular characteristics during hemodialysis and ultrafiltration by a perturbation accurately defined in its magnitude and directly relevant to the problem of volume adjustment in stable hemodialysis patients.

Excess fluid volume was removed by constant ultrafiltration-rate as prescribed. Hemodynamic variables were continuously measured throughout treatments using non-invasive finger plethysmography. In addition to ongoing volume reduction by ultrafiltration (long-term perturbation), well-defined magnitudes of intravascular volume were transiently and reversibly sequestered (short-term perturbation) into the extracorporeal circulation at hourly intervals. Sensitivities of hemodynamic variables and of the baroreflex to the acute change in intravascular volume (volume sensitivities) were analyzed.

Eight stable patients were assessed during two subsequent treatments. Treatments were accompanied by a decrease in cardiac output (p<0.05) and stroke volume (p<0.01), and by an increase in peripheral resistance (p<0.05) and diastolic pressure (p<0.05). Mean arterial pressure remained unchanged for the whole group but correlated with the change in total peripheral resistance in individual treatments (p<0.01). The average volume sensitivity of mean arterial pressure was 11.9±9.9 mmHg/L and increased (p<0.01) during treatments, while the average volume sensitivity of heart rate remained unchanged at -7.9±8.58 1/(min L). The corresponding volume sensitivity of the baroreflex was -0.81±1.5 1/(min mmHg) and remained unchanged for the whole group, but the change correlated with the change in mean arterial pressure in individual treatments (p<0.05).

The changes in arterial pressures during hemodialysis appear to relate to an unbalanced response of barocontrol mechanisms characterized by a compromised chronotropy and vascular over-reactivity.