Norepinephrine-induced vasoconstriction results in decreased blood volume in dialysis patients

Background. Hypotension during haemodialysis results from an inadequate cardiovascular response to ultrafiltration-induced hypovolaemia. It has been suggested that plasma volume could be increased as a result of systemic vasoconstriction. Methods. We studied the effect of a norepinephrine (NOR) infusion (30 min), compared with no infusion, on relative blood volume (RBV) in six haemodialysis patients. During infusion we measured RBV, systolic blood pressure (SAP), heart rate (HR), stroke volume index (SI), total peripheral resistance (TPRI), ejection fraction (EF), inferior vena cava diameter (VCD) and core temperature. Results. At the end of the NOR infusion, we observed a significant increase in TPRI (47±47% vs 4±17%; P <0.01) and SAP (27±12% vs 0±8%; P <0.01). Norepinephrine-induced vasoconstriction resulted in a significant decrease in RBV (-9±3% vs 0±1%; P <0.01). No significant changes were seen in SI (-4±21% vs 0±8%), HR (-5±19% vs -4±5%), EF (7±14% vs -2±10%), VCD or temperature. Conclusions. We conclude that norepinephrine-induced vasoconstriction results in a decrease in RBV. This indicates that improved haemodynamic stability during haemodialysis through vasoconstriction can be accompanied by a decrease in RBV and that part of the variability in blood volume may be due to changes in arterial tone. Such changes must be taken into account if RBV measurements are used to improve the haemodynamic tolerance of dialysis.

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