Hemodynamic evaluation of hypotension during chronic hemodialysis

Hypotensive episodes occur frequently during hemodialysis; they are often sudden and difficult to prevent despite careful clinical control. Their etiology was studied by investigating the hemodynamic response of five patients submitted to ultrafiltration during their three first dialyses. A Swan Ganz catheter was inserted and left in position for 5 days. Simultaneous determination of cardiac output, mean pulmonary artery (PAP) and capillary and systemic arterial pressures were recorded. 10 hypotensive episodes were observed. In 3 patients in whom the first hypotensive episode occurred 10 minutes after the start of dialysis, there was a significant drop in PAP, cardiac index and stroke index while heart rate and peripheral resistance remained unchanged. Paradoxical bradycardia was observed. In 4 patients hypotension was observed more than one hour after initiation of dialysis. Before the hypotensive episode there was moderate elevation of heart rate and peripheral resistance and an insignificant reduction in PAP. Cardiac index and stroke index were diminished. The decrease in MAP was only 2 mm Hg. Hypovolemia is the most important factor in hemodialysis-induced hypotension but other factors such as vagal stimulation, autonomic neuropathy and osmotic disequilibrium can interfere with blood pressure control and trigger hypotension. Methods of preventing hypotension during dialysis, including the infusion of low molecular weight dextran, are discussed.