Hemodynamic effects of acetate in man

Effects of acetate-free double-chamber hemodiafiltration and standard dialysis on systemic hemodynamics and troponin T levels

Using acetate as a buffer during hemodialysis is recognized to predispose to intradialytic hypotension; however, bicarbonate-based dialysis is not acetate free. Paired hemodiafiltration (PHF) is a novel online acetate-free technique. We investigated whether PHF is capable of abrogating the changes in systemic hemodynamics and troponin T (cTnT) seen with conventional hemodialysis. Twelve patients entered a randomized crossover study. Blood pressure (BP) and a full range of hemodynamic variables were measured throughout PHF and standard dialysis using continuous pulse wave analysis. We also measured predialysis cTnT in 54 stable and unstable dialysis patients. BP was lower during PHF but without increased instability. Stoke volume and cardiac output declined progressively during both treatments but to a much lesser extent during PHF (p = 0.003, p < 0.0001 respectively), whereas peripheral resistance rose to a larger degree during hemodialysis (p < 0.0001). cTnT levels were lower before PHF as compared with hemodialysis (p = 0.023), with levels falling after PHF and rising after hemodialysis (p < 0.0001). In the supplementary patient group, predialysis median serum cTnT was higher in the unstable patients (p = 0.0001). This study demonstrates that PHF (without exposure to acetate) is associated with less deterioration in systemic hemodynamics, maintenance of BP, and less suppression of myocardial contractility as compared with bicarbonate dialysis.

Acute cardiovascular and metabolic effects of acetate in men

We studied the potential contribution of acetate to the cardiovascular effects of ethanol in 12 healthy male volunteers. Sodium acetate, or sodium chloride in control experiments, was infused i.v. at the rate of 0.033 mEq/kg/min for 60 min. Left ventricular function was examined by M-mode echocardiography and systolic time intervals during infusion and for 60 min thereafter. Blood acetate rose during infusion from 0.19 +/- 0.02 (mean +/- SEM) to a maximum of 0.99 +/- 0.08 mmol/liter. Changes in serum free fatty acids, glycerol, and ketone bodies indicate that acetate inhibited peripheral lipolysis. The volume of urine excreted during the acetate experiment (305 +/- 37 ml) was significantly larger (p less than 0.01) than during the chloride experiment (181 +/- 21 ml). Left ventricular function did not differ between the experiments during the infusions even though at 45 min heart rate was increased by acetate (7%; p less than 0.01, between infusions). After the infusion period, at 75 min the treatment by acetate increased cardiac output from the baseline by 17% (p less than 0.05, between infusions), and decreased peripheral arterial resistance (19%, p less than 0.05), and diastolic blood pressure (10%, p less than 0.01). Circumferential fiber shortening velocity was increased during the acetate experiment maximally by 7% (p less than 0.01) from the baseline at 120 min. These data indicate that acetate is an arterial vasodilator and a mild diuretic and may slightly improve myocardial performance in the concentrations encountered during ethanol metabolism in men.

Effects of acetate and bicarbonate dialysate in stable chronic dialysis patients

The effects of acetate and bicarbonate dialysate on the biochemical and clinical parameters of 16 stable chronic hemodialysis patients were investigated in a double-blind crossover study. A central delivery system was used for both types of dialysates with identical sodium concentrations (138 mEq/liter) and osmolality in a single-pass dialysate flow. The results indicate that dialysis with bicarbonate leads to significantly less hypoxemia (P less than or equal to 0.001) and hypotensive episodes (P less than or equal to 0.002) than with acetate. Pre- to post-dialysis blood pressure changes were also more marked during acetate dialysis. Older patients with recurrent hypotension on acetate benefit most from bicarbonate dialysate. This group of patients appears to metabolize acetate more slowly and has a significantly lower post-dialysis bicarbonate concentration (P less than or equal to 0.005) than asymptomatic patients during dialysis with acetate dialysate.

Effects of acetate and bicarbonate hemodialysis on cardiac function in chronic dialysis patients

Previous studies have suggested that acetate hemodialysis causes myocardial depression. This study examines the acute effects of hemodialysis using, alternately, bicarbonate and acetate in the dialysate, on cardiac function in ten patients. These patients were also studied during acetate dialysis using a large surface area (SA) dialyzer. Each patient was dialyzed for 4 hr with: (1) 1.0 m2 SA dialyzer and bicarbonate dialysate; (2) 1.0 m2 SA dialyzer and acetate bath, and; (3) 2.5 m2 SA dialyzer and acetate dialysate. All studies were performed during isovolemic dialysis to separate the effects of changes in cardiac filling volume with hemodialysis, from changes in myocardial contractility. Myocardial function, as assessed by pre- and postdialysis echocardiographically derived fractional shortening (Fs) and mean velocity of circumferential shortening (VCF), improved (P less than 0.05) to the same extent, after all three dialysis treatments. This occurred despite greater increases (P less than 0.002) in pH and bicarbonate after bicarbonate dialysis and decreases (P less than 0.05) in PO2, PCO2 and bicarbonate after acetate dialysis with 2.5 m2 SA dialyzer. These results indicate that diffusive dialysis with both acetate and bicarbonate dialysate improves myocardial function and do not support the view that acetate influx during dialysis can lead to myocardial depression.

The role of acetate in the etiology of symptomatic hypotension

Acetate, although widely used as the source of buffer in hemodialysis, has been implicated in the development of symptomatic hypotension and hypoxemia during dialysis. Studies of acetate infusion clearly indicate a vasodilatory effect. Acetate also increases cardiac output. If the increase in cardiac output is not adequate to compensate for the decrease in peripheral resistance, hypotension can result. Acetate infusion studies indicate a significant increase in oxygen consumption. This may be the most plausible explanation for dialysis-induced hypoxemia. Correction of the hypoxemia with supplemental oxygen has been shown to reduce the incidence of hypotensive episodes and intradialytic symptoms. Studies comparing cardiovascular stability during acetate and bicarbonate dialysis indicate that bicarbonate dialysis is beneficial only when the fall in serum osmolality during dialysis is significant. If the fall in serum osmolality is blunted either with a high-sodium dialysate or mannitol infusions, there is little difference between acetate and bicarbonate. From a practical viewpoint, high-sodium dialysis is technically less complex and expensive than bicarbonate dialysis.

Long-term use of a "stable" bicarbonate containing dialysate

We present an original method for the preparation of "stable" dialysate containing 35 mEq/l of bicarbonate. The dialysate was utilized with 4 patients for periods ranging from 4 months to 1 year according to a short-term recirculated dialysis schedule in closed circuit (20-40L) (2-2 1/2 hrs) on alternate days. Preliminary results are reported here with respect to the tollerance of the dialytic run and correction of the acid-base balance equilibrium. The clinical tollerance is excellent despite high dehydration rates even in patients particularly sensitive to ultrafiltration. The acidosis correction would seem to be much better with bicarbonate than with traditional dialysis. The difference is even higher if we consider the brevity of the dialysis. During the bicarbonate dialysis we do not observe any fall of the PCO2 or significant difference in PO2 in the patient's blood. The correction of acidosis probably causes the normalization of pre-dialytic potassiemia in spite the "net" removal of K with short dialysis is considerably less.