Experimental therapies in renal replacement: the effect of two different potassium acetate-free biofiltration protocols on striated muscle fibers.

Dramatic removal of potassium during hemodialysis sessions can induce changes in the electrical properties of nerve cells or muscle fibers, which may underlie neuromuscular symptoms referred by end-stage renal disease patients. The primary aim of our study was to investigate the effects of acetate-free biofiltration (AFB) on the amplitude of compound motor action potential (cMAP) obtained after stimulation of the ulnar nerve at the wrist. The secondary aim was to compare the effect of two different potassium removal modalities on cMAP amplitude and to analyze the effects on muscular force by specific dynamometric tests. Twenty-eight patients received dialysis for 4 h, 3 times per week, first with standard AFB with constant potassium (AFB) and then with AFB with a variable concentration of potassium in the dialysis bath (AFB(K)). The amplitude of cMAP was determined after ulnar nerve stimulation at the wrist at different time intervals: at the start of dialysis; at 15, 45, 90, and 120 min after beginning the session; and at the end of treatment. At the same time intervals, muscle force generation was determined using a dynamometer. Finally, we measured plasma electrolytes, intraerythrocytic potassium, and the electrical membrane potential at rest (REMP) of the erythrocytic membrane. The main finding of this study was a significant reduction of cMAP amplitude in the first 45 min after AFB, which paralleled the reduction in serum potassium levels. Moreover, there was a reduction of muscular strength determined with dynamometric measurements. Potassium removal induced by the two different modalities of AFB may significantly affect myocardial and fibromuscular cells by modulating the electrochemical balance of cell membranes. The transient alteration of the electrical properties on voluntary striated muscle fibers may contribute to the brief reduction in muscular strength we detected in patients who underwent AFB. AFB(K) can minimize the negative effects of standard AFB treatment on neuromuscular excitability, most likely through a more gentle variation of potassium levels during dialysis.

The effect of two different protocols of potassium haemodiafiltration on QT dispersion.

BACKGROUND: The risk of developing cardiovascular diseases is higher in patients on haemodialysis than in the general population. These patients may develop arrhythmias that depend on the extra- and intracellular concentrations of potassium. ECG findings, particularly the QT interval and its dispersion (QT(d)) and the QT(c) (QT interval corrected for heart rate according to Bazett's formula) and its dispersion (QT(cd)), may be direct indicators of the risk of developing arrhythmia. METHODS: Our cohort comprised 28 patients who were dialysed for 3.5-4 h three times per week, first with haemodiafiltration with a constant potassium concentration (HDF) in the dialysis bath then with haemodiafiltration with variable concentrations of potassium (HDF(k)). ECGs were done at different time intervals: at the start of dialysis (T(0)), at 15 (T(15)), 45 (T(45)), 90 (T(90)) and 120 min (T(120)) after the beginning of the session, and at the end of treatment (T(end)). ECG-derived data (QT, QT(d), QT(c) and QT(cd)) were measured. At the same time points, plasma electrolytes, intra-erythrocytic potassium and the electrical membrane potential at rest (REMP) of the erythrocytic membrane were measured. RESULTS: Plasma potassium concentration diminished more gradually in HDF(k) than in HDF, the difference being statistically significant at T(15) and T(45) (P<0.05), and T(90) (P<0.01). The intra-erythrocytic potassium concentration remained constant throughout the observation period. In both HDF and HDF(k), REMP was lower at all points after T(0) (P<0.05), but the reduction was greater and more significant in HDF than in HDF(k) at T(15) and T(120) (P<0.05). ECG revealed a statistically significant diminution in HDF(k) vs HDF in the measures of dispersion of QT and QT(c) at T(15), T(90), T(120) and T(end) (P<0.01) and of QT(cd) at T(45) (P<0.05). The mean of QT(d), adjusted for plasma potassium, increased over time in HDF with large alternate mean increase and decrease peaks and error intervals. In HDF(k), instead, there was a progressive and constant diminution with minor error intervals. QT(cd) adjusted for plasma potassium had the same trend. A marked difference was found between the final values in standard HDF and those in HDF(k). CONCLUSIONS: HDF and HDF(k) have significantly different effects on QT(c). ECG data demonstrate that the risk of arrhythmia could be lower, with a variable removal of potassium during haemodialysis. With HDF but not HDF(k), hyperpolarization of the cell membrane is detected, and this could have a destabilizing effect on different types of cardiac cell, giving rise to retrograde circuits.

QTc interval and QTc dispersion during haemodiafiltration.

BACKGROUND AND AIM: Our aim was to evaluate QTc interval and QTc dispersion in 27 end-stage renal disease (ESRD) patients undergoing Acetate Free Biofiltration (AFB) in order to ascertain any correlations between the electrrocardiographic (ECG) parameters, serum Na+, K+, Ca++, Mg++ and intraerythrocytic Mg++ (Mg++e) concentrations. All measures were made at t0 (session beginning), t1 (first hour), t2 (second hour), t3 (third hour), and t4 (session end). RESULTS: Blood pressure, heart rate, bodyweight and total ultrafiltration in the three dialysis sessions were constant. A significant progressive increase occurred in serum Ca++ during the sessions, while there was a significant diminution in serum K+. The pattern for Mg++ concentrations in serum and erythrocytes differed: in serum it decreased, whereas Mg++e increased. At t4, the QTc interval was reduced to a significant extent with respect to the baseline value. QTc dispersion significantly increased at t1 without there being significant variations at other times with respect to t0. At t2, t3 and t4, values promptly returned to baseline levels. QTc had a negative correlation with serum Ca++ levels at t4. In contrast, an inverse correlation was found between QTc dispersion and serum K+ at t1. No other correlations could be found between any other electrolytes, QTc interval or QTc dispersion. CONCLUSION: In conclusion, the decrease observed in the QTc interval at the end of an AFB session was inversely related to serum Ca++ concentrations. Moreover, an increase in QTc dispersion occurred during the first hour of the session, and was negatively correlated with serum K+.