To the editor: Hemodynamic instability (arrhythmias, hypotension) is one of the most frequent complications found during dialysis. For years, the usefulness of ultrafiltration and/or conductivity profiling to prevent the appearance of such problems has been the subject of debate.



We report the case of a 75-year-old male initially subjected to peritoneal dialysis due to chronic renal failure secondary to diabetic kidney disease who required transfer to hemodialysis because of peritonitis, with a poor course one year after treatment. After starting hemodialysis, and as a result of nutritional problems, dry weight began to decrease (over 4 kg), with good hemodynamic tolerance. However, after two months the heart rate ¿ which at the start of the session was 60-70 bpm ¿ suddenly increased in the last hour to 110-120 bpm. In some cases this situation was accompanied by severe hypotension. Continuous electrocardiographic monitorization of several hemodialysis sessions was thus decided. In the first three hours the patient showed sinus rhythm with a heart rate of 60-70 bpm, though after the third hour rapid atrial fibrillation was recorded that only reverted after conclusion of the dialysis session. The previous and posterior blood pressure values remained at 120- 130/70-80 mmHg. In view of this situation, the dialysis machine conductivity and ultrafiltration parameters were changed during the session, applying a descending logarithmic profile for conductivity (start 15.7 mS/cm, end 13.8 mS/cm) and ultrafiltration (dialysis previously being carried out with a constant conductivity of 14.2 mS/cm). This measure improved tolerance during the sessions, with no severe hypotension and presenting a stable heart rate. Over the following four months the patient gained 2 kg in dry weight, but the blood pressure did not increase (110-120/70

mmHg); no antihypertensive medication was needed, and no edema or other signs of volume expansion were noted. Likewise, there were no increases in pre-dialysis sodium level (134-135 mEq/l in the determinations with constant conductivity at 14.2 mS/cm versus 135 mEq/l in those made with the exponential profile).



The use of conductivity and ultrafiltration profiling during hemodialysis has been studied by a number of authors. The objective of such profiling is to improve hemodynamic tolerance by preventing vascular depletion secondary to sodium loss during dialysis.1 However, the different series found in the literature report quite variable results ¿ reflecting the use in many cases of very different profiles. Some studies have reported no significant differences in

hemodynamic tolerance on applying combined conductivity and ultrafiltration profiles.2 Other studies involving linear profiles starting with high conductivities (15-15.5 mS/cm) and ending with values close to 14 mS/cm have observed a reduction in hypotensive episodes ¿ though at the expense of an increased volume expansion (increase in blood pressure before and after dialysis).3-5



In other cases the applied profile exhibited end conductivity values lower than those of the serum sodium concentration before dialysis. In this way elimination is secured of the excess sodium that may have diffused in the first phase of the dialysis session, achieving a neutral balance without inducing volume expansion.6,7



Likewise, series have been published in which conductivity and ultrafiltration begin at very high values close to 15.8-15.9 mS/cm, followed by a rapid exponential reduction until ending at values close to 14 mS/cm. In this way most of the ultrafiltration takes place in the first moments of the session, when conductivity is very high, though on quickly reducing the sodium concentration, accumulation and subsequent overhydration are avoided.8



In sum, the use of combined conductivity and ultrafiltration profiling may prove useful for controlling hemodynamic

instability (arrhythmias, hypotension) during hemodialysis, though great care is required on selecting the starting and ending conductivities, in order to avoid volume expansion.