Pre-HD dilution acidosis, without post-HD contraction alkalosis in uremic patients

The aim of this study was to verify if the degree of pre-HD acidosis and its correction post-HD is related to body fluid expansion during the interdialytic period. Twelve uremic patients without major problems, with stable hematocrit, with regular and similar HD-session characteristics, but widely varying amounts of body fluid expansion in the interdialytic period were included. Blood samples were collected from arterial line pre- and post-HD, anaerobically in heparinized syringes, for determination of HCO3-, pH and PaCO2 (radiometer Copenhagen ABL 300 Acid-Base Laboratory), in two similar HD-sessions for each patient (12 patients, 24 HD-sessions). The percentage (%) of body weight gain in the interdialytic period was also estimated. For each patient, the mean value of parameters studied in the two HD-sessions was used for the evaluation of findings. According to mean values (+/-SD) of HCO3-, pH and PaCO2 Pre-HD (18.26+/-1.99 mmol/L, 7.31+/-0.03, 36.27+/-2.5 mmHg respectively) and post-HD (26.37+/-1.7, 7.43+/-0.03, 38.43+/-2.10 respectively) patients are acidotic pre-HD and slightly alkalemic post-HD. Correlation between the percentage (%) of interdialytic body weight gain (IBWG) and the values of HCO3-, pH and PaCO2, Pre-HD (r=-0.814, p<0.001; r=-0.931, p<0.001; r=0, 100 NS; respectively) and post-HD (r=-0.958, p<0.001; r=-0.937, p<0.001; r=-0.504 NS; respectively) indicates a significant and negative relationship of IBWG% with HCO3- and pH pre- and post-HD, but not with PCO2. In conclusion, the negative relationship of IBWG% with HCO3- and pH pre- and post-HD indicates that the body fluid expansion during the interdialytic period contributes to a dilutional acidosis pre-HD, but not to a contraction alkalosis post-HD, by the elimination of fluid during the HD-session.