Central venous blood composition and the pulmonary ventilation during hemodialysis

The elimination of CO2 across the dialyzer has been reported as the cause of pulmonary hypoventilation during hemodialysis. There are some evidences that the venous line blood composition could influence the central venous blood and this one the pulmonary ventilation. Our purpose was to analyze (1) the influence of the changes in composition of the venous line blood on the central venous blood and (2) the possible role of the central venous blood composition on the pulmonary ventilation of 10 chronic renal failure patients during hemodialysis performed twice in the same patients in two different conditions: acetate dialysate without (condition I) and with (condition II) constant addition of 100% CO2 bubbling into the dialysis bath. During condition I the venous line blood pH was kept in a normal range, and the PCO2 was low, whereas during condition II the pH was very low and the PCO2 extremely high. The patients during condition I decreased their pulmonary ventilation and lost CO2 across the dialyzer as the central venous blood pH and HCO3- increased, and PCO2 did not change. The same patients during condition II increased their pulmonary ventilation and absorbed CO2 across the dialyser as the central venous blood pH decreased and PCO2 increased. Thus, the venous line blood has influence on the central venous blood composition, and this plays a role on the control of pulmonary ventilation of these patients.