[Gas analysis in bicarbonate dialysis]

The acid-base abnormalities in uremic patients on hemodialysis are well known. There is less awareness of the fact that during bicarbonate dialysis patients are simultaneously exposed to the four fundamental acid-base disorders. Attempts at compensation involving the respiratory system persist in the hours following hemodialysis. Furthermore, several landmark publications in addition to more recent papers clearly show that bicarbonate HD is only able to compensate for uremic acidosis through the elimination of surplus CO2 from dialysate via the lungs. The artificial kidney and lungs of the patient work together to ensure the efficiency of hemodialysis. Dialysate is a more acidic solution than the patient's blood and contains, in addition to oxygen and bicarbonate, at least twice the CO2 concentration of blood. The high dialysance of CO2 allows for its rapid diffusion from the dialysate to the blood compartment and can be a clinically relevant issue in patients with co-morbidities, especially respiratory disease. In such circumstances, hemodialysis may cause iatrogenic respiratory acidosis which, if not recognized, can require ventilatory assistance and advanced life support. Checking for such problems in a real life setting, such as an outpatient hemodialysis unit, is an important part of the nephrologists day-to-day work.