On the CO₂ gain in on-line hemodiafiltration

Area of Science:

• Nephrology
• Biomedical Engineering

Background:

• Dialysis fluid contains high levels of carbon dioxide (CO2) to maintain pH and salt solubility.
• In post-dilution on-line hemodiafiltration (HDF), CO2-rich dialysis fluid (infusate) is directly administered to patients, bypassing the dialyzer membrane.
• The exact amount of CO2 delivered to patients during on-line HDF is not precisely known.

Purpose of the Study:

• To investigate the extent of carbon dioxide (CO2) delivery to patients during on-line hemodiafiltration (HDF).
• To determine the contribution of infusate to CO2 gain in post-dilution on-line HDF.

Main Methods:

• Blood gas analysis was performed on 18 outpatients undergoing regular on-line HDF.
• Arterial blood samples were collected pre-dialysis.
• Venous blood samples were analyzed from the extracorporeal circuit, both with and without infusate flow.

Main Results:

• Pre-dialysis arterial pCO2 showed mild hypocapnia (35.40 ± 3.22 mmHg).
• Venous pCO2 significantly increased to 69 ± 5.5 mmHg, indicating CO2 gain during on-line HDF.
• Disabling the infusate pump reduced venous pCO2 to 63.1 ± 5.8 mmHg, confirming the infusate's contribution to CO2 delivery.

Conclusions:

• On-line HDF leads to a measurable delivery of carbon dioxide (CO2) to patients.
• The infusate used in post-dilution on-line HDF significantly contributes to this CO2 gain, although the overall amount is relatively small.