Carbon Monoxide-based Rebreathing Method and Bioimpedance to Assess Intra- and Extravascular Volume in Hemodialysis Patients

Aim:

1. To combine a carbon monoxide rebreathing method and bioimpedance which allows to objectively measure the amount of fluid in the bloodstream (intravascular) and throughout the body, and thereby test the actual amount of fluid in the body when patients are hydrated according to their clinical dry weight.
2. To validate carbon monoxide rebreathing method in hemodialysis patients compared against a radioactive labeling of erythrocytes and albumin (the gold standard).
3. To investigate whether hemoglobin is a valid marker of anemia in this patient population by measuring the erythrocyte volume and hemoglobin mass by the carbon monoxide rebreathing method and correlating this to the hemoglobin concentration.

Background:

Anemia and overhydration are challenging conditions in patients on hemodialysis. Overhydration is associated with hypertension, cardiomyopathy and increased mortality. In assessing the patient's volume status, blood pressure, body weight and peripheral edema are used as indicators. To achieve a more accurate estimate, these measures have been combined with various techniques, such as relative changes in blood volume (measured with blood volume sensor (BVS)) and bioimpedance. These methods are used to varying degrees in everyday clinical practice.

In case of overhydration, fluid is distributed intravascularly and can thereby expand blood volume. The primary clinical problem with an expanded blood volume is hypertension and increased risk of cardiovascular complications. Measurement of the intravascular volume can therefore have great clinical relevance, but currently there are no direct measures for this implemented in the clinical daily routine. Various techniques have been used for research purposes. These include fluorescent dilution techniques, radioactive labeling of erythrocytes and albumin, as well as infusion of dialysate during dialysis where changes in BVS measurements can be used to calculate the intravascular volumes.