Oxidative metabolism appears to be reduced in long-term hemodialysis patients

As part of a study of whole-body protein metabolism in hemodialysis (HD) patients, we obtained values for whole-body bicarbonate production in control subjects and HD patients before and during dialysis by using stable isotopically labeled bicarbonate. Indirect calorimetry measurements have shown normal or increased energy expenditure in HD patients, which has been used to explain the malnutrition in many of these patients. However, this method becomes inaccurate when the dynamics of whole-body bicarbonate production change during measurement, as is the case with HD patients during dialysis.

Whole-body bicarbonate production was measured in 6 control subjects, 9 patients on a nondialysis day (HD-), and 8 patients during an HD session (HD+) by means of a primed constant infusion of carbon 13 (13C)-labeled sodium carbonate (NaH13CO3). 13C-abundance of expired carbon dioxide was measured by means of isotope ratio mass spectrometry.

Carbon dioxide production was 141 +/- 12, 123 +/- 11*, and 148 +/- 19 micromol/kg/min for the control, HD-, and HD+ groups, respectively (*P < 0.05 compared with the control and HD+ groups). Values for energy expenditure were derived and were 29.1 +/- 2.4, 24.9 +/- 2.1*, and 32.6 +/- 2.0 kcal/kg/day, respectively (*P < 0.05 compared with the control and HD+ groups).

Whole-body oxidation in HD patients is reduced compared with control subjects. During dialysis, bicarbonate turnover, as well as carbon dioxide expiration, increases because of the influx of bicarbonate from the dialyzer.