O038 - INDIRECT CALORIMETRY DURING CVVHDF: FEASIBLE AND MORE ACCURATE THAN PREDICTIVE EQUATIONS

O038

INDIRECT CALORIMETRY DURING CVVHDF: FEASIBLE AND MORE ACCURATE THAN PREDICTIVE EQUATIONS

W. Wasyluk^1,*, R. Fiut², M. Czop³, A. Zwolak¹, W. Dąbrowski⁴, J. Jonckheer⁵

¹Department of Internal Medicine and Internal Medicine in Nursing, ²Department of Clinical Physiotherapy, ³Department of Clinical Genetics, ⁴1st Department of Anaesthesiology and Intensive Therapy, Medical University of Lublin, Lublin, Poland, ⁵Department of Intensive Care Medicine, Universitaire Ziekenhuis Brussel (UZ Brussel), Vrije Universiteit Brussel (VUB), Brussels, Belgium

Rationale: Indirect calorimetry (IC) is the recommended method for measuring resting energy expenditure (REE) in critically ill patients. However, its accuracy may be influenced by continuous renal replacement therapy (CRRT). This study evaluated how continuous veno-venous hemodiafiltration (CVVHDF) affects O₂ and CO₂ removal and REE measured using IC.

Methods: This was a prospective observational single-center study. CO₂ (QCO₂) and O₂ (QO₂) flows were measured at multiple points in the extracorporeal circuit during CVVHDF. REE was calculated using the Weir equation based on carbon dioxide production (V̇CO₂) and oxygen consumption (V̇O₂), corrected for CO₂ loss through CVVHDF (true REE), and estimated using the Harris-Benedict equation. Respiratory quotients (RQ) were also analyzed. Paired t-tests and Friedman tests were used for comparisons.

Results: Thirty-one septic ICU patients were included. The mean QCO₂ levels measured upstream of the filter were 76.26 ± 17.33 ml/min and significantly decreased to 62.12 ± 13.64 ml/min downstream of the filter (p < 0.0001), while the mean QO₂ levels remained stable. The mean true REE was 1774.28 ± 438.20 kcal/day, significantly different from both the mean measured REE (1758.59 ± 434.06 kcal/day, p = 0.0029) and the mean estimated REE (1619.36 ± 295.46 kcal/day, p = 0.0475). The mean true RQ was significantly higher than the mean measured RQ (0.731 ± 0.121 vs 0.693 ± 0.118, p < 0.0001).

Conclusion: CVVHDF significantly reduces QCO₂ but does not affect QO₂. While this alters V̇CO₂-based calculations, its impact on REE measured by IC is minor. IC remains more accurate than predictive equations and is reliable for REE assessment during CVVHDF. However, CVVHDF may significantly affect RQ, which could influence substrate interpretation and the reliability of metabolic profiling.

Disclosure of Interest: None declared