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The following is a summary of “Evaluating the effects of continuous veno-venous hemodiafiltration on O₂ and CO₂ removal and energy expenditure measurement using indirect calorimetry,” published in the January 2025 issue of Critical Care by Wasyluk et al. 

The impacts of continuous veno-venous hemodiafiltration (CVVHDF) on O₂ and CO₂ removal and the accuracy of resting energy expenditure (REE) measurement via indirect calorimetry (IC) are not well understood.  

Researchers conducted a retrospective study to evaluate the effects of CVVHDF on O₂ and CO₂ removal and the accuracy of REE measurement using IC in patients undergoing continuous renal replacement therapy.  

They measured CO₂ flow (QCO₂) and O₂ flow (QO₂) at multiple points before and after the filter in patients with sepsis undergoing CVVHDF. The REE was calculated using the Weir equation based on V̇CO₂ and V̇O₂ values from IC, with true V̇CO₂ accounting for the continuous renal replacement therapy (CRRT) balance and REE was also estimated using the Harris-Benedict equation. The respiratory quotient (RQ), the ratio of V̇CO₂  to V̇O₂, was assessed by comparing measured and true values.  

The results showed that mean QCO₂ levels upstream of the filter were 76.26 ± 17.33 ml/min, significantly decreasing to 62.12 ± 13.64 ml/min downstream of the filter (P < 0.0001). The QO₂ remained stable. The mean actual REE was 1774.28 ± 438.20 kcal/day, significantly higher than the measured REE of 1758.59 ± 434.06 kcal/day (P = 0.0029) and estimated REE of 1619.36 ± 295.46 kcal/day (P = 0.0475). The mean measured RQ was 0.693 ± 0.118, while the true RQ was 0.731 ± 0.121, with a significant difference (P < 0.0001).  

Investigators concluded that CVVHDF might significantly alter QCO₂ levels without affecting QO₂, influencing REE and RQ results measured by IC; however, the impact on REE was not clinically significant, with IC-derived REE closer to the actual value than the estimate from the Harris-Benedict equation.  

Source: annalsofintensivecare.springeropen.com/articles/10.1186/s13613-025-01426-2