Renal replacement therapy may affect carbon dioxide elimination, which may theoretically influence measurement of energy expenditure by means of indirect calorimetry. However, available clinical studies are noct conclusive on this issue. This observational study aims to investigate the effect of renal replacement therapy on indirect calorimetry in critically ill mechanically ventilated patients.

Optimal Nutrition of the critically ill is still a clinical challenge. Current guidelines recommend that measurement of energy expenditure using indirect calorimetry should be favoured in critically ill patients. The technique is based on measurement of oxygen consumption and carbon dioxide elimination. Experimental studies have reported on carbon dioxide elimination via renal replacement therapy. Since acute kidney injury with requirement for renal replacement therapy (RRT) is common in the intensive care unit, the significance of carbon dioxide elimination via the dialyser should be clarified. However, available evidence from clinical studies is contradictory, one reason being the heterogenous study design.

In this prospective observational study on critically ill mechanically ventilated medical patients requiring RRT, indirect calorimetry (IC) will be conducted twice on the same day with and without RRT: either immediately before commencement of RRT followed by a second IC with RRT after an RRT run time of an hour, or immediately before the end of an RRT session followed by a second IC an hour after the termination of RRT.

Inclusion Criteria:

• simultaneous requirement for mechanical ventilation and renal replacement therapy
• informed consent

Exclusion Criteria:

• age <18 years
• requirement for therapeutic hypothermia
• serum lactate >4 mmol/l
• requirement for inspiratory oxygen fraction >0.6 and positive end-expiratory pressure >12 mbar
• leak in the ventilator circuit (e.g. due to a chest tube)
• requirement for extracorporeal circulatory support
• refusal to participate in the study.

critically ill mechanically ventilated medical patients requiring renal replacement therapy