Indirect Calorimetry

Patients admitted to the intensive care unit frequently exhibit abnormal blood bicarbonate levels. These abnormalities are associated with patient outcomes and often prompt clinicians to modify management, either diagnostically or therapeutically (e.g., initiation or adjustment of mechanical ventilation, initiation or modification of extracorporeal renal replacement therapy, administration of specific diuretics, or sodium bicarbonate infusion). Currently, the only way to determine blood bicarbonate concentration is through repeated blood sampling for laboratory analysis. However, this method is both discontinuous and invasive. We have generated an in silico hypothesis suggesting that the mismatch between cellular CO₂ production/elimination and pulmonary CO₂ elimination reflects changes in blood bicarbonate levels. We propose to test this hypothesis in a cohort of intensive care unit patients. If confirmed, indirect calorimetry could be positioned as a continuous, non-invasive monitoring tool for blood bicarbonate.