Resting Energy Expenditure of Patients on Venovenous Extracorporeal Membrane Oxygenation for Adult Respiratory Distress Syndrome: A Pilot Study

OBJECTIVES: The objectives of this study were to 1) in patients without pulmonary function, determine resting energy expenditure (REE) in venovenous extracorporeal membrane oxygenation (ECMO) acute respiratory distress syndrome (ARDS) patients by paralysis status and 2) determine the threshold tidal volume (TV) associated with meaningful gas exchange as determined by measurable end-tidal carbon dioxide elimination (etV̇co(2)). DESIGN: Retrospective observational study. SETTING: A tertiary high ECMO volume academic institution. PATIENTS/SUBJECTS: Ten adult ARDS patients on venovenous ECMO. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The modified Weir equation, Fick principle, Henderson-Hasselbalch equation, ECMO flow, hemoglobin, and pre and post oxygenator blood gases were used to determine ECMO carbon dioxide production (V̇co(2)), ECMO oxygen consumption, and REE. REE values were matched to patients’ paralysis status based on medication flowsheets and compared using a paired t test. Linear regression was performed to determine the threshold TV normalized to ideal body weight (IBW) associated with measurable ventilator etV̇co(2), above which meaningful ventilation occurs. When lungs were not functioning, patients had significantly lower mean REE when paralyzed (23.4 ± 2.8 kcal/kg/d) than when not paralyzed (29.2 ± 5.8 kcal/kg/d) (p = 0.02). Furthermore, mean REE was not similar between patients and varied as much as 1.7 times between patients when paralyzed and as much as 1.4 times when not paralyzed. Linear regression showed that ventilator V̇co(2) was measurable and increased linearly when TV was greater than or equal to 0.7 mL/kg. CONCLUSIONS: REE is patient-specific and varies significantly with and without patient paralysis. When TV exceeds 0.7 mL/kg IBW, ventilator V̇co(2) increases measurably and must be considered in determining total REE.