Continuous Indirect Calorimetry in Critically Injured Patients Reveals Significant Daily Variability and Delayed, Sustained Hypermetabolism.

BACKGROUND: Previous studies have used using Indirect Calorimetry (IC) with solitary or sparse measurements of resting energy expenditure (REE). This "snapshot" may not capture the dynamic nature of metabolic requirements. Using continuous IC, we describe the variation of REE during the first days in the intensive care unit. METHODS: Injured adults (≥18 years) requiring mechanical ventilation from March 2018 to September 2018 were enrolled. IC was initiated within 4 days of admission and continuous REE recorded until 14 days, extubation, or death. Multiple 10-minute periods collected during steady state were used to calculate daily REE maximum, minimum, average, and variability [(REEmax - REEmin/2)/average REE]. RESULTS: We included 55 patients. Median age was 38 [27-58] years, 38 (69%) were male, body mass index was 28 [25-33] kg/m2 , and Acute Physiology and Chronic Health Evaluation II was 17 [14-24]. Mechanism of injury was: blunt (n = 38, 69%), penetrating (n = 9, 16%), and burn (n = 8, 15%). Average REE increased gradually from 1,663 kcal [1,435-2,143] to a maximum of 2,080 [1,701-2,336] on day 7, a relative 25% increase, which was sustained through day 14. REE variability ranged 8%-13% and was not reliably predicted by fever, tachycardia, elevated intracranial pressures, hypertension, or hypotension. CONCLUSION: In critically injured patients, steady-state REE measurements display fluctuations over a 24-hour period and demonstrate a gradual rise over the first few days after injury. Continuous REE, if available, is recommended for more precise matching of energy delivery to metabolic requirements.

Use of Predictive Equations for Energy Prescription Results in Inaccurate Estimation in Trauma Patients.

BACKGROUND: Overfeeding and underfeeding are associated with poor clinical outcomes. In the absence of indirect calorimetry (IC), the Society of Critical Care Medicine/ASPEN recommend prescribing 25-30 kcal/kg. The Harris-Benedict equation (HBE) multiplied by a stress factor is commonly applied in critically ill patients. We describe the difference between estimated and actual energy needs in critically injured patients. METHODS: From March to November 2018, we collected demographics and energy needs determined by continuous IC (started within 4 days) in intubated adults. Ideal or adjusted body weight was used for 25-30 kcal/kg, and HBE was multiplied by a 1.3 stress factor (1.3HBE). Daily requirements up to 14 days, extubation, or death were calculated using all 3 methods and compared with IC. RESULTS: Fifty-five subjects were included. Median age was 38 [27-58] years, 38 (69%) were male, body mass index was 28 [25-33] kg/m2 , and Acute Physiology and Chronic Health Evaluation II score was 17 [14-24] Mechanism of injury was blunt (38, 69%), penetrating (9, 16%), and burn (8, 15%). By day 14, compared with measured energy requirements by IC, the other methods could result in a cumulative 1827-kcal (+7%) surplus (1.3HBE), a 1313-kcal (-5%) deficit (25 kcal/kg), or a 3950-kcal (+14%) surplus (30 kcal/kg) per patient over a median 9 days. CONCLUSION: In critically injured patients, predictive equations for energy needs do not account for dynamic metabolic changes over time and could result in underfeeding or overfeeding. Adjusting daily prescription based on continuous IC may result in better individualized treatment.