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Indirect Calorimetry or Predictive Equations? Determining Nutritional Requirements for Ventilated Surgical Trauma ICU Patients

Nicholas Harris, Jessica Justice, R.D, LDN, CNSC, Christopher Watson, MD, FACS, Phillip Prest, DO, FACOS, FACS

Diagnosing and adequately treating nutritional deficits in ventilated, critically ill patients is necessary to create favorable outcomes for patients and reduce costs associated with nutrition related exacerbation of disease. While current standards for determining resting energy expenditure (REE) in ventilated patients, a measure of caloric requirements, rely on indirect calorimetry (IC) and predictive equations, these methods have not yet been extensively studied for the complex and fluctuating needs specific to surgical/trauma intensive care unit (STICU) patients. IC is the currently accepted standard for estimating a ventilated patient’s nutritional requirements, but high costs, reliance on trained respiratory therapists, long operation times, and limitations for use cause many health professionals to use predictive equations, such as the Penn State equations, for their estimations.
A retrospective analysis was performed to identify if there is a significant difference between IC measurements and Penn State calculations in estimating the caloric requirements of adult, ventilated STICU patients at Richland Hospital that received at least one IC study between November 2013 and June 2019. 
370 valid IC studies were obtained, along with the recorded REE and associated anthropometrics for each patient at the time of each study:
Age and Sex, height(cm), weight at admittance(kg), BMI, ideal body weight (IBW), Diagnosis and comorbidities at time of cart study, ISS (Injury Severity Score), TRISS (Trauma and Surgery Severity Score), Nutritional Rx, Calories (kcal/day) and Caloric Needs, Protein (g/kg) and Protein Needs, RASS, GCS, Min. Ventilation, Max Temperature (24hour), Blood Glucose(24hour)
REE was then calculated using the pertinent Penn State Equation for all valid IC studies, analyzed for accuracy, and compared to collected Indirect calorimetry measurements.
The highest difference between a Penn State estimation and IC measurement was a 65% underestimation of nutritional needs by the Penn State formula.
58.4% (216/370) of calculated Penn State estimations of REE were either more than or less than 10% of the REE measured by IC. 
While preliminary conclusions show that IC more accurately predicted REE, limitations of both the retrospective analysis and IC requirements for accurate estimations in STICU patients create cause for further evaluation.

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