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Prediction of Resting Energy Expenditure in Morbidly Obese Mechanically Ventilated Patients in the Medical ICU FREE TO VIEW

Michael Reilly, DO; Nancy MacGarvey, MD; Michael Sherman, MD
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Drexel University College of Medicine, Philadelphia, PA

Chest. 2013;144(4_MeetingAbstracts):366A. doi:10.1378/chest.1704885
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SESSION TITLE: Critical Care Posters

SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 30, 2013 at 01:30 PM - 02:30 PM

PURPOSE: An increased prevalence of obesity has been reported worldwide, and upwards of 30% of patients admitted to medical ICUs are reported to be obese or morbidly obese. Estimation of caloric requirements is often performed using the Ireton-Jones ventilator equation for obese patients, however this was validated for obese surgical and trauma patients. The application of this equation to morbidly obese patients in a medical ICU is not known.

METHODS: We retrospectively reviewed indirect calorimetry results on 42 ventilated medical ICU patients with BMI greater than 40. Limits-of-agreement analysis determined bias (mean difference between measured and predicted equation values) and precision (standard deviation of the bias) to evaluate the accuracy of Harris-Benedict and Ireton-Jones equations compared with measured resting energy expenditure (MREE) by a Sensormedics Metabolic Cart. Acceptable predictive accuracy for the predictive equations was determined to be within + 20% of MREE.

RESULTS: Demographics of the study population include age 55.7 ± 12.7 years, 71% female, BMI 52.6 ± 11.0 kg/m2. The mean MREE was 1920 ± 707 kcal/day and mean VO2 was 1.89 ± .63 ml/min/kg. The Harris-Benedict equation yielded a mean calculated REE of 2298 ± 546 kcal/day with a bias of 377 ± 667 kcal/day. In 15 (36%) subjects, the Harris-Benedict equation results were accurate to within 20% of MREE. The Ireton-Jones equation yielded a mean calculated REE of 1990 ± 312 kcal/day, with a bias of 69 ± 601 kcal/day. In 20 (48%) of subjects, the Ireton-Jones equation results were within the 20% of MREE precision criteria.

CONCLUSIONS: Ireton-Jones is more accurate than Harris-Benedict for our cohort of morbidly obese ventilated medical ICU patients, but due to extremes in both hyper- and hypo-metabolism seen in these medical ICU patients, neither equation is an accurate predictor of nutritional needs.

CLINICAL IMPLICATIONS: Current prediction equations are inadequate for calculating energy needs of morbidly obese ventilated patients. Without a reliable predictive equation, such patients may require indirect calorimetry for accurate estimation of their nutritional requirements.

DISCLOSURE: The following authors have nothing to disclose: Michael Reilly, Nancy MacGarvey, Michael Sherman

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