University of Virginia Health System
Nutrition Support E-Journal Club
January is one of the few months when we do not run a traineeship or other program, due to the winter travel nightmare potential. We are currently gearing-up for Clinical Nutrition Week in New Orleans at the end of the month, where we will participate in several presentations and poster sessions.
This month's JPEN had several good articles, so choosing just one was a bit of a challenge. We decided to start with an article discussing calorie expenditure, and save some others for next month.
Frankenfield DC, Coleman A, Alam S, et al. Analysis of Estimation Methods for Resting Metabolic Rate in Critically Ill Adults. JPEN J Parenter Enteral Nutr 2008;33(1):27-36.
An analysis of the accuracy of 17 different calculations (9 different formulas with variations for stress and/or adjusted weights) for estimating energy expenditure compared to indirect calorimetry in 202 critically ill patients, in other words: the Baskin-Robbins approach to caloric provision to the critically ill.
Inclusion and Exclusion Criteria were:
Inclusion criteria were patients admitted to an adult intensive care unit (ICU), > 18 years of age, requiring mechanical ventilation, with orders written and implemented for enteral or parenteral nutrition support.
Exclusion criteria included air leak in the ventilation circuit, FiO2 > 60%, intermittent hemodialysis (continuous renal replacement therapy was allowed), shivering or agitation, or orders for limited support. Patients with paraplegia and quadriplegia were excluded (due to attenuated metabolic rate compared with other critically ill patients) as well as those with cystic fibrosis (because of the potential for excessive work of breathing). No burn injuries were included.
Major Results reported by authors:
The authors reported that accuracy of the calculations (defined as within 10% of measured expenditure) for the entire population of patients ranged from 67% for the Mifflin-variant of the Penn State equation to 18% for the weight-adjusted Harris Benedict equation (without stress factor). Within subgroups, the highest accuracy rate was 77% in the elderly non-obese using the Penn State equation, and the lowest was 0% for the weight-adjusted Harris Benedict equation.
The authors concluded that the Penn State equation provides the most accurate assessment of metabolic rate in critically ill patients if indirect calorimetry is unavailable.
This is one of the largest studies of this nature; testing a broad range of formulas and variations of formulas using a mixture of adjusted weights and stress factors. However, the major limitation of this study is that it used a single indirect calorimetry measurement per patient, in a heterogeneous group of patients, over a wide range of clinical conditions. The single indirect calorimetry was done anywhere between day 2 and day 64 of a patient's hospital stay, and between day 2 and day 27 of their ICU stay. Critically ill patients have a significant day to day variation in their metabolic rate. A recent study demonstrated that during the first week in the ICU daily energy expenditure changed an average of 31% per day! (1). This study also established that even when indirect calorimetry was done each day, and feeding rate was adjusted based on the actual energy expenditure, that the delivery of enteral feeding was so variable that a significant cumulative discrepancy between prescribed and delivered feedings developed.
However, much more pertinent to clinical practice than accuracy of prediction equations or formula delivery compared to indirect calorimetry measurements, is the fact that in 2009 we have not yet identified the level of feeding that will result in the best outcome for critically ill patients.
Our Take Home message:
There is inadequate data regarding the outcome of critically ill patients to support a strong recommendation supporting indirect calorimetry or any particular prediction equation. In lieu of adequate data it would seem reasonable to base feeding on a prediction equation that is expedient and will prevent gross overfeeding/underfeeding, and then, most importantly, to monitor the actual amount of feeding delivered to the patient and adjust feedings as needed based on clinical progress and current goals.
- 1) Reid CL. Poor agreement between continuous measurements of energy expenditure and routinely used prediction equations in intensive care unit patients. Clin Nutr. 2007;26(5):649-57. (See April 2008 e-journal club for our evaluation of this study).
Our next Weekend Warrior 2-day mini-traineeship program is scheduled for Saturday and Sunday, March 7th & 8th. If you know anyone who might not be able to get away for our full week traineeship, please let them know about our weekend program, and to check out our website for full information-we have a few slots left!
Check out the last 2 Practical Gastroenterology articles at:
- 1. daSilva L, McCray S. Vitamin B12: No One Should Be Without It. Practical Gastroenterology 2009; XXIX(1):34-46.
- 2. DiBaise JK. Nutritional Consequences of Small Intestinal Bacterial Overgrowth. Practical Gastroenterology 2008;XXXII(12):15-28.
Joe Krenitsky MS, RD
Carol Parrish RD, MS
PS - Please feel free to forward this on to friends and colleagues.