January 2013 e-journal Club

 
Greetings,

We generally do not plan for a training program in January because the fickle nature of the weather this time of year can make travel and schedules too much of an adventure.  We have been trying to stay on schedule with our journal club however, because there have several new articles out that we want to be sure to include.

January Citation:

Frankenfield DC, Ashcraft CM, Galvan DA.  Longitudinal prediction of metabolic rate in critically ill patients.  JPEN 2012;36(6):700-12.

Summary: 

This study was designed to establish the cumulative error of the Penn State equation for estimation of energy expenditure of ICU patients over 7 days compared with daily measured calorie expenditure via indirect calorimetry (IC). The secondary goals were to measure the cumulative error of 25 kcal/kg (American College of Chest Physicians - AACP) compared to daily indirect calorimetry, and also to measure the cumulative error of a single IC measurement compared with daily measurements of resting energy expenditure.

The investigators tested a modified version of the Penn State equation designed for patients over 60 years who had a BMI > 30, because a previous study had demonstrated that the standard Penn State equation was not accurate in those patients.

Adjusted weight (25% correction factor) was used for the AACP calculations when BMI was > 30.  Variables used to calculate the Penn State equation were collected upon completion of the IC measurements, and weight used for calculations was the lower number of either the admission weight or weight upon study entry.

Inclusion and Exclusion Criteria were:

Inclusion criteria:

Patients over 18 years in the surgical/trauma, neuroscience, or medical ICU who were mechanically ventilated for at least 7 days and able to remain in a resting state during indirect calorimetry measurements.

Exclusion criteria:

Patients with an air leak anywhere in the ventilator circuit (chest tubes, endotracheal cuffs, etc.) or those with a fraction of inspired oxygen > 60%.

Major Results:

There were 32 patients evaluated who met inclusion criteria, and ultimately 13 patients were able to complete the full protocol (6 trauma, 3 neurologic/neurosurgery, 2 sepsis, and 2 abdominal surgery).  Six patients were > 60 years with a BMI > 30 (modified Penn State), and 7 entered the standard Penn State equation group.

The mean cumulative difference between:

  • Standard Penn State equation (calculated daily) and daily IC measurements was: - 618 Kcals +/- 774 kcals (-4.7% +/- 6.2%).
  • Modified Penn State equation and daily IC: - 331 kcals +/- 467 kcals (- 2.5% +/- 3.7%).
  • AACP equation (25 kcals/kg) and daily IC: - 387 kcals +/- 1597 (- 2.2 +/- 11.9%)
  • A single IC measurement used X 7 days and daily IC: - 684 +/- 1731 kcals (- 4.1% +/- 11.1%).
  • Using 2X/week IC compared to daily IC: - 109 kcals +/- 705 kcals

Author’s Conclusions:

1)   The Penn State equations predict resting metabolic rate over time within 5% of the measured value.

2)   The performance of the Penn State equation is similar to that of using 1 IC measurement over 7 days.

3)   The ACCP method has an unacceptably wide limit of agreement.

Evaluation:

This study confirms several things that we know, including the fact that there is a daily variation in the energy expenditure of critically ill patients.1,2  The results of this study validate prior work documenting that a single IC measurement is not substantially more accurate than most prediction equations for energy expenditure over time.2  This study also confirms prior indirect calorimetry studies demonstrating that if variables used to calculate the Penn State equation (T-max, minute ventilation) are collected at the same time as the IC measurement, then the predicted and measured energy expenditure are similar.3 Additionally, this study confirms that the ACCP method (25 kcals/kg) is a “rough” estimate of calorie expenditure.3

What this study is not designed to address is the fact that we do not yet know what calorie level to provide the critically ill patient at various stages of their illness to allow the best outcome.  Additionally, the actual amount of nutrition that patients receive is also quite variable (usually much more so than the calorie calculations !).  A prior study demonstrated that even when continuous IC data was available, patients did not receive the full amount that was ordered.2  From a practical standpoint, it seems hard to justify more time for calculations, with greater chance for math error, when patients receive variable amounts of nutrition.   

Our Take Home Message (s)

1.   The Penn State equation is similar to calorimetry results when the variables used for calculations are collected at the same time as the IC measurement.

2.   A single indirect calorimetry has similar accuracy as prediction equations for predicting mean energy expenditure of ICU patients. 

3.   It is past time to stop referring to a single IC measurement as a “Gold Standard.”

4.   There is no data about clinical outcomes relating to different methods used to estimate nutrition goals.

5.   We still don’t know the best calorie and protein level to feed sick people.

References

1.   Vermeij CG, et al.  Day-to-day variability of energy expenditure in critically ill surgical patients.  Crit Care Med. 1989;17(7):623-6.

2.   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):649-657.

3.   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.

Other News on the UVAHS GI Nutrition Website: (www.ginutrition.virginia.edu):

Upcoming Webinars for 2013:

  • February 26:  Clinical Cases for the Nutrition Support Clinician
  • March 26:  Building Collaboration Between Physical Therapy and Nutrition to Improve Patient Outcomes
  • April 16:  Nutrition Support in the Adult Cystic Fibrosis Patient
  • May 14:  The Role of Fiber in Nutrition Support
  • June 18:  Nutrition Management of Food Allergies in the Pediatric Patient
Check out What’s New:

Latest Practical Gastroenterology article:

  • Rogers, C. Nutritional Management of the Adult with Cystic Fibrosis – Part I.  Practical Gastroenterology 2013;XXXVII(1):10.  

 

Joe Krenitsky MS, RD

Carol Rees Parrish MS, RD

PS – Please feel free to forward on to friends and colleagues.