Nutrition Support Traineeship
We are at the end of another great traineeship week. We still have cold weather, but we were lucky that the snowstorm missed us! Our February traineeship week was at the very end of the month, so we decided to make this update a long one, and combine February and March. Our journal club for February was on a very recent article.
We had reviewed a study in October by the same group, but this one expanded on their previous report, including calorie needs and looking more directly at nitrogen balance. The citation for the one in October is:
Scheinkestel CD, Adams F, Mahony L, Bailey M, Davies AR , Nyulasi I, Tuxen DV. Impact of increasing parenteral protein loads on amino acid levels and balance in critically ill anuric patients on continuous renal replacement therapy. Nutrition. 2003 Sep;19(9):733-40.
February’s ’s article was a prospective trial of 50 critically ill ventilated patients who required continuous dialysis. The subjects were randomized into two groups; One group of 10 patients served as a “control”, and received 2.0 gm protein/Kg for the entire study period. The other group received a variable protein load. They started at 1.5gm protein/Kg for 2 days, were increased to 2.0 gm/Kg for 2 days, then were increased to 2.5 gm/Kg for 2 days. All patients were studied for six days total, and received calories that met their measured (or estimated if metabolic cart not possible) energy expenditure (an average of 34 calories/Kg).
Nitrogen balance was measured on days 2, 4, and 6 by analyzing the nitrogen in the dialysate fluid (and urine if the patient made >500 ccs/day).
The findings that were reported were:
The major limitation of this study is that the patients were only studied for six days, and were maintained at each protein level for two days. There was inadequate time to reach equilibrium at each new protein intake. It is possible to transiently appear in positive balance if you measure right after an increase in protein. It is important to note that that the “control” group who received 2.0 gm protein/Kg each day had an increasingly negative balance over the six days. On day 4 of the study, when both groups were getting the same nutrition (2.0 gm protein /Kg), the control had a nitrogen balance of negative 7gm, and the group who had just had their protein increased had a positive 0.4gm nitrogen balance.
Clearly, something was different between these two groups, even when they were getting the same nutrition. The authors also imply that since nitrogen balance was related to outcome, that you should give more protein. When you read the whole study you learn that protein intake was NOT associated with outcome. Nitrogen balance was related to outcome, but not protein intake. It makes sense that those who were sicker, had worse nitrogen balance, also had worse outcome. This is a great “teaching” study to demonstrate that associations do not imply cause-and-effect.
The methods were clearly not adequate to answer the question studied. They would need to randomize two larger groups to high vs moderate protein, and study for a longer period of time if they really wanted to answer if vs. these patients need more protein.
Take home message:
The methods used in this study are inadequate to suggest any changes in practice.
This is just another example of why it is important to differentiate
between association and cause. Our practice is to provide approx.
1.5 gms of protein per Kg to patients on HD or CVVHD.
Our March discussion was a review of a number of articles that investigated assessment and feeding of obese patients. We reviewed several articles that presented evidence that the use of a “25% correction factor” for adjusted body weight in patients with a BMI >30 significantly underestimates calorie expenditure if standard equations are used. Two articles suggest that the use of a 50% correction factor for adjusted weight with standard equations and stress factors approximates indirect calorimetry numbers (Note: this does not translate into evidenced-based outcomes). There was a general consensus that in the vast majority of obese patients we do NOT want to meet calorie expenditure, and that most often hypocaloric feeding is desirable. However, there was a passionate discussion regarding what calculations and adjusted body weight should be used for these patient’s calculations. The discussion does stem from the fact that all of these studies have limitations, and that no study has adequately looked at what level of feeding produces the best outcomes for these patients.
It is worth noteworthy that the calculations for adjusted body weight that appear in the 5th edition of ADA ’s Manual of Clinical Dietetics were removed from the 6th edition. According to the ADA ’s Knowledge Center this is “because there is a lack of evidence to support the use of adjusted body weight calculations”.
Our take-home message is that the use of a 50% adjustment factor was the best supported adjusted weight calculation for calorie expenditure in obese patients. However, there is no data about the use of adjusted body weight with a 50% factor for calculating protein needs, or (more important) the proper way to determine the best level of feeding using this weight.