Nutrition Goals and Obese ICU Patients
July 19, 2011
We have invested a bit of time this year reviewing our protocols and practices for calorie and protein needs of critically ill obese patients. We reviewed the ASPEN/SCCM guidelines, re-looked at the original study data, and did a number of sample calculations with a variety of “case study” patients of different genders and degrees of obesity.
One of the difficulties is that there is still such a limited amount of data to guide the clinician. The available studies have primarily used nitrogen balance as the outcome. There is data demonstrating that there is no metabolic down-side, and potential advantages to hypocaloric, full protein feedings in obese patients. However, we still do not have randomized studies with different degrees of reduced calories and increased protein to tell us what just how low to drop calories or how much to increase protein to achieve the best outcomes (including long term/rehab). The ASPEN/SCCM guidelines (see link below) state that obese patients “should not exceed 60%-70% of target energy requirements,” but you will note that this is a level D recommendation, and even these studies only compared full feeding with only one level of hypocaloric feedings.
Our calculations demonstrated that using adjusted weight (25% calculation factor) with 20-25 calories/kg for our initial goal gave us very similar numbers to the APSEN/SCCM guidelines. Additionally, one of the few studies that looked at patient outcome (Dickerson 2002) used adjusted weight for the calculations, so we have continued to use adjusted weight for our calorie calculations in obese patients until better data is available. Although it is popular to suggest that obese patients should have indirect calorimetry, I am not sure how important it is to be precisely accurate in determining calorie expenditure when we are not even sure how low to decrease calories for best outcome. It seems to me that as long as you are feeding mildly hypocaloric you are doing as well as we are able, and if you are using 20 kcals/kg adjusted weight (25% adjustment factor)you are replicating the only decent outcome study we have.
One of our clinical conundrums is the morbidly obese patient that needs to lose substantial weight in order to wean from the ventilator. Ideally we would like them to lose weight rapidly, but do not want to drop calories too low - to the point that they have negative nitrogen balance and accelerated skin breakdown. Without better data what we have done in these (relatively rare) cases is once they are stable we obtain a baseline nitrogen balance. Then we incrementally decrease calories and monitor nitrogen balance to make sure they remain in neutral-positive balance.
1) Dickerson RN, Boschert KJ, Kudsk KA, Brown RO. Hypocaloric enteral tube feeding in critically ill obese patients. Nutrition. 2002 Mar;18(3):241-6. Erratum in: Nutrition. 2003 Jul-Aug;19(7-8):700.
“There's no sense in being precise when you don't even know what you're talking about”
- John von Neumann 1903-1957