There are few methods to determine protein needs in patients under nutrition therapy. Nitrogen balance studies are plenty of bias, but may provide some information. Or not. I would like to know if colleagues use it as a tool for decision making at bedside.
We don't do nitrogen balances any more. As you mention there are plenty of bias. It is important to give adequate nitrogen input, especially in critical ill patients (1.5-2.0 g protein/kg). Many parenteral all-in-one-infusions have a low protein content. There is no evidence based tool for decision making besside. I would prefer functional tests like grip strength etc.
Although nitrogen balances tend to overestimate intake and underestimate output they may be of use when attempting what is adequate and what is not. The key issue is whether patients are in negative or positive balance and whether this is paralleled by changes in blood urea nitrogen ± functional tests. For patients on parenteral nutrition only accurate urine collections may be of value.
Are you talking about parenteral, enteral, normal feeding?
As a Nutritionist, always surprised me that doctors prefer to resolve an ecuation rather than feed a person with the food that they will provide to their relatives on that situation.
Plenty of studies show that hospital stay result in increased malnutrition, and malnutrition worse as hosital stay increases. That is unnaceptable.
Just follow general population guidelines. As Christiane Goeters pointed, 1,5-2g/Kg for critically ill. For most people, 1 to 1,2 g /kg will be enough.
The notion described by Richard Cooke, of a qualitative, and not a quantitative and precise view of nitrogen balance is interesting in my point of view. Another interesting aspect mentioned by Dr. Cooke is the precision of this method in patients under parenteral nutrition - mode of nutrition therapy that bypasses the "absorptive phase". I know that many arguments that are physiologically sound are not confirmed at the bedside. For me (and I recognize a very subjective standpoint) it is hard not to consider the studies of Elwyn, Kinney and Bursztein.
I should have indicated that while accurate urine collections may be feasible and useful during total parent nutrition, they are of little value during enteral nutrition when stool collections are necessary.
not only at the ward but also at the ICU we preferd impedanciometry, nitrogen balance is from las century, sorry but is the sad true
The question is: what do you want to evaluate? If the answer is: success of nutritional therapy, the tools are: RBP in the first 24-36 hours, transferrin in the following week, than albuminemia. Also, those plasma parameters, that are strictly linked to liver synthesizing efficiency, and thus survival of patients with any illnesses, may be used for detecting protein-calories malnutrition and the time of onset of undernutrition. Urea synthesis is quite totally under control of arginine provided by diet, so false improvement can be elicited just by implementing only this amino acid, and not by replenishing adequately patients by all necessary EAAs , and in the right stoichiometric ratios required by human metabolism.
We do not use nitrogen balances routinely . The majority of our patients are enterally fed and the TPN patients often have large nitrogen wastes to contribute - ie high output ECfistulas
A further use of UUN measurements is warning of sepsis. Because WBC and temp can both fall from high through the normal range and CRP alone may not provide a 'picture' of a worsening clinical state, UUN warns of a sharp rise in catabolism resulting from systemic infection. Also, though I agree it is crude, it does show catabolic anabolic trends, facilitating adjustment of NPE:gN ratio. Sadly my institution largely ceased use, not because of expense (v. cheap), rather to remove non-std tests.
Parameters for monitoring of protein intake are levels of serum urea, ammonia, total protein, arterial blood gas, and nitrogen balance. Nitrogen balance estimates
protein metabolism and ingestion over 24 hrs. It must be made in the absence of diarrhea or abnormal losses and a 24-hr urinary volume is required. The aim is to obtain a positive nitrogen balance as a reflection of anabolism. If the balance proves negative, it could be due to insufficient protein ingestion; or hypercatabolism. Unmeasured losses (burns, renal disease, diarrhea, protein-losing enteropathy) can contribute to a negative nitrogen balance that is not reflected by the calculation.
In adult patients, indirect measurement of total urea nitrogen (TUN) can be obtained from urinary urea nitrogen (Dickerson RN et al. Nutrition. 2005;21(3):332-8.)
In younger children we use a normogram for the estimation of total nitrogen losses. (Watters J.M, Wilmore DW. The metabolic responses to trauma and sepsis. In: Degroot LJ, Jameson JL. Endocrinology. Philadelphia: WB Saunders Co., 1989;2367–93.)
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