Nutrition Support Blog:Protein Needs in Acute Kidney Injury
October 13, 2013
Horror movies have never held much allure for me. I suspect that the idea of supernatural foes that can’t be defeated, or those who keep coming back to life were just too unsettling. Stories about normal people thrown into circumstances who managed to use their wits and/or bat-utility belts to defeat the villain and save the day were always much more appealing.
Clinical nutrition is plagued by a number of concepts that remind me of undead movie horrors, because despite the scientific evidence that should put them to rest, they keep coming back to haunt us. Myths about serum proteins as indicators of nutrition status, enteral feeding formulas causing diarrhea, water bolus causing duodenal ulceration, or dietary indiscretion as a source of hepatic encephalopathy continue to arise, despite the growing evidence to the contrary. One of the most persistent misconceptions is the idea that the degree of uremia in critically ill adults with acute kidney injury can be moderated by limiting the protein provided in EN or PN.
I suspect that part of the difficulty with addressing the issues relating to protein provision in acute kidney injury (AKI) relates to the fact that a protein restriction, while providing full calories to “spare” protein, can delay the need to start renal replacement therapy in chronic renal insufficiency. However, AKI in the setting of critical illness is a completely different process from chronic renal insufficiency, with a radical change in metabolism and nutrient utilization. Increasing calories does not decrease protein breakdown in critical illness, while providing nutrition with full protein will increase hepatic protein synthesis.1, 2 We know that patients who receive renal replacement therapy require increased protein provision, but many clinicians struggle over patients that are not yet receiving (or have advanced directives forbidding) dialysis. Metabolic studies in patients with AKI who are not receiving dialysis have demonstrated that even when protein intake was doubled (from 75 to 150 grams/day), the blood urea and creatinine were not significantly different.3 However, nitrogen balance was improved, suggesting that the increased protein was utilized, which is consistent with the older data of increased protein synthesis.3 There is no data to suggest that protein is damaging to the kidney in AKI, in fact, protein seems to increase renal blood flow and may be beneficial overall. Nutrition and metabolism experts have noted for a number of years that increased protein provision in the setting of AKI may actually hasten renal recovery.4 See the full text of our review of protein in AKI for more details on the studies, metabolism, and some hard numbers for protein amounts.
However, if debating the metabolic fate of nitrogen in critical illness is not your idea of a fun time, don’t despair. When we are asked to evaluate protein dose in patients with increasing uremia, we have found that common sense and an eye for details are the most useful weapons in our nutrition support-utility belt. In practice, our first stop is to look at the actual amount of nutrition delivered to the patient (usually from the feeding pump history function). We have found that the most common occurrence when investigating protein and uremia is that the patient actually received far less than was ordered, and was already essentially on a restriction of all nutrients. It is helpful to remind the team that burning several hundred grams of body protein to meet energy needs creates a lot more uremia than feeding adequate protein. Hyperglycemia, GI bleeding, blood products can also sometimes contribute more to the total nitrogen provision than nutrition support. I have found that most of the time, I don’t even have to reach for the studies!
I have fears that generations from now, nutrition support clinicians will still be battling the concept of protein in AKI, like some string of really bad movie sequels (Attack of the Killer Proteins IV, Bride of Killer Proteins, Return of Ureagenesis). We really need to be educating dietetic, pharmacy, nursing and medical students about the realities of protein metabolism and AKI so that we can put this zombie-like nutrition myth to rest for good.
Ipsa scientia potestas est (Knowledge itself is power)
- Francis Bacon
“I do nothing that a man of unlimited funds, superb physical endurance and maximum scientific knowledge could not do.”
1) Shaw JH, Wolfe RR. An integrated analysis of glucose, fat, and protein
metabolism in severely traumatized patients. Studies in the basal state and the response to total parenteral nutrition. Ann Surg. 1989;209(1):63-72.
2) Shaw JH, Wildbore M, Wolfe RR. Whole body protein kinetics in severely septic patients. The response to glucose infusion and total parenteral nutrition. Ann Surg. 1987;205(3):288-294.
3) Singer, P. High-dose amino acid infusion preserves diuresis and improves nitrogen balance in non-oliguric renal failure. Wien Klin Wochenschr 2007: 119; 218-222.
4) Pazirandeh S, Maykel JA, Bistrian BR. Hidden nutrition studies. Crit Care Med. 2003 Feb;31(2):662.