Nutrition Support Blog: Glucose Control during Enteral Nutrition
March 27, 2014
Several years ago I had the opportunity to review and summarize data about glucose control in the intensive care unit (http://www.ncbi.nlm.nih.gov/pubmed/21266695 While existing research and reviews have not always properly considered the amount of nutrition being provided, at least we do have a number of studies investigating the effect of different strategies for glucose control on safety and outcome in the ICU.
Unfortunately, there is very limited data on the optimal methods for glucose control of hospitalized patients that receive nutrition support outside of the ICU. Patients that are transferred to a floor bed are frequently transitioned to bolus or nocturnal feeding schedules, and continuous insulin infusions are changed to alternate regimens. The nurse to patient ratio outside the ICU generally requires a more liberal interpretation of adequate glucose control (compared to the ICU) in order to reduce the risk of hypoglycemia. However, we know that hyperglycemia consistently greater than 200 mg/dl compromises immune function, wound healing and essentially negates the benefits of nutrition support because hyperglycemia accelerates proteolysis.1, 2 Discussions with nutrition support clinicians who attend our training sessions, as well as our own experiences, suggest that glucose control issues are a challenging and even frustrating experience at many facilities.
Considering that most enteral feeding regimens provide balanced fuel sources (fat/CHO ratio) and consistent delivery of carbohydrate and calories compared to most oral diets, it is a bit surprising that glucose control during EN is frequently problematic. Obviously, most patients are in the hospital because they are ill, injured or postoperative, and as a result have insulin resistance and/or medications such as corticosteroids that exacerbate hyperglycemia. Changes in the severity of illness, IV fluid rate, medication doses and the amount of EN received all add a level of complexity to keeping glucose controlled. I am frequently asked if changing the carbohydrate to fat ratio, or use of a “slower digesting” carbohydrate in EN will be helpful. However, the most common problem that we have observed is not too much carbohydrate, but rather an obvious calorie (and CHO) to insulin mismatch. Patients with well controlled serum glucose while receiving 2 units of insulin infusion/hour who are transferred to a floor bed with the same continuous tube feeding and “sliding scale” insulin at breakfast, lunch, supper and bedtime will be inevitably hyperglycemic (especially by 03:00 hrs), regardless of the feeding formula chosen. Changing to a more expensive specialty formula, without fixing the basic and ultimately unavoidable issue of insulin insufficiency, really does not make sense, and we have found that fixing the basic problem obviates the need for special formulas. While we would love to be able to address hyperglycemia with nutritional manipulations, the reality is that altering CHO to fat has limited effect, and human nature being what it is, attempting a nutritional bandaid sometimes just delays getting the necessary interventions done, which can result in longer hospital stays and putting patients at risk for hydration and infectious complications. Study data is consistent with our experience: decreasing carbohydrate provision may decrease insulin requirement to a degree, but does not affect long-term glucose control.3
In regards to how fast carbohydrates are delivered, it would be hard to slow down delivery of carbohydrate much more than we already are. A typical 75 kg patient on continuous feeding receives about 10 gm carbohydrate/hour so 0.17 gm/minute (20gm/hour, 0.34 gm minute on nocturnal cycle) – so it is hard to get much slower than that. Usually the most important part of glucose control during EN is to work with the primary team to coordinate the type of insulin with nutrition delivery, such as 12-hour feedings with NPH-type insulin, or short acting insulin timed with bolus feeding.
I suspect that there may be a niche for reduced and/or slowly digested carbohydrate formulas in a very small number of selected individuals with very brittle DM, or non-insulin dependent patients with marginal control on oral medications. Admittedly, there are no studies to date of “glucose control” EN formulas in these hard to control patients, likely because they are so few and far between that it would be near impossible to get enough patients for a study. Common sense would then suggest that our use of these specialty formulas should be just as few and far between.
“Libenter homines id quod volunt credunt” (Men gladly believe that which they wish for)
“Quidquid latine dictum, altum videtur” (Whatever is said in Latin sounds profound)
1. Hsu CW1, Sun SF, Lin SL, et al. Moderate glucose control results in less negative nitrogen balances in medical intensive care unit patients: a randomized, controlled study. Crit Care. 2012 Dec 12;16(2):R56.
2. Flakoll PJ, Hill JO, Abumrad NN. Acute hyperglycemia enhances proteolysis in normal man. Am J Physiol. 1993 Nov;265(5 Pt 1):E715-21.
3. Pohl M, Mayr P, Mertl-Roetzer M, et al. Glycemic control in patients with type 2 diabetes mellitus with a disease-specific enteral formula: stage II of a randomized, controlled multicenter trial. JPEN 2009 Jan-Feb;33(1):37-49.