Volume-Based Feeding in Enteral Nutrition: What About Diabetes?

Q At my hospital, we have a volume-based tube feeding practice. If a patient’s tube feeding rate is adjusted up and down to ensure delivery of the 24-hour volume, how do you control blood glucose level? This would be especially important in a patient receiving an insulin infusion with hourly checks of blood glucose level. Is the blood glucose level significantly affected by changes in the tube feeding rate? If so, do you find that the standard ordered insulin scales are adequate?A Mary E. Lough, rn, phd, ccrn, ccns, replies:Volume-based feeding (VBF) is a proactive approach to enteral nutrition delivery. VBF is nurse-driven and the goal is to provide 100% of the calories and protein needed via a feeding tube in critically ill patients receiving mechanical ventilation.Heyland et al1 compared a VBF protocol with traditional enteral nutrition protocols in a multicenter, randomized, controlled trial in the United States and Canada. The 18 intensive care units (ICUs) that participated in this study volunteered for a specific reason. In the annual International Nutrition Audit, they reported that their patients receiving mechanical ventilation received less than 50% of expected calories via eternal nutrition.1 In the study, half of the ICUs used standard care (control, n = 9) and half used a new VBF protocol (intervention, n = 9). The VBF protocol moved the focus away from the hourly rate goal (eg, 70 mL/h) to a 24-hour goal (eg, 1680 mL/d). The VBF protocol also included higher starting rates and higher gastric residual volumes.1In the VBF protocol, when an interruption in tube feeding not due to gastrointestinal intolerance occurred, the nurse increased the hourly rate to replace the missed volume following a standardized format.2 The makeup hourly amounts varied depending on the basal rate, how many hours the tube feedings were stopped, and how many hours remained in the 24-hour cycle (7 am–7 am).2 For example, in a patient receiving 50 mL/h, if the enteral nutrition was stopped for 7 hours (missing 350 mL), when tube feedings were restarted, 350 mL were evenly divided across the remaining hours in the 24-hour cycle. Using a standardized chart, if 7 hours remained, the hourly rate increased from 50 mL/h to 70 mL/h to meet the 24-hour target.2On average, ICUs using the VBF protocol provided 12% more calories via enteral nutrition than did the standard nutrition ICUs.1 Research studies and quality improvement projects report that use of a VBF 24-hour protocol increases delivery of enteral nutrition calories by 10% to 26% per day,2–4 compared with protocols focused only on the hourly rate (89% vs 63%2; 60% vs 50%3; 92% vs 81%4). Multimodal education and follow-up with all clinicians involved in care (ie, nurses, physicians, and dietitians) are essential for successful implementation.5Whether the VBF protocol is safe for patients with diabetes who receive a continuous insulin infusion is a question that has not been addressed in the literature, and none of the VBF studies mention blood glucose or insulin. An increase in the hourly rate of enteral nutrition will increase blood glucose in patients who have diabetes or other risk factors for hyperglycemia.6 However, this situation can be anticipated and managed by following the clinical guidelines for blood glucose control in critical illness.7,8 Insulin coverage is recommended for critically ill patients with blood glucose values greater than 180 mg/dL.8 In critically ill patients, the target range is 150 to 180 mg/dL.8 Hypoglycemia protocols are required when the blood glucose level falls below 70 mg/dL.8 In most ICUs, a standardized insulin infusion and a point-of-care blood glucose protocol can be used in tandem with the VBF protocol.Blood glucose checks will always be more frequent when the enteral nutrition is stopped for a long time, and then restarted. Frequent point-of-care blood glucose checks are needed to ensure patient safety.6 Published enteral nutrition VBF protocols recommend starting an intravenous dextrose solution when the tube feedings are stopped to lessen the risk of hypoglycemia.2 The patient with known diabetes may also be receiving a diabetes-specific enteral nutrition formula with lower levels of carbohydrate compared with standard enteral formulas.6 The glycemic formulas are designed to achieve more stable blood glucose values, although these formulas have not been tested in a VBF trial. Critical care nurses expect changes in patients’ blood glucose level for many reasons, including VBF. The prudent choice is to use a standardized insulin protocol to maintain the patient’s blood glucose level within the target range recommended in national guidelines (150–180 mg/dL).8In summary, VBF is a proactive nurse-driven measure to increase delivery of enteral nutrition for patients receiving mechanical ventilation. Research suggests that adoption is not uniform across ICUs and that education is important for successful implementation. The increase in the VBF “catch-up” hourly rate is modest and a gradual increase in blood glucose may occur. There are no published studies on patients with hyperglycemia, diabetes, and VBF. A clinical recommendation would be to use a standardized insulin/blood glucose protocol in tandem with VBF to maintain blood glucose levels within the therapeutic range.8