Health care and nursing are rich in traditions. These traditions have given us the foundational knowledge that the patient must be the focus of care and successful outcomes are essential to patient care. Another tradition worth keeping is the end-of-shift report, which promotes continuity of care.
But not all traditions benefit patients. The tradition of nurses wearing caps was misguided; the caps were bacterial breeding grounds. Keeping patients immobile in bed for many days after surgery led to increased postoperative complications. Only after scientific evidence was introduced were these traditions challenged and ultimately discarded.
A critique of sliding-scale insulin
Another long-held tradition is use of the sliding scale for glycemic control in hospitalized patients, with insulin doses based on the patient’s blood glucose (BG) level. Sliding-scale insulin (SSI) is familiar to most nurses, but evidence shows it’s largely ineffective because it treats hyperglycemia after it occurs; it doesn’t prevent elevated BG or its recurrence. SSI in the hospital setting has been passed down from attending physicians to residents despite lack of supporting evidence.
Not only are SSI orders ineffective; they can be dangerous. Traditionally, SSI regimens use regular insulin without intermediate or long-acting insulin. The SSI regimen prescribed on admission is likely to remain unmodified throughout the patient’s hospital stay. But this approach, while simple, exacerbates hyperglycemia and hypoglycemia caused by rapid BG alterations, increasing the risk of poor clinical outcomes and even death. For several years, the American Diabetes Association (ADA), which publishes standards of care for diabetes annually in its Diabetes Care journal, has discouraged SSI.
Sometimes SSI uses rapid-acting insulin (lispro, aspart, glulisine) instead of regular insulin. Rapid-acting insulin more closely mimics normal physiologic insulin production than regular insulin; it has a rapid onset, peaks sooner to cover postprandial glucose excursions, and lasts only 4 to 5 hours. Compared to regular insulin, rapid-acting insulin results in fewer hypoglycemia episodes and less insulin “stacking” (the practice of giving additional insulin before the scheduled or previous dose has finished working). But use of SSI alone still allows hyperglycemia to occur, treating it only after the fact.
Latest recommendations
A 2009 consensus statement on inpatient glycemic control management from the American Association of Clinical Endocrinologists and the ADA calls for scheduled subcutaneous insulin administration with basal, nutritional, and correctional components—an approach that promotes the best outcomes. It discourages both prolonged SSI as the sole regimen and use of noninsulin agents for most hospitalized patients. Largely a response to published research calling for possible reexamination of in-hospital BG goals, the consensus statement addresses both critical and noncritical patients. (Note: This article addresses recommendations for noncritical patients only.)
The statement recommends preprandial BG targets of 140 mg/dL or lower, plus random BG targets of 180 mg/dL or lower. Tighter BG control may be appropriate for stable patients with previous tight control, whereas less stringent BG targets may be acceptable for end-of-life care and patients with multiple comorbidities.
Three-pronged approach
A three-pronged subcutaneous insulin management program with basal, nutritional, and correctional components has proven safe and effective in managing hyperglycemia in noncritical hospital patients.
Basal insulin component
The basal insulin component covers basic energy needs by addressing normal hepatic glucose production. Long-acting insulin (detemir or glargine) or intermediate-acting insulin (premixed combinations, such as detemir/lispro or human/regular) is used to cover the basal component.
Nutritional insulin component
The nutritional insulin dose covers the amount of insulin needed to convert mealtime glucose into energy without postprandial hyperglycemia. Rapid-acting insulin is used to cover nutritional intake and correct hyperglycemia. Basal plus rapid-acting insulin (often called basal/bolus insulin therapy) most closely mimics normal physiologic insulin production and controls BG more effectively. Regular insulin isn’t recommended for the nutritional component because its longer duration doesn’t mimic normal physiologic insulin production; also, timing of preprandial insulin administration is hard to manage in the hospital.
To determine how much insulin the patient needs to cover meals, clinicians must calculate the carbohydrate-to-insulin ratio (C:I), which determines how many carbohydrate grams are covered by 1 unit of rapid-acting insulin. In hospital settings, this is usually done by the physician, dietitian, or diabetes practitioner using the “500 rule,” which assumes a daily carbohydrate intake of 500 g. This value is divided by the total daily dose (TDD) of all insulin (basal, nutritional, and correctional) the patient received in the previous 24 hours. 500 ÷ TDD = carbohydrate g covered by 1 unit of insulin. Thus, a patient with a TDD of 50 units has a C:I ratio of 10:1.
The “500 rule” works best for patients with type 1 diabetes who use rapid-acting insulin. For patients taking regular insulin, the assumed carbohydrate intake is 450 g. For patients with type 2 diabetes, weight-based C:I can be calculated using a C:I of 1:15. Thus, 1 unit of rapid-acting insulin covers 15 g (or one serving) of carbohydrates. For example: C (80 g) ÷ 15 = 5.3 units (to be rounded down to 5 units) of rapid-acting insulin to cover meals.
Hospital patients typically receive carbohydrate-controlled meals and a set premeal insulin dose to simplify glucose and insulin management.
Correctional insulin component: The sensitivity factor
The correction factor, also called the sensitivity factor (SF), reflects the patient’s sensitivity to insulin. SF is the degree to which 1 unit of rapid-acting insulin lowers the patient’s BG, expressed as mg/dL.
SF can be calculated in several ways. For patients receiving insulin, it’s calculated by dividing 1500 by the patient’s TDD of insulin. Suppose a patient has a TDD of 60. 1500 ÷ 60 = 25. Thus, the patient’s SF is 25.
For insulin-naïve patients (those who haven’t been using insulin), SF is calculated based on the patient’s admission weight (in kg). This value is used throughout the hospital stay, unless determined otherwise by the diabetes clinician or physician. To calculate SF for an insulin-naïve patient, divide 3000 by the patient’s weight. So if the patient weighs 90 kg, 3000 ÷ 90 kg = 33.3. This patient has an SF of 33.3.
Formula for the correction bolus
Once SF has been determined, the correction insulin dosage can be calculated by taking the patient’s current BG value minus a set target BG divided by SF. The set target BG is determined by the provider or institutional BG goals. The target may be 100 mg/dL, 110 mg/dL, or even higher when less strict BG control is acceptable.
Suppose a patient has a BG target of 110 mg/dL, a BG level of 385 mg/dL, and SF of 33.3. Here’s how to calculate the correction bolus: 385 – 110 = 275. 275 ÷ 33.3 = 8.25 (rounded down to 8). So you’d give 8 units of rapid-acting insulin.
For patients who are eating, the correction dose is based on the preprandial BG level and added to the nutritional dose to obtain the total rapid-acting insulin dose for that meal. Say, for instance, your patient needs a nutritional insulin dose of 5 units to cover food eaten, and a correction dose of 8 units to cover preprandial hyperglycemia. In this case, you’d give a total dose of 13 units of rapid-acting insulin for that meal.
Weight-based correction insulin (WBCI) is individualized for each patient. But with SSI, a patient weighing 90 kg would receive the same amount of insulin as one who weighs 60 kg; the first patient may not receive enough insulin to correct hyperglycemia, while the second may get too much insulin and suffer hypoglycemia. (See Comparing insulin requirements by patient weight by clicking the PDF icon above.)
WBCI can make a crucial difference in controlling hyperglycemia and reducing hypoglycemic episodes. But not all patients fit neatly into the formula. Such factors as body build need to be considered. A patient weighing 80 kg with a muscular frame may need less insulin than an obese patient of the same weight.
Overcoming barriers to implementation
Obstacles to changing from SSI to weight-based insulin administration include:
- resistance to change
- fear of hyperglycemia overcorrection, which can lead to hypoglycemia
- failure to obtain a patient’s weight on admission
- failure to maintain BG monitoring throughout hospitalization
- reluctance to take on the extra work of calculating SF and the correctional dose
- need for more frequent insulin calculations, which can increase the potential for mathematical error
- increased time required to prepare insulin injections and obtain secondary dosage verification by another nurse
- lack of understanding of weight-based insulin administration and the implications of hyperglycemia.
To overcome these barriers, the entire healthcare team—administrators, physicians, nurses, pharmacists, and dietitians—need to be educated. Showing evidence of the benefits of WBCI (decreased length of stay, improved patient outcomes, and fewer hypoglycemia episodes) is crucial in convincing the healthcare team to ditch SSI.
Finding administrators, physicians, pharmacists, dietitians, and nurses to champion the change can help overcome resistance. Developing appropriate policy and designing preprinted order sets to ease implementation and provide calculation guidelines also support change efforts. If electronic medical records are in use, the information technology department can help by including weight-based calculations in the documentation program. Continuing education for pharmacy, nursing, and other providers promotes implementation, maintenance, and compliance with new WBCI orders.
Implications for practice
WBCI principles aren’t difficult to grasp, but creating practice change can be challenging. The more long-standing and familiar a tradition, the harder it falls. Like many other bedside care traditions, SSI is based on belief, not scientific evidence. With a solid foundation of scientific evidence to back them, nurses can take this information to professional practice committees to help effect change. By making an effort to continually educate themselves and colleagues about inpatient glycemic control, we can continue another time-honored tradition—one well worth upholding: Always making the patient the focus of everything we do.
Selected references
Clement S, Braithwaite SS, Magee MF, et al. Management of diabetes and hyperglycemia in hospitals. Diabetes Care. 2004;27(2):553-591. doi:10.2337/diacare.27.2.
Hirsch IB, Farkas-Hirsch R. Sliding scale or sliding scare: it’s all sliding nonsense. Diabetes Spectrum. 2001;14(2):79-81. doi:10.2337/diaspect.14.2.79.
Moghissi ES, Korytkowski MT, DiNardo M, et al. American Association of Clinical Endocrinologists and American Diabetes Association Consensus Statement on Inpatient Glycemic Control. Endocr Pract. 2009;15(4):353-369. www.aace.com/pub/pdf/guidelines/InpatientGlycemicControlConsensusStatement.pdf. Accessed March 21, 2011.
Summary of Revisions for the 2010 Clinical Practice Recommendations. Diabetes Care. 2010;33(suppl 1):S3. doi:10.2337/dc10-S003. www.ncbi.nlm.nih.gov/pmc/articles/PMC2797388. Accessed March 21, 2011.
Thompson D, Cundiff H. Weight-based insulin correction: moving away from the sliding scale. Poster session presented at the Annual Meeting of the American Association of Diabetes Educators, Atlanta, Georgia. August 2009.
Umpierrez GE, Smiley D, Zisman A, et al. Randomized study of basal-bolus insulin therapy in the inpatient management of patients with type 2 diabetes (RABBIT 2 trial). Diabetes Care. 2007;30(9):2181-2186. doi:10.2337/dc07-0295.
Joanne DeYoung is an instructor in adult nursing at Rasmussen College School of Nursing in Ocala, Florida. Renee Bauer is an instructor at Indiana State University in Terre Haute. Cynthia Brady is a nursing coordinator/educator in perinatal rapid testing implementation in Illinois and an adjunct professor at Marian University in Indianapolis, Indiana. Susan Eley is an associate professor of nursing at Indiana State University in Terre Haute.
