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Twilight of the Sliding Scale


 

An explosion of interest in managing hyperglycemia in the hospital has resulted from recent evidence that glycemic control can reduce mortality and other morbidities. Programs of intensification using historical controls for comparison and clinical trials demonstrating the ability of glycemic control to improve outcomes have mandated specific blood glucose thresholds for initiating intensive therapy in the ICU.1-12 These studies have convinced the world that in the ICU intravenous insulin infusion should supplant sliding scale.

A large body of observational data point to the likelihood that the benefits of glycemic control might extend to the general hospital ward.13,14 Although intravenous infusion of insulin might be more widely used in the future than it is now, the standard practice at most hospitals is to address glycemic control on general wards through the use of subcutaneous insulin.15,16

Two recent publications from Rush University Medical Center in Chicago and from St. Joseph’s/Candler Health System in Savannah, Ga., added weight to older literature and to a large body of long-held expert opinion that the anticipatory use of subcutaneous insulin in the hospital outperforms sliding scale.

Sliding Scale and Its Flaws

Throughout a half century of PubMed indexing, the medical literature has referred to sliding scale insulin.17 In its simplest form at a given blood glucose level, sliding scale delivers the same number of units of subcutaneous regular insulin to every patient. For example, it might require:

150-199 + 2

200-249 + 4

250-299 + 6

300-349 + 8

350-399 +10

400 and up Call physician

Protocols attempting to improve upon the scale offer differing amounts of insulin at several assumed degrees of insulin sensitivity.18,19 However, these protocols still retain a reactive approach to glycemic management such that hyperglycemia will recur given the absence of adequate basal and nutritional insulin coverage. Under sliding scale the risk of ketoacidosis in type-1 diabetes is not addressed. Overcompensation for hyperglycemia results in hypoglycemia for some patients. By writing sliding scale orders physicians may create the appearance of having designed a detailed and attentive care plan, while in reality they neglect to individualize care to meet the patient’s needs.20

Discussions about sliding scale and correction dose insulin are frequently misinterpreted because of differences in use of terminology. Practitioners who disagree with use of sliding scale monotherapy nevertheless recommend using correction doses or supplements of insulin for patients already receiving anticipatory insulin.21 Some practitioners may refer to correction doses used in addition to anticipatory insulin as sliding scale insulin.22,23 Patients themselves sometimes use the term sliding scale.

A patient may, for example, use glargine and aspart and, when asked how she determines the dose of aspart, she may say she uses “sliding scale.” What she means, though, may be one of several possible management styles. She may mean that she uses aspart only for correction of hyperglycemia. She may mean that she has a table with two columns, showing paired blood glucose ranges and premeal aspart doses, such that the prandial and correction components of the aspart doses are bundled. She may mean that she practices advanced carbohydrate counting, utilizes an insulin-to-carbohydrate ratio to determine aspart coverage for the meal, and additionally calculates a premeal correction dose of aspart for hyperglycemia (i.e., she may practice basal-prandial-correction therapy).24-26

For purposes of this discussion, by “sliding scale” insulin, I mean monotherapy with sliding scale without concomitant anticipatory use of insulin (scheduled, routine, standing, or programmed insulin) or sliding scale with its faults, as described by Saul Genuth, MD.27

Why has use of the sliding scale persisted in practice? Is it for fear of hypoglycemia? Is it for lack of evidence on the importance of glycemic control? Is it because physicians do not know how to write insulin orders? Or is it all in a name?

Evidence Against Sliding Scale

Relying on sliding scale insulin sometimes causes hypoglycemic events, severe hyperglycemic events, patient relapse after treatment of ketoacidosis, and the in-house development of diabetic ketoacidosis. In the study by Kathleen and colleagues, using sliding scale doses too high for patients with renal insufficiency was identified as the cause of six episodes of hypoglycemia.28

In the quality improvement project by Roman and colleagues, the use of quality indicators of a) BG < 40 mg/dL, b) BG > 450 mg/dL on two occasions, or c) BG > 45 with acetone, revealed that five cases were caused by physician failure to respond appropriately to hyperglycemia, despite administration of large amounts of additional regular insulin as coverage for capillary blood glucose (one of which resulted in the in-house development of ketoacidosis).29

In a retrospective review of management following ketoacidosis Gearhart and colleagues showed a higher median glucose among the patients treated with sliding scale than those treated proactively with insulin (prospective or anticipatory insulin), or treated with a combination of proactive insulin and “sliding scale” (correction dose insulin).30 Queale and colleagues showed that the use of either a standing dose of insulin or an oral hypoglycemic agent was associated with a reduced risk of hyperglycemic episodes, whereas sliding scale insulin regimens (when used without a standing dose of intermediate-acting insulin) were associated with an increased rate of hyperglycemic episodes.31

Baldwin and colleagues at Rush University Medical Center in Chicago recently reported the superiority of glycemic control among 88 patients for whom sliding scale was not allowed, in comparison with 98 well-matched controls from a historical comparison period.32 In the study group, standing orders for insulin were not permitted. House staff reviewed the results of glucose monitoring performed four times daily, and they twice daily reordered anticipatory insulin if appropriate. Glargine and rapid-acting analog were continued only for those patients already using such therapy prior to admission. Premixed insulins were not used. Oral agents were not used in combination with insulin and sometimes were discontinued for medical reasons.

In the control group, the percentages of patients with specific orders were: 100% sliding scale as defined by the authors, 32% twice-daily dosing with NPH/regular insulin, 37% orals agents, and 15% combination oral agents with NPH/regular insulin. In the study group, the percentages were: 0% sliding scale, 68% twice-daily NPH/regular insulin, 30% orals, and 0% combination NPH/regular with oral agents. For the study patients versus the historical controls, the mean blood glucose was 150 ± 37 mg/dL mg/dL versus 200 ± 51 mg/dL (p<0.01). The frequency of hypoglycemia between the two groups did not differ.

Schoeffler and colleagues in the St. Joseph’s/Candler Health System in Savannah, Ga., recently conducted a randomized study of 20 patients that reported the use of a 70/30 dose titration algorithm is superior to sliding scale insulin in achieving glycemic control.33 Patients were identified for possible enrollment through discovery of orders for sliding scale insulin in the pharmacy. After exclusion of patients receiving tube feeds or TPN and patients having type-1 diabetes, those consenting to be randomized either received the sliding scale as written by their physician or titration of 70/30 insulin given twice daily under algorithm. Hypoglycemia did not occur in either group. Downward trend over time and lower mean blood glucose (151.3 versus 175.6 mg/dL, p = 0.042) were observed in the 70/30 insulin group.

Glycemic Management Plan for Subcutaneous Insulin

  • Point of care testing of capillary blood glucose;
  • Call parameters;
  • Consistent carbohydrate diet (for patients who are eating);
  • A1C;
  • Dextrose 50% in water prn hypoglycemia (per protocol);
  • Glucagon prn hypoglycemia (per protocol);
  • Peakless long-acting or intermediate-acting insulin (scheduled, routine, standing, or programmed);
  • Short-acting or rapid-acting insulin (scheduled, routine, standing, or programmed);
  • Correction-dose short-acting or rapid-acting insulin (prn levels of hyperglycemia);
  • Cancellation of conflicting orders;
  • Education of patient; and
  • Consultations (nutrition, endocrinology).

Special Pathways

  • Intravenous insulin infusion; and
  • Diabetes hospital patient self-management.

Anticipatory Use of Insulin in the Hospital

The components of anticipatory subcutaneous insulin order-writing have been described according to preference of several authors (having basal, nutritional, and correction components). But in the hospital no style has been validated as superior to any other.34-37 The anticipatory delivery of nutritional insulin must match the expected pattern of exposure to carbohydrate. Specific standing orders should include additional nursing directions such as “do not withhold” or “hold if NPO.” For abrupt discontinuation of carbohydrate exposure, change of organ function, or decline of insulin resistance, protections must be in place to guard against hypoglycemia.38

An essential aspect of management is the frequent review of orders for subcutaneous insulin and patient response. At least once every day, the caregiver must reconsider “today’s insulin dose.”

How to Get Rid of Sliding Scale

Computerized order entry for managing hyperglycemia now is widespread among hospitals. Under a misdirected allocation of resources, motivated by concern for quality and safety, institutions have embraced the programming of order-entry options for standardized sliding scales. The sliding scale menu may provide a quick link to order entry for point-of-care blood capillary glucose monitoring, call parameters, and treatment of hypoglycemia. Nurses and doctors may come to believe that it is impossible even to order blood glucose monitoring without an accompanying sliding scale. Thus the sliding scale menu may possess all the accoutrements of glycemic management program except the one element most needed—a provision for anticipatory insulin.

One study by Achtmeyer and colleagues reduced utilization of a computerized sliding scale order by attaching a warning that the order was not approved by endocrinology.39 Emphasizing the importance of physician education to the successful abolition of sliding scale insulin, the study by Baldwin details an intensive house staff re-education program on how to write anticipatory insulin orders.32 The computerized order entry options used at Rush University Medical Center in Chicago (one of the two better performers in the recent benchmarking study of the University HealthSystem Consortium) were presented by Baldwin at the Aug. 19, 2005, “Glycemic Control Knowledge Transfer Meeting of the Consortium in Chicago.”

Why has use of the sliding scale persisted in practice? Is it for fear of hypoglycemia? Is it for lack of evidence on the importance of glycemic control? Even before computerization was sliding scale the path of least resistance? Is it because no clear superiority has been demonstrated among various styles of writing anticipatory insulin plans? Is it because physicians do not know how to write insulin orders? Or is it all in a name?

It just might seem that ordering sliding scale is the easy thing to call for or is the sophisticated thing to order. After all, sliding scale is an in-group term. A newly graduated physician is not likely to reject the suggestion of an experienced nurse that an order is needed for sliding scale.

For the next 50 years what is the call for, and what are the orders? Quite simply we have seen the twilight of the sliding scale—and “today’s insulin” dawning. TH

Dr. Braithwaite is clinical professor of medicine at the University of North Carolina, Diabetes Care Center, Durham.

References

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