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
