Glucose Control in the Hospitalized Patient

Emerg Med 36(9):12-18, 2004

The authors discuss managing the diabetic surgical patient, how to identify patients at risk for a diabetic episode, why insulin is superior to oral drugs in the hospital setting, and key issues of dosage, administration, and monitoring.

By Jeff Unger, MD, and Alan O. Marcus, MD

More than $120 billion is spent annually in the United States managing patients admitted to hospitals with significant hyperglycemia. In 2000, the diagnosis of diabetes accounted for 12% of hospital discharges, and the average length of stay of those admissions was 5.4 days. It has been estimated that discharge diagnosis codes may underestimate the true prevalence of diabetes in hospitalized patients by as much as 40%. As many as 1.5 million patients are hospitalized with significant hyperglycemia and no history of diabetes. Several studies have suggested that an early and aggressive approach to management of hyperglycemia can significantly reduce mortality, morbidity, prolonged hospital stays, and medical costs.
 

DANGER OF SLIDING-SCALE INSULIN

Consider, for example, a patient with type 2 diabetes who presents to the emergency department with chest pain and elevated cardiac enzymes. After being admitted to the cardiac care unit, his routine outpatient diabetes regimen is stopped and he is started on sliding-scale subcutaneous regular insulin, which is monitored by a nurse and administered based on blood glucose levels obtained every six hours. However, this patient's glucose levels actually increase significantly as does the size of what turns out to be a myocardial infarction (MI).

Concerns about precipitating hypoglycemia may limit a more aggressive insulin replacement approach that could improve survival rates in patients like this by more than 50%. Sliding-scale insulin coverage often results in a deterioration rather than an improvement in glycemic control. Hyperglycemia, regardless of whether or not a previous diagnosis of diabetes has been made, may pose an even greater risk than hypoglycemia by reducing hospital survival rates among patients admitted with stroke and MI.

The Diabetes Insulin-Glucose in Acute Myocardial Infarction (DIGAMI) trial demonstrated a 30% reduction in mortality one year after admission when an intensive insulin regimen was administered to hyperglycemic patients hospitalized with acute MI. Enrollment in the DIGAMI study included patients with glucose values above 198 mg/dl without regard to prior diabetes status. In fact, 15% of this study population did have a history of glucose intolerance.

A retrospective epidemiologic study by Umpierrez and colleagues reviewed 2030 consecutive adult hospitalized patients and found hyperglycemia present in 38% of them. And of these patients with hyperglycemia, 26% had a known history of diabetes and 12% had no history of diabetes prior to admission. Hyperglycemia was defined as an admission or in-hospital fasting glucose level of 126 mg/dl or a random blood glucose level of 200 mg/dl on two or more measurements.

Weir found that a plasma glucose level above 144 mg/dl within 24 hours of hospital admission was a risk factor that doubled stroke mortality independent of age and stroke type. Other studies have suggested that admission glucose levels or A₁C values, or both, correlate to stroke size, clinical severity, and prognosis. The worse the hyperglycemia on admission, the higher the risk of stroke severity and mortality.
 

USE OF INSULIN BEFORE SURGERY

The use of intravenous (IV) insulin before coronary artery bypass graft surgery has been shown to reduce perioperative complications such as deep wound infections, prolonged hospitalizations, stroke, renal failure, intraoperative balloon pump time, and postoperative deaths. Marcus optimized glucose and metabolic control in cardiac patients by using IV insulin with glucose levels above 120 mg/dl and reduced perioperative complications by 57%.

Pomposelli and colleagues found that for diabetic patients on postoperative day one a blood glucose level above 220 mg/dl was a sensitive predictor of nosocomial infections, increasing the risk of sepsis 2.7 times more than for patients with lower blood glucose levels. Van den Berge evaluated 1548 patients in a surgical intensive care unit who were receiving mechanical ventilation. Patients were randomized on admission to receive IV insulin therapy with a target blood glucose level between 80 and 110 mg/dl or conventional insulin therapy with a target level between 180 and 200 mg/dl. The intensively managed group had nearly a 50% reduction in mortality during their stay in the unit. The most significant benefit of intensive insulin therapy was seen in the mortality rates among patients who remained in the unit for more than five days (20.2% with conventional treatment, compared with 10.6% with intensive therapy).

The intensively managed patients had a 46% lower incidence of sepsis from multiple organ failure, a 34% reduction in overall in-hospital mortality, and a lower rate of renal failure resulting in a 41% reduction in the need for dialysis. Therefore, intensive insulin replacement therapy can significantly reduce morbidity, mortality and costs associated with glucose toxicity in hospitalized patients (see table below).
 

DIAGNOSING DIABETES IN THE HOSPITAL

Patients admitted to the hospital should be questioned to see if they have a history of diabetes or glucose intolerance. Those at risk for diabetes include patients who are obese, have hypertension or a first-degree relative with diabetes, and patients who come from high-risk populations such as Native Americans, Pacific Islanders, Hispanics, and African Americans. These patients should receive a two-hour postprandial glucose challenge even if their fasting blood glucose level is below 100 mg/dl.

Approximately 25% of patients with abnormal glucose tolerance during a hospitalization, characterized by glucose levels between 140 and 199 mg/dl, will develop diabetes within three months of discharge. An A1C of 6% or higher in patients with a random blood glucose of 126 mg/dl or higher and no history of diabetes may be predictive of diabetes in the hospital setting.

Besides reducing hyperglycemia, insulin has other beneficial actions that are important for managing critically ill patients. Insulin inhibits lipolysis, the breakdown of fat. Elevated free fatty acids have been associated with poor outcomes, particularly cardiac arrhythmias. Insulin also inhibits inflammatory growth factors (activator protein 1 and early growth response gene-1), which are especially important in extending acute MIs. In addition, insulin stimulates endothelial nitric oxide synthase, which subsequently results in arterial dilation and a reduction in arterial inflammation. Finally, insulin inhibits proinflammatory cytokines and adhesion molecules. One or more of these mechanisms may be responsible for the improved outcomes reported with insulin-treated hyperglycemia.
 

TARGET BLOOD GLUCOSE RANGES

The table below lists the recommended target ranges for plasma glucose levels for hospitalized patients. Blood glucose levels above 180 mg/dl are an indication to monitor levels more frequently to determine the direction of any glycemic trend and the need for more intensive intervention.
 

Although many patients with type 2 diabetes use sulfonylureas as part of their standard outpatient diabetes regimen, continued use of these oral agents in the hospital setting is generally not indicated. Their long duration of action may result in hypoglycemia, especially in patients who are not consuming their normal levels of nutrients. In addition, sulfonylureas do not allow for rapid dose adjustments to meet changing inpatient metabolic needs.

Metformin has many limitations as well. The most common contraindications for metformin use relate to the potentially fatal complication of lactic acidosis. Risk factors for lactic acidosis in metformin-treated patients include heart failure, renal failure, sepsis, and chronic obstructive pulmonary disease. Up to 50% of all hospitalized patients have at least one of these diagnoses on their discharge summaries. Metformin is continued in many of these patients despite the fact that they have at least one absolute contraindication.

Metformin's side effects include diarrhea, nausea, and decreased appetite, which can impair recovery during an acute illness. In addition, metformin must be held for 24 hours prior to the administration of IV contrast material for procedures such as computed tomography, heart catheterization, and IV pyelograms. Many of these procedures are performed on an emergent basis after an acute hospitalization, and physicians may not have the luxury of stopping metformin abruptly with some patients.

Thiazolidinediones (TZDs) have few adverse effects but can increase intravascular volume, which can be problematic in patients with heart failure and left ventricular dysfunction. In addition, TZDs take several weeks to improve hyperglycemia, so starting one of these drugs in the hospital is not effective for this purpose.

Thus, oral agents have significant limitations for inpatient use and provide little flexibility for titration in a setting where acute changes are so vital to patient management. The drug that is best suited to management of hyperglycemia in the hospitalized patient is insulin.
 

COMPONENTS OF INSULIN THERAPY

In the hospital setting, insulin therapy should have three components: basal, prandial, and correction doses. Basal insulin refers to the amount of the drug needed to maintain euglycemia while the patient remains in the fasting state. The liver, through gluconeogenesis, produces large amounts of glucose that raise fasting blood glucose levels. In addition, low levels of circulating endogenous insulin will result in ketogenesis, the release of free fatty acids, and diabetic ketoacidosis.

Approximately 50% of an individual's total daily dose of insulin is provided as basal insulin. Basal insulin requirements may increase with acute illness because counter-regulatory hormone levels rise in response to physiologic stress and with the use of corticosteroid medications.

Prandial insulin, also known as nutritional insulin, is given to patients based on their intake of carbohydrates. It will also need to cover IV dextrose infusions, total parenteral nutrition, enteral feedings, nutritional supplements, and scheduled meals. About 50% of an individual's total daily dose of insulin is provided in the form of prandial insulin.

A patient's total daily dose of insulin is approximately 0.7 u/kg per day. Thus, a 70-kg person would require about 50 units of insulin in 24 hours, 25 units provided as basal insulin and 25 units as a bolus dose. The insulin sensitivity or correction factor can be calculated by dividing 1500 by the total daily dose of insulin. So, if a patient requires an estimated 50 units of insulin in 24 hours, one unit will lower the blood glucose level 30 mg/dl. This allows correction of hyperglycemia to a predetermined target level.

For example, if the patient's postprandial blood glucose level is 300 mg/dl and the target level is 150 mg/dl, administering a correction dose of five units of an analog insulin such as lispro or aspart should lower the blood glucose level close to the target level within two to three hours. The table lists suggestions for dosing subcutaneous insulin in nonacute hospitalized patients with diabetes.
 

CORRECTION-DOSE INSULIN THERAPY

The term "correction-dose insulin therapy" refers to insulin used to treat hyperglycemia that occurs before meals or postprandially. It can also be used to correct elevated blood glucose levels in patients who are NPO and receiving basal insulin. Correction-dose insulin therapy is not a sliding-scale form of insulin replacement, which is given to patients regardless of their prior nutritional or food intake status. Sliding-scale insulin regimens are often written at the time of admission and are used throughout the patient's hospital stay without modification. This is a reactive approach to diabetes management that will result in wide glycemic fluctuations with periods of hyperglycemia and hypoglycemia. Correction-dose insulin therapy should be evaluated daily. If correction doses are frequently needed, the scheduled insulin doses should be increased.

We prefer using insulin analogs rather than traditional insulin (NPH and regular) in the hospital setting. NPH insulin has been shown to have a significant 52% day-to-day variation in absorption, which make glycemic predictability extremely difficult. The absorption of insulin glargine is much more predictable and has a flat peak, making it much easier to work with in patients with type 1 diabetes.

The absorption of regular insulin is also dependent on the dose given at any one time. Smaller doses are more rapidly absorbed, whereas larger doses (more than 10 units) may be absorbed more slowly and actually display pharmacokinetic principles that resemble those of NPH. Insulin analogs (such as lispro/aspart) are rapidly absorbed and have a duration of action of up to five hours that is independent of the dose injected when used subcutaneously. Therefore, the insulin analogs are preferred both in the hospital and the outpatient setting. Regular insulin is still used for IV insulin infusion therapy.
 

INTRAVENOUS INSULIN INFUSIONS

The table below lists the indications for using IV insulin infusions in nonpregnant adults with hyperglycemia. Because the half-life of IV insulin is only seven minutes, hypoglycemia, when it occurs, is very short-lived. However, hypoglycemia that is induced by subcutaneous insulin "stacking" (repeat insulin injections that are given before the previously injected insulin has been fully absorbed) can be prolonged and problematic in the hospital, especially when blood glucose levels are not being frequently monitored by nurses. With IV insulin infusions, the glycemic threshold for the initiation and titration of dosing, as well as for the correction of hyperglycemia out of the target range, can be determined in advance. Management of hypoglycemia using infusions of dextrose solutions and lower doses of IV insulin may also be part of a standard protocol.
 

Insulin infusions are initiated by mixing regular insulin in a solution of 1 unit per 1 ml of normal saline (100 units regular insulin in 100 ml normal saline). The insulin drip is then piggybacked into a dedicated running IV line. Most patients require 1 unit per hour, but higher infusion rates may be necessary to maintain euglycemia. The maximum glycemic-lowering effect of insulin drips is probably 10 units per hour.

Patients receiving insulin drips should have hourly blood glucose determinations until their glucose stability has been maintained for six hours. At that time, testing can be done every two to three hours. For patients who are being switched to subcutaneous insulin, the insulin drip should be discontinued three hours after the initial subcutaneous dose.

Providing care for patients with diabetes requires a team approach. Adjustment in hospital protocols may be required to meet the unique needs of diabetes patients. Meal trays must be delivered on a timely basis. Bedside glucose testing and administration of diabetes medications must be carried out by a nursing staff that has been educated to provide these services and understands the pharmacokinetics of insulin replacement therapy. Diabetes educators and discharge planners must teach basic diabetes-related survival skills to all patients admitted with hyperglycemia. Follow-up appointments should also be made to assess improvement in hyperglycemia and other metabolic parameters after the patient is discharged.
 

USING INSULIN PUMPS

Over 230,000 Americans are using continuous subcutaneous insulin infusion, also referred to as insulin pump therapy, to manage their diabetes. Pumps can be useful in treating both type 1 and type 2 diabetes. The vast majority of patients who use insulin pumps are very adept at managing their diabetes, but like anyone else, these patients may require a scheduled or acute hospitalization. Unless the nurses and physicians are familiar with insulin pumps and trust the patient to manage his own insulin needs, the tendency in most hospital units is to ask the patient to remove the pump and allow the staff to deal with the diabetes in a more traditional way. This can lead to mistrust between the patient and the staff. In addition, wide glycemic variations are bound to occur unless insulin pump therapy is allowed to continue under the direct supervision of the medical team.

There are no published guidelines for managing insulin pump patients in the hospital setting. For patients in the intensive care unit, IV insulin infusions should be used instead of pump therapy. However, in other units, when patients are eating routinely, are alert, and are able to monitor their own blood glucose levels, continuing pump therapy is reasonable. Patients may have to check their blood glucose levels every four or five hours and add correction-dose or supplemental insulin to maintain glucose levels in the 70 to 100 mg/dl range between 7 a.m. and midnight. From midnight to 7 a.m., glucose levels should be maintained between 100 and 150 mg/dl to avoid hypoglycemia. This may require the patient to program a separate basal rate into the pump, which will slow the flow of insulin overnight. In addition, the patient may have to make adjustments for reduced activity while in the hospital and an even lower intake of carbohydrates during meal times.

Patients on insulin pump therapy should always be reminded to change their infusion sets every 72 hours to avoid infections at the delivery site. While the patient is in the hospital, a dietitian can reinforce the concept of carbohydrate counting and the proper use of correction-dose insulin. Newer pumps have a "bolus wizard" that can help patients with insulin dosing based on their blood glucose level, amount of carbohydrates consumed, insulin-to-carbohydrate ratio, and supplemental insulin correction factors.
 

AGGRESSIVE MANAGEMENT

Hospitalized patients should be screened for hyperglycemia. Those who have any degree of impaired glucose intolerance should be aggressively managed during their admission with insulin replacement therapy. Such aggressive management can reduce morbidity and mortality and decrease the length of hospital stays in this high-risk population.

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