Perioperative management of blood glucose

Published on 07/02/2015 by admin

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Last modified 22/04/2025

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Perioperative management of blood glucose

Aaron M. Joffe, DO and Douglas B. Coursin, MD

Critical illness, anesthesia, and the metabolic stress of surgery result in neurohormone and metabolic dysregulation, leading to elevated rates of perioperative hyperglycemia. Although perioperative hyperglycemia was once believed to be a normal adaptive response supplying more substrate to stressed organs, it is now clear that outcomes are worse in patients who have hyperglycemia. Unfortunately, a dearth of direct evidence is available to guide anesthesia providers within the operating room as to what is an acceptable blood glucose level and how to achieve that level; most of the current recommendations are based on data extrapolated from studies of patients admitted to general medical or surgical wards or the intensive care unit.

The avoidance of hyperglycemia, hypoglycemia, loss of electrolytes, and loss of free water and the prevention of ketogenesis are the main goals of perioperative glycemic control. To accomplish these goals, consideration should be paid to the type of diabetes mellitus (DM) the patient has, the antecedent pharmacologic therapy of the DM, the degree of metabolic control prior to surgery, and the type and duration of the operation the patient is to undergo. A summary of this approach is presented in Table 226-1.

Table 226-1

Perioperative Management of Patients with Diabetes Mellitus

Surgical Scenario Fasting BGC Treatment
Minor operation, patient has type 2 DM, NOT treated with insulin All patients Hold oral agents day of operation.
<180 mg/dL* Cover with regular or rapid-acting insulin (lispro, aspart, glulisine) as needed.
>180 mg/dL† Plan to initiate a continuous insulin infusion.
All patients Target BGC 80-180 mg/dL.
Minor operation, patient has type 1 or type 2 DM, treated with insulin <180 mg/dL* Give ½ of intermediate-acting insulin dose morning of operation.
  Consider adding 5% dextrose-containing solution to IV infusion with or without potassium, depending on starting lab values and time of NPO.
  Check serial BGC q4-6 h while patient is NPO and supplement with short-acting insulin.
  Those taking basal insulin, by injection or continuous pump, should receive their usual basal dose or infusion rate.
  Restart preadmission insulin therapy once oral intake tolerated.
180 mg/dL† Start continuous insulin infusion and check BGC q1-2 h.
Major operation, patient has type 1 or type 2 DM treated with insulin All patients Hold oral agents day of surgery.
  Start continuous insulin infusion in OR and continue postoperatively.
  Target BGC of 150 mg/dL; avoid hypoglycemia (<80 mg/dL).

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BGC, Blood glucose concentration; DM, diabetes mellitus; NPO, nothing by mouth (nil per os); OR, operating room.

*Fair control.

†Poor control.

Adapted with permission from Smiley DD, Umpierrez GE. Perioperative glucose control in the diabetic or nondiabetic patient. South Med J. 2006;99:580-589.

Preoperative management of glycemic control

All oral agents should be held the day of surgery, and a preoperative blood glucose level obtained. In a stable nonhypotensive patient undergoing an elective procedure, a fingerstick point-of-care (POC) measurement will suffice (see later discussion under “Blood Glucose Measurement”). Patients whose DM is well controlled with diet and exercise alone do not require any special preoperative glucose intervention. Patients with type 2 DM not routinely treated with insulin, who exhibit fair chronic glycemic control (preoperative fasting glucose concentration 130-180 mg/dL) and who are undergoing minor operations, may not require insulin or can be given a small dose of rapid-acting insulin in the holding area. In patients with poorer glycemic control (preoperative fasting glucose concentration > 180 mg/dL), consideration should be given to providing a larger dose of rapid-acting insulin, particularly if the operation is expected to be short in duration. However, for longer operations and for those patients who will be admitted to the hospital for postoperative care, a continuous insulin infusion is recommended. Patients with type 1 and type 2 DM treated chronically with insulin who undergo minor operations and exhibit fair glycemic control may be given half of their intermediate-acting insulin the morning of surgery and may be supplemented with short-acting insulin if, for whatever reason, the preoperative holding time is extended and, thus, the patient is receiving nothing by mouth for longer than 4 to 6 h and a repeat glucose determination continues to indicate only fair glycemic control. Patients receiving insulin glargine should be given their usual basal dose, and those with a continuous insulin pump should be continued on their usual basal rate. Continuous insulin infusion is recommended when glycemic control is poor. All insulin-requiring patients with DM undergoing major operations should be started on a continuous insulin infusion, as needed, after induction of anesthesia. Serial blood glucose levels should be monitored along with serum potassium, which may require supplementation.

Intraoperative management of glycemic control

Current recommendations are based largely upon the understanding of physiologic derangements related to hyperglycemia and outcome studies in cardiac surgical and critically ill patients. The issue of what to do for many surgical patients undergoing noncardiac operations is further confounded by the wide range of targeted blood glucose concentrations among available studies (125-200 mg/dL, 100-150 mg/dL, 125-175 mg/dL, 150-200 mg/dL, <180 mg/dL, and 80-110 mg/dL), their control ranges (<250 mg/dL, ≤180 mg/dL, or <200 mg/dL), the population studied, and the constituents of the infusion itself. Some studies have employed a glucose-potassium-insulin mixture rather than insulin alone. To date, the results of only two prospective randomized trials of intraoperative glycemic control, both in patients undergoing cardiac operations, are available. One showed a decrease in the length of stay and the rate of postoperative arrhythmia, wound infections, and mortality rate at 2 years, whereas the other found no difference in a composite endpoint of death, sternal infections, prolonged mechanical ventilation, arrhythmia, stroke, and renal failure at 30 days. Data on intraoperative glucose control in noncardiac surgical patients are lacking. The result of this discordant information is a general recommendation to initiate insulin therapy when the plasma glucose concentration exceeds 180 mg/dL and to target a goal of approximately 150 mg/dL. Consensus is that such a target should minimize the potential for hypoglycemic episodes, which would be otherwise silent and potentially catastrophic in anesthetized patients. The reader should note that variation exists among guidelines from various organizations and such guidance may change in the future.

Postoperative management of glycemic control

A recent consensus statement of the American Association of Clinical Endocrinologists and the American Diabetes Association recommends a premeal blood glucose concentration of less than 140 mg/dL and a random blood glucose concentration of less than 180 mg/dL for non–critically ill hospitalized patients. They further recommend that these targets be achieved and maintained with the use of scheduled subcutaneously administered insulin with basal, nutrition, and correction components. The use of “sliding-scale” insulin dosing as the sole insulin preparation or the administration of oral hypoglycemic agents is strongly discouraged. Although not identical, these recommendations are comparable with those published in 2007 by the American College of Endocrinology and in 2008 by the Canadian Diabetes Association and seem to be a justifiable goal in the postoperative period. Currently, there is no single universally accepted target for blood glucose control for all critically ill patients. Investigators who studied the morbidity and mortality benefits derived from intensive glucose control (80-110 mg/dL) in a predominantly postcardiac surgical population were unable to reproduce the results in an exclusively medical population. Subsequently, the Efficacy of Volume Substitution and Insulin Therapy in Severe Sepsis (VISEP) trial was suspended after the first safety analysis because of an increased number of severe hypoglycemic episodes (<40 mg/dL) in the intensive glucose-control group versus conventional insulin therapy. Most recently, the Normoglycemia in Intensive Care Evaluation and Survival Using Glucose Algorithm Regulation (NICE-SUGAR) Trial reported a significantly increased mortality rate in adult patients in the intensive care unit who were treated with intensive glucose control (81-108 mg/dL), compared with a control group treated to maintain blood glucose concentration less than 180 mg/dL. Based upon these data and others not specifically discussed here, maintenance of blood glucose concentration in critically ill adults at less than 150 mg/dL, as advocated by the Surviving Sepsis Campaign guidelines, is a reasonable target. The mechanism of hyperglycemia should also be taken into account when considering treatment and goals of therapy. Patients without known DM who exhibit stress-induced hyperglycemia appear to benefit more from stricter glucose targets than do those patients with preexisting DM. Although no prospective studies have specifically examined the impact of intensive insulin therapy (IIT) on patients with DM versus hyperglycemic patients without known DM, subgroup analyses of critical care data suggest it may be reasonable to initiate insulin therapy earlier, say, at a level of 150 mg/dL, rather than at 180 mg/dL, and to target a level between 110 and 140 mg/dL in these acutely ill hospitalized patients.

Blood glucose measurement

It is not commonly appreciated that blood glucose measurements are not direct determinations of blood glucose concentrations. Rather, all glucose measurement devices in current clinical use, whether a central laboratory or POC device, utilize an indirect enzyme technique. Glucose oxidase, glucose 1-dehydrogenase, and hexokinase are the three enzyme systems most commonly employed. Of these, the hexokinase reaction is used most commonly in central laboratories and is considered to be the gold standard. Further, POC devices measure whole blood, not plasma, and are calibrated to then report plasma values, in contrast with central laboratory devices, which directly report plasma glucose concentrations. This is important because the glucose concentration in plasma is approximately 11% higher than in whole blood and the physiologic activity of glucose corresponds more closely with plasma concentration. Therefore, it is not surprising that a variety of factors—including sampling site, peripheral vasoconstriction, anemia, high or low PaO2, interference from other sugars or medications, electrolyte abnormalities, hyperbilirubinemia, and hyperuricemia—can all affect POC glucose determinations. Underscoring this fact, POC measurements utilizing glucose testing strips, whether from capillary blood or arterial blood, disagree 15% of the time. It is important to note that discordance is defined by a deviation of greater than 20%. Furthermore, agreement between methods becomes worse in the presence of hypoglycemia, with the tendency for overestimation to occur. Despite their widespread clinical use among hospital wards, the intensive care unit, and the operating room, POC devices have never received U.S. Food and Drug Administration approval for such use. In these settings, the use of venous blood samples is recommended.

Treatment protocols

A variety of IIT protocols have been used to achieve glycemic control with varying degrees of success. Whether automated, based upon a computer-generated algorithm, or paper-based utilizing simple bedside calculations, the goal is to obtain blood glucose values within the specified target range for the most time possible without causing significant hypoglycemia. The majority of these IIT protocols were developed for and tested in acutely ill hospitalized patients and were nurse driven; staffing was plentiful. An implementation study performed at the University of California at San Francisco reported that each glucose determination required an average of 7 min of nursing time and that, considering the usual nursing-to-patient ratio of 1:2, if both patients had been on an IIT protocol, nearly 17% of a 12-h shift would have been spent solely on obtaining samples, performing tests, and following the IIT protocol. Inasmuch as the anesthesia provider is often caring for a patient in the operating room alone, with many tasks to perform, it is not surprising that a study of intraoperative IIT in patients without diabetes who were undergoing cardiac operations was terminated early due to “unobtainable” glucose goals. The reader should be aware that the Surgical Care Improvement Project, a joint effort between the Joint Commission and Centers for Medicare and Medicaid Services, which ultimately determines the perceived quality of care of a particular institution, requires that patients who have had cardiac operations have a morning blood glucose concentration less than 200 mg/dL on postoperative days 1 and 2—regardless of the impact of achieving that goal on patient care. Although, the benchmark of 200 mg/dL is entirely arbitrary and not based on current evidence, it is being used to define, along with other predetermined quality benchmarks, “top-performing” hospitals and reimbursement levels.

Summary

The stress of surgery, anesthesia, and critical illness often results in patients developing hyperglycemia in the perioperative period. Anesthesia providers should consider patient factors (type, duration, and control of diabetes) as well as surgical factors (duration, degree of insult, and pathophysiologic derangement) when choosing perioperative glycemic control management strategies. Despite the acknowledgment that hyperglycemia is deleterious, there is no universally agreed upon blood glucose level for which insulin therapy should be initiated, nor is a single glucose concentration target suitable for all patients. Further, hypoglycemia is a real possibility in perioperative patients even when some higher-risk patients (sepsis, renal failure, those on continuous venovenous hemofiltration or receiving inotropic agents) are not receiving insulin. Individuals may have limited signs or symptoms of significant hypoglycemia, which may be unrecognized if POC devices are routinely used to measure blood glucose, and may have increased morbidity and mortality risks.

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