As the role of the podiatric service becomes more integral to a multidisciplinary approach to diabetic limb salvage at an increasing number of institutions nationwide, many podiatric surgeons find themselves admitting these patients to their own service. The surgical and anesthesia teams often execute perioperative assessment and preparation, especially in non-elective procedures. This article serves as a primer in glucose management for podiatric surgeons working in this capacity and in no way supersedes the utility of a medical consult when indicated. Evaluation and assessment of other common comorbidities such as the cardiovascular and renal function are also equally important in the preoperative examination and determination of the overall optimization of a patient.
What The Research Reveals About Metabolic Changes Due To Surgery
Currently, there is no universal perioperative protocol for glycemic control. This is largely due to the variety of available treatment regimens and the degree of customization required to optimize the patient.1,2 Patients respond differently to insulin and other hypoglycemic medications based upon many confounding factors, such as the type of diabetes, level of insulin resistance, overall metabolism and the stresses placed upon the body among other factors. A complex metabolic process ensues in response to surgery and anesthesia. Briefly, insulin resistance develops from increased secretion of varying amounts of the counter-regulatory hormones glucagon, epinephrine, norepinephrine, cortisol and the growth hormone produced during times of stress. There is also an overall decreased amount of insulin secretion due to increased sympathetic response and general anesthesia. This insulin resistance causes further hepatic glucose production and decreased peripheral glucose utilization.3,4,5 Furthermore, the type of anesthesia used and extent of surgical intervention undertaken creates large variations in these counter-regulatory hormones, making glucose homeostasis difficult to predict and highly variable. This catabolic fasting state of gluconeogenesis, glycogenolysis, ketosis, proteolysis and even lipolysis places the diabetic patient at risk for developing severe hyperglycemia and even potentially ketoacidosis if he or she has type 1 diabetes.6
Emphasizing The Importance Of Tighter Glycemic Control
Even though glycemic control seems to be of obvious importance in the perioperative period, the saying “better sweet than sour” is still a frequent consensus. The reasons to maintain an inpatient’s blood glucose levels somewhat higher than normal in preparation for surgery are often multifactorial. However, recent literature has been rife with data regarding tighter control of glucose in the perioperative setting. Although the exact mechanism is not fully understood, researchers have shown in multiple publications that hyperglycemia, especially blood glucose levels greater than 200 mg/dL, increases the risk of developing postoperative infections.7,8 A recent article by Hruska, et. al., clearly showed that instituting a strict blood glucose level between 120 and 160 mg/dL immediately following open heart surgery resulted in a statistically significant decrease in postoperative infection rates in their diabetic patients. After patients maintained well controlled blood glucose levels through an insulin infusion, researchers found that the infection rate diminished from 73 percent to 25 percent in their diabetic population.9 Various researchers have also demonstrated that good glucose control minimizes perioperative morbidity and mortality. The classic prospective randomized study Diabetes Mellitus Glucose Infusion in Acute Myocardial Infarction (DIGAMI) showed the long-term benefit and reduction in mortality from myocardial infarction due to tight glucose control with the use of initial intravenous insulin infusion.10 There have been several subsequent studies that have looked at the positive impact that insulin may have on improving operative outcomes, particularly with cardiothoracic surgery.11 The reason for improved survival was probably multifactorial and included improved glucose homeostasis and possible improved oxygenation of the tissues through insulin’s vasodilatory effects to skeletal muscle via increased production of nitric oxide in vascular endothelium.12,13 Hyperglycemia may also accentuate the risk of thrombotic complications.14 Finally, studies have shown that hyperglycemia has deleterious effects on essential wound healing events such as decreased chemotaxis, polymorphonuclear leukocyte mobilization and phagocytosis. When it comes to patients with diabetes, skin fibroblasts reportedly do not proliferate as well in a hyperglycemic milieu and this may impair wound closure.15,16,17 Indeed, there are a multitude of reasons to avoid hyperglycemia, even for short-term intervals. Therefore, it is probably not ideal to aim for higher glucose levels than outpatient goals due to the fear of perioperative hypoglycemia. However, future prospective, controlled, randomized studies are necessary for further evaluation of safe modalities to improve glycemic control in the perioperative period. At Beth Israel Deaconess Medical Center (BIDMC), our relationship with the Joslin Diabetes Center allows for frequent collaboration and many of our glycemic control practices are a result of those interactions. As we noted previously, while clinicians utilize many approaches, this following protocol is the one we employ most frequently.
Key Considerations With Perioperative Glycemic Control
Regardless of the aforementioned factors, four primary glycemic goals remain paramount. These goals include: preventing hypoglycemia, preventing hyperglycemia, avoiding ketosis and reducing morbidity and mortality. The risks associated with hypoglycemia (defined as <60 mg/dL) are easily understood as hypoglycemia carries a significant risk of mortality. This state may trigger events such as cardiac arrhythmias or altered mental status, and it can be difficult to detect in the immediate postoperative period. Severe hyperglycemia may induce diabetic ketoacidotic (DKA) and hyperosmolar nonketotic states, as well as an increased potential for volume depletion secondary to osmotic diuresis. While those with type 2 diabetes are less likely to develop ketosis, patients with type 1 diabetes may progress to ketoacidosis without insulin. This becomes important when considering the management of elevated glucose in those with type 1 and type 2 diabetes, and each type carries different consequences. While a patient with type 2 diabetes can tolerate some mildly elevated plasma glucose values and still hold insulin dosing, this may prove catastrophic for type 1 diabetes patients, who may become ketotic as a result. Patients with type 2 diabetes are more prone to nonketotic states but may develop ketoacidosis at the extremely high range. Beyond these prime directives, the necessary stringency of glycemic control is unclear. The long-term benefits of tight glucose control are well documented in both diabetic types as evidenced by the Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS).18,19 However, fewer reports address the perioperative period. Those that do consider this sensitive period generally are in reference to major surgical interventions and those in critical care units. Although tight glycemic control has shown promise in these patients with decreased morbidity and mortality, the applicability to less critically ill patients is poorly understood. If possible, one should schedule surgery early in the morning in order to avoid severe hypoglycemia and hyperglycemia, and most physicians aim to maintain a preoperative blood glucose level between 150 and 200 mg/dL. If the patient is actively receiving an insulin infusion, one can achieve tighter glucose control and the overall glucose goal becomes 101 to 150 mg/dL.20,21 At our institution, we divide patients into two groups when it comes to managing glucose. The first group includes all patients with type 1 diabetes or type 2 diabetes who require multiple daily insulin injections (sliding scales). The second group includes the remainder of patients who are not in the first group, namely those with type 2 diabetes who have a controlled diet, those taking oral hypoglycemics and those who take subcutaneous insulin once or twice daily. Regardless of which group a patient fits into, we strongly recommend surgery first thing in the morning, if at all possible, in order to avoid prolonged fasting.
A Guide To Preoperative And Perioperative Measures
Both groups require little intervention prior to the day of surgery. Emphasize continued outpatient insulin regimens and diets without alterations. For those taking oral hypoglycemics, no change is required until the day of surgery. Remind patients to check fingerstick glucose levels before every meal and at bedtime. If the glucose is poorly controlled, a common occurrence in the face of infection, use a sliding scale of short-acting insulin (regular or lispro for example) to supplement control. The BIDMC podiatry service utilizes a weight-based sliding scale developed by the Joslin Diabetes Center. One may need to adjust and individualize sliding scales for each patient to optimize glucose control. Also, if the patient is on a basal-bolus regimen of insulin, one should continue the basal rate (glargine, detemir). On the day of surgery, the patient should begin fasting at midnight. One may administer D5W or D5 1/2NS unless the blood glucose level is >200 mg/dL. In these cases, the surgeon can usually administer normal saline instead if there are no contraindications. However, there are exceptions to this guideline and medical judgment should override this recommendation as needed. For patients in group one, one should withhold all scheduled fast- or very fast-acting insulin. Cut intermediate or long-acting insulin in half. Typically, one would reduce peakless or relatively peakless insulins such as glargine or detemir into two-thirds of the usual dose. However, if the glucose levels have been high, give the entire dose. If a patient receives an insulin mixture, hold the fast-acting portion of the mixture and cut the intermediate portion in half. Monitor glucose levels every two hours before and during surgery. For group two, hold all oral hypoglycemic medications and all scheduled fast-or very fast-acting insulins. If the patient takes intermediate or long acting insulin as an outpatient, reduce the dose by half. If a patient receives an insulin mixture, hold the fast-acting portion of the mixture and cut the intermediate portion in half. For both groups, an insulin sliding scale supplements glucose control. When it comes to preoperative and perioperative measurements, one should use the bedtime portion of the sliding scale since the patient is not eating. If the glucose cannot be controlled, then one may initiate an insulin intravenous infusion. If the glucose levels fall below 80 mg/dL, give 100 cc of D10W IV and recheck the glucose in 30 minutes.
What You Should Know About Post-Op Management
Following surgery, manage both groups similarly. Check the glucose levels when the patient reaches the postoperative care unit. Continue the bedtime insulin sliding scale until the patient can tolerate at least 50 percent of his or her prescribed diet. If the patient takes metformin, draw a serum creatinine prior to resuming that medication. If the serum creatinine is elevated, hold this medication until you have identified the cause for this and continue coverage with the sliding scale. Special circumstances, such as insulin pump management and IV insulin infusions, warrant further discussion and are beyond the scope of this article. In general, physicians maintain insulin pump use for these patients while they are inpatients and adjust this use as needed. If the patient is unable to manage the pump (due to illness, medications, anesthesia, etc.), then he or she will usually receive an insulin infusion or a calculated basal-bolus or subcutaneous insulin regimen.
This article gives a brief presentation on the perioperative glycemic controls we use at our institution. A well-considered protocol is important in delivering consistent quality care but each patient is unique in his or her metabolic needs, and requires careful scrutiny. If the complexity of your patient’s medical status exceeds your comfort level in managing the patient, we strongly advise having a medical or endocrinology consult to assist you. Dr. Emily Cook is a Chief Resident in the Division of Podiatry at Beth Israel Deaconess Medical Center in Boston and is a Clinical Fellow in Surgery at Harvard Medical School. Dr. Jeremy Cook is a Chief Resident in the Division of Podiatry at Beth Israel Deaconess Medical Center in Boston and is a Clinical Fellow in Surgery at Harvard Medical School. Dr. Rosenblum is Director of Podiatric Residency Training at Beth Israel Deaconess Medical Center in Boston, and an Assistant Clinical Professor of Surgery at Harvard Medical School. Dr. Steinberg (pictured at left) is an Associate Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. For related articles, see “Is Inhaled Insulin A Viable Alternative For Patients With Diabetes?” in the October 2006 issue of Podiatry Today or “A Guide To Nutritional Supplements For Patients With Diabetes” in the March 2006 issue. Also check out the archives at www.podiatrytoday.com.
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