Preparation Of Diabetic Patient

Diabetes mellitus is a common medical condition affecting 6% of Americans younger than 50 years and 10-15% of those older than 50 years. In addition, it has been estimated that an equal number may have diabetes still undiagnosed. Diabetes frequently interfaces with surgical and anesthetic care by virtue of the absolute number of patients with diabetes, and many of the complications of the disease (eg, vascular, ophthalmologic, renal, cardiac) demand surgical intervention. An earlier report estimated that nearly 50% of individuals with diabetes undergo surgery in their lifetime.

Diabetic patients undergoing surgery present a number of unique challenges. The ultimate aim is to bring about an outcome in patients with diabetes equal to the outcome for patients without diabetes who are undergoing the same procedure. That this goal is possible is strongly suggested by evidence that diabetes mellitus per se does not increase the risks of surgery when matched to appropriate controls. Rather, it is the secondary end-organ consequences, in particular the increased incidence of coronary, cerebral, and renal vasculopathies, that heighten the perioperative dangers faced by this population. In addition, diabetes has an impact on perioperative fluid, electrolyte, and nutritional balance; cardiovascular and renal function; immunity; and wound healing, especially when the condition is poorly controlled. When severe, these derangements may further add to perioperative morbidity and mortality and should be avoided, whenever possible, by strict control of diabetes.

Studies have shown that diabetes is an independent predictor of postoperative myocardial ischemia among patients undergoing noncardiac surgery. It is likewise an independent predictor of postoperative pulmonary complications in patients undergoing abdominal surgery.

Therefore, the perioperative period requires appropriate attention to management of diabetes by the care team, working in concert. The team should include an endocrinologist, a primary care provider, an anesthesiologist, and a surgeon. Appropriate preoperative assessment and stabilization of the diabetic condition and its manifestations, followed by careful intraoperative and postoperative management of the disease, leads to a demonstrated improvement in outcome.

DIABETES, ANESTHESIA, AND SURGERY

The treatment goals of perioperative management of patients with diabetes require careful metabolic management in order to avoid (1) hypoglycemia, (2) excessive hyperglycemia, (3) electrolyte disturbance, and (4) protein catabolism, while allowing for the nutritional support of patients appropriate to the circumstances. The basis of this management is a clear understanding of the complex glucose-insulin interactions as well as the effects of anesthesia and surgery on that relationship.

Physiology of glucose and insulin

In brief, basal conditions are marked by production of glucose by the liver as well as uptake and consumption of glucose by the "periphery." Insulin may be considered an anabolic hormone that is opposed by the catabolic effects of catecholamines, cortisol, glucagon, and growth hormone. A simplified scheme is to consider glucose regulation as the net balance between decreased glycogenolysis and increased peripheral glucose uptake induced by insulin versus increased glycogenolysis and decreased glucose uptake induced by the catabolic hormones. Regulation preserves the availability of glucose to the tissues. In the fasting state, insulin secretion decreases and catabolic hormone levels rise. Absolute insulin deficiency, as is noted especially in patients with type I diabetes, leads to unopposed catabolic action, hyperglycemia, and eventually uncontrolled ketoacidosis.

Metabolic response to anesthesia and surgery

Surgery elicits a stress response that is directly proportional to the degree of tissue trauma. Recent work suggests that the principal mechanism lies with elevation of sympathetic tone with consequent release of cortisol and catecholamines during surgery. These hormones, in turn, lead to relative insulin hyposecretion and insulin resistance as well as increased protein catabolism. Anesthesia also principally affects glucose metabolism through modulation of sympathetic tone, though there is in vitro evidence of suppression of insulin secretion by inhalational agents. The resultant functional insulin deficiency compounds the absolute insulin deficiency present in people with insulin-dependent diabetes, raising the risks of hyperglycemia and ketogenesis.

PREOPERATIVE ASSESSMENT OF THE DIABETIC PATIENT

The perioperative management of patients with diabetes begins with preoperative assessment, including a complete history and physical examination. Even in patients who deny a history of diabetes mellitus, history and physical examination should seek undiagnosed disease (in one study of "nondiabetic" patients presenting acutely for treatment of soft tissue infections, more than 5% had blood glucose levels >180 mg/dL). History also should include type and treatment of diabetes or insulin resistance, known complications, and previous hospitalizations. Note the course and complications, if any, of prior surgeries. Questioning should elicit symptoms of ischemic cardiac, renal, and/or peripheral vascular disease, if any.

Complement the routine physical examination with a complete cardiac evaluation for diabetic patients undergoing major surgery. Identify and treat hypertension. Again, place emphasis on the status of the peripheral circulation and the sensory nerves. Since this complication may alter intraoperative cardiovascular response with resultant hypotension and increased cardiac morbidity, assess autonomic neuropathy by evaluating for the presence of orthostatic hypotension.

In addition to routine screening, preoperative laboratory values of particular interest in patients with diabetes include fasting and 2-hour postprandial serum glucose levels, as well as hemoglobin A_1c. In those on insulin therapy as well as in those whose disease is poorly controlled by diet or oral hypoglycemic medications, maximizing control may require several fasting and nonfasting serum glucose determinations in the preoperative period.

An assessment of renal function should include screening of not only BUN and creatinine, but also screening of microalbuminuria and proteinuria. In one recent study, the presence of proteinuria was a key predictor of death after isolated coronary artery bypass grafting, with mortality rising with increased levels of protein in the urine. Supplement routine ECG recordings with an assessment of the variability of the R-R interval with deep respiration, which is a further evaluation of autonomic cardiac neuropathy. (Loss of R-R variability when comparing the heart rate at maximal inspiration to the heart rate at maximal expiration implies the presence of autonomic cardiac neuropathy).

PERIOPERATIVE MANAGEMENT OF THE PATIENT WITH NON–INSULIN-DEPENDENT DIABETES

Patients with type 2 diabetes represent over 90% of diabetic patients undergoing surgery. Patients whose disease is well controlled by diet alone or by oral hypoglycemic agents tend to fare well in the perioperative period. A protocol for their management is outlined in this section.

Preoperative management of the patient with poorly controlled non–insulin-dependent diabetes

Prior to surgery, identify patients whose disease is poorly controlled on their current regimens (fasting blood sugar higher than 125 mg/dL or 2-hour postprandial level higher than 180 mg/dL). Where feasible, such patients should be switched to and controlled on insulin therapy in advance of surgery. Ideally, this would be achieved by patients’ primary care providers and/or endocrinologists. Once in the perioperative period, care would then follow the protocols outlined in the section on the perioperative management of insulin-dependent patients.

Preoperative management of the patient with well-controlled non–insulin-dependent diabetes

As noted above, careful preoperative assessment of patients with diabetes is required to ascertain that any given patient is indeed well controlled, without other significant comorbid conditions. The type of anesthesia and the extent of surgery planned determine the nature and extent of the additional workup, especially as it relates to the cardiovascular system. Proposed excision of a sebaceous cyst under local anesthesia requires little, if any, further investigation, while a proposed major vascular procedure in the same patient may prompt consideration of a detailed cardiac evaluation.

As anesthetic techniques evolve, and as increased patient comfort becomes an important marketing tool, the time frame and the extent to which patients are maintained without food prior to surgery has diminished. However, diabetic gastroparesis should be suspected in all patients with diabetes, mandating a 12-hour period of complete fasting prior to any surgical procedure. Advise patients whose conditions are controlled by diet alone to maintain their dietary regimen up to the preoperative fasting period. Monitoring on the day of surgery is similar to that for patients on oral hypoglycemic agents and is outlined below. Once patients have recovered from the procedure and are able to tolerate feedings, their diabetic diet routine should be reestablished as soon as possible.

Perioperative management of oral hypoglycemic agents in patients with well-controlled diabetes is particular to the class of medication being prescribed. Stop long-acting sulfonylnola agents (ie, Diabinese) approximately 3 days before surgery. Newer sulfonylnolas such as Glyburide and Glucotrol have a half-life of 24 hours; even patients with tight control can safely stop such agents the morning before surgery without adverse effect. Patients on sulfonylnolas who tend to have inadequate control (glucose frequently in the 200s) should take the evening dose the night before surgery so that their preoperative fasting glucose is not prohibitively high. Thiazoladinediones should be stopped the night before surgery. Metformin also should be stopped the night before surgery to avoid the risk of lactic acidosis.

Intravenous fluid (usually 5% dextrose in 0.45% sodium chloride) is begun the morning of surgery in order to maintain fluid and nutritional balance. Starvation is not an acceptable method to maintain serum glucose values within the standard range. Rather, adequate nutrition is the goal, using glucose infusion in order to assure nutritional balance while avoiding catabolism, with insulin coverage provided as needed. A baseline infusion of 150 mg of glucose per day (125 cc/h of a solution containing 5% dextrose) markedly reduces protein catabolism in patients who are not eating. Provide additional nutrition for patients with demands above the baseline, including individuals undergoing prolonged major surgical procedures and those with sepsis. Give additional fluids to match surgical losses as required, but avoid lactate-containing solutions because lactate converts rapidly to glucose in the fasting state.

Serum glucose monitoring is accomplished using finger sticks and is begun the morning of surgery prior to starting intravenous therapy and at regular intervals thereafter. Sliding scale coverage with regular insulin is administered as required (see Table 1). For those who require coverage, repeat glucose monitoring at hourly intervals is advisable. When coverage is not required (the majority), recordings may be obtained every 2-3 hours thereafter.

Intraoperative management of the patient with well-controlled non–insulin-dependent diabetes

Once in surgery, the frequency of glucose monitoring of patients with well-controlled non–insulin-dependent diabetes varies with (1) the type of anesthetic, (2) the stress of the procedure, and (3) patient response to the process. Anesthesia stresses the body independently of the surgical procedure, so record glucose levels every 1-2 hours in patients under general anesthesia. Similarly, monitor patients undergoing physiologically stressful procedures even under regional block. Patients who require insulin coverage at any point in the preoperative or intraoperative period should thereafter be cared for as per the protocol outlined in Perioperative Management of the Patient with Insulin-Dependent Diabetes Mellitus. Conversely, in stable diabetic patients undergoing a limited procedure under regional or local anesthesia, glucose monitoring may be safely limited to the preoperative and postoperative periods.

Postoperative management of patients with well-controlled non–insulin-dependent diabetes

Postoperative resumption of diet or oral hypoglycemic control depends on several factors. After minor surgery and once tolerating oral intake, patients should return to their routine diabetic dietary schedule as soon as possible. Reinstitute oral hypoglycemic agents at half the usual dose on the day oral diet is begun and, assuming adequate glucose control, advance to the full preoperative regimen the next day (assuming a full diabetic diet is resumed).

For patients who have been converted to insulin coverage, continue this coverage until such time as the stresses of the underlying disease and the surgery have abated. Patients should then be reassessed by the care team as to their current requirements and a determination should be made anew as to chronic therapy with or without insulin. For ambulatory patients who have undergone a minor procedure, this may be a simple process in the postanesthesia area, making the transition back onto preoperative therapy. On the other extreme, for patients who are hospitalized and have undergone major surgery or those with septic complications, the diabetic status on discharge may be far different from that on admission, requiring careful planning with a newly tailored therapeutic approach. Generally, the patient's usual oral agents are restarted when the patients are eating normally postoperatively, with sliding scale insulin added if the patient requires it.

Two special situations should be noted in this regard. Patients previously on metformin who have postoperative renal failure (creatinine higher than 1.5 mg/dL in males and higher than 1.4 mg/dL in females) should not be restarted on this medication. Also, thiazolidinedione medication should not be resumed in patients who have developed congestive heart failure.

PERIOPERATIVE SLIDING SCALE INSULIN COVERAGE FOR THE NON–INSULIN-DEPENDENT DIABE

Table 1. Perioperative Sliding Scale Insulin Coverage for the Non–Insulin-Dependent Diabetic Patient

Serum glucose (mg/dL)	Dose of regular insulin (subcutaneous [SC] administration)
0-150	no coverage
150-200	2 units
201-250	4 units
251-300	6 units
301-350	8 units
>350	10 units

PERIOPERATIVE MANAGEMENT OF THE PATIENT WITH INSULIN-DEPENDENT DIABETES MELLITUS

Diabetes management in patients with insulin-dependent diabetes remains similar throughout the perioperative period and is based on insulin therapy. This is in contrast to patients with non–insulin-dependent diabetes, in whom management must be dramatically changed, as oral hypoglycemic medications must be withheld. Therefore, the key in insulin-dependent patients is the balance between caloric provision and insulin requirement, a task that does not vary whether the patient is in the preoperative, intraoperative, or postoperative period.

Throughout the perioperative period, responsibility for insulin therapy frequently changes hands; from the patient to the medical clearance internist, to the preoperative preparation nurse, to the anesthesiologist, to the recovery room staff, to the surgery ward staff. Hence, it is essential that any insulin regimen be simple to institute, easily communicated, broadly applicable, and, most importantly, it must be agreed upon by all users. Several regimens of perioperative insulin management possess these traits. Clearly, no consensus has yet been reached in the literature or in everyday practice as to the optimal method.

For insulin-dependent diabetic patients on split-mixed insulin therapy (regular and long-acting insulin therapy, usually twice per day), it is traditional to continue normal dosing the day before surgery. In the morning of the day of surgery at their usual time, the patient is instructed to take half the normal neutral protamine Hagedorn (NPH) or Lente dose without the regular insulin component. They are asked to come to the hospital early that morning and, once in the preoperative staging area, an intravenous line is started containing 5% dextrose solution.

Available perioperative insulin regimens for the patient with insulin-dependent diabetes

One common regimen is to administer regular insulin by the SC route according to a sliding scale. Despite its broad application, this regimen has the disadvantage of being based on an anticipated 2- to 4-hour peak-effect of regular insulin administered by this route, upon obsolete standards of glucose monitoring, as well as upon familiarity and convenience. Absorption of SC insulin, always unpredictable, is especially erratic in the perioperative period. Even with frequent monitoring and guided insulin administration, a "roller coaster" effect on serum glucose is sometimes noted, often defying tight control.

In contrast, Alberti and Thomas showed improvement in tight control of serum glucose with an intravenous regimen. Substituting for intermittent SC injections is a single-bag intravenous solution of glucose in the form of 10% aqueous dextrose solution, regular insulin, and potassium (GIK). The scientific rationale for this is an attempt to closely mimic steady-state physiology. This is carried out by infusing 5-10 g of dextrose, 1-2 U of insulin, and 100-125 cc of fluid per hour to match required glucose production, insulin secretion, and replacement of insensitive fluid losses. In addition, this regimen has a safety feature: inadvertent overinfusion or underinfusion delivers equal proportions of dextrose and insulin.

GIK infusion, however, has 1 major drawback: responding to each abnormal glucose measurement requires providing a different dextrose-insulin ratio, which in turn requires a new bag to be mixed in each instance. In common practice, this may be safely and effectively accomplished with less time by the continuous infusion of glucose and potassium in one intravenous bag to which is piggy-backed (via short tubing) a continuous insulin infusion pump. The rate of insulin infusion then may be adjusted easily without changing intravenous solutions on each occasion.

A less common technique replaces the SC route with bolus intravenous injections of regular insulin at set intervals, commonly beginning with 10 U every 2 hours. This is supplemented with additional doses as indicated by frequent glucose measurements. While technically simple, this approach does not mimic normal physiology, since the short 20-minute physiologic half-life of intravenous insulin produces greater roller-coaster forces on glucose levels than even bolus SC administration.

Sliding-scale continuous intravenous insulin infusion still appears to be the most elemental and physiologic of all regimens. A dextrose solution and more highly concentrated insulin (by syringe) are simultaneously but independently infused through separate intravenous lines. Additional maintenance or replacement intravenous fluid is given through a third line. The advantage of this regimen is the ease and freedom of insulin titration. Also, the accuracy of insulin delivery is increased, because the use of a syringe reduces adsorption of the drug by the polymer surface area of bags and lines. The major disadvantage stems from the same freedom that separate infusion offers: the possible inadvertent overinfusion or cessation of either insulin or glucose. Additionally, the requirement for 3 separate intravenous lines becomes problematic in some patients.

Significant controversy exists as to the ideal regimen. Unfortunately, the present literature lacks a large-scale prospective study upon which to make such a determination, and outcome studies are unavailable. Further, it is questionable whether a single regimen can fit all patients, or if such a regimen is even desirable. Until the prospective evidence identifies and strengthens support for an optimal approach to insulin management, the approach practiced most often at the authors’ institution is as outlined for use in Table 2.

METHOD OF PERIOPERATIVE CONTROL OF THE INSULIN-DEPENDENT DIABETIC PATIENT

Table 2. Method of Perioperative Control of the Insulin-Dependent Diabetic Patient

Constructed by Dr N.A. Nematallah Consultant in perioperative medicine and intensive therapy, Al Razi Orthopedic Hospital , State of Kuwait, email : razianesth@freeservers.com