49: Diabetes Mellitus

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CHAPTER 49 Diabetes Mellitus

Robert H. Slover, MD, Robin Slover, MD

1 Describe the principal types of diabetes mellitus

image Type 1 diabetes mellitus: An autoimmune disorder in which destruction of the pancreatic islet cells results in the inability to produce insulin. Onset is more common in children and young adults.
image Type 2 diabetes mellitus: A disorder in the body’s ability to use insulin. Early in the course of the disease the patient may be able to make sufficient insulin, but cell-receptor impairment results in hyperglycemia despite normal or high insulin levels. Type 2 diabetes is usually a disease of older adults; onset in the sixth decade and beyond is common. As obesity increases in the population type 2 diabetes also increases. Type 2 diabetes is now commonly seen in adolescents and young adults with obesity and a sedentary lifestyle.
image Gestational diabetes: Seen in 2% to 5% of pregnant women, and 40% to 60% of these women will develop type 2 diabetes mellitus later in life.

2 What is considered ideal (target) glucose control?

The American Diabetes Association (ADA) 2008 Clinical Practice Recommendations recommend an A1C goal for nonpregnant adults in general of <7% (6% or lower is the nondiabetic A1C range). Less stringent goals apply to children, patients with a history of severe hypoglycemia, and individuals with comorbid conditions.

3 What comorbidities are frequently observed in patients with diabetes mellitus and to what significance?

image Hypertension is seen in 40% of patients with poorly controlled diabetes who undergo surgery. Hypertension is a risk factor for coronary artery disease and cardiac failure. If these patients are treated with potassium-wasting diuretic agents, there is often significant total body loss of potassium.
image Coronary artery disease is common, occurs in younger patients, and may be silent or present atypically.
image Autonomic neuropathy may compromise neuroreflexic control of cardiovascular and gastrointestinal function, manifesting as orthostatic hypotension, gastroparesis (increased risk of aspiration), ileus, and urinary retention. Peripheral neuropathies are common.
image Disturbances in renal function are common, including increased blood urea nitrogen (BUN) and creatinine, protein loss, hypoalbuminemia, acidosis, and electrolyte disturbances.
image Occult infections are present in 17% of patients with diabetes.
image Retinal hemorrhages are seen in up to 80% of patients with diabetes over 15 years’ duration and may lead to retinal detachment and vision loss.

4 What oral medications are currently used in type 2 diabetes?

There are two categories of drugs used in treating type 2 diabetes: those that enhance the effectiveness of insulin and those that increase the supply of insulin to the cells. These drugs are outlined in Table 49-1.

TABLE 49-1 Oral Drugs used in Type 2 Diabetes

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5 What insulins are in current use?

Modern intensive insulin therapy relies on newly designed insulin analogs. Insulin therapy is given using a basal-bolus construct: long-acting (24-hour) insulin is used to provide a steady basal platform, and rapid-acting insulin is used to provide boluses for carbohydrate intake in meals and snacks. This necessitates giving at least four injections per day or the use of an insulin pump. The specific insulins are outlined in Table 49-1.

6 Is there an advantage to the use of insulins that are in solution as opposed to insulin that is in a suspension?

Insulins in solution provide exact dosing. For example, 10 units of Humalog will always be exactly 10 units. NPH, the only remaining insulin that is in suspension, does not provide exact or reproducible dosing, but varies by as much as 30% either way. Ten units of NPH could really be 7 to 13 units!

7 Describe the role of insulin on glucose metabolism and the impact of stress

Insulin enhances glucose uptake, glycogen storage, protein synthesis, amino-acid transport, and fat formation. Basal insulin secretion is essential even in the fasting state to maintain glucose homeostasis.

Surgical procedures lead to increased stress and high counterregulatory hormone activity with a decrease in insulin secretion. Counterregulatory hormones, including epinephrine, cortisol, glucagon, and growth hormone, promote glycogenolysis, gluconeogenesis, proteolysis, and lipolysis. Therefore, in diabetic patients without adequate insulin replacement, the combination of insulin deficiency and excessive counterregulatory hormones can result in severe hyperglycemia and diabetic ketoacidosis, which are associated with hyperosmolarity, increases in protein catabolism, fluid loss, and lipolysis.

8 Is there evidence that tight glucose control is beneficial in critically ill patients?

It has recently been believed that intensive insulin therapy to maintain glucose at or below 110 mg/dl reduces morbidity and mortality in critically ill patients in a surgical intensive care unit (ICU). However, it has subsequently been determined that extremely tight glucose control in surgical and medical ICUs significantly increases the risk of hypoglycemia and is not associated with significantly reduced hospital mortality. However, tight control does seem to significantly reduce septicemia and improve wound healing.

9 What are the complications of hyperglycemia in the perioperative setting?

image Impaired polymorphonuclear cellular phagocytic function, increased risk of infection, and increased length of hospitalization
image Osmotic diuresis, dehydration, and hyperosmolarity
image Ketogenesis and diabetic ketoacidosis
image Proteolysis and decreased amino acid transport, resulting in retarded wound healing
image Hyperviscosity, thrombogenesis, and cerebral edema

10 What considerations are important during the preoperative evaluation?

Important considerations include type of diabetes, duration of disease, oral hypoglycemic or insulin therapy, and diabetic complications, including hypertension, renal disease, coronary artery disease (which may be silent or present atypically), and neuropathies (early satiety and reflux suggest gastroparesis). If patients have end-stage renal disease or require dialysis, fluid restrictions may be necessary.

11 What is the significance of autonomic neuropathy? How can it be assessed?

Autonomic neuropathy may affect cardiovascular (silent ischemia), gastrointestinal (gastroparesis with increased risk of aspiration), thermoregulatory (decreased ability to alter blood vessel flow to conserve temperature), and neuroendocrine systems (decreased catecholamine production in response to stimulation). Autonomic neuropathy can be assessed by these tests:

image An intact sympathetic nervous system can be assessed by the following: A normal response in diastolic pressure (from lying to standing) is a change of at least 16 mm Hg; an affected patient has a response of <10 mm Hg. Autonomic neuropathy is also evidenced by a large change in systolic blood pressure when changing from lying to standing posture. A normal decrease is <10 mm Hg; an affected patient has a decrease of at least 30 mm Hg.
image An intact parasympathetic nervous system can be assessed by observing heart rate response to breathing. Normal patients increase heart rate by at least 15 beats/min. Affected patients have an increase of 10 or fewer beats/min. Finally, concurrent with electrocardiogram (ECG) monitoring, the R-R ratio can be measured during a Valsalva maneuver. A normal ratio is >1.2; an abnormal response is <1.1.

Patients with autonomic neuropathy should be considered for preoperative aspiration prophylaxis, which may include an H2-blocking agent, a gastric stimulant to decrease gastroparesis, and/or a nonparticulate antacid.

12 What preoperative laboratory tests are appropriate for the patient with diabetes?

Evaluate electrolytes, phosphate, and magnesium, BUN and creatinine, blood glucose and ketones, urinalysis, and ECG. Proteinuria is an early manifestation of diabetic nephropathy. A cardiac stress test should be considered in sedentary patients with cardiac risk factors. Measuring hemoglobin A1C will provide valuable information about the level of glucose control. Patients with hemoglobin A1C >9% are usually noncompliant and have an increased risk of dehydration.

13 Are there any signs that oral intubation may be difficult?

Although the remainder of the airway examination may be normal, patients with diabetes may have decreased mobility in the atlanto-occipital joint, which can complicate oral intubation. This can be evaluated radiographically. Patients may also have stiff joint syndrome with anterior fixation of the larynx. Stiff joint syndrome is suggested by the inability to approximate the palmar aspect of the pharyngeal joints of the fingers (also known as the prayer sign, the patient cannot touch the palmar aspects of the fingers together when the palms are together). The palmar print is another way of assessing stiff joints.

14 How should the patient with diabetes be prepared before surgery? Should all patients with diabetes receive insulin intraoperatively?

Patients with type 1 diabetes having short or minimally invasive procedures should receive a reduced dose of insulin and have their serum glucose followed. Patients with type 2 diabetes on oral medications should not take these medications the day of surgery. It is ideal to schedule the surgery early in the day.

Patients having longer or more stressful surgeries have increased levels of counterregulatory hormones and are likely to benefit from tighter glucose control. Furthermore, insulin requirements are increased by infection, hepatic disease, obesity, steroids, and cardiovascular procedures and pain. An insulin infusion may be considered to establish tighter glucose control. Before surgery, hyperglycemia, fluid and electrolyte imbalances, and ketosis should be corrected. Ideally in patients with renal failure surgery should occur the day after hemodialysis.

Blood glucose levels under 200 mg/dl in the days preceding surgery are ideal and ensure adequate glycogen stores and insulin sufficiency. On the day before surgery glucose should be monitored at bedside before each meal, at bedtime, and in the early morning. The goal is to have most glucose between 120 and 180 mg/dl.

15 How do you make an insulin and glucose infusion?

Ideally the glucose and insulin infusion should be started at least 1 hour before surgery. Glucose and insulin can be mixed together. They can also be given as separate infusions, but the combination infusion is safer because it is hard to have an accidental bolus of one or the other. Add 8 units regular insulin to 500 ml D5W. Connect the tubing, shake well, and discard the first 100 ml through the tubing since insulin binds to polyvinyl chloride (PVC) bags and tubing. If a non-PVC bag is used, only 5 units of regular insulin is added to 500 ml of glucose. Again discard the first 100 ml of fluid. The mixture is infused at a rate of 100 ml/hr, and a blood glucose measurement should be obtained 20 minutes after starting the infusion and then hourly. The infusion will usually maintain the blood glucose level, although it may lower the level by 20 to 40 mg/dl.

For longer cases or in more fragile patients, 16 units of regular insulin is added to 1000 ml of D5W. Consider adding 20 mEq/L of potassium, unless the patient’s potassium is >5.5 mEq/L. If the patient’s potassium is <4 mEq/L, 40 mEq/L should be added to the infusion. After mixing and discarding the first 100 ml through the tubing, the infusion is run at 100 ml/hr. Again blood glucose measurements are checked 20 minutes after starting the infusion and then hourly. The infusion may be increased or decreased by 4-unit increments.

16 How fast can the blood glucose be lowered in a markedly hyperglycemic patient?

Blood glucose levels should not be lowered more than 100 mg/dl/hr if possible. Since the blood-brain barrier is slower to respond, a rapid drop in blood glucose could lead to cerebral swelling and in rare cases to symptomatic cerebral edema.

17 Describe the postoperative management of the patient with diabetes

In significant procedures with prolonged recovery, it is easier to manage the patient by continuing the insulin and glucose infusion for up to 48 hours, matching increased or decreased insulin needs with changes in rate or concentration of the infusion. Continue bedside monitoring of glucose, electrolytes, and fluids. A blood glucose goal of 120 to 180 mg/dl is reasonable. If total parenteral nutrition is used, the insulin rate may need to increase and should be adjusted based on glucose monitoring.

With the resumption of oral feeding, insulin is given subcutaneously according to the patient’s preoperative schedule. If pain or stress is still significant, it will be necessary to increase the dosage by as much as 20%. Monitor glucose at bedside before meals, at bedtime, and early in the morning, adjusting doses as necessary.

18 How do you manage patients using subcutaneous insulin pumps?

Insulin pumps are now commonly used and can ensure good glucose control. The pumps use one of the newer analog insulins (Humalog, Novolog, and Apidra) and deliver both basal and bolus insulin doses. Since the basal rate is set to deliver necessary insulin for the fasting state, the pump can be used for insulin delivery during the perioperative and intraoperative periods, continuing the established basal rates. Check blood sugars at regular intervals, every 1 to 2 hours, to ensure that the patient’s blood sugar stays between 80 and 180 mg/dl. If the stress of a long surgery raises glucose levels, the basal infusion rate can be safely raised in increments of 0.1 unit per hour. If glucose levels fall, the rate can be safely reduced in increments of 0.1 unit per hour, or the pump can be suspended until glucose levels rise. When the patient is fully recovered, return to normal routines for pump use. The patients may consume a regular diet, as appropriate, when fully alert, awake, and with good bowel sounds.

19 What insulins are preferred for pump use?

The rapid-acting analogs (Novolog, Humalog, Apidra) are used in the insulin pumps. Interestingly, when insulin is given intravenously, there is no advantage to the analogs compared to regular human insulin. For that reason the less expensive regular insulin is usually used for intravenous therapy.

20 Describe the management of patients with diabetes requiring urgent surgery

If at all possible, electrolyte and glucose imbalance should be corrected before surgery. Sufficient rehydration, electrolyte replacement, and insulin treatment can be achieved in 4 to 6 hours, improving hyperglycemia, ketosis, and acidosis. Rehydration is initiated with 10 to 20 ml/kg of normal saline (NS). Infuse insulin at 0.1 unit/kg/hr using 0.45 NS (or D10 in 0.45 NS if glucose is <150 mg/dl). Patients in ketoacidosis requiring emergency surgery may receive insulin therapy according to the guidelines in Table 49-2.

TABLE 49-2 Insulin Therapy Guidelines

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21 Are regional anesthetics helpful in patients with insulin-dependent diabetes? Can epinephrine be added to local anesthetic solutions?

Regional anesthetic techniques decrease the stress response and may help maintain a more stable blood glucose and decrease stress on the cardiovascular system. Epinephrine should not be used in peripheral nerve blocks (e.g., ankle blocks) because of the risk of decreasing blood flow to an area possibly already affected by impaired microcirculation. In blocks with high systemic absorption such as brachial plexus or intercostal blocks, low-dose epinephrine may be used.

22 Is it possible to achieve continuous monitoring of glucose levels in the operating room and in the perioperative period?

The technology is commercially available to have continuous glucose monitoring before, during, and after a procedure. Currently there are three continuous glucose monitoring (CGM) systems that have Food and Drug Administration approval. Each of these samples interstitial fluid every 30 seconds to report an interstitial fluid glucose level every 5 minutes. Adjustment to insulin infusions can be made in response to changing glucose levels. Within a few years we expect to see continuous glucose tracings just as we now see continuous oxygen tracings.

Key Points: Diabetes Mellitus image

1. Careful attention to glucose control before, during, and after surgery is important to reduce risk of infection, promote more rapid healing, avoid metabolic complications, and shorten hospital stay.
2. The goal for insulin management during surgery is to maintain glucose between 120 and 200 mg/dl.
3. Intraoperative glucose control in all but the shortest cases is best achieved by using a glucose-insulin intravenous infusion or a pump.
4. Patients with diabetes have a high incidence of coronary artery disease with an atypical or silent presentation. Maintaining perfusion pressure, controlling heart rate, continuous ECG observation, and a high index of suspicion during periods of refractory hypotension are key considerations.
5. The inability to touch the palmar aspects of index fingers when palms touch (the prayer sign) can indicate a difficult oral intubation in patients with diabetes.

Websites image

American Diabetes Association

http://www.diabetes.org

The Children’s Diabetes Foundation at Denver

http://www.childrensdiabetesfdn.org

Juvenile Diabetes Research Foundation

http://www.jdrf.org

SELECTED READINGS

1. Burant C.F., editor. Medical management of type 2 diabetes. Alexandria: American Diabetes Association. 2004;ed 5:52-59.

2. Davidson M.B. Standards of medical care in diabetes. Diabetes Care. 2005;28(Suppl):S4-S36.

3. Ferrari L.R. New insulin analogues and insulin delivery devices for the perioperative management of diabetic patients. Curr Opin Anaesthesiol. 2008;21(3):401-405.

4. Fonseca V.A. Standards of medical care in diabetes—2008. Diabetes Care. 2008;31(Suppl):S12-S54.

5. van den Berghe G., Wouters P., Weekers F., et al. Intensive insulin therapy in the critically ill patients. N Engl J Med. 2001;345:1359-1367.

6. Wiener R.S., Wiener D.C., Larson R.J. Benefits and risks of tight glucose control in critically ill adults: a meta-analysis. JAMA. 2008;300(8):933-944.

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