Roy Phitayakorn, MD, MHPE (MEd)
You are taking care of a 65-year-old man with Type 1 diabetes, which is well controlled using an insulin pump. Unfortunately, he was recently admitted with his second attack of diverticulitis and is now on your service for an elective sigmoidectomy. His surgery is uncomplicated, but now you have to write his postoperative orders.
1. Is glycemic control really that important for patients after surgery? Why or why not?
2. What types of insulin does a surgical patient require?
3. How would you handle the insulin requirements of this Type 1 diabetic?
4. What if the patient is a Type 2 diabetic who uses insulin at home?
5. What if the patient is a Type 2 diabetic who is non–insulin dependent at home, but now requires insulin as an inpatient to maintain proper glycemic control?
1. Diabetes is very common in hospitalized patients and inpatient hyperglycemia has been associated with an increase in overall infection rate, morbidity, mortality, and length of stay in surgical patients. These complications are probably because hyperglycemia triggers phagocyte and endothelial cell dysfunction, as well as increased vascular inflammation, platelet activation, and oxidative stress. Exogenous insulin administration not only decreases blood glucose levels but may also have a direct anti-inflammatory effect on vascular endothelial cells. However, overaggressive glycemic management can lead to hypoglycemia with possible coma, neurological injury, and death. In short, while hypoglycemia is more dangerous than hyperglycemia, both are bad. Therefore, it is essential that you understand how to properly manage perioperative insulin dosages.
2. In broad terms, the easiest way to think about insulin requirements is the concept that inpatients require a basal or baseline amount of insulin and then a prandial or nutritional requirement (see Figure 47-1). The baseline amount is the quantity of insulin that patients need to avoid unchecked gluconeogenesis and ketogenesis. The prandial amount is the quantity of insulin needed to cover meals, dextrose in intravenous fluids, enteral feeds, and/or TPN. If the patient is eating, then ideally the prandial amount is given as a correction-dose therapy before or between meals. Sliding insulin scales are substandard for this purpose since the dosage of insulin is given without regard to meals and after hyperglycemia has already occurred. If the patient is NPO and on a continuous infusion of intravenous fluids that contain dextrose, then sliding insulin scales may be sufficient to cover nutritional insulin requirements, although they should be adjusted daily until optimal glycemic control is achieved.
Figure 47-1. Components of total insulin requirements.
3. By definition, these patients are insulin deficient and therefore require a constant basal supply of insulin to avoid entering diabetic ketoacidosis. Adult Type 1 diabetics are frequently very familiar with how much insulin their bodies require and are very comfortable recognizing sensations of hyperglycemia or hypoglycemia. Often these patients will be able to subcutaneously administer insulin to themselves via an insulin pump that lets them control the precise dosage of insulin administered to their bodies. In my experience, it is best to work/negotiate with these patients and let them control their own insulin delivery. If they are eating, these patients should be on a long-acting insulin (such as NPH or lente) that they administer in the morning or evenings. In addition, a bolus of short-acting insulin (such as lispro or aspart) is given before or after eating to cover carbohydrates that will be or were consumed. If Type 1 diabetics are not eating, it is essential that they still receive their basal insulin requirements! For many patients, the basal insulin requirement will not change even when they are NPO. If you are unsure or the patient is particularly brittle, you can start at half of the basal insulin requirement and increase accordingly. Fluctuations in blood glucose levels secondary to dextrose in intravenous fluids or TPN should be covered by a sliding insulin scale. Note that patients who had a recent pancreatectomy or who have severe pancreatic dysfunction may now be considered Type 1 diabetics.
4. Unlike Type 1 diabetics, these patients have a problem with insulin resistance. Initially, Type 2 diabetics have high levels of basal insulin secretion, but may need additional prandial insulin to defeat this resistance. When eating, these patients should be on all of their insulin sensitizers and secretagogues (such as metformin, sulfonylureas, glitazones, exendin-4, etc) in addition to their basal and nutritional insulin requirements to maintain glucose levels less than 180 mg/dL. Over time, these patients may lose some of their insulin production capacity and therefore require supplemental basal insulin as well. Interestingly, the glycemic profile of Type 2 diabetics is frequently diet related and their total insulin needs typically decrease when they are NPO even without their normal oral diabetes agents. Therefore, Type 2 diabetics who are NPO may only require a correction dosage or sliding-scale coverage. However, it is important to remember that these patients still have insulin resistance so their overall insulin requirements may still be quite high.
5. Often, these patients were precariously close to requiring insulin at home, but either did not have regular glucose checks or the stress of surgery has pushed them into requiring insulin. Patients may also receive postoperative corticosteroids that can exacerbate preexisting poor glycemic control. Starting de novo insulin treatments may seem daunting to new resident physicians, but is actually quite straightforward.
First, check a HbA1C to get a rough idea of preoperative glycemic control and then multiply the body weight in kilograms by 0.4 U of insulin (0.3 if very elderly, 0.5 if morbidly obese) to get a total daily insulin requirement. Give half of the daily requirement as glargine at night or in divided NPH dosages every 12 hours. If the patient is able to eat, give the other half as short-acting insulin divided into 3 equal correctional dosages shortly before meals. The patient should also be restarted on his or her oral diabetic agents. The patient’s nurse should be asked to record the patient’s blood glucose levels prior to giving all insulin injections. A glucose reading <70 mg/dL indicates that the patient is receiving too much insulin and the dosages should be adjusted accordingly. Patients should be appropriately counseled that it is unlikely they will go home on insulin, but may require insulin therapy in the future if their diabetes worsens. If the patient will be NPO for long periods of time and therefore requires TPN or PPN, insulin should be calculated based on your institution’s protocols and included directly with the TPN. Any exogenous basal or prandial insulin should be used with caution in patients on TPN/PPN as these infusions are frequently disrupted and the patient could become quickly hypoglycemic.
TIPS TO REMEMBER
Surgical patients require good glycemic control to avoid many types of postoperative complications.
A useful framework to think about insulin replacement therapy is that each patient needs both basal and prandial insulin. Basal therapy consists of long-acting insulins given in the morning, nighttime, or both. Ideally, prandial therapy should be given before or between meals.
Sliding-scale insulin coverage is a substandard, reactive form of prandial therapy, but may be sufficient in surgical patients who are NPO.
1. Prolonged hyperglycemia in diabetic patients has been associated with all of the following except?
A. Phagocyte dysfunction
B. Endothelial cell dysfunction
C. Platelet activation
D. Vascular inflammation
E. Increased catecholamine production
2. You are going to start insulin therapy on a 55-year-old man with Type 2 diabetes who weighs 200 kg. What are his estimated total daily insulin needs?
A. 40 U of insulin
B. 60 U of insulin
C. 80 U of insulin
D. 100 U of insulin
E. 120 U of insulin
3. Which of the following complications will most likely occur if you do not give an insulin-dependent diabetic (Type 1) his or her basal amounts of insulin?
A. Diabetic ketoacidosis
C. Myocardial infarction
D. Wound infection
E. Pulmonary insufficiency
1. E. Increased catecholamine production has not been linked to prolonged hyper-glycemia in diabetic patients.
2. C. His estimated total daily insulin requirement is approximately 0.4 U/kg × 200 kg = 80 U of insulin.
3. A. Lack of insulin in Type 1 diabetics leads to ketoacidosis that features ketonemia, hyperglycemia, and an anion gap metabolic acidosis. This condition can be fatal if not recognized early.