Insulin is a hormone produced in the pancreas and secreted in response to increased levels of plasma glucose. The pancreas of Type I diabetic patients no longer manufactures insulin, whereas in Type II diabetics, the pancreas makes insulin but the body no longer (or poorly) responds to it. Insulin has many roles in maintaining physiologic homeostasis, and consequently, diabetic patients present many challenges in the perioperative period. Basal metabolic needs utilize approximately one-half of a patient’s secreted insulin, even in the fasted state. For this reason, diabetic patients presenting for surgery should not have insulin discontinued. Surgery and anaesthesia result in a neuroendocrine stress response, which releases counter-regulatory hormones.

PERIOPERATIVE MANAGEMENT

How is insulin dosed?

Diabetic patients frequently take a long-acting, basal, insulin preparation

These formulations are peakless and maintain a constant level of insulin to prevent ketosis or hyperosmolality. Basal

insulin will not cause hypoglycaemia if a meal is skipped4  and should therefore be continued perioperatively at their normal dose. If a patient has a history of morning hypoglycaemia, the dose can be reduced by 20%.

Prandial insulin is usually a rapid-acting analog preparation (such as lispro, aspart or glulisine) which is injected prior to a meal. It reduces blood sugar within 15-25 minutes after injection, remains active for only three or four hours, and closely matching the normal surge of insulin secreted after a meal. Insulin pumps are portable devices that provide continuous subcutaneous insulin infusion. It uses an ultra-rapid-acting

insulin continuously as a basal insulin and can be bolused prior to meals. A majority of patients can have their pump  continued intraoperatively, but this decision is practitioner-dependent. Recommendations are to restrict pump use to surgical procedures less than 2 hour. For longer procedures, the pump should be discontinued and replaced with an

intravenous insulin infusion.

TYPES OF INSULIN

There are numerous ways to describe the different types of insulin;

• Function (prandial vs basal)

• Biochemical structure (analog, human, porcine)

• Duration of action (short-acting, long-acting, fixed combination)

Function

Basal insulin is commonly a long-acting preparation, designed to imitate background insulin secretion, keeping blood

sugar levels consistent when patients are not eating. It does not adequately cover glucose spikes after meals. Prandial

insulin may be a rapid or short-acting preparation, designed to mimic the insulin surge that physiologically occurs with

ingestion of a meal. Prandial insulin is taken more often during the day, preceding a meal or in response to point-of-care

glucose determinations.

Biochemical Structure

There are two types of insulin structures: recombinant human insulin and analog insulin. Recombinant human insulins

are essentially identical in structure to the native insulin produced in the body. Analog insulins are similar in structure but

have minor modifications, which allow for rapid onset of action or peakless effect. While analogs cost more, they generally cause less hypoglycaemia and weight gain. Most diabetic patients in the US today use analog insulin. Porcine and bovine insulins are older, animal-derived, preparations that are seldom used in current practice. Many are

out-of-production.

Duration of action Rapid-acting prandial insulin analogues include lispro, aspart, and glulisine. They are administered just prior to a meal

and have an onset of action within 15 to 30 minutes. Their duration of action is 3-6 hours. The peak effect is reached with 15 to 75 minutes. These preparations are very useful for perioperative use in rapid correction of hyperglycaemia.

Short-acting prandial insulin, such as regular insulin, is a human recombinant DNA preparation with an onset of action of 30 to 60 minutes, and a peak effect at 2 to 3 hours. The duration of action is between 3 and 8 hours.

NPH (neutral protamine Hagedorn or Isophane insulin) is an intermediate-acting insulin that does peak in activity, and can therefore cause hypoglycaemia in a fasted patient. Intermediate acting insulins, like NPH or a combination insulin

(such as fixed-combination 70/30 preparations), are not to be treated as basal insulins, and therefore necessitate

perioperative dose adjustment.