Managing blood glucose (BG) is fundamental when preparing any patient for surgery, particularly those with pre-existing high blood sugar or diagnosed diabetes. Surgical procedures inherently induce a stress response, causing a surge of hormones that elevate blood glucose levels. This stress-induced hyperglycemia, even without a formal diabetes diagnosis, significantly increases the risk of post-operative complications. Careful control of blood sugar, both before and during the procedure, is a standard component of modern surgical care.
Defining the Immediate Surgical Threshold
A patient’s immediate blood glucose level is a primary factor in determining if an elective surgery can safely proceed. A common threshold for immediate intervention is a blood glucose reading of 180 milligrams per deciliter (mg/dL), or 10 millimoles per liter (mmol/L). Levels exceeding 180 mg/dL in the pre-operative area are typically addressed with insulin therapy before the procedure begins.
Significantly higher blood sugar levels often necessitate the postponement of elective surgery until better control is achieved. Many protocols suggest that elective procedures should be postponed if the immediate pre-operative blood glucose exceeds 250 mg/dL or 300 mg/dL. This delay allows the medical team to optimize the patient’s metabolic state, reducing the potential for complications.
Emergency surgeries, such as those for trauma or acute life-threatening conditions, cannot be delayed. In these situations, the surgical team proceeds while simultaneously administering intravenous insulin to manage hyperglycemia aggressively during the operation.
How Hyperglycemia Undermines Healing and Immunity
Elevated blood sugar directly interferes with the body’s natural defense and repair mechanisms, leading to higher rates of complications after surgery. Hyperglycemia specifically impairs the function of white blood cells responsible for fighting off bacteria. High glucose levels impede the mobility and phagocytosis (engulfing) ability of neutrophils, making the surgical site vulnerable to infection.
The body’s healing process is also compromised by sustained hyperglycemia, which affects tissue repair at a cellular level. High glucose promotes the formation of advanced glycation end products (AGEs), which stiffen tissues and blood vessels. This contributes to poor circulation, limiting the delivery of oxygen and vital nutrients to the wound site, a condition called tissue hypoxia.
Furthermore, the production of collagen, the structural protein necessary to build new tissue and close a wound, is diminished in a high-glucose environment. The prolonged inflammatory phase characteristic of hyperglycemia delays the transition to the proliferative phase of healing. This combination of impaired immune response, poor circulation, and defective collagen synthesis means wounds heal slower, are less strong, and face a higher risk of dehiscence.
Pre-Operative Blood Sugar Management
Pre-operative management focuses on two distinct timeframes: the long-term metabolic state and the acute perioperative period. Long-term control is assessed by the HbA1c test, which provides an average blood glucose level over the previous two to three months. For elective surgery, many guidelines recommend an HbA1c goal below 8.0%.
If a patient’s HbA1c is above this target, the procedure may be postponed so they can work with an endocrinology team to improve their control. The acute management phase occurs immediately before, during, and after the operation. Medical teams aim to maintain perioperative blood glucose levels within a target range, most commonly between 140 mg/dL and 180 mg/dL.
This range prevents both the risks of hyperglycemia and the danger of hypoglycemia induced by overly aggressive insulin use. To achieve this control, patients with elevated glucose are often started on intravenous insulin infusion protocols. A continuous insulin drip allows the medical team to make rapid, precise adjustments to blood sugar levels in response to surgical stress.