The management of blood sugar before, during, and after surgery directly impacts patient recovery and safety. High blood sugar (hyperglycemia) creates a hostile environment that increases the risk of complications associated with any surgical procedure. Surgical stress naturally triggers a release of hormones that can elevate glucose levels, even in people without a history of diabetes, making careful control a necessity for everyone undergoing an operation.
The Critical Thresholds for Surgery
Determining what blood sugar level is “too high” involves looking at both immediate and long-term measures of glucose control. For an elective procedure, the immediate goal for the morning of surgery is typically to maintain blood glucose below 180 milligrams per deciliter (mg/dL). Many institutions aim for an even tighter target, often below 140 mg/dL upon arrival, to provide a buffer against the stress response of surgery. If blood glucose severely exceeds 250 mg/dL, the surgical team may postpone an elective operation to reduce immediate risks.
The final decision also depends on the patient’s long-term control, measured by the Hemoglobin A1c (HbA1c) test. HbA1c provides an average of blood sugar levels over the past two to three months. A consistently high HbA1c, often cited as above 8.0%, signals a greater underlying risk of complications.
While a high HbA1c may prompt a doctor to delay an elective surgery to allow for better pre-operative control, emergency surgeries cannot be postponed. In these cases, the focus shifts to aggressive management with intravenous insulin during the procedure itself. Targets are a delicate balance, as overly aggressive lowering can cause hypoglycemia (low blood sugar), which carries its own dangers during the perioperative period.
Surgical Complications Linked to Hyperglycemia
Hyperglycemia creates several biological impairments that increase the risk of adverse outcomes. High glucose levels directly impair the function of white blood cells, the body’s primary defense against infection. This compromised immune response significantly increases the risk of developing surgical site infections, pneumonia, or urinary tract infections after the procedure.
Elevated blood sugar also disrupts wound healing by impairing the synthesis of collagen, a protein necessary for tissue repair. This effect can lead to delayed wound closure and a higher chance of the wound separating or becoming infected.
The stress of surgery combined with high glucose places significant strain on the cardiovascular system, increasing the risk of serious events like heart attack and stroke during the perioperative period. The kidneys are also vulnerable, with hyperglycemia increasing the likelihood of acute kidney injury (AKI). Managing fluid and electrolyte balance becomes more complex when blood sugar is high, further complicating stability under anesthesia and during recovery.
Preparing for Surgery: Pre-Op Glucose Management
The preparation phase requires the patient to take an active role in optimizing glucose levels. A meeting with the endocrinologist or primary care physician is necessary well in advance to create a clear medication adjustment plan. For patients taking long-acting insulin, the dose is often reduced the night before and the morning of surgery to prevent hypoglycemia while fasting.
Many oral diabetes medications, such as metformin, are typically discontinued on the day of surgery, and newer drugs like SGLT-2 inhibitors are stopped several days beforehand due to specific safety concerns. Patients must adhere strictly to the “Nothing by Mouth” (NPO) guidelines, which is particularly challenging for managing glucose levels. During the fasting period, patients should monitor their blood sugar frequently and be prepared with specific instructions on how to administer small correction doses of rapid-acting insulin if levels rise above the target.
Monitoring and Management During Recovery
Once the patient is hospitalized, the surgical team takes over the minute-by-minute management of blood sugar control. For complex or lengthy procedures, a continuous intravenous (IV) insulin infusion is the preferred method for maintaining tight control during the surgery. This method allows for immediate adjustment of insulin delivery based on frequent blood glucose checks, which are often performed hourly. The goal during the operation is to keep the blood glucose level between 100 and 180 mg/dL.
In the immediate post-operative phase, close monitoring continues, especially in the post-anesthesia care unit (PACU). The post-operative target range remains moderate, between 140 and 180 mg/dL, as this range effectively balances the need for infection control with the avoidance of dangerous hypoglycemia. As the patient recovers and can resume eating, the hospital team transitions them from IV insulin back to their home medication regimen, ensuring stable glucose levels support the final stages of healing.