A Natural History of Perioperative Metabolism

We will conduct a cross-sectional study in a cohort of patients undergoing spinal surgery for discectomy, laminectomy, or vertebral fixation. We will recruit a cohort of subjects in groups with metabolic phenotypes defined by body mass index (BMI) and glycemic control. We are choosing to use spinal surgeries as they utilize inhaled anesthetics, run hours in length, do not involve ischemic tourniquet time, and use basic elements of the anesthetic pharmacopeia including anti-emetics, opioid analgesics, and paralytics. Further the increased surgical stress of entering the thorax or peritoneum are avoided. These features provide a long steady-state of surgical intervention with minimal additional maneuvers allowing for a controlled examination of surgical metabolism.

The categorical criteria for the groups will be body type: lean (BMI<25), overweight (BMI >25, <30), and obese (BMI >30 but <40), and glycemia: normoglycemic (fasting blood glucose; FBG <100 mg/dL or HbA1c <5.5%), impaired fasting glucose (FBG >100 mg/dL and <126 mg/dL, or HbA1c >5.5% and <6.5%), Type 2 Diabetes (FBG >126 mg/dL or HbA1c >6.5%).

Subjects will be screened, enrolled, give informed consent, and have a dedicated peripheral IV line placed in pre-operative hold. A baseline blood sample will be collected in pre-operative hold, after transfer to the table in the operating room, and immediately prior to induction of anesthesia. Following induction blood samples will be collected at 15' intervals for the initial 2 hours of each case, then at 30' intervals for the remainder of the case and for 2 hours in the post-anesthesia care unit. Samples will be processed and stored at -80C until analyzed. Intra-operative data from the anesthesia record will be collected and included in the study database.

Inclusion criteria

• Subjects were eligible if they were >18 years old without acute or chronic health conditions who were undergoing multilevel lumbar fusions with an inhaled anesthetic.

Exclusion criteria

• acute or chronic health conditions including cardiac, pulmonary, hepatic, renal, auto-immune, or hematological disease. Obese subjects with body mass index >40kg/m2 were excluded. Subjects with Type 2 diabetes were eligible if they were well-controlled (HbA1c <7.5%) and treated with diet and exercise, metformin, or insulin. Subjects were excluded if taking a sulfonylurea, thiazolidindiones, DPP-4 inhibitor, GLP-1 analog, weight loss medication, or other medications affecting glucose homeostasis.