Perioperative Evaluation of Glucose Profile Using Continuous Glucose Monitoring System in Glucose Intolerant Patients

Bariatric surgery allows weight loss and obesity related comorbidities remission. In patients with type 2 diabetes (T2D), glucose intolerance (GI) and metabolic syndrome (MS), weight loss surgery improves glucose control more than medications and/or life style intervention. This approach is gaining acceptance even in patients with mild obesity and indications are now rapidly growing. Roux en Y gastric bypass (RYGB) and Sleeve Gastrectomy (SG) the gold standard operations for treating T2D, lower glycemia often very rapidly and sometime profoundly. The responsible mechanisms are not completely understood and guidelines for the early management of T2D and GI following bariatric surgery are lacking, resulting in highly variable postoperative glucose control.

The recent use of a pre-operative carbohydrate loading compared to fasting has been shown to improve the early recovery after surgical procedures by reducing the profound stress response following surgery and allowing a better postoperative blood glucose regulation by lowering insulin resistance.

Metabolic stress and insulin resistance follow major surgery. The resulting post-operative hyperglycaemia is associated with increased morbidity as well as mortality. In non-diabetic patients, avoiding pre-operative fastening substantially reduces post-operative stress and insulin resistance. A pre-operative carbohydrate load improves post-operative glycaemic control, most likely by inducing endogenous insulin release before the onset of surgery. This sets the metabolic state of the patient in a fed rather than a fasted state at the time of surgery. Metabolic reactions to surgical stress are thereby markedly reduced not only resulting in a reduced risk for hyperglycaemia during post-operative nutrition but also retained lean body mass, improved muscle strength and nitrogen economy.

The oral preparation used is a carbohydrate-rich clear beverage containing mainly polymers of carbohydrates to minimize the osmotic load. The drink, in addition to its metabolic effect, improves patient well-being (thirst, hunger, anxiety) pre-operatively. Oral preload is considered the first element in the surgical pathway to reduce patients' stress with the aim of early return to oral diet, mobility and recovery as soon as possible after surgery and had a significant effect on reducing complications and improving wellbeing.

Patients with GI and T2D are at particular risk of impaired glycaemic control peri-operatively. Most of the studies using pre-operative carbohydrate loading were performed on non-diabetic patients. A considerable number of patients going through bariatric surgery suffer from GI or T2D (respectively 30% and 15% in our experience), this patient group has been denied initially for the pre-operative carbohydrate drink because of fear of slow gastric emptying and impaired glycaemic control. We are aware of only one study that evaluated the suitability for diabetic patients to have preload drinks pre-operatively . Gustafsson et al explored the possibility of providing pre-operative carbohydrate loading in patients with mild T2D without neuropathy or delayed gastric emptying (as autonomic neuropathy is a likely cause of delayed gastric function in diabetes). In this study, T2D patients (n=25) showed no signs of hyperglycaemia. However, the wider spectrum of diabetic patients was not evaluated. Can et al. also evaluated the effects of pre-operative pre-loading in patients with or without insulin resistance. This differed from other studies, which had previously excluded those with known insulin resistance. This study included 34 cholecystectomy or thyroidectomy patients showed that the temporal pattern of plasma glucose in patients with insulin resistance who were given preload drinks pre-operatively was similar to that of patients without insulin resistance. These studies suggest that there might be a benefit without risk of hyperglycaemia to give to type-2 diabetic (and GI) patients a preload along with their usual diabetic medication. No other study has yet investigated the effect of preoperative carbohydrate loading on glucose control the first days after the bariatric surgery in patients who have poor glycemic control. Furthermore, most bariatric surgery studies include only late postoperative evaluations of glucose control, such as those made after 7 days or more.

The main hypothesis of this study is that pre-operative carbohydrate loading compared to fasting will optimize the overall pattern of postoperative glucose profile evidenced by Continuous Glucose Monitoring (CGM) with a greater impact in the first few days after surgery on lowering mean glycaemia and glycemic variability in patients with glucose intolerance.

The primary aim is to evaluate the mean of all blood glucose measures of CGM over 24-h period after surgery in patients receiving pre-operative carbohydrate loading in comparison with standard 6h fasting. The mean of all glucose measures over 24- h of CGM (around 288) reflects overall glucose control including fasting and postprandial state. It have been chose to study this early period to minimize any confounding effects of weight loss.