Does Pre-operative Carbohydrate Loading Reduce Insulin Resistance and Improve Outcomes in Elective Surgical Patients?

In many Western hospitals, including St. Michael's Hospital, fasting for 12-14 hours is the standard protocol for patients entering elective surgery. Fasting results in a depletion of energy stores and consequently, a patient enters surgery in a catabolic state. Furthermore, the human body reacts to surgery by producing a variety of stress hormones and other hormone-like proteins that enable the body to react to stress or injury appropriately. One of the changes that occurs with surgery is related to how the body stores and metabolizes glucose. During and after surgery, muscle and adipose tissue become less sensitive to the action of insulin (insulin resistant). Insulin resistance results in a reduced uptake of glucose by these tissues and subsequently to a rise in circulating blood glucose levels. Sustained high levels of blood glucose have been associated with post-surgical complications and less favourable outcomes. Previous studies have found that fasting before surgery exacerbates insulin resistance during and after surgery. The recent development of a carbohydrate drink for consumption prior to elective surgical procedures has been shown to be well tolerated and pose no additional risk of pulmonary aspiration when ingested two hours prior to surgery. Furthermore, there appears to be metabolic, psychological and possibly clinical benefits in pre-operative carbohydrate loading compared to fasting, including improvements in insulin resistance. However, the studies done to date have been limited by their small sample size, their lack of clinical outcome data and their reliance upon predominantly surgeries of shorter duration and reduced metabolic stress where insulin resistance is lower. Therefore, there is a need to investigate the effect of carbohydrate loading on insulin resistance and clinical outcomes in patients undergoing surgery of extended duration and complexity.

Patients undergoing major cardiac and spinal surgery are ideal for studying the effects of pre-operative carbohydrate loading since this type of operation is of long duration and relatively high surgical stress resulting in the development of significant insulin resistance, and thus potentially benefit from pre-operative carbohydrate loading. Therefore, we will be conducting a larger randomized trial investigating the effects of pre-operative carbohydrate loading in comparison with fasting on insulin resistance and clinical outcomes in patients undergoing invasive cardiac and spinal surgery at St. Michael's Hospital.

We hypothesize that consumption of a pre-operative carbohydrate load will reduce postoperative insulin resistance by 40% (measured by the standardized short insulin tolerance test). As secondary outcomes, we hypothesize that pre-operative carbohydrate loading will reduce circulating markers of inflammation and stress as well as improve clinical outcomes such as blood product utilization, incidence of hyperglycemia, rates of adverse events and length of stay in comparison with standard pre-operative fasting. This study will provide important information regarding the clinical benefits associated with the consumption of a pre-operative carbohydrate load. Many European centres have already liberalized their pre-operative treatments; this study will help to optimize the perioperative management and outcomes of surgical patients at our institution.

Inclusion criteria

• Adult patients undergoing elective coronary artery bypass graft or spinal (decompression and fusion) surgery
• Ability to provide informed consent

Exclusion criteria

• Patients undergoing associated cardiac procedures such as valve replacement or valve repair
• Patients undergoing spinal surgery without fusion
• Conditions likely to impair gastrointestinal motility or enhance gastrointestinal reflux
• On medications likely to delay gastric emptying
• BMI > 40
• Existing Type I or Type II diabetes
• Participated in another study in the past 30 days
• Entering surgery greater than five hours after ingestion of morning drink