Preoperative carbohydrates (CHO) supplement has been shown to alleviate postoperative insulin resistance (IR) in nondiabetic patients undergoing a variety of surgeries. However, it remains controversial whether preoperative CHO could yield similar effects in diabetic patients. Thus, the investigators design a randomized controlled trial investigating the impact of preoperative CHO on postoperative IR and clinical outcomes in diabetic patients undergoing cardiac surgery. The results of the study may give some clinical implications and further improve perioperative care for diabetic patients.

CHO supplement has been widely investigated in nondiabetic patients undergoing various surgeries. It has been proved that preoperative CHO could alleviate postoperative insulin resistance (IR) and improve patients' well-being in nondiabetic patients. However, whether preoperative CHO could yield similar effects in diabetic patients remains controversial. Till now, seldom has the administration of preoperative CHO been investigated in diabetic patients and few studies reported IR and postoperative recovery of diabetic patients undergoing cardiac surgery. The investigators present a prospective, single-center, single-blind, randomized, no-treatment controlled trial of preoperative CHO on diabetic patients undergoing off-pump coronary artery bypass grafting (OPCAB). A total of 62 patients will be enrolled and randomized to either Group CHO or Group control (CTRL). Patients in group CHO will receive CHO fluid containing 50 g of carbohydrates the evening before surgery (20:00-24:00) while their counterparts in Group CTRL will be fasted after 20:00 the evening before surgery. The primary endpoints are postoperative insulin resistance (IR) assessed via homeostasis model assessment (HOMA). The secondary endpoints are the potential mediators relating to IR including inflammatory factors and stress reactions assessed by serum cortisol. Exploratory endpoints are in-hospital clinical endpoints.

Inclusion Criteria:

1. Previously diagnosed T2DM
2. Diagnosed with CAD with coronary angiography and indicated for OPCAB
3. Age between 18 and 75 years old
4. First operation in the morning and anesthesia induced around 8:00
5. Written informed consent by the patients

Exclusion Criteria:

1. Combined with other heart diseases or vascular malformations that require surgery in addition to OPCAB
2. Presence of symptoms or signs of heart failure such as orthopnea, distended jugular vein, lower extremity edema, etc.
3. Reduced LVEF (lower than 50%)
4. Combined with gastroesophageal reflux
5. Combined with thyroid insufficiency requiring replacement therapy with levothyroxine
6. Combined with adrenal insufficiency requiring replacement therapy with corticosteroids
7. Refuse to participate.

Except for the identifying data such as patients name and admission ID, all the IPD could be available to other researchers on reasonable request.

The data will become available after the publication of the study report.

IPD could be accessed on reasonable request after approval of the principal investigator.

The surgeons, anesthesiologists, ICU staff, nurses, outcome assessors, data collectors and data analysts will be blinded to the grouping.