ERAS (enhanced recovery after surgery) was developed by Danish doctor Henrit Kehlet (1) proposed for the first time in 1997 and was first introduced into China by academician of Chinese Academy of Engineering- Jieshou Li in 2007. ERAS refers to the implementation of various proven effective methods in the perioperative period to maintain the preoperative organ function, to reduce the stress and complications of patients, reduce the physical and psychological trauma, reduce the mortality and shorten the length of hospital stay, and speed up the recovery of patients. The core measures of ERAS include preoperative education, preoperative nutritional support, avoidance of long-term food intake during the perioperative period, preoperative oral carbohydrates, corresponding anaesthesia and analgesia programs, and early mobilization (2).
Previously, to ensure that the gastric contents are completely emptied and avoid the occurrence of reflux and aspiration during anaesthesia, patients undergoing elective surgery are often required to fast for 6–8 hours or even longer. Most patients have preoperative discomfort after long-term fasting, including anxiety, thirst and hunger (3). Jonas Nygren et al (4) suggested in a study that preoperative fasting for a long time would reduce the metabolic rate of the body, induce insulin resistance, cause postoperative muscle function damage and nitrogen level disorder. In a prospective cohort study in 2015, De Amorim et al (5) found that preoperative fasting increased inflammatory response and prolonged postoperative recovery time in patients. Fasting before operation causes a stress reaction in the body, resulting in the increase of pro-inflammatory factors and growth factors, activation of endothelium and leukocytes and release of a large number of reactive oxygen species, which further aggravates the damage of endothelial cells and tissues (6), The increase of inflammatory factors can also cause the damage of intestinal mucosal barrier, thus aggravating the disorder of intestinal flora. The above-combined effect, prolonged the postoperative recovery time, increased the length of hospital stay. As the core measure of eras, preoperative carbohydrate loading has been proved to be safe and effective by more and more scholars. For more than a decade, many studies have confirmed that giving carbohydrates 2 hours before surgery does not increase the risk of aspiration during anaesthesia. A large number of international guidelines suggest shortening the time of fasting and drinking before surgery, including 6h of solid fasting and 2h of clear liquid fasting before surgery. In 2009, the American Society of Anesthesiologists issued “ the Guidelines on Fasting and Drinking Before Anesthesiology ”. It is recommended that carbohydrate should be taken orally 2 hours before surgery. The European Society of Anesthesiology (7) points out that it is safe and reliable for patients undergoing elective surgery to take oral carbohydrate clear night before the operation. According to “ the guidelines for preoperative anaesthesia for adults and children ” issued by the anesthesiology branch of Chinese Medical Association in 2014, oral carbohydrate 2 hours before the operation can prevent dehydration, improve circulation stability, relieve postoperative nausea and vomiting, and reduce the incidence of postoperative insulin resistance. Compared with standard glucose solution, carbohydrate osmotic pressure is lower, which leads to higher gastric emptiness rate (8) and oral administration is safer than intravenous administration, comfort is higher than intravenous administration, and patients' acceptance rate is higher. A large number of studies have shown that (3, 9, 10) preoperative oral carbohydrate can reduce the postoperative stress response, insulin resistance, hunger, thirst and anxiety of patients, and improve the comfort of patients. It can reduce the production of inflammatory factors and reduce the occurrence of inflammatory reaction and immune reaction (11). In recent years, the reliability and advantages of ERAS concept have been confirmed by more and more studies, supported by more experimental data, and accepted by more and more doctors and patients. In our previous prospective study, it was confirmed that preoperative oral carbohydrate can improve insulin resistance and comfort after multiple trauma surgery, including nausea and vomiting. At the same time, we also found that the first defecation time of patients in the CHO group ( preoperative oral carbohydrate ) was shorter than that in the Normal group (Preoperative fasting), and the stool characteristics were more soft and rotten. Previous studies have shown that preoperative oral carbohydrate is helpful to the recovery of postoperative intestinal function and shorten the length of hospital stay (12), Intestinal function is closely related to the balance of intestinal flora, but there are few studies on the effect of intestinal flora. Therefore, we designed this prospective experiment to actively explore the influence of preoperative oral carbohydrate on intestinal flora from the perspective of intestinal flora by 16SrRNA gene amplicon sequencing.