Fasting and drinking before elective surgery is to reduce the volume and acidity of gastric contents and to prevent vomiting and aspiration during anesthesia. At present, our textbooks still follow the traditional view that adult elective surgery patients should fast for 8-12 h and drink for 4 h. However, in recent years, it has been clinically found that the actual preoperative fasting time >10 h and drinking time >6 h can lead to adverse reactions such as thirst, hunger, anxiety, dehydration, and hypoglycemia in patients.
Therefore, the American Society of Anesthesiologists (ASA) and the Rapid Recovery Surgery (ERAS) revised their preoperative fasting guidelines in 1999 and 2012, respectively, to shorten the preoperative fasting and drinking time, especially for clear liquids. Some medical units in China have also tried to put the new fasting program into practice, but the current situation of clinical application is not optimistic. This paper reviews the research on preoperative fasting and drinking at home and abroad in recent years, in order to provide reference for clinical care work.
1.The history of preoperative fasting and fasting
In 1946, Mendelson reported that the fatal Mendelson syndrome, i.e. aspiration syndrome, could be induced by the misaspiration of gastric contents with a volume of >0.4 ml/kg and pH <2.5 during anesthesia. The reason is that the incidence of misaspiration is increased due to the suppression of the laryngeal reflex under general anesthesia. Therefore, midnight fasting and abstinence from food and drink have been clinically advocated to ensure the safety of anesthesia, and this concept has been extended to elective surgery.
Modern physiological studies have found that different foods empty at different rates. The fastest emptying of water, about 95% after ingestion Ih has been emptied by the stomach; followed by solid food, which needs to be converted into liquid form before emptying, generally 4-6h; fatty food stomach emptying is the slowest. This provides a physiological basis for the clinical shortening of preoperative fasting and drinking time, especially the shortening of transparent liquid fasting time.
2.The effect of prolonged fasting and drinking on the organism
Cao Luying et al. investigated patients undergoing elective orthopedic surgery in China and found that the actual preoperative fasting time was 12-20h and 4-10h, which was significantly longer than the traditional prescribed time. Liang Shuling found that the preoperative fasting time for most of the patients undergoing table surgery was 14-16h, with the longest being 21h; the fasting time for drinking was longer, 12-14h, with the longest being 1%.
In the fasting and drinking state, blood glucose decreases, resulting in reduced insulin secretion and increased secretion of glucagon, growth hormone and catecholamines, which accelerates glycogenolysis and increases gluconeogenesis. Prolonged fasting and drinking induce myostatin mobilization, activation of hepatic gluconeogenesis and increased gluconeogenesis to replenish blood glucose. Increased lipolysis in the body becomes the most important source of energy for the organism. Therefore, in the early phase of fasting, if glucose is supplemented in time, it can significantly reduce protein isogenesis and save protein; moreover, glucose supplementation can also prevent lipolysis from producing ketosis and reduce the incidence of acidosis.
For the organism, surgery is a trauma that can lead to insulin resistance in the postoperative period. It lasts about 2 weeks after uncomplicated elective abdominal surgery, and is especially strong on the first to second postoperative day, directly related to the intensity of the surgery, and even occurs in patients undergoing minor surgery. Moreover, prolonged preoperative fasting and abstinence from food and drink can further contribute to the development of postoperative insulin resistance, increase metabolic stress from surgical trauma, affect tissue repair and incisional healing, and reduce the body’s ability to resist infection. Therefore, if invasive surgery is performed under the stressful condition of prolonged fasting and fasting, hemodynamic disturbance, deficiency or even shock may occur. The suitability of prolonged fasting for all surgical patients has been increasingly questioned.
3.Research and exploration on shortening the duration of fasting and drinking
In order not to increase the risk of anesthesia and to allow patients to receive surgical treatment in a comfortable state, medical personnel at home and abroad have conducted a large number of clinical studies to find a reasonable duration of fasting and drinking, and Dalal et al. confirmed through clinical practice that there is no particularly close relationship between the amount of gastric contents ^ pH and the length of fasting. The amount of gastric juice in the water group [(5,5±3,7) ml] was less than in the midnight fasting group [(17,1±8,2) ml], and the pH of gastric juice was similar in both groups. Thus, prolonged fasting does not increase the pH of gastric juice, and drinking water both dilutes gastric acid and stimulates gastric emptying.
Xu Haiying et al. increased the amount of preoperative oral sugar water to 300 ml, which also did not increase the incidence of intraoperative aspiration compared with the control group. Since prolonged fasting and abstinence from food and drink can cause thickening of the blood, etc.? shortening the preoperative drinking abstinence of surgical patients from the traditional 4h to 2h and reducing the use of laxatives significantly reduced the total body water loss of patients at the beginning of surgery. An rneta analysis including 38 randomized controlled trials also showed no evidence that a shorter preoperative fasting time increased the risk of reflux and aspiration during anesthesia compared with the traditional midnight fast.
In order to put patients in a good functional state before surgery, Yagmurdur et al. gave patients oral glucose or carbohydrate-containing beverages preoperatively based on a shortened fasting and drinking time, which significantly improved discomfort such as thirst and hunger, maintained stable mean arterial pressure, and increased blood glucose and insulin concentrations. More studies have been conducted by domestic medical professionals in improving patients’ preoperative metabolism, and similar conclusions have been reached. Because carbohydrate drinks have energy levels similar to those of a mixed diet, they allow patients to reserve some energy before undergoing surgical trauma, promote the release of endogenous insulin, and reduce postoperative insulin resistance.
Perrone et al. tried preoperative supplementation of whey protein to patients, which not only effectively lowered C-reactive protein and C-reactive protein/albumin values, but also reduced postoperative acute phase reactions and insulin resistance, effectively helping to control blood glucose. When blood glucose was controlled, the incidence of perioperative complications was also significantly reduced Researchers continue to explore clear fluids that can be given preoperatively, and new options also include amino acids (glutamine) or peptides (soy peptides).
Henriksen et al. found no difference in gastric emptying time between the carbohydrate group (12,5g/100ml carbohydrate drink) and the carbohydrate plus peptide group (12,5g/100ml carbohydrate plus 3,5g/100ml hydrolyzed soy protein).Lobo et al. added glutamine and carbohydrate to 300-400ml of water, based on Gastric emptying time, the state of gastric contents could be restored to the initial baseline level after 3h of drinking this mixed liquid in healthy volunteers.
Of course, most clinical studies are still based on patients with elective, non-severe organ dysfunction, who are not at high risk of reflux and misaspiration during anesthesia. Feng Li et al [35] also extended their study to elderly patients over 65 years of age, and oral sugar water given 2 h before surgery or metformin given perioperatively was found to reduce insulin resistance after abdominal surgery in elderly patients, and the incidence of perioperative complications was significantly reduced.
A large number of clinical practices have demonstrated that shortening the duration of preoperative fasting essentially improves the clinical outcome of surgical patients, reducing complications by approximately 50% and correspondingly reducing postoperative recovery time and hospital stay.
4. New guidelines for preoperative fasting
Based on randomized controlled studies and evidence-based medicine, in 1999, the American Society of Anesthesiologists (ASA) revised its guidelines for preoperative fasting, calling for shorter periods of fasting and abstinence, especially for clear liquids, to allow patients to undergo surgery in a state of comfort without increasing the risk of anesthesia. The guidelines stipulate that patients of any age can have clear liquids without alcohol and with a little sugar, such as water, tea, coffee and juice, 2h before surgery; adults and children can have easily digestible food, such as bread and milk, 6h before surgery, and normal diet 8h before surgery.
In 2012, the Rapid Recovery Surgery (ERAS) guidelines were also published, and the abstinence from solid food for 6h and clear liquids for 2h before induction of anesthesia in patients undergoing elective colorectal surgery, and oral carbohydrate-containing liquids before surgery in non-diabetic patients are both strongly recommended levels of evidence-based medicine.
The new 2013 guidelines on the perioperative period for 3 types of surgery (colectomy, rectal/pelvic surgery, and pancreaticoduodenectomy) also state that several traditional perioperative management, such as bowel preparation prior to surgery, routine overnight fasting, and routine use of nasogastric tubes for 3 traditional preoperative preparations, are not supported by all evidence-based medical evidence and are even strongly opposed to their use.
The new fasting protocol is applicable to most patients undergoing elective surgery, but strict preoperative fasting and abstinence from food and drink are still recommended for patients undergoing emergency surgery. Importantly, fasting from solid foods for 6-8 h before elective surgery is mandatory, and, the time limit for carbohydrate consumption is 2 h before surgery. patients with any disturbance of gastrointestinal activity, such as gastroparesis, gastrointestinal obstruction, gastroesophageal reflux, and morbid obesity, are contraindications to the new guidelines and still require routine preoperative fasting and abstinence from food and drink.
5. Outlook
Although a large amount of evidence shows that it is safe and beneficial to shorten the preoperative fasting time. However, because there is no authoritative guideline in China, most hospitals still basically implement the traditional fasting method in clinical practice, or even longer. We still need sufficient evidence-based medical evidence, especially multicenter studies with large samples, to support new preoperative fasting protocols and to develop new preoperative fasting guidelines suitable for the Chinese context.
Both metabolic basic research and clinical practice of preoperative fasting are yet to be aligned with international standards, especially for some special populations, such as patients with metabolic diseases like diabetes [18], elderly, pediatric, and ASAin-iv still need further clinical exploration for better fasting protocols.