question: What reactions happen to our body that it is very important not to EAT before surgery?
comment: One of the major dangers in out-patient surgery is that the patient will vomit while unconscious and inhale that vomit into their lungs. This is very dangerous, potentially lethal, and difficult to recover from. By not eating prior to surgery the amount of stomach contents available for vomiting is reduced and the danger of aspirating the vomit is lower. Considering the benefits compared to the burden it is a good trade.
passages: Many patients will be in pain and have a loss of appetite after surgery. Part of the body's response to surgery is to direct energy to wound healing, which increases the body's overall energy requirements. Surgery affects nutritional status indirectly, particularly during the recovery period, as it can interfere with wound healing and other aspects of recovery. Surgery directly affects nutritional status if a procedure permanently alters the digestive system. Enteral nutrition (tube feeding) is often needed. However a policy of 'nil by mouth' for all gastrointestinal surgery has not been shown to benefit, with some suggestion it might hinder recovery.
   Preoperative fasting
  
  Preoperative fasting is the practice of a patient abstaining from oral food and fluid intake for a time before an operation is performed. This is intended to prevent pulmonary aspiration of stomach contents during general anesthesia.
  
  Section::::Pulmonary aspiration.
   Nutritional deficiencies are often seen in patients after the surgery due to malabsorption. They include: 
  
  Section::::Nutritional deficiencies and solutions.:Loss of appetite.
  
  Anorexia is considered to be a normal response found after the first few weeks of the surgery but after four to six weeks, most patients gain back their initial appetite before receiving the surgery.
  
  Section::::Nutritional deficiencies and solutions.:Electrolyte imbalance.
   After surgery, patients may have trouble with a regular diet and may have to consume softer foods, avoid liquids at meals, and stay upright for 1–3 hours after eating. Dysphagia is common and patients are encouraged to chew foods very well or grind their food. Patients may complain of substernal pain that resolves by sipping fluids or regurgitating food. Reflux-type symptoms can be severe, including intolerance to acidic foods and large, fatty meals. Jejunal feeding tubes may be placed during surgery to provide a temporary route of nutrition until oral eating resumes.
  
  Section::::Process.
   Section::::Before operation.:Dietary rules for surgery day.
  
  Infants 0 to 6 months:
  
  BULLET::::1. No solids the day of surgery
  
  BULLET::::2. Formula or breast milk until four hours before procedure
  
  BULLET::::3. Clear liquids (water, apple juice, flat 7-up, Pedialyte) until three hours before procedure
  
  BULLET::::4. Nothing by mouth thereafter
  
  Children 7 months and older:
  
  A. No solids the day of surgery;
  
  B. Formula or breast milk until 6 hours before procedure;
  
  C. Clear liquids (water, apple juice, flat 7-up, Pedialyte) until three hours before the procedure;
  
  D. Nothing by mouth thereafter.
   The recovery time after the surgery depends on the extent of the surgery itself. Patients are usually advised to eat soft foods for days, or sometimes weeks, to allow their jaw time to heal. They also require regular checkups with the doctor to monitor bone displacement, signs of infection, or other issues.
   After surgery, patients feel fullness after ingesting only a small volume of food, followed soon thereafter by a sense of satiety and loss of appetite. Total food intake is markedly reduced. Due to the reduced size of the newly created stomach pouch, and reduced food intake, adequate nutrition demands that the patient follow the surgeon's instructions for food consumption, including the number of meals to be taken daily, adequate protein intake, and the use of vitamin and mineral supplements. Calcium supplements, iron supplements, protein supplements, multi-vitamins (sometimes pre-natal vitamins are best), and vitamin B (cyanocobalamin) supplements are all very important to the post-operative bypass patient.
   Immediately after surgery no food or drink is allowed due to involvement of the gastrointestinal tract in the surgery. The diet will then be slowly advanced to liquids and then solid foods as tolerated. If gastrointestinal complications such as nausea, vomiting, or abdominal bloating occur the diet may be stopped or advancement of the diet slowed down depending on the severity.
  
  Section::::Recovery.:Pain control.
  
  Intravenous pain medication such as narcotics are typically used immediately after surgery. Pain medications can be switched to an oral form once a diet is tolerated.
  
  Section::::Recovery.:Activity.
   The vertical incision, pictured and listed above, is no longer usually required, though many incisions have been horizontal in the past years.
  
  Once the stomach can empty into the duodenum, feeding can begin again. Some vomiting may be expected during the first days after surgery as the gastrointestinal tract settles. Rarely, the myotomy procedure performed is incomplete and projectile vomiting continues, requiring repeat surgery. Pyloric stenosis generally has no long term side-effects or impact on the child's future.
  
  Section::::Epidemiology.
   When anaesthesia is required in an emergency, nasogastric aspiration is usually performed to reduce gastric contents and the risk of its pulmonary aspiration.
  
  Section::::Unrestricted clear fluids.
  
  Fasting guidelines often restrict the intake of any oral fluid after two to six hours preoperatively. However, it has been demonstrated in a large retrospective analysis in Torbay Hospital that unrestricted clear oral fluids right up until transfer to theatre could significantly reduce the incidence of postoperative nausea and vomiting without an increased risk in the adverse outcomes for which such conservative guidance exists.
   The Consensus Panel also emphasized the necessity of multidisciplinary care of the bariatric surgical patient by a team of physicians and therapists to manage associated comorbidities and nutrition, physical activity, behavior, and psychological needs. The surgical procedure is best regarded as a "tool" which enables the patient to alter lifestyle and eating habits, and to achieve effective and permanent management of obesity and eating behavior.
   Eating or drinking during labour is an area of ongoing debate. While some have argued that eating in labour has no harmful effects on outcomes, others continue to have concern regarding the increased possibility of an aspiration event (choking on recently eaten foods) in the event of an emergency delivery due to the increased relaxation of the esophagus in pregnancy, upward pressure of the uterus on the stomach, and the possibility of general anesthetic in the event of an emergency cesarean. A 2013 Cochrane review found that with good obstetrical anaesthesia there is no change in harms from allowing eating and drinking during labour in those who are unlikely to need surgery. They additionally acknowledge that not eating does not mean there is an empty stomach or that its contents are not as acidic. They therefore conclude that "women should be free to eat and drink in labour, or not, as they wish."
   To gain the maximum benefit from this physiology, it is important that the patient eat only at mealtimes, 5 to 6 small meals daily, and "not" graze between meals. Concentration on obtaining 80–100 g of daily protein is necessary. Meals after surgery are 1/4–1/2 cup, slowly getting to 1 cup by one year. This requires a change in eating behavior and alteration of long-acquired habits for finding food. In almost every case where weight gain occurs late after surgery, capacity for a meal has not greatly increased. Some assume the cause of regaining weight must be the patient's fault, e.g. eating between meals with high-caloric snack foods, though this has been debated. Others believe it is an unpredictable failure or limitation of the surgery for certain patients (e.g. reactive hypoglycemia).
   The main reason for preoperative fasting is to prevent pulmonary aspiration of stomach contents while under the effects of general anesthesia. Aspiration of as little as 30–40 mL can be a significant cause of suffering and death during an operation and therefore fasting is performed to reduce the volume of stomach contents as much as possible. Several factors can predispose to aspiration of stomach contents including inadequate anesthesia, pregnancy, obesity, difficult airways, emergency surgery (since fasting time is reduced), full stomach and altered gastrointestinal mobility. Increased fasting times leads to decreased injury if aspiration occurs.
  
  Section::::Gastric conditions.
   The patient is kept NPO (Nil per os) or NBM (Nothing By Mouth) that is, told not to eat, for at least 4 hours before the procedure. Most patients tolerate the procedure with only topical anesthesia of the oropharynx using lidocaine spray. However, some patients may need sedation and the very anxious/agitated patient may even need a general anesthetic. Informed consent is obtained before the procedure. The main risks are bleeding and perforation. The risk is increased when a biopsy or other intervention is performed.
   After completion of surgery, the patient is transferred to the post anesthesia care unit and closely monitored. When the patient is judged to have recovered from the anesthesia, he/she is either transferred to a surgical ward elsewhere in the hospital or discharged home. During the post-operative period, the patient's general function is assessed, the outcome of the procedure is assessed, and the surgical site is checked for signs of infection. There are several risk factors associated with postoperative complications, such as immune deficiency and obesity. Obesity has long been considered a risk factor for adverse post-surgical outcomes. It has been linked to many disorders such as obesity hypoventilation syndrome, atelectasis and pulmonary embolism, adverse cardiovascular effects, and wound healing complications. If removable skin closures are used, they are removed after 7 to 10 days post-operatively, or after healing of the incision is well under way.
   When the patient ingests just a small amount of food, the first response is a stretching of the wall of the stomach pouch, stimulating nerves which tell the brain that the stomach is full. The patient feels a sensation of fullness, as if they had just eaten a large meal—but with just a thimble-full of food. Most people do not stop eating simply in response to a feeling of fullness, but the patient rapidly learns that subsequent bites must be eaten very slowly and carefully, to avoid increasing discomfort or vomiting.
   After the surgery, the patient’s breathing, blood pressure, temperature, heart rate, fluid intake and output, respiration, and operative site will be monitored. Typically, about 8 hours after surgery the patient may be able to walk a short distance, and walk increasing distances over the next 2–3 days. Most patients are released after 24 hours and recover quickly and completely. Most people can slowly begin a regular diet within 2–3 weeks.
  
  Section::::Risks.
   The minimum fasting times prior to surgery have long been debated. The first proposition came from British anesthetists stating that patients should be nil by mouth from midnight. However, since then, the American Society of Anesthesiologists (ASA), followed by the Association of Anaesthestists of Great Britain and Ireland (AAGBI), recommended new fasting guidelines for the minimum fast prior to surgery. This was based upon evidence by Canadian anesthesiologists who found that drinking clear fluids two hours prior to surgery decreased pulmonary aspiration compared to those nil by mouth since midnight. The following are the recommended guidelines for nil by mouth prior to surgery in healthy patients:
   Section::::Mechanisms of weight reduction.:Conditioning of appetite.
  
  If the patients take excessive food after the surgery, they will experience abdominal discomforts such as steatorrhea and abdominal pain, as patients' digestive system capacity has been reduced drastically. 
  
  Section::::Selection Criteria.
  
  Intestinal bypass, in spite of its highly effectiveness in weight reduction, is a risky and irreversible. Thus, it requires rigorous assessment and selection before the surgery is carried out. The following are the normal selection criteria:
  
  BULLET::::- Overweight for more than 100 lbs.
  
  BULLET::::- Readiness to accept the side effects and hence all the follow-up procedures.
   Vomiting is sometimes impossible or, if not, very painful after a fundoplication, with the likelihood of this complication typically decreasing in the months after surgery. In some cases, the purpose of this operation is to correct excessive vomiting. However, when its purpose is to reduce gastric reflux, difficulty in vomiting may be an undesired outcome. Initially, vomiting is impossible; however, small amounts of vomit may be produced after the wrap settles over time, and in extreme cases such as alcohol poisoning or food poisoning, the patient may be able to vomit freely with some amount of pain.
  
  Section::::See also.
   A common form of gastric bypass surgery is the Roux-en-Y gastric bypass, designed to reduce the amount of food a person is able to eat by cutting away a part of the stomach. Gastric bypass is a permanent procedure that helps patients by changing how the stomach and small intestine handle the food that is eaten to achieve and maintain weight loss goals. After the surgery, the stomach will be smaller. A patient will feel full with less food.
   In addition to fasting, antacids are administered the night before (or in the morning of an afternoon operation) and then once again two hours prior to surgery. This is to increase the pH (make more neutral) of the acid present in the stomach, helping to reduce the damage caused by pulmonary aspiration, should it occur. H2 receptor blockers should be used in high-risk situations and should be administered in the same timing intervals as antacids.
   BULLET::::- Protein malnutrition is a real risk. Some patients suffer troublesome vomiting after surgery, until their GI tract adjusts to the changes, and "cannot" eat adequate amounts even with 6 meals a day. Many patients require protein supplementation during the early phases of rapid weight loss to prevent excessive loss of muscle mass. Hair loss is also a risk of protein malnutrition.
   BULLET::::- Evidence of failure in all previous attempts in weight reduction.
  
  BULLET::::- Stable mental health status.
  
  BULLET::::- Psychiatric evaluation showing the obese state.
  
  BULLET::::- An absence of all types of endocrinopathies that are correctable.
  
  This surgery serves as the LAST approach to lose weight when all other weight-losing methods have failed and at the same time, morbid obesity remains a life-threatening problem. It is crucial for patients to understand all the pros and cons of this surgery, despite the weight loss they aimed for.
  
  Section::::Health impacts.
  