Preoperative fasting

Learning objectives

Preoperative fasting is defined as abstaining from eating or drinking for some time by surgical patient before having an operation
Preoperative fasting allows sufficient time for gastric emptying of ingested food and liquid
This minimizes the risk of pulmonary aspiration during anesthesia as aspiration of as little as 30-40 mL can be a significant cause of suffering and death
Pulmonary aspiration of gastric contents is a rare but potentially life-threatening complication
Aspiration is uncommon in healthy ASA I or II patients, 1.1/10,000 adults, and 1.3/10,000 children, but may lead to pneumonitis, pneumonia, bronchospasm, and acute respiratory distress syndrome

Be aware that excessive fasting times are unpleasant for patients and are associated with medical morbidity
Therefore, avoid prolonged fasting and minimize fasting times

	Factors increasing emptying	Factors decreasing emptying
Physiological factors	Large gastric volume Liquid gastric contents solids <2 mm Parasympathetic stimulation Secretion of motilin and gastrin Sitting position (for non-caloric liquids)	Large duodenal volume High-calorie chyme Acidic chyme Hypo-/hyper-osmolar chyme Fatty and amino acid-rich chyme Hot and cold chyme Sympathetic stimulation Secretion of cholecystokinin, secretin, somatostatin, vasoactive intestinal peptide, and gastric inhibitory peptide
Pharmacological factors	Anticholinergics Metoclopramide Domperidone Erythromycin	Antimuscarinics Opioids
Patient factors	Hyperthyroidism	Pain Anxiety and stress Trauma Pregnancy Alcohol ingestion Hypothyroidism Diabetes Pyloric stenosis Intestinal obstruction Vagotomy

Clear liquids such as water, black coffee, black tea, and juice without pulp are safe to drink until 2h before general anesthesia
Healthy adults are allowed to drink carbohydrate-containing clear liquids until 2h before elective procedures requiring general anesthesia, regional anesthesia, or procedural sedation
- In this way, the patient is hydrated and in a more normal metabolic state
Protein-containing clear liquids should not be recommended over other clear liquids before elective procedures requiring general anesthesia, regional anesthesia, or procedural sedation
Elective procedures requiring general anesthesia, regional anesthesia, or procedural sedation should not be delayed in healthy adults chewing gum
Avoid prolonged fasting in children by allowing children at low risk of aspiration to drink clear liquids as close to 2h before procedures as possible
- Consider even a 1-h fast for clear liquids in children as there is no increased risk for pulmonary aspiration