Reviewed and revised 26 August 2015
- Peri-procedural fasting is widely performed with little evidence base
- NBM = nil by mouth; NPO = nil per oral
PHYSIOLOGY OF GASTRIC EMPTYING
In normal patients gastric emptying of liquids is rapid and linear
- half-emptying time (T ½) (the time to empty half of the oral liquid meal) of a non fatty, liquid meal is 15–20 minutes
- by 90 minutes after ingestion, virtually all of the liquid meal has been emptied
Gastric emptying of solids, in normal patients, is more complex
- lag phase, dependent on the amount of physical digestion or trituration needed to break down the solid particles to ≤1 mm in diameter so they may empty through the pylorus
- exponential phase of emptying dependent on quantity and type of nutrient (fats empty slower than proteins or carbohydrates)
- Each type of solid meal will have slightly different physical characteristics and therefore different emptying times
- Ingested solids that cannot be broken down by trituration to ≤1 mm eventually leave the stomach at the end of the postprandial motor pattern (which usually lasts 2–3 h after a meal) with the return of the so-called interdigestive motor pattern or the migrating motor complex which very effectively empties the stomach during fasting
- After a breakfast-like meal of easily digestible solids (toast, eggs, etc.) the stomach should be virtually empty of the meal by 3 hours after ingestion
Certain patient groups may have abnormal gastric emptying
- e.g. gastric outlet obstruction, diabetes, gastro-oesophageal reflux disease, trauma, obesity and exposure to medications such as opioids
- pregnancy per se does not delay gastric emptying, but labour does
- gastric emptying times in these patients may be prolonged and difficult to predict
RATIONALE FOR FASTING
- Concern about pulmonary aspiration of gastric content stems from the very real possibility of esophagopharyngeal reflux of intragastric contents on induction of general anesthesia in patients with a full stomach.
- The possibility of reflux or aspiration is especially pertinent in patients with recent oral intake of liquids or solids (or both) or in patients with gastric outlet or intestinal obstruction
- risk of gastrointestinal ischemia and anastomotic breakdown
FASTING BEFORE GENERAL ANAESTHESIA
For healthy patients undergoing elective sedation/analgesia, American Society of Anesthesiologists recommendations are:
- 2-hour fasting time for clear liquids
- 4-hour fasting time for breast milk
- 6-hour fasting time for solids
Unfortunately ‘NBM from midnight’ is still widely practiced.
In emergency cases the benefits of proceeding outweigh the risk of not being fasting and there should be no delay.
Problems with these guidelines include some studies suggesting that:
- preoperative fluids actually decrease gastric residual volumes
- carbohydrate-enriched fluids for oral use in the preoperative phase have a positive effect on postoperative metabolism
Prokinetics (e.g. metoclopramide, erythromycin) may be useful to help empty the stomach in patients undergoing general anesthesia for emergency procedures
- Czrnetzki et al, 2015: RCT (n=110) showed that, compared with placebo, IV erythromycin, 3 mg/kg, 15 minutes before tracheal intubation was more likely to result in a clear stomach in patients requiring general anaesthesia for emergency procedures (80% vs 64%; risk ratio, 1.26 [95% CI, 1.01-1.57])
FASTING BEFORE PROCEDURAL SEDATION
- Extrapolation of guidelines for general anesthesia cases in the operating room, in which airway manipulation during intubation and extubation increases the aspiration risk, to procedural sedation in the ED is likely inappropriate
- a study of Australian EDs showed that patients had consumed food or fluid in the previous 6 h over over 50% of procedural sedation cases
- The recommendation from the 2014 ACEP Clinical Policy is:
Do not delay procedural sedation in adults or pediatrics in the ED based on fasting time.
Preprocedural fasting for any duration has not demonstrated a reduction in the risk of emesis or aspiration when administering procedural sedation and analgesia.
- There is no evidence to support a specific fasting period before ED procedural sedation
- Regardless of fasting status some high-risk patients (e.g. gastric outlet obstruction) may not be suitable for procedural sedation and rapid sequence intubation with general anaesthesia may be safer. Which patients constitute this high risk group is controversial and risks should be considered on a case-by-case basis.
PERIPROCEDURAL FASTING PROS AND CONS
- proposed to reduce risk of vomiting and aspiration (not supported for ED procedural sedation)
- procedural difficulty
- ED or ward resource utilization
- pediatric hypoglycemia
- paradoxical increased gastric secretions
- failure to meet nutritional requirements (malnutrition)
- impaired immune response
- impaired post-operative metabolism
- impaired bowel mucosal growth and repair
POST-OPERATIVE FASTING AND EARLY ENTERAL NUTRITION
- The role of early postoperative enteral nutrition after gastrointestinal surgery is controversial
- Traditional management consist of ‘nil by mouth’, where patients receive fluids followed by solids when tolerated; enteral feeding is not started until bowel motility has recovered after elective surgery on the GI tract
- patients that undergo emergency GI surgery have an oedematous or ischemic bowel, anastomosis healing is usually delayed, and this can result in anastomotic disruption or leakage
- A Cochrane review of 13 RCTs looked at early enteral nutrtion in post-colorectal surgery patients. It found no significant differences in GI complications, but had a trend in favour of early enteral nutrition. These findings support the use of early enteral feeding in post-colorectal surgery patients.
Exceptions commonly cited include:
- severe shock
- intestinal ischemia
- sustained bowel perforation
- or short bowel syndrome
- AAA surgery
Haemodynamically unstable patients
- Concomitant use of EEN with vasopressors has been associated with nonocclusive bowel necrosis in critically ill patients with hemodynamic instability
- patients at high risk of postoperative complications who cannot be fed adequately by the oral route within 7–10 days should be treated by post-operative parenteral nutrition
- patients with pre-operative severe under-nutrition should be treated with parenteral nutrition without delay if an inadequate oral intake for more than 7 days postoperatively is anticipated
References and Links
- American Society of Anesthesiologists Committee. Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: application to healthy patients undergoing elective procedures: an updated report by the American Society of Anesthesiologists Committee on Standards and Practice Parameters. Anesthesiology. 2011 Mar;114(3):495-511. .[pubmed]
- Andersen HK, Lewis SJ, Thomas S. Early enteral nutrition within 24h of colorectal surgery versus later commencement of feeding for postoperative complications. Cochrane Database Syst Rev. 2006 Oct 18;(4):CD004080. Review.[pubmed]
- Bell A, Taylor DM, Holdgate A, MacBean C, Huynh T, Thom O, Augello M, Millar R, Day R, Williams A, Ritchie P, Pasco J. Procedural sedation practices in Australian Emergency Departments. Emerg Med Australas. 2011 Aug;23(4):458-65. [pubmed]
- Brady M, Kinn S, Stuart P. Preoperative fasting for adults to prevent perioperative complications. Cochrane Database Syst Rev. 2003;(4):CD004423. [pubmed]
- Czarnetzki C, Elia N, Frossard JL. Erythromycin for Gastric Emptying in Patients Undergoing General Anesthesia for Emergency Surgery: A Randomized Clinical Trial. JAMA surgery. 150(8):730-7. 2015. [pubmed]
- Godwin SA, Burton JH, Gerardo CJ, Hatten BW, Mace SE, Silvers SM, Fesmire FM; American College of Emergency Physicians. Clinical policy: procedural sedation and analgesia in the emergency department. Ann Emerg Med. 2014 Feb;63(2):247-58.e18. [pubmed]
- Levy DM. Pre-operative fasting—60 years on from Mendelson. Contin Educ Anaesth Crit Care Pain (2006) 6 (6): 215-218. [Free Full Text]
FOAM and web resources
- EM Updates — The Harms of Fasting (2014)
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health, a Clinical Adjunct Associate Professor at Monash University, and the Chair of the Australian and New Zealand Intensive Care Society (ANZICS) Education Committee. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of LITFL.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of two amazing children.
On Twitter, he is @precordialthump.