Delayed Gastric Emptying

Disorders of gastric motility, pyloric obstruction, gastroesophageal reflux and diabetic gastroparesis delay gastric emptying. Indigestible solids are the first to be affected, followed by digestible solids and finally liquids. Because the rate of gastric emptying of clear fluids is not affected until these conditions are far advanced, most patients may still be allowed to drink on the morning of surgery. Different investigators have found obese patients to have either a larger^[16] or smaller^[17] residual fasting gastric fluid volume than non-obese patients. These comments only apply to patients scheduled for elective surgery. All emergency cases, especially those involving trauma and women in labour, should always be assumed to have delayed gastric emptying.

Gastric emptying is normal in all three trimesters of pregnancy and beyond 18 hours post-partum, but is delayed in the first 2 hours post-partum.^[18] Labour causes an unpredictable delay in gastric emptying that is markedly potentiated by opioids.^[19] Nevertheless, there is a move towards less rigid fasting guidelines during labour, especially in women who are not expected to require operative intervention.^[20] 

Development of American Society of Anesthesiologists (ASA) fasting guidelines

The ASA formed a Task Force in 1996 to review relevant clinical human research studies published 1966 to 1996. Over 1100 citations were initially identified, of which 232 articles contained relationships between preoperative fasting and pharmacological prophylaxis of pulmonary aspiration. Expert opinion was also obtained from international anaesthesia and gastroenterologist consultants in preparing clinical guidelines for preoperative fasting (Table 2) and pharmacological prophylaxis in healthy patients undergoing elective (elective) surgery. These were approved by the House of Delegates at the 1998 ASA Annual Meeting and were published in the March 1999 issue of Anesthesiology.^[21] The Canadian Anesthesio-logists' Society has published similar guidelines.^[22]

Table 2. American Society of Anesthesiologists fasting guidelines
Ingested material	Minimum fasta
Clear liquidsb	2 hours
Breast milk	4 hours
Infant formula	6 hours
Non-human milk	6 hours
Light mealc	6 hours
a Fasting times apply to all ages. b Examples: water, fruit juice without pulp, carbonated beverages, clear tea, black coffee. c Example: dry toast and clear liquid. Fried or fatty foods may prolong gastric emptying time. Both amount and type of food must be considered. The guidelines recommend no routine use of gastrointestinal stimulants, gastric acid secretion blockers or oral antacids.

Implementation of new fasting guidelines

Cooperation of anaesthesia colleagues, surgeons and nurses are essential for implementation. In our hospital, we presented the evidence at a meeting of the anaesthesia department, then to a joint meeting of surgeons and anaesthetists, and also to a meeting of head nurses of our surgical wards. The clinical heads of anaesthesia and surgery then sent a joint letter to all consultant and trainee surgeons and anaesthetists, with copies to the head nurses to provide details of the revised guidelines. The nursing staff then used the guidelines to revise the fasting instructions in the hospital's nursing policy manual. 

Conclusion

The order 'nothing by mouth after midnight' should apply only to solids for patients scheduled for surgery in the morning. An early light breakfast of easily digested toast or similar food with clear liquid is permissible for afternoon cases. Clear liquids should be allowed until 3 hours before the scheduled time of surgery so that a change in the surgical schedule can be made and still allows 2 hours before the actual time of surgery. For patients with true gastroesophageal reflux, whether or not they drink, an H2-receptor blocker (ranitidine) or proton pump inhibitor (omeprazole) may be advisable to minimize gastric acid secretion. 

References

1. Warner MA, Warner ME, Weber JG. Clinical significance of pulmonary aspiration during the perioperative period. Anesthesiology 1993; 78: 56-62.
2. Lister J. On Anaesthetics. In: The Collected Papers of Joseph, Baron Lister, Volume 1 Oxford: Claridon Press 1909: 172.
3. Roberts RB, Shirley MA. Reducing the risk of gastric aspiration during cesarean section. Anesthesia and Analgesia 1974; 53: 859-68.
4. Coté CJ. NPO after midnight in children - a reappraisal. Anesthesiology 1990;72:589-92.
5. Rocke DA, Brock-Utne JG, Rout CC. At risk for aspiration: new critical values for volume and pH. Anesthesia and Analgesia 1993; 76: 666.
6. Schreiner MS. Gastric fluid volume: is it really a risk factor for pulmonary aspiration? Anesthesia and Analgesia 1998; 87 754-6.
7. Moyers JA. Preoperative medication. In :Barash PG, Cullen BF, Stoelting (Eds). Clinical Anesthesia, 3rd ed. New York:Lippincott-Raven, 1997: 519-33.
8. Raidoo DM, Rocke DA, Brock-Utne JG, Marszalek A, Engelrecht HE. Critical volume for pulmonary acid aspiration: reappraisal in a primate model. British Journal of Anaesthesia 1990; 65: 248-50.
9. Guyton AC. Textbook of Medical Physiology. 8th ed. Philadelphia: W.B. Saunders Company 1991: 700-3.
10. Plourde G, Hardy J-F. Aspiration pneumonia: assessing risk of regurgitation in the cat. Canadian Anaesthetists Society Journal 1986; 33: 345-8.
11. Minani H, McCallum RW. The physiology and pathophysiology of gastric emptying in humans. Gastroenterology 1984;86:1592-1610.
12. Miller M, Wishart HY, Nimmo WS. Gastric contents at induction of anaesthesia. Is a 4-hour fast necessary? British Journal of Anaesthesia 1983; 55:1185-8.
13. Splinter WM, Stewart JA, Muir JG. The effect of preoperative apple juice on gastric contents, thirst and hunger in children. Canadian Journal of Anaesthesia 1989; 36:55-8
14. Schreiner MS, Triebwassen A, Keon TP. Ingestion of liquids compared with preoperative fasting in pediatric outpatients. Anesthesiology 1990; 72:593-7.
15. Dubin SA, McCraine JM. Sugarless gum chewing before surgery does not increase gastric fluid volume or acidity. Canadian Journal of Anaesthesia 1994; 41: 603-6.
16. Vaughan RW, Bauer S, Wise L. Volume and pH of gastric juice in obese patients. Anesthesiology 1975; 43: 686-9.
17. Harter LR, Kelly WB, Kramer MG, Perez CE, Dzwonczk RR. A comparison of the volume and pH of gastric contents of obese and lean surgical patients. Anesthesia and Analgesia 1998; 86: 147-52.
18. Whitehead EM, Smith M, Dean Y, O'Sullivan G. An evaluation of gastric emptying times in pregnancy and the puerperium. Anaesthesia 1993; 48:53-7.
19. Davison JS, Davison MC, Hay DM. Gastric emptying time in late pregnancy and labour. British Journal of Obstetrics and Gynaecology 1970; 77: 37-41.
20. O'Sullivan G. The stomach - fact and fantasy: eating and drinking during labour. In: Rocke DA (Ed). International Anesthesiology Clinics 1994:32(2): 31-44.
21. Practice guidelines for preoperative fasting and the use of pharmacological agents for the prevention of pulmonary aspiration: application to healthy patients undergoing elective procedures. Anesthesiology 1999; 90; 896-905.
22. CAS Guidelines to the Practice of Anesthesia. The Canadian Anesthesiologists' Society, 1 Eglinton Avenue East, Suite 208, Toronto ON, Canada M4P 3A1, 1999: 7. 

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