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British Journal of Anaesthesia 1993; 70: 6-9




PATIENTS AND METHODS KEY WORDS Gastrointestinal tract: fasting, gastric volume, preoperative fluid intake.

It is accepted widely that the risk of Mendelson's syndrome is reduced by minimizing the volume and increasing the pH of the gastric contents. To minimize the residual gastric volume (RGV), patients have been fasted traditionally for 4-6 h before surgery. This fasting interval is standard practice [1-3], but is not in keeping with the physiology of gastric emptying. A light meal leaves the stomach in 1.5-3 h and clear fluids almost immediately [1, 4]. Thus the conventional fast may be over-cautious, and reducing the fasting time may not increase the risk of pulmonary aspiration. The preoperative fast is unpleasant for patients, who complain frequently of thirst and dry mouth. This is especially so in hot weather, when antisialagogue premedication has been prescribed and when theatre delays and cancellations occur. The ensuing dehydration may make anaesthesia more hazardous and contributes to perioperative morbidity [5-7]. Several workers have questioned the need for the conventional preoperative fasting period [8, 9]. In

The study was a prospective, randomized controlled trial. The investigation was approved by the local Ethics Committee and each patient gave written informed consent. One hundred patients (ASA grades I—III, > 18 yr) undergoing elective surgery were studied. Patients were excluded if factors known to affect the gastric contents were present—pregnancy, gastrointestinal disease and the ingestion of alcohol, opioids, anticholinergics, histamine type-2 receptor antagonists or metoclopramide in the 24 h before surgery. Patients were allocated randomly, on alternate weeks, to either the control or the study group and received either no premedication or temazepam 10-20 mg with water 30 ml 2 h before operation, at the discretion of the anaesthetist in charge of the case.

This article u accompanied by Editorial I. STEPHANIE PHILLIPS*, B.MED., F.R.CANAES., SUSAN HUTCHINSON,

M.B., B.S., F.R.CANAES. (Department of Anaesthetics); TIMOTHY DAVIDSON, CH.M., M.R.C.P., F.R.C.S. (Department of Surgery);

Kingston Hospital, Kingston-upon-Thames, Surrey KT2 7QB. Accepted for Publication: June 23, 1992. *Prcsent address, for correspondence: Department of Anaesthetics, St George's Hospital, Blackshaw Road, London SW17.

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We have compared the effect of allowing free clear fluids until the time of oral premedication with conventional preoperative fasting. In a prospective, randomized trial, the residual volume and pH of gastric contents after induction of anaesthesia were measured in 100 elective surgical patients allocated randomly to a group in whom the intake of free clear fluids up to the time of premedication was measured (mean 388 ml in 6 h before surgery) or a control group who were fasted for 6 h. Preoperative drinking did not affect either mean (so) residual gastric volume (22 (21) ml in the study group vs 19 (16) ml in the control group) or pH (study group 2.64 (1.57) vs control group 2.26 (1.45)). The study group experienced less preoperative thirst. Problems with aspiration or regurgitation were not encountered. We believe that allowing elective surgical patients to drink clear fluids until 2 h before anaesthesia may enhance patient comfort without compromising safety. (Br. J. Anaesth. 1993; 70: 6-9)

children, allowing clear fluid ingestion up to 2 h before surgery does not affect the volume or pH of. gastric contents [10-12]. In adolescents, unlimited fluid ingestion until 3 h before surgery decreased thirst and did not affect gastric contents [13]. In adult practice, the same findings have not been documented in any controlled study. The incidence of aspiration pneumonitis is low [14] and appears to be unrelated to the gastric volume [15]. The ingestion of 150 ml of orange juice or coffee, 2-3 h before operation [16], or of 150 ml of tea, coffee or apple juice 3 h before operation in patients undergoing day-case surgery [17] did not increase the risk of aspiration pneumonitis; unrestricted oral fluids until 3 h before surgery also had no effect in a retrospectively controlled trial [18]. Our study was designed to assess if allowing unrestricted clear fluids until 2 h before anaesthesia would alter the gastric volume and pH, affect anaesthetic complications such as regurgitation or aspiration, and enhance patient comfort.

PREOPERATIVE DRINKING AND GASTRIC CONTENTS TABLE I. Patient characteristics {number, or mean {range or SD))

Age (yr) Sex (M:F) Height (cm) Weight (kg) ASA (I:II:III) Operation (major: intermediate) Premedication

Study group (n = 50)

Control group (n = 50)

64(21-88) 34:16 169(11) 72(15) 18:30:2 18:32

55(20-86) 40:10 169(10) 73 (14) 29:19:2 23:27



TABLE II. Fasting duration and volume of fluid ingested in 6 h before surgery (mean (SD))

Control group

14.8 (8.9) 2.2 (0.7) 388(238)

14.6 (8.9) 12.9 (9.0) 13(15)

Patients in the control group were fasted from midnight for a morning list and from 06:30 for an afternoon list. Patients in the study group were allowed unrestricted clear fluids (alcoholic drinks and those containing milk or sugar were not allowed), until 2 h before surgery was expected to begin, a time marked by the administration of the premedication if prescribed. The volume of fluid consumed and the time at which the "nil by mouth" order was implemented were recorded on the ward fluid balance chart by the nursing staff. No changes were made to theatre schedules in order to accommodate the varying fasting intervals. The following data were recorded for each patient: age, sex, height, weight, ASA grade, smoking habit, fasting duration, volume of fluid ingested in the 6 h before surgery and the occurrence of complications possibly attributable to recent ingestion of fluid. Patients were asked to grade the degree of thirst and hunger as nil, mild, moderate or severe immediately before induction of anaesthesia. Anaesthesia was administered according to the surgical requirements and the preference of the anaesthetist in charge of the case. Immediately after induction, an 18-French gauge Salem sump tube (Argyle) was passed orally into the stomach and correct positioning confirmed either by aspiration of gastric contents or, if none was obtained, by auscultation of 2 ml of insufflated air. Aspiration was performed by an assistant who was unaware of the duration of the patient's fluid fast. All aspiration was performed with the patient supine, in three different tube positions with the stomach being massaged to


Patient characteristics were similar in both groups (table I). The groups were comparable also with respect to ASA grade, smoking history and surgical procedure. Major procedures included cholecystectomy, transurethral resection of the prostate and bowel resection. Intermediate procedures included varicose vein surgery, inguinal hernia repair and cystodiathermy. Premedication was prescribed more often in the study group. No patient was permitted solid food for 6 h before operation; in both groups, the duration of this fast was usually considerably longer (table II). As expected, the duration of the nil-by-mouth period varied less in the study group (1-4 h) than in the control group (6-23 h). In the study group, the fluid intake in the 6 h before surgery ranged from 50 to 1200 ml. Fluid was ingested by the control group for the purposes of taking oral premedication only. RGV and pH were similar in both groups (table III). The number of patients considered to be at risk of Mendelson's syndrome (those with RGV greater than 0.4 ml kg"1 with pH less than 2.5 [19]) was the same in both groups. Ingested fluid volume did not correlate with RGV or pH. The gastric pH of patients drinking until 2 h before operation was greater than in those who had fasted, but this was not statistically significant. Patients in the study group experienced less thirst than those in the control group (table IV). No patient regurgitated or aspirated. DISCUSSION

Our study has shown that allowing elective surgical patients to drink until 2 h before surgery decreases thirst without prejudicing safety. The ingestion of

TABLE III. Residual gastric volume (RGV) and pH (mean (range)). Cl = Confidence interval for difference

RGV (ml) PH

Percent of patients with RGV > 0.4 ml kg"1 pH < 2.5 Both

Study group

Control group



21(0-80) 2.64(1.07-6.82)

19 (0-63) 2.26 (1.25-7.03)

- 5 to +9 -2.5 to +0.8

0.58 0.07

- 1 3 to +21 - 2 4 to +6 - 1 6 to +17

0.64 0.25 0.96

26 76 20

22 87 20

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Solids fast (h) Fluid fast (h) Fluid intake (ml)

Study group

assist complete emptying. The volume of fluid and pH were measured as soon as possible after collection. The pH was measured with a radiometer (Coming 150), calibrated to two points, 4.0 and 7.0. Throughout the study, comparison of the groups was made after every 10 patients, to ensure that the study group was not at an increased risk of Mendelson's syndrome. RGV and pH were compared using the twosample Student's t test. Proportions were compared using the standard error of the difference between two proportions method. Results are presented as confidence intervals for the difference, with probability levels. Thirst and hunger were compared using the chi-square test.

BRITISH JOURNAL OF ANAESTHESIA TABLE IV. Thirst and hunger Thirst Study group Nil Mild Moderate Severe

34 13 2 2

Control group

7 9 11 23 P< 0.001

Hunger Study group

Control group

23 9 11 7

12 11 12 15 P = 0.09

ACKNOWLEDGEMENTS We thank Dr M. Bland, Senior Lecturer in Medical Statistics, St George's Hospital Medical School and Mr D. Simms, Top-Grade Biochemist, Kingston Hospital for the gastric pH estimations.

REFERENCES 1. Gregory IC. Anaesthesia and the gastrointestinal tract. In: VPylie and Churchill Davidson's A Practice of Anaesthesia, 5th Edn. London: Lloyd Luke, 1984; 940-942. 2. Atkinson RS, Rushman GB, Lee JA (eds). A Synopsis of Anaesthesia, 10th Edn. Bristol: Wright, 1987; 112. 3. Aitkenhead AR, Smith G (eds). Textbook of Anaesthesia, 2nd Edn. London, Edinburgh: Churchill Livingstone, 1990; 341. 4. Beaumont W. Gastric Juice and the Physiology of Digestion. Blattsburgh: Allen, 1833; 159-160, 277. 5. Sutherland T, Davies JM, Stock J. The price of preoperative outpatient fasting—effects on gastric contents and outpatient morbidity. Canadian Anaesthetists Society Journal 1985; 32: S100. 6. Sutherland AD, Stock JG, Davies JM. Effects of preoperative fasting on morbidity and gastric contents in patients undergoing day-stay surgery. British Journal of Anaesthesia 1986; 58: 876-878. 7. Goodwin APL, Rowe WL, Ogg TW, Samaan A. Oral fluids prior to day surgery—the effect of shortening the preoperative fluid fast on postoperative morbidity. Anaesthesia 1991; 46: 1066-1068. 8. Maltby JR, Sutherland AD, Sale JP, Shaffer EA. Preoperative oral fluids: is a five-hour fast justified prior to elective surgery? Anesthesia and Analgesia 1986; 65: 1112— 1116. 9. Miller M, Wishart HY, Nimmo WS. Gastric contents at induction of anaesthesia. Is a four-hour fast necessary? British Journal of Anaesthesia 1983; 55: 1185-1187. 10. Crawford M, Lerman J, Christensen S, Farrow-Gillespie A. Effects of duration of fasting on gastric fluid pH and volume in healthy children. Anesthesia and Analgesia 1990; 71: 400-403. 11. Splinter WM, Schafer JD. Unlimited clear fluid ingesuon two hours before surgery in children does not affect volume or pH of stomach contents. Anaesthesia and Intensive Care 1990; 18: 522-526. 12. Schreiner MS, Triebwasser A, Keon TP. Ingesuon of liquids compared with preoperative fasting in pediatric outpatients. Anesthesiology 1990; 74: 593-:597. 13. Splinter WM, Schafer JD. Ingesnon of dear fluids is safe for adolescents up to three hours before anaesthesia. British Journal of Anaesthesia 1991; 66: 48-52. 14. Olsson GL, Hallen B, Hamraes-Jonzon K. Aspiration during anaesthesia: a computer aided study of 185,358 anaesthetics. Acta Anaesthesiologica Scandinavica 1986; 30: 84-92. 15. Hardy JF, Lepage V, Bonneville-Chouinard N. Occurrence of gastroesophageal reflux on induction of anaesthesia does not correlate with the volume of gastric contents. Canadian Journal of Anaesthesia 1990; 37: 502-508. 16. Hutchinson A, Maltby JR, Reid CRG. Gastric fluid and pH in elective patients. Part I: Coffee or orange juice versus overnight fast. Canadian Journal of Anaesthesia 1988; 35: 12-15. 17. Scarr M, Maltby JR, Jani K, Sutherland LR. Volume and acidity of residual gastric fluid after oral ingestion before elective ambulatory surgery. Canadian Medical Association Journal 1989; 141: 1151-1154. 18. Maltby JR, Lewis P, Martin A, Sutherland LR. Gastric fluid volume and pH in elective patients following unrestricted oral fluid until 3 hours before surgery. Canadian Journal of Anaesthesia 1991; 38: 425-429.

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free clear fluids until the time of oral premedication does not affect either the volume or pH of gastric contents. If the risk of regurgitation is related to the RGV, it is unaltered by preoperative drinking. Should regurgitation occur, patients who have been drinking are at no greater risk of Mendelson's syndrome than those who have fasted. The gastric pH in the study group tended to be greater, and greater than 2.5 more often, than in the control group, although this difference was not significant. This finding may reflect the dilution of gastric acid by the ingested fluids. In practice, the period of preoperative fast is often prolonged and the mean fasting period of around 13 h in our control group is not atypical. Indeed, the inevitable constraints of conventional fasting, together with alterations in theatre schedules imply that there is a wide variability in the fasting period. Patients find the ensuing hunger and thirst unpleasant, and if antisialagogue premedication had been used this may be even more pronounced than in our control group. In the study group, thirst was a less common and less severe complaint. Measurement of gastric volume using an aspiration technique may be criticized as underestimating the RGV, but when a multi-orifice sump tube is used the method has been shown to be valid [20]. In any event, any sampling error should be small and consistent between groups. Temazepam has no effect on gastric emptying or pH [21]. Temazepam was prescribed more often in the study group than in the control group. It is possible that control group patients may have been more anxious, resulting in delayed gastric emptying compared with study group patients. Nevertheless, the RGV was the same in both groups. We excluded patients with factors likely to delay gastric emptying, such as pregnancy, trauma, opioid administration, and when mechanical or neurological factors such as pyloric stenosis, vagotomy or autonomic neuropathy existed. Our findings cannot be extrapolated to such patients. Further studies are needed to evaluate the effect of preoperative drinking in patients prescribed opioidanticholingeric premedication. Similarly, the relevance of our findings in day-case patients should be investigated. Nausea and vomiting are known to be related to the duration of the preoperative fasting period [6]. These aspects were not examined in our study, but investigation of the effect of preoperative drinking on patient recovery is warranted. In the U.K., patients are scheduled to fast for 4-6 h before induction of anaesthesia, although

recent guidelines from the Canadian Anaesthetists' Society have reduced the fluid fast period to 3 h [22]. Our findings support this shorter fluid fast on the basis that patient comfort is increased and safety is not compromised.

PREOPERATIVE DRINKING AND GASTRIC CONTENTS 19. Roberts RB, Shirley MA. Reducing the risk of acid aspiration syndrome during Caesarean section. Anesthesia and Analgesia 1974; 53: 859. 20. Hardy JF, Plourde G, Lebrun M, Cote C, Dube S, Lepage Y. Determining gastric contents during general anaesthesia: evaluation of two methods. Canadian Journal of Anaesthesia 1987; 34: 474-177.

21. Goodman LS, Gilman A, eds. Goodman and Gilman's The Pharmacological Basis of Therapeutics, 6th Edn. London: Macmillan, 1980; 346. 22. The shortened fluid fast and the Canadian Anaesthetist's Society's new guide-lines for fasting in elective/emergency patients. Canadian Journal of Anaesthesia 1990; 37: 905-906.

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