Dig Dis Sci DOI 10.1007/s10620-014-3404-z


Effect of Gum Chewing on the Volume and pH of Gastric Contents: A Prospective Randomized Study Basavana Gouda Goudra • Preet Mohinder Singh • Augustus Carlin • Amit K. Manjunath • Joel Reihmer • Gowri B. Gouda • Gregory G. Ginsberg

Received: 22 August 2014 / Accepted: 13 October 2014 Ó Springer Science+Business Media New York 2014

Abstract Background Insufficient fasting prior to endoscopic procedures performed under sedation may result in potential aspiration of gastric contents. Fasting as per ASA guidelines is recommended prior to these procedures. However, the effect of chewing gum on fasting status has been a subject of debate and often leads to procedural delays. Objective Evaluation of the effect of chewing gum on the gastric volume and pH. Methods In this randomized controlled prospective observer blinded trail, ASA I–III patients aged more than 18 years scheduled for esophagogastroduodenoscopy (EGD) or a combined EGD and colonoscopy under

B. G. Goudra (&)  A. Carlin  A. K. Manjunath  J. Reihmer  G. B. Gouda Department of Anesthesia, Hospital of the University of Pennsylvania, Philadelphia, PA, USA e-mail: [email protected] A. Carlin e-mail: [email protected] A. K. Manjunath e-mail: [email protected] J. Reihmer e-mail: [email protected] G. B. Gouda e-mail: [email protected] P. M. Singh Department of Anesthesia, All India Institute of Medical Sciences, New Delhi, India e-mail: [email protected] G. G. Ginsberg Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA, USA e-mail: [email protected]

conscious sedation were studied. Patients randomized to the chewing gum group (Group-C) were allowed to chew gum until just before the start of their procedure; the remaining patients were included into Group-NC. After sedation and endoscope insertion, stomach contents were aspirated under vision of a gastroenterologist (blinded to groups). Results Volume and pH of gastric contents aspirated from 67 patients (34 in Group-C and 33 in Group-NC) were analyzed. The demographic parameters of the groups were comparable. Gastric volume (median-interquartile range) was statistically higher in Group-C (13 ml (7.75–40.75) vs Group-NC 6 ml (1.00–14.00) (P \ 0.001)]. The mean pH in both groups was comparable: 2.84 ± 2.11 in Group-C and 3.79 ± 2.53 in Group-NC (P = 0.141). Conclusion Although our results show gastric volume in patients chewing gum was statistically higher, clinical relevance of such a small difference is questionable. Thus patients who chewed gum inadvertently prior to procedure should not be denied or delayed administration of sedative and anesthetic medications. Keywords Chewing gum  Fasting guidelines  Gastric volume  Chewing gum endoscopy

Introduction Propofol sedation is commonly employed to support gastroenterological endoscopic procedures. Patients are typically instructed to fast for a minimum of 2–4 h before their scheduled procedure time [1]. Despite orders to the contrary, many patients do not regard gum chewing as a violation of the ‘‘nil by mouth’’ instructions. Owing to the unpleasantness of the fast or as is their routine, it is not


Dig Dis Sci

uncommon for patients to continue chewing gum up to the time of their arrival for their endoscopic procedure. Preoperative fasting guidelines recommended by the American Society of Anesthesiologists (ASA) do not allow oral ingestion including liquids, for varying time periods before the induction of anesthesia [1]. Although these guidelines do not explicitly mention chewing gum, many ad hoc anesthesiology policies prohibit the administration of sedation immediately following gum chewing as it is considered as clear liquid ingestion and needs to be stopped for 2 or more hours prior to the administration of sedation. This is based on a commonly held notion that the simple act of mastication promotes increased gastric acid secretion with resultant increase in retained gastric fluid volumes and lowered gastric fluid pH. An unsuspecting patient, discovered to be chewing gum on arrival to the preoperative ambulatory endoscopy facility, may face cancelation or delay of patients’ procedure. Many patients are surprised when they are denied or delayed anesthesia on these grounds. Studies (only 3 available on PubMed) evaluating the effect of gum chewing on the volume and pH of residual gastric contents have used an orogastric tube for suctioning of stomach contents [2–4]. The completeness of suctioning with this method is poor [5]. The anesthetic agent propofol has become the standard sedative for gastrointestinal (GI) endoscopic procedures in many hospitals. At the Hospital of the University of Pennsylvania, Philadelphia, Endoscopy Center, patients undergoing these procedures are sedated with propofol on an ‘‘as clinically indicated’’ basis. Endotracheal intubation is rarely performed, even for advanced endoscopic procedures like ERCP [6]. However, during propofol sedation, unlike intravenous conscious sedation, patients are more deeply sedated to the point of general anesthesia [7]. Protective laryngeal reflexes are likely to be obtunded with an increased risk of aspiration in the presence of substantial gastric contents. As a result, strict fasting guidelines are enforced in patients scheduled for GI endoscopic procedures with propofol sedation. Due to preservation of laryngeal reflexes in patients undergoing these procedures with intravenous conscious sedation (without propofol), such rigid fasting guidelines are not enforced and the occasional patient discovered with chewing gum in his or her mouth is not delayed. The aim of this study was to evaluate the effects of gum chewing on residual gastric fluid volumes in patients undergoing endoscopic procedures.

Methods After an institutional review board approval, over 200 adults scheduled to undergo an esophagogastroduodenoscopy (EGD) or a combined EGD and colonoscopy, who


met the study criteria, were contacted over the telephone on the evening before the procedure for this randomized control trial. Only patients scheduled to undergo the stated procedure under intravenous conscious sedation were included in the study. Of those contacted (over a period of 2 years), 73 patients agreed to participate in the study. They were randomly allocated to either chewing gum group (C) or non-chewing gum group (NC) using computer-generated table of random numbers. To simulate reallife chewing habits, no restrictions were placed on the type, quantity, or duration of gum chewing. Telephone study consent was obtained on the evening before the procedure, which was supplemented with a written consent about 30 min before the endoscopic procedure. Patients allocated to group C were allowed to chew gum up until the initiation of sedation, prior to which the gum was spit out. The gastroenterologist performing the procedure was kept unaware whether patient had chewed gum or not and was only allowed to enter the operating room once anesthesia had been induced and thus was blinded to the gum chewing status of the patient. We did not restrict the procedure to single gastroenterologist as performance bias was unlikely because gastroenterologists were blinded to patient grouping and suction of gastric content was to be done under vision for all patients. Intravenous conscious sedation was provided with a combination of midazolam, fentanyl, and in rare cases, diphenhydramine. An endoscope was inserted after achieving adequate sedation depth, and the stomach contents were suctioned completely under vision into an empty plastic container. The endoscopist avoided water insufflation or flushing before the gastric contents were aspirated. The container was removed and replaced immediately after the stomach was completely emptied. The volume was measured with an appropriately sized syringe, and the pH was measured with a pH indicator strip (Merck, CORPAK MedSystems UK). Statistical Analysis Statistical analysis was performed using SPSS-21, IBM Inc (Chicago, USA) for Macintosh; sample size calculations were done using JMP-10 (SAS corporation, USA). Based on previous study by Dubin et al. [2], to estimate a minimum difference of 15 ml of gastric volume with a power of 85 % and an alpha error of B5 %, a sample size of at least 32 patients was required in each group. We planned to contact 200 patients and accepted that high rates of attrition are likely when efforts are made to recruit over the telephone. A total of 73 patients were successfully recruited. Six patients were excluded from final analysis for the following reasons: Inability of the research assistant to be present for sample collection at the start of the procedure in two cases; one patient was given 100 ml of water for

Dig Dis Sci


Assessed for eligibility (n= ≥200)

Declined to participate (n= ≥125 )

Randomized (n= 73)

Allocation Allocated to Chewing Gum Group (n= 38) ♦ Received allocated intervention (n= 38 )

Volume measured in (n= 34)

Allocated to Non Chewing gum Group (n= 35) ♦ Received allocated intervention (n= 35 )

Gastric volume measured in

Volume measured in (n= 33)

Technical error in measuring volume (n=4)

Technical error in measuring volume sample (n= 2)

Analysis Analysed (n= 34) ♦ Excluded from analysis (n= 0)

Analysed (n= 33) ♦ Excluded from analysis (n= 0)

Fig. 1 Consort diagram showing study plan

manometry study 30 min before sedation; and three patients were deemed unsuitable for intravenous conscious sedation and required propofol administration. The recruitment and eventual analysis of patients is shown in Fig. 1 (consort diagram). The data were checked for normal distribution using the Kolmogorov–Smirnov test. Descriptive statistics were used for demographic data, gastric volume, and pH data; these data points were compared using Student’s unpaired t test. Frequency data (gender) were compared using the Chi-square test. An alpha error value was set at \5 %, making a P value of \0.05 statistically significant for the aforementioned tests. Results Seventy-three patients consented for participation in the study between November 2011 and July 2013. The data analysis included 67 patients, 34 in Group C, and 33 in Group NC. The demographic profile of patients was comparable in both the groups, as displayed in Table 1.

Table 1 Table showing demographic parameters in both the groups Patient Demographic Profile Group C

Group NC

Statistical significance

Age (years)

50.56 (14.28)

50.09 (14.75)

P = 0.895

BMI (kg/m2)

28.67 (10.57)

28.46 (6.99)

P = 0.924

Gender (M:F)



P = 0.271 (Chi-square test)

A Mann–Whitney U test was used to compare the median gastric volumes in both groups, and the difference was found to be highly significant (P = 0.001). Gastric Volume The median gastric volumes along with inter quartile range are shown in Fig. 2. The mean volume/kg was statistically


Dig Dis Sci Gastric Volume Comparison 80

Gastric Content Volume (ml)

Fig. 2 Box plot showing comparison of measured gastric volumes in both the groups. Boxes represent the 25th to 75th interquartile range; whiskers represent the 95 percentile values. Asterisk represents the outliers



20 13.00 (7.75-40.75) 6.00 (1.00-14.00) 0 Chewing Gum Group

Non-Chewing Gum Group


different in both groups; they were 0.345 ± 0.311 and 0.112 ± 0.110 ml/kg in Group C and Group NC, respectively (P \ 0.001). However, the median volume in group NC and C were only 6 and 13 ml, respectively (Fig .2). Gastric Content pH The mean pH value was higher in Group NC (3.79 ± 2.53) when compared with Group C (2.84 ± 2.11); however, it failed to achieve statistical significance (P = 0.141).

Discussion This study addresses several important aspects relating to gum chewing in the preoperative period. Residual gastric volumes are higher in the group of patients allowed to chew gum in the pre-procedural period. These findings are in agreement with those of Schoenfelder et al. [4] and differ from those of Dubin et al. [2]. In their studies, an orogastric tube was inserted after induction of anesthesia and endotracheal intubation and gastric contents were blindly aspirated. The validity of our study is supported by the methodology of direct visual aspiration of the gastric contents. If the gastric contents are of very high acidity, even small volumes can cause life-threatening aspiration pneumonitis [8]. Our findings indicate little or no difference in the pH of gastric contents associated with pre-procedure gum chewing. As such, while the increase in gastric


residual volume is statistically significant, its relevance is deemed clinical insignificant, given the low volume and lack of effect on pH. Even though the chewing gum group had statistically significant increase in the residual gastric volume, it is less than what was expected. Studies have shown that normal salivary secretion in response to chewing is 1.6–2 ml/min [9]. It can increase up to 5.18 ml/min with gum chewing [10]. This is probably explained by the reported increase in intestinal motility associated with gum chewing [11–16]. There is evidence that gum chewing promotes gastrointestinal motility and physiologic gastric emptying [17]. Many studies have found increased motility and decreased flatus, with a possible decrease in the severity of postoperative ileus when gum was chewed in the postoperative period. While the above discussion has dealt with the effect of gum chewing on the residual gastric volume and pH, the risk of aspirating any remaining piece of gum in the mouth and stomach needs to be considered [17]. A potential limitation of our study is that we did not control for proton pump inhibitor or H2 blocker use. However, given our randomization, it is not likely that this would have contributed to meaningful differences in outcome measures. Also, the total number of chewing gums were not standardized, as number of gums chewed could have possible relation to gastric volume. Endoscopy findings were not compared; however, possibility of pathological condition leading to alteration of gastric acidity/ volume cannot be negated.

Dig Dis Sci

Conclusions Our study results, obtained with enhanced methodology, reinforce that gum chewing during pre-anesthetic fasting does not increase the volume or acidity of gastric juice in a manner that would increase the risk of subsequent aspiration. Our findings emphasize physiologic analysis by Poulton who states: ‘‘Recommendations against pre-anesthetic gum chewing do not withstand scrutiny and miss an opportunity to enhance comfort and sense of wellbeing for patients awaiting anesthesia.’’ While it may be inadvisable to actively encourage gum chewing in patients presenting for procedures conducted with anesthesia assistance, in the absence of other aspiration risk factors, patients who chewed gum inadvertently should not be denied or delayed administration of sedative and anesthetic medications. Acknowledgments We wish to acknowledge the help of Dr Lakshmi Penugonda MD, Research Scholar, Department of Anesthesiology and Critical Care Medicine, Hospital of the University of Pennsylvania, Philadelphia who is currently an Anesthesiology Resident, Department of Anesthesiology and critical care medicine, Drexel University, Philadelphia, USA Conflict of interest


References 1. 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;114:495–511. 2. Dubin SA, Jense HG, McCranie JM, Zubar V. Sugarless gum chewing before surgery does not increase gastric fluid volume or acidity. Can J Anaesth. 1994;41:603–606. 3. Søreide E, Holst-Larsen H, Veel T, Steen PA. The effects of chewing gum on gastric content prior to induction of general anesthesia. Anesth Analg.. 1995;80:985–989. 4. Schoenfelder RC, Ponnamma CM, Freyle D, Wang S-M, Kain ZN. Residual gastric fluid volume and chewing gum before surgery. Anesth Analg. 2006;102:415–417.

5. Taylor WJ, Champion MC, Barry AW, Hurtig JB. Measuring gastric contents during general anaesthesia: evaluation of blind gastric aspiration. Can J Anaesth. 1989;36:51–54. 6. Goudra B, Singh P, Sinha A. Outpatient endoscopic retrograde cholangiopancreatography: safety and efficacy of anesthetic management with a natural airway in 653 consecutive procedures. Saudi J Anaesth. 2013;7:259. 7. Goudra BG, Singh PM, Manjunath A, Reihmer J. Sedation spectrum in patients undergoing advanced gastrointestinal (GI) endoscopic procedures with propofol. Presented at the annual meeting of international society of anesthetic pharmacology, San Fransisco October 11th 2013. 8. James CF, Modell JH, Gibbs CP, Kuck EJ, Ruiz BC. Pulmonary aspiration-effects of volume and pH in the rat. Anesth Analg. 1984;63:665–668. 9. Heintze U, Birkhed D, Bjo¨rn H. Secretion rate and buffer effect of resting and stimulated whole saliva as a function of age and sex. Swed Dent J. 1983;7:227–238. 10. Jensen JL, Karatsaidis A, Brodin P. Salivary secretion: stimulatory effects of chewing-gum versus paraffin tablets. Eur J Oral Sci. 1998;106:892–896. 11. Husslein H, Franz M, Gutschi M, Worda C, Polterauer S, Leipold H. Postoperative gum chewing after gynecologic laparoscopic surgery: a randomized controlled trial. Obstet Gynecol. 2013;122:85–90. 12. Leier H. Does gum chewing help prevent impaired gastric motility in the postoperative period? J Am Acad Nurse Pract. 2007;19:133–136. 13. Hocevar BJ, Robinson B, Gray M. Does chewing gum shorten the duration of postoperative ileus in patients undergoing abdominal surgery and creation of a stoma? J Wound Ostomy Cont Nurs. 2010;37:140–146. 14. Va´squez W, Herna´ndez AV, Garcia-Sabrido JL. Is gum chewing useful for ileus after elective colorectal surgery? A systematic review and meta-analysis of randomized clinical trials. J Gastrointest Surg. 2009;13:649–656. 15. Parnaby CN, MacDonald AJ, Jenkins JT. Sham feed or sham? A meta-analysis of randomized clinical trials assessing the effect of gum chewing on gut function after elective colorectal surgery. Int J Colorectal Dis. 2009;24:585–592. 16. Zaghiyan K, Felder S, Ovsepyan G, et al. A prospective randomized controlled trial of sugared chewing gum on gastrointestinal recovery after major colorectal surgery in patients managed with early enteral feeding. Dis Colon Rectum. 2013;56:328–335. 17. Poulton TJ. Gum chewing during pre-anesthetic fasting. Paediatr Anaesth. 2012;22:288–296.


Effect of Gum Chewing on the Volume and pH of Gastric Contents: A Prospective Randomized Study.

Insufficient fasting prior to endoscopic procedures performed under sedation may result in potential aspiration of gastric contents. Fasting as per AS...
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