ASA Monitor 2 2019, Vol.83, 56-57.
You are working in the ambulatory center and learn that your next patient, scheduled for inguinal hernia repair, was chewing gum while entering the building. The admitting nurse asks whether you will delay or cancel the surgery. According to a recent randomized crossover trial of healthy adult volunteers, what effect will gum chewing most likely have on gastric emptying?
- (A) No effect on gastric fluid volume
- (B) Prolonged total gastric emptying time
- (C) Increased gastric fluid volume two hours later
- (D) Prolonged half-time to gastric emptying
Opinions differ regarding the proper response to a patient chewing gum during the preoperative fasting period. The ASA practice guidelines published in 2017 do not address this issue, whereas the European Society of Anaesthesiology’s fasting guidelines indicate that gum chewing during preoperative fasting should not delay surgery.
A recent randomized crossover study of 20 healthy adult volunteers used gastric antrum measurements obtained by ultrasound to calculate gastric fluid volumes before and up to 120 minutes after ingestion of 250 mL of water. Each volunteer attended two sessions, separated by at least two weeks: a chewing gum session and a no-chewing-gum (control) session. In the chewing gum session, volunteers chewed sugar-containing gum for the first 45 minutes after ingesting water.
The main results were as follows:
- ■ Gastric fluid volumes were similar in the control and chewing gum sessions at all times.
- ■ The mean difference between sessions for gastric fluid volume at 120 minutes was 6 mL (95 percent CI, –5 to 16).
- ■ Total gastric emptying time was similar in the control and chewing gum sessions (mean [SD], 42  minutes vs. 39  minutes, respectively).
- ■ Half-time to gastric emptying was similar in the control and chewing gum sessions (mean [SD], 23  minutes vs. 21  minutes, respectively).
This study’s conclusion differs from that of a meta-analysis of four randomized controlled trials (three adult studies and one pediatric study) published in 2015, which detected a small increase in gastric fluid volume in participants who chewed gum. However, all volume measurements in the meta-analysis studies were performed by blind suctioning of the stomach after intubation, which may be less accurate than determining gastric volume by ultrasound. Furthermore, baseline gastric volume was not assessed. In the three studies involving adults, gastric volumes were less than 40 mL, which likely explains why a 0.12 mL/kg increase (8.4 mL in a 70-kg person) was found to be statistically significant (Table 1). This small effect size is, however, not clinically relevant. Indeed, it may be similar to the volume of water consumed when patients take sips of water with their preoperative medications.
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