Canadian Journal of Anesthesia

, Volume 51, Issue 2, pp 111–115 | Cite as

Drinking 300 mL of clear fluid two hours before surgery has no effect on gastric fluid volume and pH in fasting and non-fasting obese patients

  • J. Roger Maltby
  • Saul PytkaEmail author
  • Neil C. Watson
  • Robert A. McTaggart Cowan
  • Gordon H. Fick
General Anesthesia



To determine whether, in obese [body mass index (BMI) > 30 kg·m2] patients, oral intake of 300 mL clear liquid two hours before elective surgery affects the volume and pH of gastric contents at induction of anesthesia.


A single-blind, randomized study of 126 adult patients, age ≥18 yr, ASA physical status I or II, BMI > 30 kg·m2 who were scheduled for elective surgery under general anesthesia. Patients were excluded if they had diabetes mellitus, symptoms of gastroesophageal reflux, or had taken medication within 24 hr that affects gastric secretion, gastric fluid pH or gastric emptying. All patients fasted from midnight and were randomly assigned to fasting or fluid group. Two hours before their scheduled time of surgery, all patients drank 10 mL of water containing phenol red 50 mg. Those in the fluid group followed with 300 mL clear liquid of their choice. Immediately following induction of general anesthesia and tracheal intubation, gastric contents were aspirated through a multiorifice Salem sump tube. The fluid volume, pH and phenol red concentration were recorded.


Median (range) values in fasting vs fluid groups were: gastric fluid volume 26 (3–107) mL vs 30 (3–187) mL, pH 1.78 (1.31–7.08) vs 1.77 (1.27–7.34) and phenol red retrieval 0.1 (0–30)% vs 0.2 (0–15)%. Differences between groups were not statistically significant.


Obese patients without comorbid conditions should follow the same fasting guidelines as non-obese patients and be allowed to drink clear liquid until two hours before elective surgery, inasmuch as obesity per se is not considered a risk factor for pulmonary aspiration.


Gastric Emptying Lower Esophageal Sphincter Gastric Content Gastric Fluid Clear Liquid 
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Le fait de boire 300 mL de liquide clair deux heures avant d’être opéré n’a pas d’effet sur le volume de liquide ni sur le pH gastriques chez des patients obèses à jeun ou non



Déterminer si, chez des patients obèses [indice de masse corporelle (IMC) > 30 kg·m2], la prise orale de 300 mL de liquide clair deux heures avant de subir une opération réglée a un effet sur le volume et le pH du contenu gastrique lors de l’induction anesthésique.


Une étude randomisée, à simple insu, a été menée auprès de 126 patients adultes, ≥18 ans, d’état physique ASA I ou II, d’IMC > 30 kg·m2, devant subir une intervention chirurgicale réglée sous anesthésie générale. La présence de diabète, ou de symptômes de reflux gastro-œsophagien ou la prise de médicaments, dans les 24 h avant l’opération, pouvant affecter la sécrétion gastrique, le pH du liquide gastrique ou l’évacuation gastrique entraînaient l’exclusion du patient. Tous les patients, à jeun depuis minuit, ont été répartis en deux groupes :jeûne ou liquide. Deux heures avant l’heure prévue de l’opération, tous les patients ont bu 10 mL d’eau contenant 50 mg de rouge de phénol. Les patients du groupe «liquide» ont pris ensuite 300 mL d’un liquide clair de leur choix. Immédiatement après l’induction de l’anesthésie et l’intubation endotrachéale, le contenu gastrique a été aspiré au moyen d’une sonde multiorifice Salem. Le volume de liquide, le pH et les concentrations de rouge de phénol ont été notés.


Les valeurs moyennes (étendue) du groupe de jeûne vs le groupe «liquide» ont été : volume de liquide gastrique 26 (3–107) mL vs 30 (3–187) mL, pH 1,78 (1,31–7,08) vs 1,77 (1,27–7,34) et repérage du rouge de phénol 0,1 (0–30) % vs 0,2 (0–15) %. Il n’y avait pas de différence intergroupe significative.


Les patients obèses, sans symptômes comorbides, devraient suivre les mêmes directives de jeûne que les patients non obèses. Ils peuvent boire un liquide clair jusqu’à deux heures avant une opération réglée, étant donné que l’obésité en elle-même n’est pas considérée comme un facteur de risque d’aspiration pulmonaire.


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Copyright information

© Canadian Anesthesiologists 2004

Authors and Affiliations

  • J. Roger Maltby
    • 1
  • Saul Pytka
    • 1
    Email author
  • Neil C. Watson
    • 1
  • Robert A. McTaggart Cowan
    • 1
  • Gordon H. Fick
    • 2
  1. 1.Department of AnesthesiaUniversity of CalgaryCalgaryCanada
  2. 2.Community Health SciencesUniversity of CalgaryCalgaryCanada

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