How often do patients have a full stomach before their anaesthetic?

“When the stomach is full, it is easy to talk of fasting.” – St. Jerome

Prevalence and factors predictive of full stomach in elective and emergency surgical patients: a prospective cohort study


This prospective study aimed to establish the rate of full and empty stomachs in both elective and emergency patients and additionally to identify factors associated with full stomach.


The study was undertaken in a single university hospital over a 6 month period having sought ethical approval from local ethics committee. The study was designed as a non-interventional trial due to ultrasound assessment of full stomach already being an established procedure at this centre. Consent for the trial was verbal and established during the anaesthetic consultation.

A total of 495 patients were enrolled in the study; 289 emergency and 206 elective cases. Three physicians blinded to the fasting status of the patient conducted the ultrasound. Ultrasound was performed in 2 positions; semi upright and right lateral decubitus positions.

Results were defined into the following categories:

  • Grade 0 – flat antrum, no contents in semi-upright and right lateral decubitus positions
  • Grade 1 – appearance of content in RLD position only
  • Grade 2 – appearance of content in both S and RLD positions

In addition, size of antrum was measured and combined with final risks defined as:

Low Risk: Perlas Score = 0, Perlas Score = 1, Cross-sectional Area (CSA) <340mm2

Increased Risk : Perlas Score = 2

Intermediate Risk : Perlas Score = 1, CSA >340mm2

Secondary risk factors investigated were age, sex, BMI, Emergency vs Elective & type of surgery (subspecialty), fasting time (ingestion to examination), pre-op morphine consumption, diabetes, GORD, CKD & hypothyroidism


The prevalence of full stomach was 56% in emergency patients and 5% in elective patients. The study also identified fasting duration for solids < 6 hours, preoperative morphine consumption, obesity and diabetes had a strong association with full stomachs.



·        Ultrasound technique was based around a previous study looking directly at classifying antral contents on ultrasound

·        Calculated measurements of cross sectional area of antrum

·        Specific ultrasound views were set to calculate measurements, reducing user bias

·        Defined what each grade likely equated to in mls of gastric content

·        Physicians performing US blinded to history – could not see what they wanted to see

·        Variety of patient factors including pathologies

·        Combining two scoring systems reduced the frequency of doubtful examinations to 5%



·        Primary outcome became less important, secondary outcomes became the focus as results discussed

·        Only 3 operators available for U/S

·        Reduced patient cohort above ASA 2

·        Approx 15% emergency patients were undergoing “digestive” surgery and therefore may have skewed that data set

·        There is no evidence of powering the study to analyse pathologies such as hypothyroidism and chronic renal disease

·        No trial/data to confirm what each grade/risk on US directly correlated with on invasive measurement of gastric contents.


Summary by Dr Mayavan Abayalingam

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