Background:
The relationship between gastric fluid volume, volume of fluid regurgitated, and aspirated fluid volume remains unclear. Using a life-like manikin suitable for a pulmonary aspiration model, we aimed to assess the relationship between regurgitated and aspirated clear fluid volumes, and to determine the minimal value of the volume of liquid regurgitated that may lead to pulmonary aspiration of fluid volume ≥ 0.8 mL kg-1 (around 60 mL) that is likely to cause lung injury.

Methods:
Several volumes of water ranging from 30 to 150 mL were injected in a randomized order, at a flow rate of 20 mL per second, into the esophagus of a manikin lying in the supine position on a non-tilted table, with the manikin head in the extension or in the sniffing position. Aspirated volumes were measured in the manikin bronchi, by an investigator blinded to the volume injected. Aspiration was defined as positive when the volume of collected water was ≥ 60 mL for at least one of the five injections of each volume of water.

Results:
The minimal volume of water injected into the esophagus for an aspirated volume ≥ 0.8 mL kg-1 was 85 mL in the sniffing position, and was 150 mL in the extension position.

Conclusions:
These results suggest that the critical cut-off value of gastric fluid volume to be considered for the risk of significant pulmonary aspiration would be ≥ 85 mL (≥ 1 mL kg-1), in the sniffing position. These results should however be confirmed in further studies using other models.