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Critical volume for pulmonary acid aspiration: reappraisal in a primate model
D M Raidoo1, D A Rocke, J G Brock-Utne
1Department of Physiology, University of Natal, Congella, Republic of South Africa.
Abstract:
We have studied, in the monkey, the critical volume for the production of severe pneumonitis following pulmonary aspiration of gastric contents. Aspiration of 0.4 ml kg-1 and 0.6 ml kg-1 at pH1 produced mild to moderate clinical and radiological changes, but no deaths. Aspiration of 0.8 ml kg-1 and 1.0 ml kg-1 at pH1 was associated with an increasingly severe pneumonitis. At 1.0 ml kg-1, 50% of the animals died--a mortality rate considerably less than that reported previously in animal studies. If these results were to be extrapolated to humans, the critical volume for severe aspiration could be increased from 25 ml to 50 ml (0.8 ml kg-1), considerably reducing the percentage of patients perceived to be "at risk".
Insights
This study in monkeys found that a larger volume of gastric acid aspiration (0.8 ml/kg) is needed to cause severe pneumonitis. This suggests the critical volume for severe aspiration in humans may be higher than previously thought.
Area of Science:
- Pulmonary Medicine
- Critical Care Medicine
- Gastroenterology
Background:
- Pulmonary aspiration of gastric contents is a significant cause of severe pneumonitis.
- Previous animal studies suggested a lower critical volume for severe aspiration.
Purpose of the Study:
- To determine the critical volume of gastric acid aspiration required to induce severe pneumonitis in a primate model.
- To re-evaluate the human risk threshold for aspiration pneumonitis based on animal data.
Main Methods:
- Monkeys underwent pulmonary aspiration of varying volumes (0.4-1.0 ml/kg) of gastric contents at pH 1.
- Clinical, radiological, and mortality data were collected and analyzed.
Main Results:
- Aspiration of 0.4-0.6 ml/kg resulted in mild to moderate pneumonitis without mortality.
- Aspiration of 0.8-1.0 ml/kg led to increasingly severe pneumonitis, with 50% mortality at 1.0 ml/kg.
- The mortality rate was lower than previously reported in similar animal studies.
Conclusions:
- The critical volume for severe aspiration pneumonitis in monkeys is higher than previously estimated.
- Extrapolation to humans suggests the critical volume for severe aspiration may be 50 ml, potentially reducing the number of patients considered at risk.
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