Pulmonary Aspiration of Acid: An Experimental Study on Cats

Acid aspiration is followed by a moderate to severe fall in systemic arterial blood pressure, and it has been suggested that release from the lung parenchyma of vasoactive substances may be an important causal factor. We have tested this hypothesis by twice establishing cross circulation between one cat which received hydrochloric acid (4 ml/kg b.w., pH 1.5) intratracheally and another, untreated cat. Instillation of acid caused an immediate fall in heart rate and arterial blood pressure of the aspiration animal, suggesting a reflex inhibition of the heart triggered within the lung. Cross circulation with the untreated animal did not improve the situation of the aspiration animal; nor did it cause any change in arterial blood pressure or lung mechanics in the untreated animal, although most of the blood volumes of the two animals was exchanged. In a separate series of experiments including four cats, we investigated the relative advantages of various patterns of positive pressure ventilation in the treatment of the aspiration syndrome. Early onset of positive pressure ventilation (PPV) with a moderate positive end‐expiratory pressure (PEEP) (+ 6 cmH 2 O) was an effective treatment. We conclude that local lung tissue injury with a secondary fall in estimated dynamic lung compliance and arterial pH and P o 2 is the most important feature in the pathophysiology of aspiration.