The pulmonary consequences of aspiration of gastric contents at pH values greater than 2.5.

Physiologic and pathologic responses of dogs were studied to assess the effect on the lungs of aspiration of gastric contents at a pH value greater than 2.5. Experimental solutions were administered into the lungs at a dose of 2 ml/kg. Animals were divided into 5 groups: group 1 (n = 13) received saline at a pH of 5.9; group 2 (n = 8) received hydrochloric acid (HCl) at a pH of 1.8; group 3 (n = 6) received gastric contents containing small food particles at a pH of 5.9; group 4 (n = 6) received gastric contents containing food particles at a pH of 1.8; group 5 (n = 6) received gastric contents at a pH of 5.9 from which food particles had been filtered. Arterial blood gas tension, fractional intrapulmonary shunt, and blood pressure were measured at intervals for 48 h. Animals that received gastric contents at a pH of 5.9 and severe hypoxia and increased intrapulmonary shunting that were significantly greater than those of animals receiving saline and were as severe as those of animals receiving HCl at a pH of 1.8. If food particles were in the aspirate, hypercapnia and acidosis were noted. There was pneumonitis in lung sections taken from animals in groups 2, 3, and 4, but not groups 1 and 5. These findings contradict the common belief that aspiration of gastric contents at a pH greater than 2.5 is benign.