Effect of Continuous Positive-Pressure Ventilation and Steroids on Aspiration of Hydrochloric Acid (pH 1.8) in Dogs

Abstract

Forty mongrel dogs were studied to determine whether pharmacologic doses of methylpredniso-lone sodium succinate alone, or in combination with continuous positive-pressure ventilation (CPPV), would alter the course of pneumonitis after aspiration of hydrochloric acid (HCl) of pH 1.8. The dogs were anesthetized and divided into four equal groups. One group aspirated 2 ml./kg. of HCl and was not treated. A second group was treated 21 minutes after aspiration with 30 mg./kg. of methylprednisolone intravenously (I.V.) every 8 hours for 72 hours. A third group received mechanical ventilation (15 ml./kg. VT) with 10 cm. of water PEEP (CPPV) until 300 minutes after aspiration. The last group received CPPV plus steroid therapy. Half of the animals in each group were sacrificed after 300 minutes for lung examination. The remaining animals were sacrificed after 2 weeks. The Pao2 fell in all animals after aspiration of HCl; however, Pao2 improved with time, 95 percent of the animals surviving the experiment. No beneficial effect of methylprednisolone was demonstrated in improving arterial oxygenation, pathologic changes in lungs, or survival rate, but CPPV dramatically improved the gross appearance of the lungs compared to those of dogs allowed to breathe spontaneously following aspiration. Both cardiac output and mean arterial blood pressure decreased following aspiration and still further decreased following the institution of CPPV. The authors recommend that when CPPV is indicated in the treatment of aspiration pneumonitis, attention be given to maintenance of an adequate blood volume and cardiac output.