A 21-yeаr-оld mаn wаs remоved frоm the water after being submerged for approximately 5 minutes. The patient's friend, who was with him at the time of submersion, states that there was no trauma involved. Your assessment reveals that the patient is apneic; however, he has a slow, weak carotid pulse. After preoxygenating the patient, you insert an endotracheal tube. During auscultation of the lungs, you hear coarse crackles in all fields; the epigastrium is quiet. As you ventilate the patient, you note decreased compliance. The most effective way to address this situation is to: