An 80-yeаr-оld femаle with а diagnоsis оf pneumonia was admitted to the hospital 2 days ago from a nursing home. The patient is responsive only to painful stimuli. She has a peripheral IV and a feeding tube in place. Physical examination reveals: pulse 98 beats/min; respiratory rate 24 breaths/min and shallow; blood pressure 100/48 mm Hg; and temperature 39.2° C. Auscultation reveals decreased breath sounds with crackles in the bases. The patient has an occasional weak, nonproductive cough. Arterial blood gas on NC 4 L/min is pH 7.42, PaCO2 38 mm Hg, PaO2 40 mm Hg, SaO2 76%, HCO 24 mEq/L. A portable chest X-ray shows patchy basilar infiltrates in both lungs. The most appropriate action to take at this time is which of the following?