A 72-year-old man is admitted to the ICU for severe community-acquired pneumonia. He was admitted to the hospital 2 days ago with cough and dyspnea. Despite appropriate intravenous antibiotics, his respiratory status declined and he was transferred to the ICU, was intubated, and was placed on mechanical ventilation. A vasopressor was needed for persistent hypotension. Since ICU admission 36 hours ago, he has had stable oxygenation and blood pressure and his oxygen and vasopressor dose are being decreased. Medical history is otherwise unremarkable. Medications are ceftriaxone, azithromycin, norepinephrine, and low-molecular-weight heparin prophylaxis.

On physical examination, the patient is intubated but responsive. Temperature is 38.3 °C (100.9 °F), blood pressure is 95/58 mm Hg, and pulse rate is 110/min; BMI is 27. Chest examination shows decreased breath sounds at the left lung base. Cardiac examination reveals a grade 2/6 systolic flow murmur. The remainder of the examination is unremarkable.

Laboratory studies are significant for a leukocyte count of 15,000/µL (15 × 109/L); the complete blood count is otherwise normal. Complete metabolic profile is normal. Blood and sputum cultures are negative since admission.

A chest radiograph is significant for left lower lobe consolidation but is otherwise unremarkable.

Which of the following is most likely to prevent deconditioning in the ICU?