Question

A 72-year-old woman is evaluated in the hospital for progressive lethargy and confusion over the past 24 hours. She was admitted 4 days ago for an acute exacerbation of chronic obstructive pulmonary disease (COPD). On admission, she was started on intravenous methylprednisolone, nebulized ipratropium-albuterol, and empiric piperacillin-tazobactam. She was also continued on her home dose of furosemide for a history of ischemic cardiomyopathy with a left ventricular ejection fraction of 35%. Her other home medications include lisinopril and levothyroxine.

Her temperature is $37.4^\circ\text{C}$ ($99.3^\circ\text{F}$), blood pressure is $100/60\text{ mm Hg}$, pulse is $110\text{/min}$, and respirations are $22\text{/min}$. Physical examination shows dry mucous membranes. The jugular venous pressure is $4 \text{ cm H}_2\text{O}$. Lung auscultation reveals distant breath sounds with faint expiratory wheezes and fine bibasilar crackles. Cardiac examination shows a regular tachycardia with no murmurs or gallops.

Laboratory studies show:
Sodium: $136 \text{ mEq/L}$
Potassium: $2.8 \text{ mEq/L}$
Chloride: $92 \text{ mEq/L}$
Bicarbonate: $36 \text{ mEq/L}$
Blood urea nitrogen: $52 \text{ mg/dL}$
Creatinine: $2.3 \text{ mg/dL}$ (baseline $1.1 \text{ mg/dL}$)
Thyroid-stimulating hormone (TSH): $0.1 \mu\text{U/mL}$ (normal: $0.4–4.0 \mu\text{U/mL}$)
Free T4: $1.0 \text{ ng/dL}$ (normal: $0.9–1.7 \text{ ng/dL}$)

Arterial blood gas on $2 \text{ L/min}$ oxygen by nasal cannula shows:
pH: $7.54$
PaCO₂: $48 \text{ mm Hg}$
PaO₂: $68 \text{ mm Hg}$

Which of the following is the most appropriate next step in management?