Question

Paramedics bring a $72$-year-old woman to the emergency department due to a two-day history of severe, progressively worsening shortness of breath and a dry cough. She reports that her breathing becomes significantly worse when she lies flat, forcing her to sleep upright in a chair. Her medical history includes a previous myocardial infarction, hypertension, and a $30$-pack-year history of smoking, though she quit $15$ years ago. Her temperature is $37.0^\circ\text{C}$ ($98.6^\circ\text{F}$), blood pressure is $168/96\text{ mmHg}$, pulse is $112/\text{min}$, and respirations are $26/\text{min}$. Pulse oximetry shows an oxygen saturation of $89\%$ on ambient air. Physical examination reveals prominent jugular venous distention when seated at a $45$-degree angle. Lung auscultation demonstrates bilateral crackles at the lung bases and scattered expiratory wheezes in all lung fields. Cardiac examination reveals a regular tachycardia and a third heart sound ($S_3$) gallop. Arterial blood gas analysis on ambient air shows:

$pH$: $7.49$
$PaCO_2$: $28\text{ mmHg}$
$PaO_2$: $58\text{ mmHg}$

Which of the following is the most appropriate initial pharmacologic therapy for this patient's respiratory distress?