Question

Emergency medical services bring a somnolent $74$-year-old female to the resuscitation bay following the abrupt onset of severe respiratory distress and palpitations at her nursing home two hours ago. The patient has a documented medical history of severe chronic obstructive pulmonary disease, hypertension, and osteoarthritis. Upon arrival, her blood pressure is $78/52 \text{ mmHg}$, pulse is $152/\text{min}$ and irregularly irregular, and respiratory rate is $30/\text{min}$. Oxygen saturation is $85\%$ on room air.

Physical examination reveals a diaphoretic, lethargic patient with pale, cool extremities. Jugular venous pressure is markedly elevated up to the angle of the mandible. Auscultation of the lungs demonstrates diffuse expiratory wheezing and coarse bilateral inspiratory crackles up to the mid-lung fields. Cardiac auscultation reveals a rapid, irregular rhythm with no distinct murmurs.

An arterial blood gas on room air shows:
$pH$: $7.21$
$PaCO_2$: $64 \text{ mmHg}$
$PaO_2$: $52 \text{ mmHg}$
$HCO_3^-$: $25 \text{ mEq/L}$

A 12-lead electrocardiogram demonstrates a narrow-complex tachycardia with an irregularly irregular R-R interval and absent P waves.

What is the most appropriate next step in the management of this patient?