A 60-kg (154-lb), 170-cm (67-inch), 69-year-old woman with severe chronic obstructive pulmonary disease (COPD) is admitted to the ICU for management of an acute COPD exacerbation. Despite albuterol, ipratropium, and IV methylprednisolone, she has become somnolent. Arterial blood gas analysis on FIO2 0.35 shows: pH 7.20, PCO2 110 mm Hg, and PO2 108 mm Hg. The ICU physician decides that invasive ventilation is needed. The patient is administered IV ketamine, 120 mg, to facilitate endotracheal intubation, which is accomplished easily. The physician sets the ventilator to assist control mode/volume control, with tidal volume 440 mL, rate 24 breaths/min, positive end-expiratory pressure (PEEP) 5 cm H2O, and FIO2 0.35, and orders a chest radiograph. Fifteen minutes later, the physician is emergently called back to the patient's bedside because her blood pressure has fallen to 70/40 mm Hg. On examination, her breath sounds are equal bilaterally and chest rise is symmetrical. Peak airway pressure is 59 cm H2O, and plateau pressure is 18 cm H2O. Airway pressure measured after an end-expiratory hold is 18 cm H2O. Results of emergent ECG and cardiac enzymes are normal. Which of the following is the most likely explanation for her hypotension?

A. Myocardial ischemia
B. Tension pneumothorax
C. Intrinsic PEEP (auto-PEEP)
D. Intubation medication