An agitated and nervous 24-year-old woman has had severe wheezing and shortness of breath for 2 days. After receiving oxygen, steroids, and salbutamol (Ventolin) in the emergency room, her breathing improves. She is still wheezing and now feels tremulous and anxious with a pulse of 110/min and respirations 30/min. Arterial blood gases on oxygen reveal a pH of 7.40, PO2 340 mm Hg, PCO2 40 mm Hg, and bicarbonate of 24 mEq/L. She is hospitalized for further treatment. Which of the following treatments or medications should be avoided in her?