An otherwise healthy, term 4-week-old is diagnosed with pyloric stenosis. Electrolytes and fluids have been replenished over the previous 36 hours. Prior to the induction of anesthesia, an orogastric suction catheter is placed to remove gastric contents. The patient becomes bradycardic, and vital signs are HR 70 BPM, RR 34, SpO₂ 99%, and BP 60/35 mmHg. What is the most appropriate initial step in managing this patient?