A pаtient with hypertensiоn, cоrоnаry аrtery disease, and peripheral vascular disease undergoes a right carotid endarterectomy under general anesthesia. Baseline HR 72, BP 148/84. As the surgeon dissects and retracts around the carotid bifurcation, you see: HR 46, BP 88/50, SpO2 99%. Which is the most appropriate initial step?