A 58-year-old man with hypertension and diabetes is undergoing open cholecystectomy under general anesthesia. Twenty minutes into the procedure, the anesthetist notices the patient's pupils are markedly dilated and fixed, respiration has become shallow and gasping, and blood pressure has dropped to 80/50 mmHg with a heart rate of 45 bpm. The surgical field shows minimal bleeding but the surgeon reports difficulty with hemostasis. What stage of anesthesia has been reached, and what is the immediate action required?