the thing about general anesthetic that frightens everyone is the idea of waking up in the middle an operation. the anesthetist's job is to prevent this from happening by monitoring the patient every step of the way.
the patient is given a general anesthetic in three parts. the first is a drug that puts you to sleep. it works very fast. You are told to count backwards from 100,and you are usually asleep before you reach 95. From that point on wards, your brain waves are monitored by EEG, which warn if you are making up.
the second drug paralyses the muscle, so your need a ventilator to breath. The percentage of oxygen in the air in controlled by the ventilation. An alarm will sound if it drops too low.
the heart still works under general anesthetic, and your heart rate is recorded by and ECG. The anesthetist also monitors the percentage of hemoglobin in the blood and level of Carbon dioxide . Body temperature is constantly measured because hypothermia can occur under general anesthetic.