Anaesthesiology- science of anaesthesia (i.e. loss of sensation) without loss of consciousness.
From Greek anaesthesia  means no feeling.

Different types of Anesthesia
General Anesthesia: General anesthesia puts the patient to sleep.
In general anesthesia, the patient is completely unaware of his surroundings (unconscious). Messages of pain or sensations that normally travel to your brain for processing are no longer processed. Usually with General Anesthesia, your breathing is controlled with a breathing tube placed in your airway after you are asleep.

Local Anesthesia: Local anesthesia numbs a specific body part.
Local anesthetic (numbing medication) is injected into or around the area on which the surgeon is operating.

Regional Anesthesia:. Regional anesthesia, such as spinal anesthesia and epidural anesthesia, numbs the nerves that conduct sensation to a circumscribed body area. With regional anesthesia, a local anesthetic (numbing medication) is injected close to or around a group of nerves to block the feeling to one part of your body, such as your arm, your hand, or your foot.

Spinal Anesthesia:
In spinal anesthesia, you are given an injection in your lower back. The medication blocks the messages carried to the brain from the nerves in the lower half of your body. After the injection, you feel numb from about your waist down to your toes. The spinal anesthetic will only last from one to three hours.

Epidural Anesthesia:
It is similar to spinal anesthesia, except during the shot in your back, a tiny catheter (a plastic tube that is about the size of a pencil lead) is inserted through the needle. After the needle is removed, medicine can be given through the catheter into the "epidural space". This medication will block your sensations or feelings from about your waist down. More medication can be given throughout the procedure as needed to maintain your anesthesia. Although the effect of the epidural anesthetic and spinal anesthetic may be identical, the epidural catheter allows prolonged anesthesia and analgesia after surgery. The spinal anesthetic will only last from one to three hours.


Monitored Anesthesia Care (M.A.C.)-
You are given medicine (usually through your IV) which sedates you or makes you sleepy. The sedation may range from very light (you are comfortable but aware of everything around you) to heavy sedation (completely unaware of your surroundings and can feel only intense pain). MAC may be combined with local or regional anesthesia.