Anaesthesia has traditionally meant the condition of having sensation (including the feeling of pain) blocked or temporarily taken away. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. Anesthesia is a pharmacologically induced reversible state of amnesia, analgesia, loss of responsiveness, loss of skeletal muscle reflexes and decreased stress response.
Terms: Today, the term general anaesthesia in its most general form can include:

1. Analgesia: blocking the conscious sensation of pain.
2. Hypnosis produces unconsciousness but not necessarily freedom from pain registration..
3. Amnesia: preventing memory formation; if you are unconscious, by definition you will be unable to recall events.
4. Paralysis: preventing unwanted movement or muscle tone.
5. Obtundation of reflexes, preventing exaggerated autonomic reflexes.

Patients undergoing anaesthesia usually undergo preoperative evaluation. It includes gathering history of previous anesthetics, and any other medical problems, physical examination, ordering required blood work and consultations prior to surgery.
There are several forms of anaesthesia. The following forms refer to states achieved by anesthetics working on the brain:

1. General anaesthesia: "Drug-induced loss of consciousness during which patients are not arousable, even by painful stimulation." Patients undergoing general anesthesia can often neither maintain their own airway nor breathe on their own. While usually administered with inhalational agents, general anesthesia can be achieved with intravenous agents, such as propofol.
2. Deep sedation/analgesia: "Drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation." Patients may sometimes be unable to maintain their airway and breathe on their own.
3. Moderate sedation/analgesia or conscious sedation: "Drug-induced depression of consciousness during which patients respond purposefully to verbal commands, either alone or accompanied by light tactile stimulation." In this state, patients can breathe on their own and need no help maintaining an airway.
4. Minimal sedation or anxiolysis: "Drug-induced state during which patients respond normally to verbal commands." Though concentration, memory, and coordination may be impaired, patients need no help breathing or maintaining an airway.

The level of anesthesia achieved ranges on a continuum of depth of consciousness from minimal sedation to general anesthesia. The depth of consciousness of a patient may change from one minute to the next.
The following refer to the states achieved by anesthetics working outside of the brain:

1. Regional anaesthesia: Loss of pain sensation, with varying degrees of muscle relaxation, in certain regions of the body. Administered with local anesthesia to peripheral nerve bundles, such as the brachial plexus in the neck. Examples include the interscalene block for shoulder surgery, axillary block for wrist surgery, and femoral nerve block for leg surgery. While traditionally administered as a single injection, newer techniques involve placement of indwelling catheters for continuous or intermittent administration of local anesthetics.
2. Spinal anaesthesia: Also known as subarachnoid block. Refers to a Regional block resulting from a small volume of local anesthetics being injected into the spinal canal. The spinal canal is covered by the dura mater, through which the spinal needle enters. The spinal canal contains cerebrospinal fluid and the spinal cord. The sub arachnoid block is usually injected between the 4th and 5th lumbar vertebrae, because the spinal cord usually stops at the 1st lumbar vertebra, while the canal continues to the sacral vertebrae. It results in a loss of pain sensation and muscle strength, usually up to the level of the chest (nipple line or 4th thoracic dermatome).
3. Epidural anesthesia: Regional block resulting from an injection of a large volume of local anesthetic into the epidural space. The epidural space is a potential space that lies underneath the ligamenta flava, and outside the dura mater (outside layer of the spinal canal). This is basically an injection around the spinal canal.

Local anesthesia is similar to regional anaesthesia, but exerts its effect on a smaller area of the body.
Surinder Pal Singh Bedi MBBS, MD, DNB is one of the founder members of the Tricity anaesthesia associates. He did his graduation from Punjabi University, Patiala in 1998 and went on to do his post graduation from GMC Amritsar in 2004.Thereafter he joined asSenior Resident at GMCH Sec 32 Chandigarh and later on shifted to PGIMER Chandigarh. He was appointed Assistant Professor of Anaesthesia at PGIMER.He has been very active in the formation of this Group. His areas of interest include neonatal anaesthesia, regional anaesthesia, neuro anaesthesia, fibro-optic intubation, labour analgesia,USG in anaesthesia and critical care. Outside anaesthesia he has special interests in Operation theatre management, Policy formulation and implementation, NABH accreditation, Practice management, Negotiation and mediation, emergency service management and equipment procurement. . He holds memberships of various scientific societies and has many research publications to his credit.
Dr Devinder Singh Grewal MBBS,MD did his graduation from Panjab University, Chandigarh in 1996 and his post graduation from GMCH Sec 32 Chandigarh in 2005.Thereafter he started his Senior Residency at GMCH Sec 32 Chandigarh and later joined PGIMER Chandigarh. He has experience of working in Transfusion medicine for three years in addition to anaesthesia. He always has been very active member of this Anaesthesia Group. His areas of interest include obstetric anaesthesia, regional anaesthesia, anaesthesia for elderly, cardiac patient for non-cardiac surgery, difficult airway and difficult vascular access. Outside operation theatre he has special interests in Intensive care, mechanical ventilation and enteral nutrition. .He is a member of various scientific societies and has many research publications to his credit.
Dr Jogesh Agarwala MBBS,MD is the youngest and most vibrant members of Tricity anaesthesia associates. He did his graduation from Guwahati University, Assam in 2004 and went on to recieve his post graduation degree from PGIMER Chandigarh in 2008.He has the rare experience of working on closed loop anaesthesia delivery systems. His areas of interest include Cardiac anaesthesia, hypotensive anaesthesia, paediatric anaesthesia, cardiac patient for non-cardiac surgery, difficult airway management, Transplant anaesthesia, pain management and Cath lab anaesthesia. Outside operation theatre he has special interests in critical care, non invasive ventilation, teaching and training for BLS and ACLS, statistical analysis, quality management and patient counseling. He is chairperson of hospital code blue team and Consultant in charge CPR training. He is a member of various scientific societies and has many research publications to his credit. He is very keen on scientific research and adoption of newer techniques for overall benefits of his patients.