Q.Write short notes on anaesthetics.

Anaesthetics are pain-relieving drugs classified as general (whole-body, CNS-depressant, unconsciousness) or local (regional nerve-block, patient remains conscious); common examples and their uses are listed below.

Definition. An anaesthetic is a drug that brings about a loss of sensation (particularly pain, i.e. analgesia), used to permit surgery and other painful medical procedures without distress to the patient.

1. General anaesthetics. These act on the central nervous system (CNS) and produce complete loss of sensation together with loss of consciousness; they are administered by inhalation or intravenous injection for major surgery.

• Diethyl ether, $C_2H_5-O-C_2H_5$: one of the earliest general anaesthetics; volatile, inhaled; drawback — highly inflammable and causes post-operative nausea.
• Chloroform, $CHCl_3$: a powerful general anaesthetic, but toxic to the liver and heart on prolonged use, so largely replaced.
• Halothane, $CF_3CHClBr$: a modern, non-inflammable, relatively safe general anaesthetic widely used in surgery.
• Nitrous oxide, $N_2O$ ('laughing gas'): a mild general anaesthetic/analgesic used in short procedures and dentistry, often combined with oxygen.
• Cyclopropane: a potent inhalation anaesthetic (less used now owing to flammability).

2. Local anaesthetics. These block nerve impulse conduction in a specific, limited region of the body; the patient remains conscious throughout. They are used for minor surgery, dental work, and childbirth.

• Procaine (Novocaine): an ester-type local anaesthetic, injected near nerves to numb a localized area; historically important in dentistry.
• Lignocaine (Xylocaine, lidocaine): an amide-type local anaesthetic, widely used today (dental, minor surgical, and topical applications) — faster acting and longer lasting than procaine. …