GENERAL ANAESTHETICS

GENERAL ANAESTHETICS

General anaesthetics depress the central nervous system and produce loss of consciousness.

Ĝeneral anaesthesia is the controlled, reversible depression of the functional activities of the central nervous system producing loss of sensation and consciousness.The stages of anaesthesia vary for all agents producing general anaesthesia.

Stage I (Cortical stage) :Analgesia is produced, consciousness persists, but the patient is sleepy due to depression of the higher cortical centres

Stage II (Excitement) illoss of consciousness occurs, but depression of higher motor centres involving the brainstem and the cerebellum leads to excitement and delirium.

Stage III (Surgical Anaesthesia) : (the activity of spinal cord reflexes is minimized, and skeletal muscle relaxation is obtained. In this stage most of the operations are performed

Stage IV (Medullary Paralysis): Respiratory failure and vasomotor collapse occur due to depression of vital functions of the medulla and the brain stem.

Generalanaesthetics are administeredeither by inhalation or by intravenous or sometimes muscularinjection. Chloroform, cycloprapone, enflurane, ether, fluroxene, halothane, isoflurane, nitrous oxide and trichloroethylene are given by inhalation.

General anaesthesia may be produced by different type of compounds. The saturated hydrocarbons possess an anaesthetic effect which increases from methane to octane and then decreases. Cyclopropane and ethylene are used as anaesthetic drugs.

The anaesthetic potency of the lower hydrocarbons is increased as hydrogen is successively replaced by halogen; the order of increment is as : methane, methyl chloride, dichloromethane, chloroform, carbon tetrachloride, ethyl chloride, trichloroethylene and halothane.

An ideal anaesthetic agent should be inert, potent, nonflammable, non-irritating to mucous membranes and nontoxic. It should produce rapid and smooth induction and should be compatible with other anaesthetics.

An ideal anaesthetic agent should produce unconsciousness, analgesia, and muscle relaxation suitable for all surgical procedures and be metabolically inert and rapidly eliminated. No single agent in safe concentrations fulfils all these requirements. The activity of any anaesthetic is dependent on its ability to reach the brain.

Adverse effects which may occur during general anaesthesia include involuntary muscle movements, hiccup, coughing, bronchospasm, laryngospasm, hypotension, cardiac arrhythmias. respiratory depression, emergence reactions, and postoperative nausea and vomiting.