CHAPTER XXXIII ASPHYXIANTS (IRRESPIRABLE GASES) CARBON DIOXIDE (CARBONIC ACID GAS, CARBONIC ANHYDRIDE), CO2 This is a heavy, colourless, inodorous gas, having a slightly acid taste. It islTconstituent of the atmospheric air in which it exists to an extent of 0.04 per cent. A proportion of 2 or 3 per cent of carbon dioxide in air does not produce any injurious effects except that it increases the rate and de^Jh of respiration. A concentration of 5 per cent of carbon dioxide in air cau^s discomfort and distressing symptoms of dyspnoea, while a concentration of 25 to 30 per cent exercises a direct toxic action on the nerve cells and is likely to cause death. A concentration of carbon dioxide of even 0.5 per cent in a badly ventilated and overcrowded room produces symptoms of languor and headache, especially due to increased temperature, humidity and stagnation. Exposure to such air for a prolonged period produces loss of appetite, indigestion, debility and anaemia. Carbon dioxide is given off in the process of respiration, combustion, fermentation and putrefaction of animal matter. It forms the choke damp or after damp of the coal mines. It is also evolved in the neighbourhood of lime kilns on account of decomposition of carbonates. Being heavier than air it tends to accumulate at the bottoms of old wells, damp cellars, mine shafts, brewers' vats, grain pits, etc. Carbon dioxide (Carbonei dioxidum) is a pharmacopoeial preparation and stimulates the respiratory centre, when administered by inhalation in dilutions of 5 to 7 per cent with oxygen, but as a stimulant of a depressed respiratory centre it has practically no place. It acts as a mild rubefacient when applied externally in the form of a solution, but in the solid form it acts as a caustic. Solid carbon dioxide is sold in the market as " dry ice *\ and figures as a commercial refrigerant. Symptoms.—These are heaviness in the head, throbbing of the temporal arteries, giddiness, ringing in the ears, a sensation of oppression, muscular weakness, mental weakness, drowsiness and insensibility passing into coma with stertorous breathing. Death occurs from asphyxia or apoplexy. Some- times there may be convulsions and delirium. When inhaled in a high concentration of 60 to 80 per cent, immediate insensibility occurs followed by death from spasm of the glottis causing suffocation. Treatment—The patient must at once be removed into the open air, and artificial respiration should be started with inhalation of oxygen, This ought to be assisted by galvanism and friction of the extremities. After breathing is established, the body should be well covered with blankets* and coffee or brandy should be administered internally. If a patient is seen lying uncon- scious at the bottom of a well or pit used for storing grain, an attempt should be made to discharge oxygen from an oxygen holder into the bottom of the well or pit by means of a hose that it may not only revivify the patient but displace the carbon dioxide, so that others can descend to render him help. Post-mortem Appearances.—The body heat is retained for a longer period. The^face is usually paleTmd placid, but may be swollen and cyanosed. The pupils are dilated. ^ TheJ^rain and lungs are deeply con- gested. The right side of the heart contains dark fluid blood with venous engorgement, and the left is empty. Ecchymosed patches are noticed in the small intestine. The other internal organs are dark in colour and congested.