Asphyxiants : Gases which produce asphyxia are called asphyxiants like CO2, CO, Nitrous oxide, WAR gases etc …. CARBON MONOXIDE
Physical Properties : o This gas is colourless, odourless and has specific gravity of 0.96. o When it combines with metals like nickel, iron, it produces carbonate. o When it combines with chlorine, it produces carbonate chloride (phosgene gas ). o It burns with BLUE FLAME.
SOURCES It is present 7- 5 % in Coal Gas. Our sources beside coal gas are : 1) Natural Sui Gas, which though does not contain it, yet when burnt in an unventilated atmosphere, produces it. 2) Water Gas (while producing hydrogen) : 25% 3) Blast furnaces : 25 – 30 % 4) Charcoal fires : 15 – 20 % 5) Fire lamps : 0.5 – 11 % 6) Car exhaust fumes : 7 %
1. CO is prepared by decomposition of oxalic acid with H2SO4. 2. Combustion of any carbonaceous material or carbon. 3. From blast furnaces,charcoal fire,Gas heaters,Gas engines,H2O heaters,house on fire etc.. 4. Explosion of dynamite or explosion of mines. 5. Coal gas contains 4 - 7 % of CO. 6. Exhaust gases of Motor cars. 7. Constituent of natural gases used for illumination purposes. 8. Tobacco Smoke.
Relationship of percentage of gas in AIR to that of the blood is that … a. 0.1 % of gas in air will produce blood saturation of 50- 60 % in 2 – 3 hours. b. 1 % of gas in air will produce the above blood saturation causing unconsciousness in 12-20 minutes. c. 7-15 % which is the percentage of coal gas is likely to produce fatal results in 2-5 minutes. Inadequate supply of O2 and obstruction of ventilation by blocking doors and ventilators results in partial or inefficient combustion which in turn produces CO and precipitates fatal outcome.
Signs and symptoms : Depend on blood concentration and whether onset of poisoning is acute or chronic.If the concentration of CO is less than 10%, there will be no symptoms. 1 % is found in nearly all people of average living, 3 % in people living in Industrial areas and 5 % in smokers.
Mechanism of Action : CO is most poisonous gas.When it is inhaled, it is absorbed and combines with Hb to form Carboxy – Hb (cherry red in colour) which is a very stable compound. Thus there is no Hb left for carrying of O2 because the affinity of CO is 210-300 times more than O2.
Carbon Monoxide is chemical asphyxiant and tissue poison. Toxicity depends upon quantity of Hb, so in an anemic person, Hb level is low and is affected quickly and drastically.
Mode of Action : Exercise causes rapid breathing and children with rapid rate quickens the process of uptake. Being odourless, fatal level may be attained long before its presence is recognised. Leakage is more dangerous especially when smell is lost from filtration. Use of deodorants mask smell and is a factor for its non- recognition. Lethal Dosage is variable depending upon the physical health of the individual.Most people dying of complicated poisoning have 65-75 % in the blood.
Acute Poisoning (Signs n Symptoms) a) It occurs at blood concentration more than 30%. Inhaled form of CO causes dizziness,weakness,coma and sudden death due to Respiratory failure. Sometimes coma lasts for 3-8 days. b) Amnesia and disorientation also occur if it is in high concentration. c) Degeneration of Basal Ganglia due to Brain Anoxia may produce Parkinsonism.
d) Skin lesions: They take the form of Bullae,Necrosis and ulceration of skin in areas of pressure takes several hours to develope.Such lesions are also seen in barbiturate poisoning
e) If CO is taken in diluted form,there will be dizziness, confusion,throbbing,headache,Tinnitis,nausea, vomiting,muscular weakness,lethargy, drowsiness, fixed dilated pupil. f) Increased breathing,dimness of vision,coma and death.But before death one feels convulsions and tremors,rapid feeble pulse and low B.P. g) Nervous Symptoms: There may be some nervous symptoms after recovery as cerebral hemorrhage, Encephalitis,Mental confusion,dementia and retrograde mania.Sometimes you may also see patches of erythema and Blisters on body surface.
Chronic Poisoning(Symptoms) Symptoms resemble with the symptoms of Psychomoter Epilepsy. Such a patient has upto 20% CO. Level gets down rapidly in acute poisoning, whereas in chronic cases lowering is not easy. CO is bowed up with tissues such as Myoglobin and this is very slowly released. Example : When person is exposed to CO for longer period, that is working in gasages,workshops or living in rooms which are not ventilated,without window or where incomplete combustion of charcoal and wood takes place.
Symptoms : Dull frontal headache,nausea,digestive disturbances, dysnea,dizziness,loss of memory,palpitation,loss of sensations in fingers,anemia and visual disturbances. (some patients survive upto 70% and die at 80%). If a patient of T.B, his Hb is low and death may occur in concentration of 40%. Symptoms depend upon concentration of Carbon Monoxide.
Depending on concentration,symptoms of chronic poisoning are : 30%: Nausea,confusion,fatigue,Malaise,headache, irritibility,giddiness,increase pulse and respiration. 40%: Nausea,sick feeling,vomiting,lethargy,loss of memory, profound confusion,slurring of speech,slight incoordination. 50%: Marked confusion,in coordination,ataxia,Nausea, Drunken Gait (patient behaves like collapsed man ) 60%: consciousness is lost, Syncope, Coma, Convulsions,Sphincters relaxed,Incontinuence of urine and feaces. 70% and above: Deep Coma,Respiratory paralysis and collapse.
Autopsy Findings : External : 1. Lips and nails are bright red or cherry red in colour. 2. Erythmatous patches on Anterior aspect of body. 3. Post mortem lividity is also cherry red in colour. Internal : 1. Due to formation of carboxy-Hb,blood is fluid bright red in colour. 2. Internal organs are hyperemic and red due to colour of blood; 3. Mucus membrane of Air passages is red and covered with froth.
Autopsy Findings : 4) Lungs are edematous and congested. 5) There are hemorrhages and necrotic lesions in heart muscle. 6) Petechial hemorrhages are found in cerebral cortex. 7) Renal Failure.
Medicolegal Importance : I. CO is mostly an accidental poison and common in diseased,disabled and dragged person as they will not be able to leave the site e.g ( burning house) effecting elderly people because loss of their senses of hearing and smell. II. Other accidental poisonong is common when people are sleeping in a room with combustion of wood and charcoal or coal or there may be leaky gas pipe in house or street or accidental poisoning in streets due to traffic. III. CO can be used for suicidal poisoning,sometimes they take pipe into mouth.
Medicolegal Importance : IV. Homocide is very rare.In homocide one opens the tap of pipe when victim is already sleeping in the room. V. Putrefaction will dissociate carboxy-Hb or destroy it. It resists putrefaction and CO is present in bone marrow of exhumed body if it is putrefied. VI. CO is also produced during putrefaction.
Sample Collection : I. Taking of samples both from the scene and the victim. Locally the source of CO is AIR sample collected by gas engineers.An early sample is necessary for correct diagnosis from the victim blood is the specimen of choice. II. Preliminary Chemical Test : It is done with famine acid and NaOH. Blood containing CO (with famine acid)brown colour Blood containing carboxy-Hb cherry red Oxy-Hb turns Greenish brown.
III. Spectroscopic Examination : This method is very reliable, sensitive and accurate. IV. Gas Chromatography : It is most sensitive and can detect very small amounts. Treatment Of CO Poisoning : Schafer’s Method : i. Remove the patient from source of poisoning into fresh air. ii. Remove any obstruction to respiratory tract ( external or internal ). iii. Give 100% Oxygen by nasal catheter method or by mask method.Medical Research Council advises that you add 5% CO2 to O2 and this will increase the seperation of CO from Hb.
Treatment : iv. Give Adrenaline 1 ml, Coramine 5 ml. If there is cerebral edema, give 50% dextrose. When the patient is recovered give coffee or tea and Antibiotics to avoid infections. Prophylactic Measures : Those working in gasage and workshops must have mask Respirators.