Corrosives and Asphyxiants MCQs

Hemoglobin has 210 x greater affinity for carbon monoxide than for oxygen. Thus, in carbon monoxide poisoning, the amount of dissolved oxygen, as reflected by the PaO2 may be normal, but the saturation of hemoglobin with oxygen will be lower than expected for a given PaO2. V/Q mismatch with low V/Q units, hypoventilation, and right-to-left shunting are all causes of hypoxemia (decreased PaO2). In anemia, hemoglobin concentration is reduced, but the saturation of hemoglobin O2 is normal. Reference: Ganong, pp 683-691. Levitzky, pp 180-183.

Victims of smoke inhalation are affected by carbon monoxide poisoning . In carbon monoxide poisoning, the cause of death is anaemic hypoxia Carbon monoxide has a higher affinity to haemoglobin compared to oxygen and hence the amount of haemoglobin available for oxygen transport is markedly reduced. It displaces oxygen from its combination with haemoglobin and forms a relatively stable compound known as carboxyhemoglobin . It thus reduces the oxygen content of the blood, and hence, that of the tissues. It acts as a chemical asphyxiant and produces death due to anaemic anoxia. References: Textbook of Forensic Medicine & Toxicology: Principles & Practice 5th edition Page no: 113; The Essentials of Forensic Medicine & Toxicology, KS Narayan Reddy, 35th Edition, Page No. 101

Lee Jones test is used to detect cyanide. Lee Jones test: To 5 ml of stomach contents add few crystals of ferrous sulphate and 5 drops of 2% sodium hydroxide. Boil and cool and add 10 drops of 10% hydrochloric acid. Greenish-blue colour indicates cyanide, and purplish colour salicylates. Reference: The Essentials of Forensic Medicine & Toxicology, KS Narayan Reddy, 35th edition, Page No. 480

Ans. is 'b' i.e., Wash with mild alkali agent [Ref Reddy 30Th le p. 485] The most critical aspect of acid burn care is the constant and prolonged washing of the area with water at a room temperature to get the acid out immediately. To try and minimize the damage, the effects of acid should be neutralized by applying a mild alkali solution to the affected area (solution of sodium bicarbonate and water.

Ans. is 'b' i.e., Carbolic acid [Ref Reddy 30th/e p. 489] Chronic carbolic acid poisoning/phenol marasmus The poisoning is characterised by anorexia, weight loss, headache, vertigo, dark urine and pigmentation of skin & sclera. Carbolic acid/ Phenol is converted into hydroquinone & pyrocatechol in the body before being excreted in the urine. Hydroquinone er pyrocatechol may cause pigmentation in the cornea and various cartilages- Oochronosis. Oochronosis is commonly associated with alkaptonuria, in which homegentisic acid gets deposited in cartilages, ligaments & fibrous tissues.

CO combines reversibly with haemoglobin to form carboxyhemoglobin (COHb) producing anaemic hypoxia (Blood O 2 -carrying capacity is reduced). It has a high affinity for Hb (about 250 times more than O2). It inhibits electron transport by blocking cytochrome A3 oxidase and cytochrome P450 and hence intracellular respiration. Anaemic hypoxia occurs when the oxygen carrying ability of the blood decreases, and thus, this defect is specifically associated with the blood. This implies that fewer hemoglobin molecules (or oxygen-binding sites) are available for binding oxygen. Reference: Review of Forensic medicine and toxicology, Gautam Biswas, 5 th Edition, Page No. 645