Читать книгу Fundamentals of Analytical Toxicology - Robin Whelpton - Страница 58

Gastric lavage is rarely performed nowadays in treating acute poisoning. However, if a sample of stomach contents is obtained soon after a poisoning episode, large amounts of poison may be present while metabolites may be absent. When investigating possible poisoning, it is important to obtain the first sample of any lavage fluid because later samples may be very dilute. A representative portion (ca. 50 mL) without preservative should be taken for analysis. However, all stomach contents should be retained and the volume noted, and this information passed to the laboratory. If the blood concentration is difficult to interpret, most notably in post-mortem work, it can be helpful to measure the amount of poison present in the stomach.

Stomach contents are especially useful if poison(s) which are not easy to measure reliably in blood such as cyanide have been taken orally. However, great care is needed if cyanide salts or phosphides, for example aluminium phosphide, are thought to have been ingested, particularly on an empty stomach, because highly toxic hydrogen cyanide or phosphine gas may be released because of reaction with stomach acid. Additionally, the presence of these and other volatile materials can lead to cross-contamination of other biological specimens unless due precautions are taken.

With stomach contents (and also scene residues – Section 2.3.20), characteristic colours or smells (Table 2.8) may indicate a variety of substances. Many other compounds (for example, ethchlorvynol, methylsalicylate, paraldehyde, phenelzine) also have distinctive smells. Very low or high pH values may indicate ingestion of acids or alkali, while a green/blue colour suggests the presence of iron or copper salts.

Table 2.8 Smells associated with particular poisons.^a

Smell	Possible cause
Almonds	Cyanide
Cloves	Oil of cloves
Fruity	Alcohols (including ethanol), esters
Garlic	Arsenic, phosphine
Mothballs	Camphor or naphthalene
Nail-polish remover	Acetone, butanone
Pears	Chloral
Petrol	Petroleum distillates (may be vehicle in pesticide formulation)
Phenolic (carbolic soap)	Disinfectants, cresols, phenols
Shoe polish	Nitrobenzene
Stale tobacco	Nicotine
Sweet	Chloroform and other halogenated hydrocarbons

^a CARE – specimens containing cyanides may give off hydrogen cyanide gas, especially if acidified – stomach contents are often acidic. Genetic variation means that not everyone can detect hydrogen cyanide by smell. Similarly, sulfides evolve hydrogen sulfide and phosphides evolve phosphine – the ability to smell hydrogen sulfide (rotten egg smell) is lost at higher concentrations

Examination using a polarizing microscope may reveal the presence of tablet or capsule debris. Starch granules used as ‘filler’ in some tablets and capsules may be identified by microscopy using crossed polarizing filters when they appear as bright grains marked with a dark Maltese cross. If distinct tablets or capsules are observed, these should be placed in individual containers. Such items and any plant remains or specimens of plants thought to have been ingested should be examined separately.

The local poisons information service or pharmacy will normally have access to publications or other aids to the identification of legitimate and sometimes illicit tablets/capsules by weight, markings, colour, shape, and possibly other physical characteristics. Identification of such material by reference to a computerized product database may be possible.